Pine Pollen-Derived Activated Carbon for High-Performance Supercapacitor Electrodes: A Comparative Study of KOH and CuCl 2 Activation

Pine Pollen-Derived Activated Carbon for High-Performance Supercapacitor Electrodes: A Comparative Study of KOH and CuCl 2 Activation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Pine Pollen-Derived Activated Carbon for High-Performance Supercapacitor Electrodes: A Comparative Study of KOH and CuCl 2 Activation Funda Ersoy Atalay, Harun Kaya, Aydan Aksogan Korkmaz, Seher Guler This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5742394/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Carbon-containing materials are vital for supercapacitor electrodes. Activated porous carbons are especially attractive due to their high surface area, conductivity, and porous structure, making them ideal for double-layer supercapacitors. Recently, researchers have turned to biological materials like bacteria, algae, fungi, and pollen to create porous carbon structures. Among these, pine pollen stands out for its abundance and ease of collection. This study focused on converting pine pollen into porous carbon using hydrothermal carbonization in water, followed by activation with different agents. The carbonized pollen was activated with KOH and CuCl 2 at various ratios to form nanostructured porous carbons. Scanning electron microscope images showed that activation with KOH and CuCl 2 partially altered the pollen morphology. The sample with a 1:2 pollen-to-KOH ratio had the highest surface area at 2030.32 m²/g. To evaluate their electrochemical performance, supercapacitor electrodes were created using two types of activated carbons. The specific capacitance of KOH-activated carbon (KAC) was 230 F/g, while CuCl 2 -activated carbon (CuAC) showed 175.9 F/g, both at 5 A/g. After 5000 charge-discharge cycles, KAC retained 76% of its capacitance, and CuAC retained 93%. These results demonstrate pine pollen's potential as a precursor for high-performance porous carbons. Pine pollen activated carbon supercapacitor electrodes energy storage Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Electrochemical energy storage devices, such as lithium-ion batteries and supercapacitors, play a crucial role in various applications, ranging from electronics to electric vehicles. While both lithium-ion batteries and supercapacitors have their strengths, supercapacitors are known for their high power density (410 kW/kg) and exceptional cycle stability. However, they do have a limitation when it comes to energy density, typically ranging from 5 to 10 Wh/kg [ 1 ]. Supercapacitors operate based on the principle of ion adsorption from an electrolyte onto an electrode with a large surface area [ 2 ]. They can be broadly classified into three categories: electrical double-layer capacitors, hybrid capacitors, and pseudocapacitors [ 3 ]. Electrical double-layer capacitors store charge purely through electrostatic charge accumulation at the electrode interface. On the other hand, pseudocapacitors store charge through fast and reversible surface redox processes [ 4 ]. Despite their remarkable capabilities, supercapacitors have not yet achieved widespread adoption in the energy storage market due to their limited energy density. However, researchers are actively working on overcoming this challenge by developing innovative energy storage materials. The ultimate goal is to enhance the energy density of supercapacitors without compromising their high power density and cycling stability. This requires the discovery and design of new electrode materials with increased energy storage capacity. Researchers are exploring various approaches such as advanced carbon-based materials, metal oxides, conducting polymers, and hybrid materials. Carbon-based materials, such as activated carbon and carbon nanotubes, are widely used in supercapacitor electrodes due to their high surface area and electrical conductivity. Metal oxides, including manganese oxide and ruthenium oxide, offer higher energy storage capabilities through redox reactions. Conducting polymers, such as polyaniline and polypyrrole, exhibit pseudocapacitive behavior and can store charge through redox processes. Hybrid materials, combining two or more components, aim to leverage the advantages of different materials to achieve improved energy density. In addition to material advancements, researchers are also investigating novel electrode architectures and electrolyte systems to enhance the overall performance of supercapacitors. By tailoring the electrode structure and optimizing the electrolyte composition, it is possible to further enhance the energy storage capabilities of supercapacitors. The ongoing efforts to enhance the energy density of supercapacitors are driven by the desire to develop energy storage systems that can provide both high power and high energy density. Such advancements would open up new possibilities for applications requiring rapid energy delivery and high cycling stability, such as electric vehicles, renewable energy integration, and grid-scale energy storage. In conclusion, while supercapacitors have not yet achieved widespread adoption in the energy storage market due to their limited energy density, ongoing research and development efforts are focused on overcoming this challenge. By exploring new energy storage materials, optimizing electrode architectures, and refining electrolyte systems, researchers aim to unlock the full potential of supercapacitors as a viable and efficient energy storage solution. To evaluate the performance of a supercapacitor, it is essential to consider critical aspects related to electrodes and electrolytes. The capacitive performance of electrodes can be enhanced by utilizing electrode materials that are stable, long-lasting, and electrically conductive [ 5 ]. Commonly used materials for supercapacitor electrodes include metal oxides like MnO 2 , NiO, and Co 3 O 4 , conductive polymers such as polypyrrole, polythiophene, and polyaniline, as well as various carbon materials. Additionally, researchers are continuously developing new electrode materials such as metal phosphites, metal sulfides, and porous organic polymers. Among these options, low-cost carbon materials derived from renewable biomass sources like cellulose, chitin, chitosan, and lignin have gained significant attention in recent years due to their appealing structure, abundance, renewability, and environmental friendliness when compared to conventional carbon materials [ 6 , 7 ]. Biomass-based supercapacitors have become a subject of great interest because of their excellent electrochemical properties [ 8 ]. Unlike other carbon materials, carbon materials derived from biomass have the advantage of inheriting the unique structure, defects, and chemical composition of their precursor biomass during the carbonization process. Consequently, biomass-derived carbon materials offer high capacitance, improved stability in terms of speed, and excellent cycling performance in supercapacitors [ 7 ]. Activated carbon is a carbon-based material known for its amorphous nature, large internal surface area, and extensive porosity. It possesses a non-graphite, microcrystalline carbon structure, and exhibits remarkable properties such as excellent electrical conductivity, high thermal stability, and notable surface reactivity. Activated carbon production involves various methods, including pyrolysis, hydrothermal processes, and chemical or physical activation techniques. Additionally, microwave-assisted treatment with activation agents can also be employed [ 9 ]. In the field of electrode applications for supercapacitors, numerous techniques have been developed to prepare carbons with a significantly high specific surface area. One such approach involves a two-stage process combining pyrolysis and activation, which continues to be extensively investigated using a diverse range of biomass wastes, coals, and polymers [ 10 ]. Many studies have successfully utilized activated carbons derived from biomass sources in the design of supercapacitors [ 11 ]. Examples include eucalyptus wood [ 12 ], coconut bark [ 13 ], bamboo [ 14 ], banana fiber [ 15 ], sugar cane pulp [ 16 ], argan seed shell [ 17 ], apricot peel [ 18 ], and sunflower seed husk [ 19 ], among others. These biomass-derived activated carbons exhibit desirable characteristics for supercapacitor applications, owing to their unique pore structures and surface properties. It is worth noting that activated carbons produced through chemical activation using agents like KOH, K 2 CO 3 , ZnCl 2 , or H 3 PO 4 tend to possess more well-developed pore structures compared to those obtained via physical activation using CO 2 or water vapor [ 20 ]. Such variations in activation methods and carbon sources provide researchers with a wide range of options for tailoring the properties of activated carbons, enabling the design of supercapacitors with enhanced performance and energy storage capabilities. Also, supercapacitor electrodes have been produced using plant pollen as a source of activated carbon. Zhang et al. [ 21 ] conducted research on supercapacitor electrode materials using plant pollen like lotus, peony, and camellia. By carbonizing lotus pollen, they achieved a high surface area of 3037 m²/g and a large pore density of 2.27 cm³/g. Peony and camellia pollen carbonization resulted in surface areas of 2673 m²/g and 2765 m²/g, respectively. The symmetrical supercapacitor using lotus pollen exhibited a capacitance of 207 F/g at 1 A/g current in the EMIMBF4 electrolyte. Wang et al. [ 22 ] synthesized nanolayered, porous NiO elliptical microstructures using rapeseed pollen as a template. The resulting pollen-molded NiO served as a supercapacitor electrode with high specific capacitance (198.7 mAh/g at 1 A/g), excellent capacity (89.2 mAh/g at 30 A/g), long cycle life (103.3% retention after 10,000 cycles), and high energy/power density (66.4 Wh/kg energy density and 22.2 kW/kg power density). Lu et al. [ 23 ] developed carbon material for supercapacitor electrodes from camellia pollen through a hydrothermal process with controlled NH 4 BF 4 content and subsequent carbonization. The sample treated with 0.015 g/ml NH 4 BF 4 during hydrothermal treatment exhibited the highest specific surface area of 526 m²/g at a current density of 0.5 A/g. It also demonstrated a significant specific capacitance of 205 F/g in a 2 M KOH solution, along with excellent cycle stability by retaining 96.2% of its initial capacitance after 10,000 cycles. In a study conducted by Zhang et al. [24] in 2018, they used pine pollen to produce activated carbon material for sodium-ion batteries. By carbonizing pine pollen at 900°C for 1 hour with a heating rate of 5°C/min in an Ar atmosphere, they obtained a material with a specific surface area of 171.54 m 2/ g and a larger layer spacing of 0.41 nm. The initial discharge capacity of this material was determined to be 370 mAh/g at a current density of 0.1 A/g. Impressively, even after 200 cycles, the material maintained 98% of its initial capacitance, demonstrating good discharge capacity. In another study by Liu et al. [ 25 ] in 2018, they investigated the synthesis of porous carbon using rapeseed pollen activated by CuCl 2 for supercapacitors. The resulting rapeseed pollen carbon exhibited a sphere-like structure with a large specific surface area of 2488 m 2 /g and a high heteroatom content. When tested as an electrode in a 6 M KOH aqueous electrolyte at a current density of 0.5 A/g, the rapeseed pollen carbon electrode showed a capacitance of 390 F/g. Furthermore, the electrode displayed excellent cycle stability, retaining 92.9% of its initial capacitance after 10,000 cycles at 20 A/g. In 2019, Wan et al. [ 26 ] utilized carbon material derived from N-doped pine pollen, where MgCO 3 served as the activation agent, for supercapacitors. The N-doped pine pollen exhibited a hierarchical porous structure with interconnected meso/macropores, a large surface area of 1311.2 m 2 /g, and high nitrogen and oxygen content. As a supercapacitor electrode in a three-electrode system, the N-doped pine pollen demonstrated a high specific capacitance of 419.6 F/g at a current density of 1 A/g, with favorable behavior from 1 to 100 A. Moreover, the 6 M KOH aqueous electrolyte showcased superior long-term cycling stability, with only a 2.6% loss in initial capacitance after 10,000 cycles. Liu et al. [ 27 ] in 2020 examined the supercapacitor properties of peony pollen. They prepared porous carbon microspheres by employing a hydrothermal method followed by carbonization, with NH 4 BF 4 as an abrasive and KOH as an activator to modify the material's porosity. The resulting material exhibited a high BET-specific surface area of 824.69 m 2 /g. Cao et al. [ 2 ] conducted a study where they successfully developed a controllable carbon material with a hierarchical porous structure through an integrated process involving carbonization, activation, and nitrogen doping. In their research, they utilized nitrogen-rich camellia pollen as the carbon precursor and introduced NH 4 Cl as an activator and additive. The resulting N-doped carbon material exhibited a higher nitrogen content of 3.82%, along with a desirable distribution of pore sizes and a larger specific surface area of 810 m 2 /g. They further constructed a symmetrical supercapacitor using this material, which demonstrated a high energy capacity of 13.3 Wh/kg in a 6 M KOH electrolyte. Remarkably, the supercapacitor also exhibited excellent cycling stability, with a capacitance retention rate of 85.4% after undergoing 20,000 cycles at 20 A/g. In this study, pine pollen was utilized as an activated carbon material for the first time in the design of a supercapacitor electrode. Pine pollen was chosen due to its easy accessibility, low cost, and eco-friendly nature. The activation process involved hydrothermal carbonization of pine pollen, followed by the use of two chemical activation agents, namely KOH and CuCl 2 . This innovative utilization of activated pine pollen as the active material for the electrode makes the study original and holds promise for future research in this field. 2. Experimental methods Preparation of active carbon Pine pollen was harvested from pine trees in Malatya, Inonu University campus, in April and May. Male pine flowers were collected before they were fully pollinated and dried by laying them on blotting paper in the sunlight parts of the laboratory or dried at 60°C in a drying oven. It was observed that the flowers spontaneously release pollen powders within 2 or 5 days, depending on the weather conditions. For the purification of pollen from dust, garbage, etc., foreign materials involved in the collection and drying stages, pollen was sieved with 106 µm and 75 µm sieves (Retsch), respectively. Then 45 µm sieve suitable for pine pollen size was used to obtain pure pollen. 15 g of dried pollen was subjected to a hydrothermal reaction in 80 ml of deionized water for 12 hours at 200°C after washing several times with deionized water and ethanol. The hydrothermal reaction was carried out in a 100 ml Teflon liner stainless steel container (Step 1). Then, the product was filtered through a microporous filter by the vacuum filtration method, and the resulting residue was dried in a vacuum oven at 60°C for 36 hours. The resulting pollen powder material was mixed separately with KOH and CuCl 2 in 1:1, 1:2, 1:3, 1:5, 1:10, and 1:20 until a homogenous mixture was obtained (Step 2). Then heat-treated in nitrogen flow to 900°C with a heating rate of 2°C/min and held for 2 hours (Step 3). The obtained powder was washed with 0.5 M HCl and deionized water. Washing processes with deionized water were continued until the pH was 7 (Step 4). It was dried at 60°C in a vacuum oven for 36 hours (Step 5). Eventually, this porous carbon material to be used for the electrode was obtained. Pollen isolation process steps are presented in Figure S1 . Preparation of electrode In the production of supercapacitor electrodes, porous carbon (75%) was used as active material, acetylene black (15%) as a conductivity agent, and PVDF (10%) as a binder. In the first stage, porous carbon and acetylene black were mixed in the Zr 2 O 3 mortar in the glovebox for 45 min, then PVDF was added to the mixture and mixed homogeneously in the mortar for 30 min in total. In the second stage, a slurry was formed by adding approximately 0.5 ml of NMP to this homogeneous mixture. Ni foam used as a collector, with acid, acetone, and purified water, has been cleared. 5 g of the slurry material was taken and dropped on the pre-cleaned pure Ni foam of 13 mm diameter. The carbon-containing electrode activated with KOH and CuCl 2 was KAC and CuAC, respectively. The formed porous carbon material was used as a working electrode in a three-electrode electrochemical cell. A platinum plate with an area of 2.5x2.5 cm with 99.99% purity was used as the counter electrode. Leak-free reference electrode (Ag/AgCl) was used as a reference electrode. 6 M KOH was put into the electrochemical cell as an electrolyte. The cell preferred in the experiments was made of pyrex glass with a length of 8.5 cm, an inner diameter of 4.5 cm and an outer diameter of 5.5 cm, and a Teflon cap with the same characteristics as the internal diameter dimensions were also used. Characterization of materials The porous carbon material morphology was obtained using Scanning Electron Microscopy (SEM, FEI Nova Nano SEM 450). The structure was investigated by X-ray diffraction (XRD, Cu-Kα) and Raman Spectroscopy (532 nm, UniRAM Micro Raman System). Brunauer–Emmett–Teller (BET) analysis was used to determine specific surface area by N 2 adsorption/desorption at 77 K (Gemini VII2390t, Micrometrics). The specific surface area was calculated using adsorption data at the relative pressure range of 0–1. The Barrett-Joyner-Halenda (BJH) pore size distribution was calculated based on the adsorption branch of the isotherm. Before analysis, each sample was degassed at 300°C in an argon atmosphere for 2 hours. TGA-50, Shimadzu, from ambient temperatures to 900°C conducted thermogravimetric analysis (TGA) of carbon materials curves. The elemental compositions of carbon (C), hydrogen (H), and nitrogen (N) contents of obtained materials were determined by a CHNS analyzer (Perkin Elmer Series II 2400). Electrochemical performance tests The electrochemical performance was tested by cyclic voltammetry (CV), charge-discharge (CD) testing, and impedance spectroscopy techniques using a Gamry 3000 interface potentiostat/galvanostat/ZRA. CV measurements were made at different scan rates (1-200mV/s). Also, CD measurements were performed between 1–5 A/g of constant current density. Nyquist curves were obtained at open circuit potential applying 5 mA constant current. The frequency limits were typically set between 3mHz and 100kHz. 3. Results The TGA/DTA analysis graph of pine pollen is given in Fig. 1 . It is seen that the first 16.6% mass loss in pine pollen is from room temperature to 170°C, and it is thought that the mass loss here is due to the removal of water and ethanol. It is believed that the second and highest mass loss is 43.9% at an average of 210–400°C, and the reason for the mass loss here is the removal of carbohydrates and proteins. It is estimated that the 20.4% mass loss in the last stage is at 410–560°C due to the lipid removal. The remaining substance amount at 900°C is 9.12%. Carbonization starts after approximately 610°C. Figure 1 . TGA/DTA analysis of pine pollen. The surface area parameters of the samples obtained by activation with different chemicals are presented in Table 1 . While the surface area of the pure pine pollen powder calculated from N 2 adsorption-desorption isotherms was 2.41 m 2 /g, the pore volume was 1.92x10 − 3 cm 3 /g and the pore size was 4.9 nm. After the hydrothermal reaction, the surface area increased to 5.18 m 2 /g. The best surface area value was obtained as 2030.32 m 2 /g in the sample KAC at the ratio of 1:2. The pore volume also increased from 1.92x10 − 3 cm 3 /g to 1219.26x10 − 3 cm 3 /g. This is approximately 634 times greater than the initial and is a significant increase. On the other hand, the best surface area value of the sample CuAC is 736.80 m 2 /g, pore volume is 391.16x10 − 3 cm 3 /g at a ratio of 1:5. The pore volume increased approximately 203 times compared to the initial. The material obtained from CuAC contains spherical microparticles, and the sample KAC contains porous and thin flakes. Activation with KOH differs significantly from activation with CuCl 2 . Since KOH is alkaline, it is very active at high temperatures, but CuCl 2 is acidic and can cause activation at very low temperatures. In all subsequent studies, the expression of KAC at a ratio of 1:2 and CuAC at a ratio of 1:5 describe the active carbons obtained. Table 1 Change in surface parameters as a result of activation of pine pollen with KAC and CuAC. Samples (ratio of pollen:KOH) Surface area (m 2 /g) Pore volume (cm 3 /g)x10 − 3 Pore diameter (nm) Raw pine pollen 2.41 1.92 4.90 Hydrothermal-treated pine pollen 5.18 1.33 3.94 Activation rate of KAC 1:1 1709.64 878.25 2.63 1:2 2030.32 1219.26 2.59 1:3 1510.66 896.33 2.62 Activation rate of CuAC 1:1 113.88 25.80 2.93 1:2 171.67 28.67 3.01 1:3 259.76 63.95 2.90 1:5 736.80 391.16 3.54 1:10 382.61 81.23 2.76 1:20 197.55 35.80 2.67 In the SEM photographs of pine pollens, it was observed that the isolated pine pollens were approximately 40–43 µm in size. The pollen partially shrunk in size after the hydrothermal reaction and inward collapse occurred in the morphology due to pressure (Fig. 2 a). It was also observed that a porous structure was formed due to the removal of the oil layers on its surface. After the KOH activation structure of the pollen disappeared, a thin porous structure was obtained. This araises the strong etching effect of the KOH. Detailed SEM images of different KOH ratios were also given in Fig. 2 b-d. Almost no material was left after the heat treatment for larger KOH ratios (> 2). The reactions taking place in the can be expressed as Eq. (1–3). 4KOH + HO + 2C → KCO + KO + 3H + CO (1) K 2 CO 3 + 2C → 2K + 3CO (2) K 2 O + H 2 + C → 2K + CO + H 2 (3) K 2 CO 3 formed due to the reaction is another activation material for obtaining porous carbon. Therefore, the resulting product contains a large amount of K content, which agrees with the XRD results in Fig. 3 . Despite repeated washing with acid and water, K remained in the structure. This is because the melting point of K is small (63.5°C) compared to the heat treatment temperature and therefore, it is trapped in the carbon network. Even if the resulting product is low in quantity, the surface area and porosity achieved with KOH are considerable. As an alternative to KOH, chemical materials such as ZnCl 2 and CuCl 2 have been used as activation agents [ 8 ]. In contrast to the material obtained from KOH activation, spherical morphology was preserved in CuCl 2 activation. However, with the effect of high temperature, the dimensions, initially about 40 µm, decreased by 25% and were measured as 10 µm. SEM image of the material obtained as a result of CuAC is shown in Fig. 4 . The material obtained contains varying-sized microspheres with nano-grains on the surface. The reaction mechanism is as follows (Eq. 4–5). 3CuCl + 2HO + C → Cu + 2CuCl + CO + 4HCl (4) 4CuCl + 2HO + O + C → 4Cu + CO + 4HCl (5) The presence of Cu content in the structure can be seen from the XRD spectrum (Fig. 3 ) and EDX analysis (Fig. 5 b). The unlabeled peaks of around 1.74 eV and 2.12 eV in Fig. 5 a are due to the Si used as the substrate and the Au coating for good imaging, respectively. The unlabeled peaks around 1.00 eV in Fig. 5 b, is due to the Cu content of the sample. In addition, the structure consists of 90.2% C and 9.8% O in terms of atomic ratio. Like KOH, it was thought that CuCl 2 was trapped in the carbon frame due to its low melting temperature; therefore, the Cu content could not be removed. CuCl 2 was formed in the activation process and acted as an activation agent. Although the product was washed many times with either 0.5 M or 2 M HCl, the Cu content in the structure could not be removed. Liu et al. [ 25 ] stated that the rape pollen structure was preserved in the activation process with CuCl 2 . Our study observed from the SEM images in Figure 2 that the pollen structure was not preserved but that a microsphere of 2 µm diameter was formed on which 500 nm nanoparticles were located. This indicates that the two air sacs (saccus) at the edge of the pine pollen have disappeared, and the size of the spherical structure (corpus) in the middle region has shrunk after the high temperature. Similar results were obtained for the products obtained from activation at different CuCl 2 ratios (Figure 4 ). Raman results of KAC and CuAC are given in Fig. 5 c. Choi et al. [ 20 ] found a similar result in the Raman spectrum of porous carbon produced from bee pollen. Raman spectra of hydrothermal pollen show C-H stretch bands around 2000–2750 cm − 1 . It is seen from Fig. 5 c that carbonization has taken place as a result of the activations. It is seen that D and G bands are formed after activation with KOH, which indicates the obtaining of the porous carbon structure. The G band represents the in-plane motion of the C sp 2 atom pairs and expresses regular structures, while the D band is known to be characteristic of the sp 3 disordered graphite. It was observed that the peak intensities of these bands increased significantly with activation. The increase in the ID/IG ratio, that is, in the material's electrical conductivity, indicates that the electrical conductivity of the initially insulating material increases. This will directly reflect the increased capacitance of the porous carbon-containing supercapacitor electrodes to be formed. When CuCl 2 is used as an activation agent in carbonization at 900°C, first CuCl formation occurs at 500°C and then Cu formation occurs at 600°C. The low melting point (426°C) of CuCl 2 caused the pollen to be trapped inside the C skeleton. With the increased heat treatment temperature, the pollen could not preserve its structure and its size decreased to 2 µm. Figure 4 . The SEM images of pine pollen after activation with CuCl 2 at different ratios of a) 1:1, b) 1:3, c) 1:5, d) 1:20 In CuAC, the Cu content in the structure could not be removed despite washing with HCl at different molar ratios (0.5-2 M). Therefore, the structure contains more Cu than C. Figure 5 c shows the typical properties of carbon materials and indicates the porous and disordered structure of the material. Two broadband gaps were obtained around 1306 and 1603 cm − 1 , corresponding to the D and G bands of the porous carbon. CHNS analysis results are given in Table 2 . The highest C content belongs to KAC among the different pollen-based materials. While the amount of C in pine pollen was 49.22% initially, it was 60.74% with hydrothermal carbonization and then 77.39% and 62.92%, KAC and CuAC with activation, respectively. Table 2 Elemental analysis results of materials. Material C (%) H (%) N (%) S (%) Raw pine pollen 49.22 7.31 2.16 0.14 Hydrothermal processing pine pollen 60.74 7.33 3.26 0.16 KAC (1:2) 77.39 0.58 1.02 0.13 CuAC (1:5) 62.92 1.67 7.86 0.02 Electrochemical performance test results Electrochemical performance testing of supercapacitor electrodes was performed in a 6M KOH electrolyte versus Ag/AgCl electrode in a three-electrode system. Cyclic voltammetry (CVs) curves of KAC and CuAC electrodes at different scan rates with a potential window from − 1.0 to 0V are given in Fig. 6 a, b. Both electrodes showed an almost rectangular-like shape typical of capacitive or EDLC electrode materials. But only a small shoulder around − 0.75 V in the cathodic region is observed for KAC. Figure 6 c, d shows GCD curves at various current densities measured in the potential range of 0 to -1V vs. Ag/AgCl. Almost ideal triangular shapes are observed for all the GCD curves, which can be attributed to the EDCL nature arising from activated carbon curves. The observed symmetrical charge and discharge curves for both electrodes indicate excellent electrochemical reversibility. In parallel with the increase in the current value, the charge-discharge time decreased. Figure 6 e, f shows KAC’s and CuAC 's first five cyclic charge-discharge curves for a constant current value of 5 A/g. Specific capacitance is calculated 230 F/ g for KAC and 176.2 F/g for CuAC at 5 A/g current density. Due to its hierarchical porous and more disordered structure, which is caused by KOH reactivation, KAC electrode exhibits much higher capacitance compared with CuAC electrode. Variation of specific capacitance as a function of the number of cycles is given in Fig. 7 a. The specific capacitance value of KAC decreased from 230 F/g to 173 F/g in 3000 cycles of charge-discharge measurements. The electrode exhibited an almost constant specific capacitance value of approximately 175 F/g after 2000 cycles. On the contrary, the specific capacitance of the CuAC electrode, initially 176.2 F/g, decreased to 163.8 F/g after 5000 cycles. After 5000 charge-discharge cycles, KAC and CuAC retained 76% and 93% of their initial capacitance values, respectively. Maximum energy densities were calculated as 31.94 Wh/kg and 24.43 Wh/kg for KAC and CuAC, respectively. Electrochemical impedance measurements were conducted on the porous carbon electrodes that were produced. Figure 7 b illustrates the Nyquist plot for both KAC and CuAC. For KAC, the curve slope was calculated as 67.8° with an ESR (Equivalent Series Resistance) value of 206 mΩ before 5000 cycles. After 5000 cycles, these values changed to 70.4° and 170.5 mΩ respectively. Regarding CuAC, initially, the angle value was determined as 57.8°, which increased to 70.4° after 5000 cycles. Additionally, the ESR value rose from 0.162 mΩ to 170.5 mΩ. These results indicate that the electrode structure and capacitive features remain intact. Furthermore, after 5000 cycles, there is a decrease in resistance observed in the mid-frequency region of the curve, attributed to reduced transfer resistance as ions penetrate deeper over time. A curve slope value of at least 45° is required for a supercapacitor, and the electrochemical tests demonstrate that electrodes derived from carbonizing pine pollen are promising candidates for supercapacitor electrodes. AC Supercapacitor device design KAC, with the highest surface area (2030.32 m 2 /g), was used as the AC electrode. No matter how large the capacitance of the prepared AC electrode is, the energy density will be low if the potential range is small. Increasing the potential range will also significantly affect the energy to be stored. Therefore, an SC design was performed by combining two electrodes with the same properties using the Swagelok cell as shown in Figure S2. Cellulose filters with 0.45 nm were used as separators. CV curves were taken in Swagelok cells at different scanning rates in the potential range of -1.45 to + 0.42. An increase in current values were observed with an increasing scanning rate. The CV curves showed a close-to-rectangular shape in experiments where 6 M KOH was used as the electrolyte (Figure S3a, b). It is observed in Figure S3c that the initial specific capacitance value of 167 F/g hardly changes for 5000 cycles. Energy density was calculated as 81.11Wh/kg. 4. Conclusion In this study, pine pollen, an environmentally friendly, renewable and inexpensive material, was used as a carbon source to design supercapacitor electrodes. Porous carbon production was achieved by activating KOH and CuCl 2 chemicals in different pollen ratios. The highest surface area was obtained as 2030.32 m 2 /g, while the Pine: KOH ratio was 1:2 (KAC). In the sample activated Pine: CuCl 2 at a ratio of 1:5, the specific surface area was obtained as 736.8 m 2 /g (CuAC). After the hydrothermally carbonization process, it was determined from the Raman spectra that they still contained organic groups. K 2 CO 3 and CuCl are released during the carbonization process activation agent. Activation with CuCl 2 in all ratios except the 1:1 ratio has taken place. Activation with KOH at a ratio of 1:5 and above destroyed pine pollen. In addition, it has been determined that if the resulting gases are not swept away from the environment at sufficient speed, the resulting product will burn continuously and this will cause the pollen structure to disappear. Electrochemical properties of KAC and CuAC samples in 6 M KOH electrolyte were investigated. Both KOH and CuAC electrodes exhibited EDLC properties in accordance with the literature [ 27 ]. The maximum specific capacitance of the KAC electrode was 230 F/g, while that of the CuAC electrode was 176.2 F/g. It has been observed that the supercapacitor device, which is formed by combining two similar electrodes using KAC, has a wide potential window in the potential range of -1.45 V to + 0.42 V. CV curves and has a rectangular appearance. It has been observed that the initial capacitance value has almost no changes even after 5000 cycles. As a result, electrochemical measurements of the device with two electrode designs showed a close-to-rectangular shape similar to the CV curves of an ideal supercapacitor. Declarations Disclosure statement : No potential conflict of interest was reported by the author(s). Author Contribution F.E. Atalay; corresponding author; conceptualization, project administration, supervision, validation, methodology, data curation, formal analysis, writing—review and editingH. Kaya; electrode fabrication and electrochemical measurements, methodology, data curation, analysisA.A. Korkmaz; production of activated carbon, analysis, investigation, writing–original draftS. Guler; pollen harvesting, pollen isolation, analysis and investigation. Acknowledgments: This work was supported Scientific and Technological Research Council of Turkey (TUBITAK) under Grant [218M267]; Inonu University BAP under Grant [FBG-2019-1709]; and Inonu University BAP under Grant [FYL-2020-2196]. References Lyu L, Seong KD, Ko D, Choi J, Lee C, Hwang T, Cho Y, Jin X, Zhang W, Pang H, Piao Y (2019) Recent development of biomass-derived carbons and composites as electrode materials for supercapacitors. Materials Chemistry Frontiers 3(12): 2543–2570. https://doi.org/10.1039/C9QM00348G Cao L, Li H, Xu Z, Gao R, Wang S, Zhang G, Jiang S, Hou H, (2021) Camellia pollen-derived carbon with controllable N content for high‐performance supercapacitors by ammonium chloride activation and dual N‐doping. ChemNanoMat 7(1): 34–43. https://doi.org/10.1002/cnma.202000531 . Najib S, Erdem E, (2019) Current progress achieved in novel materials for supercapacitor electrodes: mini-review. Nanoscale Adv 1: 2817–2827. https://doi.org/10.1039/C9NA00345B . Han X, Jiang H, Zhou Y, Hong W, Zhou Y, Gao P, Ding R, Liu E (2018) A high performance nitrogen-doped porous activated carbon for supercapacitor derived from pueraria. Journal of Alloys and Compounds 744: 544–551. https://doi.org/10.1016/j.jallcom.2018.02.078 . Mehdi R, Khoja A H, Naqvi SR, Gao N, Amin NAS (2022) A Review on Production and Surface Modifications of Biochar Materials via Biomass Pyrolysis Process for Supercapacitor Applications. Catalysts 12(7):798. https://doi.org/10.3390/catal12070798 . Lin S, Wang F, Shao Z (2021) Biomass applied in supercapacitor energy storage devices. Journal of materials science 56(3): 1943–1979. https://doi.org/10.1007/s10853-020-05356-1 . Zhou J, Zhang S, Zhou YN, Tang W, Yang J, Peng C, Guo Z (2021) Biomass-derived carbon materials for high-performance supercapacitors: current status and perspective. Electrochemical Energy Reviews 4(2):219–248. https://doi.org/10.1007/s41918-020-00090-3 . Chen, W, Luo M, Wang X, Yang K, Zhou X (2020) Rapid synthesis of chitin-based porous carbons with high yield, high nitrogen retention, and low cost for high‐rate supercapacitors. International Journal of Energy Research 44(2):1167–1178. https://doi.org/10.1002/er.5008 . Yahya MA, Mansor MH, Zolkarnaini WA, Rusli NS, Aminuddin A, Mohamad K, Sabhan FAM, Atik AAA, Ozair LNA (2018) Brief review on activated carbon derived from agriculture by-product. AIP Conf. Proc. 1972 030023. https://doi.org/10.1063/1.5041244 . Diez N, Mysyk R, Zhang W, Goikolea E, Carriazo D (2017) One-pot synthesis of highly activated carbons from melamine and terephthalaldehyde as electrodes for high energy aqueous supercapacitors. Journal of Materials Chemistry A 5(28):14619–14629. https://doi.org/10.1039/C7TA01424D . Khalil HPS, Jawaid M, Firoozian P, Rashid U, Islam A, Akil HM (2013) Activated carbon from various agricultural wastes by chemical activation with KOH: preparation and characterization. Journal of Biobased Materials and Bioenergy 7(6):708–714. https://doi.org/10.1166/jbmb.2013.1379 . Wei L, Sevilla M, Fuertes AB, Mokaya R, Yushin G (2011) Hydrothermal carbonization of abundant renewable natural organic chemicals for high-performance supercapacitor electrodes. Advanced Energy Materials 1(3):356–361. https://doi.org/10.1002/aenm.201100019 . Wei L, Sevilla M, Fuertes AB, Mokaya R, Yushin G (2012) Polypyrrole-derived activated carbons for high‐performance electrical double‐layer capacitors with ionic liquid electrolyte. Advanced Functional Materials 22(4):827–834. https://doi.org/10.1002/adfm.201101866 . Kim YJ, Lee BJ, Suezaki H, Chino T, Abe Y, Yanagiura T, Park KC, Endo M (2006) Preparation and characterization of bamboo-based activated carbons as electrode materials for electric double layer capacitors. Carbon 44(8): 1592–1594. https://doi.org/10.1016/j.carbon.2006.02.011 . Subramanian V, Luo C, Stephan AM, Nahm KS, Thomas S, Wei B (2007) Supercapacitors from activated carbon derived from banana fibers. The Journal of Physical Chemistry C 111(20):7527–7531. https://doi.org/10.1021/jp067009t . Rufford TE, Hulicova Jurcakova D, Khosla K, Zhu Z, Lu GQ (2010) Microstructure and electrochemical double-layer capacitance of carbon electrodes prepared by zinc chloride activation of sugar cane bagasse. Journal of Power Sources 195(3):912–918. https://doi.org/10.1016/j.jpowsour.2009.08.048 . Elmouwahidi A, Zapata Benabithe Z, Carrasco Marín F, Moreno Castilla C (2012) Activated carbons from KOH-activation of argan (Arganiaspinosa) seed shells as supercapacitor electrodes. Bioresource technology 111: 185–190. https://doi.org/10.1016/j.biortech.2012.02.010 . Xu B, Chen Y, Wei G, Cao G, Zhang H, Yang Y (2010) Activated carb on with high capacitance prepared by NaOH activation for supercapacitors. Materials Chemistry and Physics 124(1): 504–509. https://doi.org/10.1016/j.matchemphys.2010.07.002 . Li X, Xing W, Zhuo S, Zhou J, Li F, Qiao SZ, Lu GQ (2011) Preparation of capacitor's electrode from sunflower seed shell. Bioresource technology 102(2): 1118–1123. https://doi.org/10.1016/j.biortech.2010.08.110 . Choi SW, Tang J, Pol VG, Lee KB (2019) Pollen-derived porous carbon by KOH activation: Effect of physicochemical structure on CO 2 adsorption. Journal of CO 2 Utilization 29:146–155. https://doi.org/10.1016/j.jcou.2018.12.005 . Zhang L, Zhang F, Yang X, Leng K, Huang Y, Chen Y (2013) High-performance supercapacitor electrode materials prepared from various pollens. Small 9(8): 1342–1347. https://doi.org/10.1002/smll.201202943 . Wang S, Li W, Xin L, Wu M, Sun W, Lou X (2017) Pollen-inspired synthesis of porous and hollow NiO elliptical microstructures assembled from nanosheets for high-performance electrochemical energy storage. Chemical Engineering Journal 321: 546–553. https://doi.org/10.1016/j.cej.2017.03.142 . Lu C, Huang YH, Wu YJ, Li J, Cheng JP (2018) Camellia pollen-derived carbon for supercapacitor electrode material. Journal of Power Sources 394:9–16. https://doi.org/10.1016/j.jpowsour.2018.05.032 . Zhang Y, Li X, Dong P, Wu G, Xiao J, Zeng X, Zhang Y, Sun X (2018) Honeycomb-like hard carbon derived from pine pollen as high-performance anode material for sodium-ion batteries. ACS Applied Materials & Interfaces 10(49): 42796–42803. https://doi.org/10.1021/acsami.8b13160 . Liu S, Liang Y, Zhou W, Hu W, Dong H, Zheng M, Hu H, Lei B, Xiao Y, Liu Y (2018) Large-scale synthesis of porous carbon via one-step CuCl2 activation of rape pollen for high-performance supercapacitors. Journal of Materials Chemistry A 6(25):12046–12055. https://doi.org/10.1039/C8TA02838A . Wan L, Song P, Liu J, Chen D, Xiao R, Zhang Y, Chen J, Xie M, Du C (2019) Facile synthesis of nitrogen self-doped hierarchical porous carbon derived from pine pollen via MgCO 3 activation for high-performance supercapacitors. Journal of Power Sources 438:227013. https://doi.org/10.1016/j.jpowsour.2019.227013 . Liu Y, An Z, Wu M, Yuan A, Zhao H, Zhang J, Xu J (2020) Peony pollen derived nitrogen-doped activated carbon for supercapacitor application. Chinese Chemical Letters 31(6):1644–1647. https://doi.org/10.1016/j.ccl . Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5742394","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":398499568,"identity":"421796b1-bca7-4135-91f9-260babcea49f","order_by":0,"name":"Funda Ersoy Atalay","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCklEQVRIiWNgGAWjYBAC9gYGBgkIC4g/GECFefBo4TkA0SLBwMzAwDgDSYsEUVqY4Ybj1SKRe/DGDwa7Ov5m5mfSNgV35MwlEhgfvG1jqDNvwKUlL9myhyFZQuIwm5l0jsEzY8sZCcyGc9sYJGQOYNdiL5FjJsHDwCzBcJgBpOVw4oYbCWzSvEAtuFzGA9Qi+YehXkL+MPs3aQuIFvbfhLRI8zAcljA4zGMmzQC1hRmvFp43xtYyBsclNx7mKbbsMThsbHDmYbPknHMSkjNwaWHPMbz5pqKaX+54+8YbP/4cljM4nnzww5syG36coQwGkBhkgSpibGDAEy0ogPkDUcpGwSgYBaNgxAEAlbxLif3Mb9IAAAAASUVORK5CYII=","orcid":"","institution":"Inonu University","correspondingAuthor":true,"prefix":"","firstName":"Funda","middleName":"Ersoy","lastName":"Atalay","suffix":""},{"id":398499569,"identity":"572bb125-3321-4dbb-b6c2-58cc7fcc834f","order_by":1,"name":"Harun Kaya","email":"","orcid":"","institution":"Malatya Turgut Ozal University","correspondingAuthor":false,"prefix":"","firstName":"Harun","middleName":"","lastName":"Kaya","suffix":""},{"id":398499570,"identity":"67d4d795-a091-4166-b22c-5d977795296e","order_by":2,"name":"Aydan Aksogan Korkmaz","email":"","orcid":"","institution":"Malatya Turgut Ozal Univ, Hekimhan MES Vocat Sch, Min Technol","correspondingAuthor":false,"prefix":"","firstName":"Aydan","middleName":"Aksogan","lastName":"Korkmaz","suffix":""},{"id":398499575,"identity":"6a0947f3-b8c9-4897-9179-12837dcf604c","order_by":3,"name":"Seher Guler","email":"","orcid":"","institution":"Inonu University","correspondingAuthor":false,"prefix":"","firstName":"Seher","middleName":"","lastName":"Guler","suffix":""}],"badges":[],"createdAt":"2024-12-31 14:08:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5742394/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5742394/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":73315230,"identity":"3d8c173a-3754-43bb-919f-aea5cd27ac75","added_by":"auto","created_at":"2025-01-08 19:54:53","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":18040,"visible":true,"origin":"","legend":"\u003cp\u003eTGA/DTA analysis of pine pollen\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/02113a11c1b652072ef2368a.png"},{"id":73315233,"identity":"ac602a43-ddf7-47b8-999e-40f5cfefcc07","added_by":"auto","created_at":"2025-01-08 19:54:53","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":260196,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of pine pollen subjected to various treatments. a) After hydrothermal treatment, b-d) After activation with KOH at different ratios; 1:1, 1:2, and 1:3, respectively.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/245b9861ace4818233e006c6.png"},{"id":73316094,"identity":"f8d34a81-e4fd-4f8b-b736-62447ade2474","added_by":"auto","created_at":"2025-01-08 20:02:53","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":9588,"visible":true,"origin":"","legend":"\u003cp\u003eXRD spectrum of raw pollen, hydrothermal processing pollen, KAC, and CuAC\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/2a0b412ee76cdd43da82f3be.png"},{"id":73317264,"identity":"745e65a0-ce05-4355-b31c-ab358682c404","added_by":"auto","created_at":"2025-01-08 20:10:53","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":200745,"visible":true,"origin":"","legend":"\u003cp\u003eThe SEM images of pine pollen after activation with CuCl\u003csub\u003e2\u003c/sub\u003e at different ratios of a)1:1, b)1:3, c)1:5, d)1:20\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/961d6b2003598a6bd991a99e.png"},{"id":73315245,"identity":"ed4787f8-817d-4d34-80d6-319d08397c5c","added_by":"auto","created_at":"2025-01-08 19:54:53","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":62138,"visible":true,"origin":"","legend":"\u003cp\u003eThe EDX spectrum of a) KAC at a ratio of 1:2 and b) CuAC at a ratio of 1:5, c) The Raman spectrum of raw pollen, hydrothermal pollen, KAC and CuAC.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/d13b5c3072c4f1c6a9fcb214.png"},{"id":73316100,"identity":"8a521cc0-ede6-4fa7-ae64-0ea5c8dcc8c2","added_by":"auto","created_at":"2025-01-08 20:02:54","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":69241,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea, b)\u003c/strong\u003eCV curves of KAC and CuAC porous carbon electrodes at different scanning rates. \u003cstrong\u003ec,d).\u003c/strong\u003e Galvanostatic CD curves of KAC and CuAC porous carbon electrodes at various current densities \u003cstrong\u003ee,f)\u003c/strong\u003e The first five cyclic charge-discharge curves of KAC and CuAC porous carbon electrodes\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/10a0fb7c754b7e5f7ebe3b52.png"},{"id":73315247,"identity":"3c242a07-56c0-45e3-8471-60065f4a1ed2","added_by":"auto","created_at":"2025-01-08 19:54:54","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":16653,"visible":true,"origin":"","legend":"\u003cp\u003ea) Comparative capacitance plot as a function of cycles of KAC and CuAC electrodes, b) \u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eNyquist curve of KAC and CuAC electrodes after CV and 5000 CD cycles.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/ab31d3b03d10aae0e8e8e6bf.png"},{"id":73317266,"identity":"fcd7c391-6aee-4a6b-8cf1-9ff000bfde0b","added_by":"auto","created_at":"2025-01-08 20:10:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1261668,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/f8fed4f5-146c-41ad-a7ef-a83faca18a71.pdf"},{"id":73315231,"identity":"b5cdec57-f737-4a41-8ad7-8c6eb02a2d8c","added_by":"auto","created_at":"2025-01-08 19:54:53","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1398238,"visible":true,"origin":"","legend":"","description":"","filename":"supplemantarymaterials.docx","url":"https://assets-eu.researchsquare.com/files/rs-5742394/v1/1334522ade2d37fef29a3bb1.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Pine Pollen-Derived Activated Carbon for High-Performance Supercapacitor Electrodes: A Comparative Study of KOH and CuCl 2 Activation","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eElectrochemical energy storage devices, such as lithium-ion batteries and supercapacitors, play a crucial role in various applications, ranging from electronics to electric vehicles. While both lithium-ion batteries and supercapacitors have their strengths, supercapacitors are known for their high power density (410 kW/kg) and exceptional cycle stability. However, they do have a limitation when it comes to energy density, typically ranging from 5 to 10 Wh/kg [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSupercapacitors operate based on the principle of ion adsorption from an electrolyte onto an electrode with a large surface area [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. They can be broadly classified into three categories: electrical double-layer capacitors, hybrid capacitors, and pseudocapacitors [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Electrical double-layer capacitors store charge purely through electrostatic charge accumulation at the electrode interface. On the other hand, pseudocapacitors store charge through fast and reversible surface redox processes [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Despite their remarkable capabilities, supercapacitors have not yet achieved widespread adoption in the energy storage market due to their limited energy density. However, researchers are actively working on overcoming this challenge by developing innovative energy storage materials. The ultimate goal is to enhance the energy density of supercapacitors without compromising their high power density and cycling stability. This requires the discovery and design of new electrode materials with increased energy storage capacity. Researchers are exploring various approaches such as advanced carbon-based materials, metal oxides, conducting polymers, and hybrid materials.\u003c/p\u003e \u003cp\u003eCarbon-based materials, such as activated carbon and carbon nanotubes, are widely used in supercapacitor electrodes due to their high surface area and electrical conductivity. Metal oxides, including manganese oxide and ruthenium oxide, offer higher energy storage capabilities through redox reactions. Conducting polymers, such as polyaniline and polypyrrole, exhibit pseudocapacitive behavior and can store charge through redox processes. Hybrid materials, combining two or more components, aim to leverage the advantages of different materials to achieve improved energy density. In addition to material advancements, researchers are also investigating novel electrode architectures and electrolyte systems to enhance the overall performance of supercapacitors. By tailoring the electrode structure and optimizing the electrolyte composition, it is possible to further enhance the energy storage capabilities of supercapacitors. The ongoing efforts to enhance the energy density of supercapacitors are driven by the desire to develop energy storage systems that can provide both high power and high energy density. Such advancements would open up new possibilities for applications requiring rapid energy delivery and high cycling stability, such as electric vehicles, renewable energy integration, and grid-scale energy storage. In conclusion, while supercapacitors have not yet achieved widespread adoption in the energy storage market due to their limited energy density, ongoing research and development efforts are focused on overcoming this challenge. By exploring new energy storage materials, optimizing electrode architectures, and refining electrolyte systems, researchers aim to unlock the full potential of supercapacitors as a viable and efficient energy storage solution.\u003c/p\u003e \u003cp\u003eTo evaluate the performance of a supercapacitor, it is essential to consider critical aspects related to electrodes and electrolytes. The capacitive performance of electrodes can be enhanced by utilizing electrode materials that are stable, long-lasting, and electrically conductive [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Commonly used materials for supercapacitor electrodes include metal oxides like MnO\u003csub\u003e2\u003c/sub\u003e, NiO, and Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, conductive polymers such as polypyrrole, polythiophene, and polyaniline, as well as various carbon materials. Additionally, researchers are continuously developing new electrode materials such as metal phosphites, metal sulfides, and porous organic polymers. Among these options, low-cost carbon materials derived from renewable biomass sources like cellulose, chitin, chitosan, and lignin have gained significant attention in recent years due to their appealing structure, abundance, renewability, and environmental friendliness when compared to conventional carbon materials [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBiomass-based supercapacitors have become a subject of great interest because of their excellent electrochemical properties [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Unlike other carbon materials, carbon materials derived from biomass have the advantage of inheriting the unique structure, defects, and chemical composition of their precursor biomass during the carbonization process. Consequently, biomass-derived carbon materials offer high capacitance, improved stability in terms of speed, and excellent cycling performance in supercapacitors [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eActivated carbon is a carbon-based material known for its amorphous nature, large internal surface area, and extensive porosity. It possesses a non-graphite, microcrystalline carbon structure, and exhibits remarkable properties such as excellent electrical conductivity, high thermal stability, and notable surface reactivity. Activated carbon production involves various methods, including pyrolysis, hydrothermal processes, and chemical or physical activation techniques. Additionally, microwave-assisted treatment with activation agents can also be employed [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the field of electrode applications for supercapacitors, numerous techniques have been developed to prepare carbons with a significantly high specific surface area. One such approach involves a two-stage process combining pyrolysis and activation, which continues to be extensively investigated using a diverse range of biomass wastes, coals, and polymers [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Many studies have successfully utilized activated carbons derived from biomass sources in the design of supercapacitors [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Examples include eucalyptus wood [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], coconut bark [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], bamboo [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], banana fiber [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], sugar cane pulp [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], argan seed shell [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], apricot peel [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], and sunflower seed husk [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], among others.\u003c/p\u003e \u003cp\u003eThese biomass-derived activated carbons exhibit desirable characteristics for supercapacitor applications, owing to their unique pore structures and surface properties. It is worth noting that activated carbons produced through chemical activation using agents like KOH, K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, ZnCl\u003csub\u003e2\u003c/sub\u003e, or H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e tend to possess more well-developed pore structures compared to those obtained via physical activation using CO\u003csub\u003e2\u003c/sub\u003e or water vapor [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Such variations in activation methods and carbon sources provide researchers with a wide range of options for tailoring the properties of activated carbons, enabling the design of supercapacitors with enhanced performance and energy storage capabilities.\u003c/p\u003e \u003cp\u003eAlso, supercapacitor electrodes have been produced using plant pollen as a source of activated carbon. Zhang et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] conducted research on supercapacitor electrode materials using plant pollen like lotus, peony, and camellia. By carbonizing lotus pollen, they achieved a high surface area of 3037 m\u0026sup2;/g and a large pore density of 2.27 cm\u0026sup3;/g. Peony and camellia pollen carbonization resulted in surface areas of 2673 m\u0026sup2;/g and 2765 m\u0026sup2;/g, respectively. The symmetrical supercapacitor using lotus pollen exhibited a capacitance of 207 F/g at 1 A/g current in the EMIMBF4 electrolyte.\u003c/p\u003e \u003cp\u003eWang et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] synthesized nanolayered, porous NiO elliptical microstructures using rapeseed pollen as a template. The resulting pollen-molded NiO served as a supercapacitor electrode with high specific capacitance (198.7 mAh/g at 1 A/g), excellent capacity (89.2 mAh/g at 30 A/g), long cycle life (103.3% retention after 10,000 cycles), and high energy/power density (66.4 Wh/kg energy density and 22.2 kW/kg power density).\u003c/p\u003e \u003cp\u003eLu et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] developed carbon material for supercapacitor electrodes from camellia pollen through a hydrothermal process with controlled NH\u003csub\u003e4\u003c/sub\u003eBF\u003csub\u003e4\u003c/sub\u003e content and subsequent carbonization. The sample treated with 0.015 g/ml NH\u003csub\u003e4\u003c/sub\u003eBF\u003csub\u003e4\u003c/sub\u003e during hydrothermal treatment exhibited the highest specific surface area of 526 m\u0026sup2;/g at a current density of 0.5 A/g. It also demonstrated a significant specific capacitance of 205 F/g in a 2 M KOH solution, along with excellent cycle stability by retaining 96.2% of its initial capacitance after 10,000 cycles.\u003c/p\u003e \u003cp\u003eIn a study conducted by Zhang et al. \u003csup\u003e[24]\u003c/sup\u003e in 2018, they used pine pollen to produce activated carbon material for sodium-ion batteries. By carbonizing pine pollen at 900\u0026deg;C for 1 hour with a heating rate of 5\u0026deg;C/min in an Ar atmosphere, they obtained a material with a specific surface area of 171.54 m\u003csup\u003e2/\u003c/sup\u003eg and a larger layer spacing of 0.41 nm. The initial discharge capacity of this material was determined to be 370 mAh/g at a current density of 0.1 A/g. Impressively, even after 200 cycles, the material maintained 98% of its initial capacitance, demonstrating good discharge capacity.\u003c/p\u003e \u003cp\u003eIn another study by Liu et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] in 2018, they investigated the synthesis of porous carbon using rapeseed pollen activated by CuCl\u003csub\u003e2\u003c/sub\u003e for supercapacitors. The resulting rapeseed pollen carbon exhibited a sphere-like structure with a large specific surface area of 2488 m\u003csup\u003e2\u003c/sup\u003e/g and a high heteroatom content. When tested as an electrode in a 6 M KOH aqueous electrolyte at a current density of 0.5 A/g, the rapeseed pollen carbon electrode showed a capacitance of 390 F/g. Furthermore, the electrode displayed excellent cycle stability, retaining 92.9% of its initial capacitance after 10,000 cycles at 20 A/g.\u003c/p\u003e \u003cp\u003eIn 2019, Wan et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] utilized carbon material derived from N-doped pine pollen, where MgCO\u003csub\u003e3\u003c/sub\u003e served as the activation agent, for supercapacitors. The N-doped pine pollen exhibited a hierarchical porous structure with interconnected meso/macropores, a large surface area of 1311.2 m\u003csup\u003e2\u003c/sup\u003e/g, and high nitrogen and oxygen content. As a supercapacitor electrode in a three-electrode system, the N-doped pine pollen demonstrated a high specific capacitance of 419.6 F/g at a current density of 1 A/g, with favorable behavior from 1 to 100 A. Moreover, the 6 M KOH aqueous electrolyte showcased superior long-term cycling stability, with only a 2.6% loss in initial capacitance after 10,000 cycles.\u003c/p\u003e \u003cp\u003eLiu et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] in 2020 examined the supercapacitor properties of peony pollen. They prepared porous carbon microspheres by employing a hydrothermal method followed by carbonization, with NH\u003csub\u003e4\u003c/sub\u003eBF\u003csub\u003e4\u003c/sub\u003e as an abrasive and KOH as an activator to modify the material's porosity. The resulting material exhibited a high BET-specific surface area of 824.69 m\u003csup\u003e2\u003c/sup\u003e/g.\u003c/p\u003e \u003cp\u003eCao et al. [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] conducted a study where they successfully developed a controllable carbon material with a hierarchical porous structure through an integrated process involving carbonization, activation, and nitrogen doping. In their research, they utilized nitrogen-rich camellia pollen as the carbon precursor and introduced NH\u003csub\u003e4\u003c/sub\u003eCl as an activator and additive. The resulting N-doped carbon material exhibited a higher nitrogen content of 3.82%, along with a desirable distribution of pore sizes and a larger specific surface area of 810 m\u003csup\u003e2\u003c/sup\u003e/g. They further constructed a symmetrical supercapacitor using this material, which demonstrated a high energy capacity of 13.3 Wh/kg in a 6 M KOH electrolyte. Remarkably, the supercapacitor also exhibited excellent cycling stability, with a capacitance retention rate of 85.4% after undergoing 20,000 cycles at 20 A/g.\u003c/p\u003e \u003cp\u003eIn this study, pine pollen was utilized as an activated carbon material for the first time in the design of a supercapacitor electrode. Pine pollen was chosen due to its easy accessibility, low cost, and eco-friendly nature. The activation process involved hydrothermal carbonization of pine pollen, followed by the use of two chemical activation agents, namely KOH and CuCl\u003csub\u003e2\u003c/sub\u003e. This innovative utilization of activated pine pollen as the active material for the electrode makes the study original and holds promise for future research in this field.\u003c/p\u003e"},{"header":"2. Experimental methods","content":"\u003cp\u003e \u003cb\u003ePreparation of active carbon\u003c/b\u003e \u003c/p\u003e \u003cp\u003ePine pollen was harvested from pine trees in Malatya, Inonu University campus, in April and May. Male pine flowers were collected before they were fully pollinated and dried by laying them on blotting paper in the sunlight parts of the laboratory or dried at 60\u0026deg;C in a drying oven. It was observed that the flowers spontaneously release pollen powders within 2 or 5 days, depending on the weather conditions. For the purification of pollen from dust, garbage, etc., foreign materials involved in the collection and drying stages, pollen was sieved with 106 \u0026micro;m and 75 \u0026micro;m sieves (Retsch), respectively. Then 45 \u0026micro;m sieve suitable for pine pollen size was used to obtain pure pollen. 15 g of dried pollen was subjected to a hydrothermal reaction in 80 ml of deionized water for 12 hours at 200\u0026deg;C after washing several times with deionized water and ethanol. The hydrothermal reaction was carried out in a 100 ml Teflon liner stainless steel container (Step 1). Then, the product was filtered through a microporous filter by the vacuum filtration method, and the resulting residue was dried in a vacuum oven at 60\u0026deg;C for 36 hours. The resulting pollen powder material was mixed separately with KOH and CuCl\u003csub\u003e2\u003c/sub\u003e in 1:1, 1:2, 1:3, 1:5, 1:10, and 1:20 until a homogenous mixture was obtained (Step 2). Then heat-treated in nitrogen flow to 900\u0026deg;C with a heating rate of 2\u0026deg;C/min and held for 2 hours (Step 3). The obtained powder was washed with 0.5 M HCl and deionized water. Washing processes with deionized water were continued until the pH was 7 (Step 4). It was dried at 60\u0026deg;C in a vacuum oven for 36 hours (Step 5). Eventually, this porous carbon material to be used for the electrode was obtained. Pollen isolation process steps are presented in Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of electrode\u003c/b\u003e \u003c/p\u003e \u003cp\u003eIn the production of supercapacitor electrodes, porous carbon (75%) was used as active material, acetylene black (15%) as a conductivity agent, and PVDF (10%) as a binder. In the first stage, porous carbon and acetylene black were mixed in the Zr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e mortar in the glovebox for 45 min, then PVDF was added to the mixture and mixed homogeneously in the mortar for 30 min in total. In the second stage, a slurry was formed by adding approximately 0.5 ml of NMP to this homogeneous mixture. Ni foam used as a collector, with acid, acetone, and purified water, has been cleared. 5 g of the slurry material was taken and dropped on the pre-cleaned pure Ni foam of 13 mm diameter. The carbon-containing electrode activated with KOH and CuCl\u003csub\u003e2\u003c/sub\u003e was KAC and CuAC, respectively. The formed porous carbon material was used as a working electrode in a three-electrode electrochemical cell. A platinum plate with an area of 2.5x2.5 cm with 99.99% purity was used as the counter electrode. Leak-free reference electrode (Ag/AgCl) was used as a reference electrode. 6 M KOH was put into the electrochemical cell as an electrolyte. The cell preferred in the experiments was made of pyrex glass with a length of 8.5 cm, an inner diameter of 4.5 cm and an outer diameter of 5.5 cm, and a Teflon cap with the same characteristics as the internal diameter dimensions were also used.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCharacterization of materials\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe porous carbon material morphology was obtained using Scanning Electron Microscopy (SEM, FEI Nova Nano SEM 450). The structure was investigated by X-ray diffraction (XRD, Cu-Kα) and Raman Spectroscopy (532 nm, UniRAM Micro Raman System). Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) analysis was used to determine specific surface area by N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption at 77 K (Gemini VII2390t, Micrometrics). The specific surface area was calculated using adsorption data at the relative pressure range of 0\u0026ndash;1. The Barrett-Joyner-Halenda (BJH) pore size distribution was calculated based on the adsorption branch of the isotherm. Before analysis, each sample was degassed at 300\u0026deg;C in an argon atmosphere for 2 hours. TGA-50, Shimadzu, from ambient temperatures to 900\u0026deg;C conducted thermogravimetric analysis (TGA) of carbon materials curves. The elemental compositions of carbon (C), hydrogen (H), and nitrogen (N) contents of obtained materials were determined by a CHNS analyzer (Perkin Elmer Series II 2400).\u003c/p\u003e \u003cp\u003e \u003cb\u003eElectrochemical performance tests\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe electrochemical performance was tested by cyclic voltammetry (CV), charge-discharge (CD) testing, and impedance spectroscopy techniques using a Gamry 3000 interface potentiostat/galvanostat/ZRA. CV measurements were made at different scan rates (1-200mV/s). Also, CD measurements were performed between 1\u0026ndash;5 A/g of constant current density. Nyquist curves were obtained at open circuit potential applying 5 mA constant current. The frequency limits were typically set between 3mHz and 100kHz.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003e \u003c/p\u003e \u003cp\u003eThe TGA/DTA analysis graph of pine pollen is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. It is seen that the first 16.6% mass loss in pine pollen is from room temperature to 170\u0026deg;C, and it is thought that the mass loss here is due to the removal of water and ethanol. It is believed that the second and highest mass loss is 43.9% at an average of 210\u0026ndash;400\u0026deg;C, and the reason for the mass loss here is the removal of carbohydrates and proteins. It is estimated that the 20.4% mass loss in the last stage is at 410\u0026ndash;560\u0026deg;C due to the lipid removal. The remaining substance amount at 900\u0026deg;C is 9.12%. Carbonization starts after approximately 610\u0026deg;C.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. TGA/DTA analysis of pine pollen.\u003c/p\u003e \u003cp\u003eThe surface area parameters of the samples obtained by activation with different chemicals are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. While the surface area of the pure pine pollen powder calculated from N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherms was 2.41 m\u003csup\u003e2\u003c/sup\u003e/g, the pore volume was 1.92x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e/g and the pore size was 4.9 nm. After the hydrothermal reaction, the surface area increased to 5.18 m\u003csup\u003e2\u003c/sup\u003e/g. The best surface area value was obtained as 2030.32 m\u003csup\u003e2\u003c/sup\u003e/g in the sample KAC at the ratio of 1:2. The pore volume also increased from 1.92x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e/g to 1219.26x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e/g. This is approximately 634 times greater than the initial and is a significant increase.\u003c/p\u003e \u003cp\u003eOn the other hand, the best surface area value of the sample CuAC is 736.80 m\u003csup\u003e2\u003c/sup\u003e/g, pore volume is 391.16x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e/g at a ratio of 1:5. The pore volume increased approximately 203 times compared to the initial. The material obtained from CuAC contains spherical microparticles, and the sample KAC contains porous and thin flakes. Activation with KOH differs significantly from activation with CuCl\u003csub\u003e2\u003c/sub\u003e. Since KOH is alkaline, it is very active at high temperatures, but CuCl\u003csub\u003e2\u003c/sub\u003e is acidic and can cause activation at very low temperatures. In all subsequent studies, the expression of KAC at a ratio of 1:2 and CuAC at a ratio of 1:5 describe the active carbons obtained.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChange in surface parameters as a result of activation of pine pollen with KAC and CuAC.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003cp\u003e(ratio of pollen:KOH)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSurface area (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePore volume (cm\u003csup\u003e3\u003c/sup\u003e/g)x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePore diameter (nm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRaw pine pollen\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHydrothermal-treated pine pollen\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eActivation rate of KAC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1709.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e878.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2030.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1219.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1510.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e896.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.62\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eActivation rate of CuAC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e113.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.93\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e171.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e259.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e63.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e736.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e391.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.54\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e382.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e81.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1:20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e197.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the SEM photographs of pine pollens, it was observed that the isolated pine pollens were approximately 40\u0026ndash;43 \u0026micro;m in size. The pollen partially shrunk in size after the hydrothermal reaction and inward collapse occurred in the morphology due to pressure (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). It was also observed that a porous structure was formed due to the removal of the oil layers on its surface. After the KOH activation structure of the pollen disappeared, a thin porous structure was obtained. This araises the strong etching effect of the KOH. Detailed SEM images of different KOH ratios were also given in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eb-d.\u003c/p\u003e \u003cp\u003eAlmost no material was left after the heat treatment for larger KOH ratios (\u0026gt;\u0026thinsp;2). The reactions taking place in the can be expressed as Eq.\u0026nbsp;(1\u0026ndash;3).\u003c/p\u003e\n\u003ch3\u003e4KOH + HO + 2C → KCO + KO + 3H + CO (1)\u003c/h3\u003e\n\u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;2C \u0026rarr; 2K\u0026thinsp;+\u0026thinsp;3CO (2)\u003c/p\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;C \u0026rarr; 2K\u0026thinsp;+\u0026thinsp;CO\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003e (3)\u003c/p\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e formed due to the reaction is another activation material for obtaining porous carbon. Therefore, the resulting product contains a large amount of K content, which agrees with the XRD results in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Despite repeated washing with acid and water, K remained in the structure. This is because the melting point of K is small (63.5\u0026deg;C) compared to the heat treatment temperature and therefore, it is trapped in the carbon network. Even if the resulting product is low in quantity, the surface area and porosity achieved with KOH are considerable. As an alternative to KOH, chemical materials such as ZnCl\u003csub\u003e2\u003c/sub\u003e and CuCl\u003csub\u003e2\u003c/sub\u003e have been used as activation agents [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In contrast to the material obtained from KOH activation, spherical morphology was preserved in CuCl\u003csub\u003e2\u003c/sub\u003e activation. However, with the effect of high temperature, the dimensions, initially about 40 \u0026micro;m, decreased by 25% and were measured as 10 \u0026micro;m.\u003c/p\u003e \u003cp\u003eSEM image of the material obtained as a result of CuAC is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The material obtained contains varying-sized microspheres with nano-grains on the surface. The reaction mechanism is as follows (Eq.\u0026nbsp;4\u0026ndash;5).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003e3CuCl + 2HO + C → Cu + 2CuCl + CO + 4HCl (4)\u003c/h3\u003e\n\n\u003ch3\u003e4CuCl + 2HO + O + C → 4Cu + CO + 4HCl (5)\u003c/h3\u003e\n\u003cp\u003eThe presence of Cu content in the structure can be seen from the XRD spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e) and EDX analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). The unlabeled peaks of around 1.74 eV and 2.12 eV in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea are due to the Si used as the substrate and the Au coating for good imaging, respectively. The unlabeled peaks around 1.00 eV in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, is due to the Cu content of the sample. In addition, the structure consists of 90.2% C and 9.8% O in terms of atomic ratio. Like KOH, it was thought that CuCl\u003csub\u003e2\u003c/sub\u003e was trapped in the carbon frame due to its low melting temperature; therefore, the Cu content could not be removed. CuCl\u003csub\u003e2\u003c/sub\u003e was formed in the activation process and acted as an activation agent.\u003c/p\u003e \u003cp\u003eAlthough the product was washed many times with either 0.5 M or 2 M HCl, the Cu content in the structure could not be removed. Liu et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] stated that the rape pollen structure was preserved in the activation process with CuCl\u003csub\u003e2\u003c/sub\u003e. Our study observed from the SEM images in Figure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e that the pollen structure was not preserved but that a microsphere of 2 \u0026micro;m diameter was formed on which 500 nm nanoparticles were located. This indicates that the two air sacs (saccus) at the edge of the pine pollen have disappeared, and the size of the spherical structure (corpus) in the middle region has shrunk after the high temperature. Similar results were obtained for the products obtained from activation at different CuCl\u003csub\u003e2\u003c/sub\u003e ratios (Figure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRaman results of KAC and CuAC are given in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec. Choi et al. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] found a similar result in the Raman spectrum of porous carbon produced from bee pollen. Raman spectra of hydrothermal pollen show C-H stretch bands around 2000\u0026ndash;2750 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. It is seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec that carbonization has taken place as a result of the activations. It is seen that D and G bands are formed after activation with KOH, which indicates the obtaining of the porous carbon structure. The G band represents the in-plane motion of the C sp\u003csup\u003e2\u003c/sup\u003e atom pairs and expresses regular structures, while the D band is known to be characteristic of the sp\u003csup\u003e3\u003c/sup\u003e disordered graphite. It was observed that the peak intensities of these bands increased significantly with activation. The increase in the ID/IG ratio, that is, in the material's electrical conductivity, indicates that the electrical conductivity of the initially insulating material increases. This will directly reflect the increased capacitance of the porous carbon-containing supercapacitor electrodes to be formed. When CuCl\u003csub\u003e2\u003c/sub\u003e is used as an activation agent in carbonization at 900\u0026deg;C, first CuCl formation occurs at 500\u0026deg;C and then Cu formation occurs at 600\u0026deg;C. The low melting point (426\u0026deg;C) of CuCl\u003csub\u003e2\u003c/sub\u003e caused the pollen to be trapped inside the C skeleton. With the increased heat treatment temperature, the pollen could not preserve its structure and its size decreased to 2 \u0026micro;m.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The SEM images of pine pollen after activation with CuCl\u003csub\u003e2\u003c/sub\u003e at different ratios of a) 1:1, b) 1:3, c) 1:5, d) 1:20\u003c/p\u003e \u003cp\u003eIn CuAC, the Cu content in the structure could not be removed despite washing with HCl at different molar ratios (0.5-2 M). Therefore, the structure contains more Cu than C. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec shows the typical properties of carbon materials and indicates the porous and disordered structure of the material. Two broadband gaps were obtained around 1306 and 1603 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to the D and G bands of the porous carbon.\u003c/p\u003e \u003cp\u003eCHNS analysis results are given in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The highest C content belongs to KAC among the different pollen-based materials. While the amount of C in pine pollen was 49.22% initially, it was 60.74% with hydrothermal carbonization and then 77.39% and 62.92%, KAC and CuAC with activation, respectively.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElemental analysis results of materials.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eH (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eS (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRaw pine pollen\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e49.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHydrothermal processing pine pollen\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eKAC (1:2)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e77.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCuAC (1:5)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e62.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eElectrochemical performance test results\u003c/b\u003e \u003c/p\u003e \u003cp\u003eElectrochemical performance testing of supercapacitor electrodes was performed in a 6M KOH electrolyte versus Ag/AgCl electrode in a three-electrode system. Cyclic voltammetry (CVs) curves of KAC and CuAC electrodes at different scan rates with a potential window from \u0026minus;\u0026thinsp;1.0 to 0V are given in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, b. Both electrodes showed an almost rectangular-like shape typical of capacitive or EDLC electrode materials. But only a small shoulder around \u0026minus;\u0026thinsp;0.75 V in the cathodic region is observed for KAC. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec, d shows GCD curves at various current densities measured in the potential range of 0 to -1V vs. Ag/AgCl. Almost ideal triangular shapes are observed for all the GCD curves, which can be attributed to the EDCL nature arising from activated carbon curves. The observed symmetrical charge and discharge curves for both electrodes indicate excellent electrochemical reversibility. In parallel with the increase in the current value, the charge-discharge time decreased. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee, f shows KAC\u0026rsquo;s and CuAC 's first five cyclic charge-discharge curves for a constant current value of 5 A/g. Specific capacitance is calculated 230 F/ g for KAC and 176.2 F/g for CuAC at 5 A/g current density. Due to its hierarchical porous and more disordered structure, which is caused by KOH reactivation, KAC electrode exhibits much higher capacitance compared with CuAC electrode. Variation of specific capacitance as a function of the number of cycles is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea. The specific capacitance value of KAC decreased from 230 F/g to 173 F/g in 3000 cycles of charge-discharge measurements. The electrode exhibited an almost constant specific capacitance value of approximately 175 F/g after 2000 cycles. On the contrary, the specific capacitance of the CuAC electrode, initially 176.2 F/g, decreased to 163.8 F/g after 5000 cycles. After 5000 charge-discharge cycles, KAC and CuAC retained 76% and 93% of their initial capacitance values, respectively. Maximum energy densities were calculated as 31.94 Wh/kg and 24.43 Wh/kg for KAC and CuAC, respectively.\u003c/p\u003e \u003cp\u003eElectrochemical impedance measurements were conducted on the porous carbon electrodes that were produced. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb illustrates the Nyquist plot for both KAC and CuAC. For KAC, the curve slope was calculated as 67.8\u0026deg; with an ESR (Equivalent Series Resistance) value of 206 mΩ before 5000 cycles. After 5000 cycles, these values changed to 70.4\u0026deg; and 170.5 mΩ respectively. Regarding CuAC, initially, the angle value was determined as 57.8\u0026deg;, which increased to 70.4\u0026deg; after 5000 cycles. Additionally, the ESR value rose from 0.162 mΩ to 170.5 mΩ. These results indicate that the electrode structure and capacitive features remain intact. Furthermore, after 5000 cycles, there is a decrease in resistance observed in the mid-frequency region of the curve, attributed to reduced transfer resistance as ions penetrate deeper over time. A curve slope value of at least 45\u0026deg; is required for a supercapacitor, and the electrochemical tests demonstrate that electrodes derived from carbonizing pine pollen are promising candidates for supercapacitor electrodes.\u003c/p\u003e \u003cp\u003e \u003cb\u003eAC Supercapacitor device design\u003c/b\u003e \u003c/p\u003e \u003cp\u003eKAC, with the highest surface area (2030.32 m\u003csup\u003e2\u003c/sup\u003e/g), was used as the AC electrode. No matter how large the capacitance of the prepared AC electrode is, the energy density will be low if the potential range is small. Increasing the potential range will also significantly affect the energy to be stored. Therefore, an SC design was performed by combining two electrodes with the same properties using the Swagelok cell as shown in Figure S2. Cellulose filters with 0.45 nm were used as separators. CV curves were taken in Swagelok cells at different scanning rates in the potential range of -1.45 to +\u0026thinsp;0.42. An increase in current values were observed with an increasing scanning rate. The CV curves showed a close-to-rectangular shape in experiments where 6 M KOH was used as the electrolyte (Figure S3a, b). It is observed in Figure S3c that the initial specific capacitance value of 167 F/g hardly changes for 5000 cycles. Energy density was calculated as 81.11Wh/kg.\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this study, pine pollen, an environmentally friendly, renewable and inexpensive material, was used as a carbon source to design supercapacitor electrodes. Porous carbon production was achieved by activating KOH and CuCl\u003csub\u003e2\u003c/sub\u003e chemicals in different pollen ratios. The highest surface area was obtained as 2030.32 m\u003csup\u003e2\u003c/sup\u003e/g, while the Pine: KOH ratio was 1:2 (KAC). In the sample activated Pine: CuCl\u003csub\u003e2\u003c/sub\u003e at a ratio of 1:5, the specific surface area was obtained as 736.8 m\u003csup\u003e2\u003c/sup\u003e/g (CuAC). After the hydrothermally carbonization process, it was determined from the Raman spectra that they still contained organic groups. K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and CuCl are released during the carbonization process activation agent. Activation with CuCl\u003csub\u003e2\u003c/sub\u003e in all ratios except the 1:1 ratio has taken place. Activation with KOH at a ratio of 1:5 and above destroyed pine pollen. In addition, it has been determined that if the resulting gases are not swept away from the environment at sufficient speed, the resulting product will burn continuously and this will cause the pollen structure to disappear.\u003c/p\u003e \u003cp\u003eElectrochemical properties of KAC and CuAC samples in 6 M KOH electrolyte were investigated. Both KOH and CuAC electrodes exhibited EDLC properties in accordance with the literature [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The maximum specific capacitance of the KAC electrode was 230 F/g, while that of the CuAC electrode was 176.2 F/g. It has been observed that the supercapacitor device, which is formed by combining two similar electrodes using KAC, has a wide potential window in the potential range of -1.45 V to +\u0026thinsp;0.42 V. CV curves and has a rectangular appearance. It has been observed that the initial capacitance value has almost no changes even after 5000 cycles. As a result, electrochemical measurements of the device with two electrode designs showed a close-to-rectangular shape similar to the CV curves of an ideal supercapacitor.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDisclosure\u003c/h2\u003e \u003cp\u003e \u003cb\u003estatement\u003c/b\u003e: No potential conflict of interest was reported by the author(s).\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eF.E. Atalay; corresponding author; conceptualization, project administration, supervision, validation, methodology, data curation, formal analysis, writing\u0026mdash;review and editingH. Kaya; electrode fabrication and electrochemical measurements, methodology, data curation, analysisA.A. Korkmaz; production of activated carbon, analysis, investigation, writing\u0026ndash;original draftS. Guler; pollen harvesting, pollen isolation, analysis and investigation.\u003c/p\u003e\u003ch2\u003eAcknowledgments:\u003c/h2\u003e \u003cp\u003eThis work was supported Scientific and Technological Research Council of Turkey (TUBITAK) under Grant [218M267]; Inonu University BAP under Grant [FBG-2019-1709]; and Inonu University BAP under Grant [FYL-2020-2196].\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLyu L, Seong KD, Ko D, Choi J, Lee C, Hwang T, Cho Y, Jin X, Zhang W, Pang H, Piao Y (2019) Recent development of biomass-derived carbons and composites as electrode materials for supercapacitors. Materials Chemistry Frontiers 3(12): 2543\u0026ndash;2570. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1039/C9QM00348G\u003c/span\u003e\u003cspan address=\"10.1039/C9QM00348G\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCao L, Li H, Xu Z, Gao R, Wang S, Zhang G, Jiang S, Hou H, (2021) Camellia pollen-derived carbon with controllable N content for high‐performance supercapacitors by ammonium chloride activation and dual N‐doping. ChemNanoMat 7(1): 34\u0026ndash;43. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/cnma.202000531\u003c/span\u003e\u003cspan address=\"10.1002/cnma.202000531\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNajib S, Erdem E, (2019) Current progress achieved in novel materials for supercapacitor electrodes: mini-review. Nanoscale Adv 1: 2817\u0026ndash;2827. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1039/C9NA00345B\u003c/span\u003e\u003cspan address=\"10.1039/C9NA00345B\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHan X, Jiang H, Zhou Y, Hong W, Zhou Y, Gao P, Ding R, Liu E (2018) A high performance nitrogen-doped porous activated carbon for supercapacitor derived from pueraria. Journal of Alloys and Compounds 744: 544\u0026ndash;551. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jallcom.2018.02.078\u003c/span\u003e\u003cspan address=\"10.1016/j.jallcom.2018.02.078\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMehdi R, Khoja A H, Naqvi SR, Gao N, Amin NAS (2022) A Review on Production and Surface Modifications of Biochar Materials via Biomass Pyrolysis Process for Supercapacitor Applications. Catalysts 12(7):798. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/catal12070798\u003c/span\u003e\u003cspan address=\"10.3390/catal12070798\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLin S, Wang F, Shao Z (2021) Biomass applied in supercapacitor energy storage devices. Journal of materials science 56(3): 1943\u0026ndash;1979. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10853-020-05356-1\u003c/span\u003e\u003cspan address=\"10.1007/s10853-020-05356-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou J, Zhang S, Zhou YN, Tang W, Yang J, Peng C, Guo Z (2021) Biomass-derived carbon materials for high-performance supercapacitors: current status and perspective. Electrochemical Energy Reviews 4(2):219\u0026ndash;248. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s41918-020-00090-3\u003c/span\u003e\u003cspan address=\"10.1007/s41918-020-00090-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, W, Luo M, Wang X, Yang K, Zhou X (2020) Rapid synthesis of chitin-based porous carbons with high yield, high nitrogen retention, and low cost for high‐rate supercapacitors. International Journal of Energy Research 44(2):1167\u0026ndash;1178. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/er.5008\u003c/span\u003e\u003cspan address=\"10.1002/er.5008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYahya MA, Mansor MH, Zolkarnaini WA, Rusli NS, Aminuddin A, Mohamad K, Sabhan FAM, Atik AAA, Ozair LNA (2018) Brief review on activated carbon derived from agriculture by-product. AIP Conf. Proc. 1972 030023. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1063/1.5041244\u003c/span\u003e\u003cspan address=\"10.1063/1.5041244\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDiez N, Mysyk R, Zhang W, Goikolea E, Carriazo D (2017) One-pot synthesis of highly activated carbons from melamine and terephthalaldehyde as electrodes for high energy aqueous supercapacitors. Journal of Materials Chemistry A 5(28):14619\u0026ndash;14629. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1039/C7TA01424D\u003c/span\u003e\u003cspan address=\"10.1039/C7TA01424D\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhalil HPS, Jawaid M, Firoozian P, Rashid U, Islam A, Akil HM (2013) Activated carbon from various agricultural wastes by chemical activation with KOH: preparation and characterization. Journal of Biobased Materials and Bioenergy 7(6):708\u0026ndash;714. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1166/jbmb.2013.1379\u003c/span\u003e\u003cspan address=\"10.1166/jbmb.2013.1379\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWei L, Sevilla M, Fuertes AB, Mokaya R, Yushin G (2011) Hydrothermal carbonization of abundant renewable natural organic chemicals for high-performance supercapacitor electrodes. Advanced Energy Materials 1(3):356\u0026ndash;361. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/aenm.201100019\u003c/span\u003e\u003cspan address=\"10.1002/aenm.201100019\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWei L, Sevilla M, Fuertes AB, Mokaya R, Yushin G (2012) Polypyrrole-derived activated carbons for high‐performance electrical double‐layer capacitors with ionic liquid electrolyte. Advanced Functional Materials 22(4):827\u0026ndash;834. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/adfm.201101866\u003c/span\u003e\u003cspan address=\"10.1002/adfm.201101866\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim YJ, Lee BJ, Suezaki H, Chino T, Abe Y, Yanagiura T, Park KC, Endo M (2006) Preparation and characterization of bamboo-based activated carbons as electrode materials for electric double layer capacitors. Carbon 44(8): 1592\u0026ndash;1594. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.carbon.2006.02.011\u003c/span\u003e\u003cspan address=\"10.1016/j.carbon.2006.02.011\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSubramanian V, Luo C, Stephan AM, Nahm KS, Thomas S, Wei B (2007) Supercapacitors from activated carbon derived from banana fibers. The Journal of Physical Chemistry C 111(20):7527\u0026ndash;7531. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/jp067009t\u003c/span\u003e\u003cspan address=\"10.1021/jp067009t\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRufford TE, Hulicova Jurcakova D, Khosla K, Zhu Z, Lu GQ (2010) Microstructure and electrochemical double-layer capacitance of carbon electrodes prepared by zinc chloride activation of sugar cane bagasse. Journal of Power Sources 195(3):912\u0026ndash;918. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jpowsour.2009.08.048\u003c/span\u003e\u003cspan address=\"10.1016/j.jpowsour.2009.08.048\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eElmouwahidi A, Zapata Benabithe Z, Carrasco Mar\u0026iacute;n F, Moreno Castilla C (2012) Activated carbons from KOH-activation of argan (Arganiaspinosa) seed shells as supercapacitor electrodes. Bioresource technology 111: 185\u0026ndash;190. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biortech.2012.02.010\u003c/span\u003e\u003cspan address=\"10.1016/j.biortech.2012.02.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXu B, Chen Y, Wei G, Cao G, Zhang H, Yang Y (2010) Activated carb on with high capacitance prepared by NaOH activation for supercapacitors. Materials Chemistry and Physics 124(1): 504\u0026ndash;509. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matchemphys.2010.07.002\u003c/span\u003e\u003cspan address=\"10.1016/j.matchemphys.2010.07.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi X, Xing W, Zhuo S, Zhou J, Li F, Qiao SZ, Lu GQ (2011) Preparation of capacitor's electrode from sunflower seed shell. Bioresource technology 102(2): 1118\u0026ndash;1123. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biortech.2010.08.110\u003c/span\u003e\u003cspan address=\"10.1016/j.biortech.2010.08.110\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChoi SW, Tang J, Pol VG, Lee KB (2019) Pollen-derived porous carbon by KOH activation: Effect of physicochemical structure on CO\u003csub\u003e2\u003c/sub\u003e adsorption. Journal of CO\u003csub\u003e2\u003c/sub\u003e Utilization 29:146\u0026ndash;155. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jcou.2018.12.005\u003c/span\u003e\u003cspan address=\"10.1016/j.jcou.2018.12.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang L, Zhang F, Yang X, Leng K, Huang Y, Chen Y (2013) High-performance supercapacitor electrode materials prepared from various pollens. Small 9(8): 1342\u0026ndash;1347. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/smll.201202943\u003c/span\u003e\u003cspan address=\"10.1002/smll.201202943\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang S, Li W, Xin L, Wu M, Sun W, Lou X (2017) Pollen-inspired synthesis of porous and hollow NiO elliptical microstructures assembled from nanosheets for high-performance electrochemical energy storage. Chemical Engineering Journal 321: 546\u0026ndash;553. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cej.2017.03.142\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2017.03.142\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLu C, Huang YH, Wu YJ, Li J, Cheng JP (2018) Camellia pollen-derived carbon for supercapacitor electrode material. Journal of Power Sources 394:9\u0026ndash;16. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jpowsour.2018.05.032\u003c/span\u003e\u003cspan address=\"10.1016/j.jpowsour.2018.05.032\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang Y, Li X, Dong P, Wu G, Xiao J, Zeng X, Zhang Y, Sun X (2018) Honeycomb-like hard carbon derived from pine pollen as high-performance anode material for sodium-ion batteries. ACS Applied Materials \u0026amp; Interfaces 10(49): 42796\u0026ndash;42803. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acsami.8b13160\u003c/span\u003e\u003cspan address=\"10.1021/acsami.8b13160\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu S, Liang Y, Zhou W, Hu W, Dong H, Zheng M, Hu H, Lei B, Xiao Y, Liu Y (2018) Large-scale synthesis of porous carbon via one-step CuCl2 activation of rape pollen for high-performance supercapacitors. Journal of Materials Chemistry A 6(25):12046\u0026ndash;12055. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1039/C8TA02838A\u003c/span\u003e\u003cspan address=\"10.1039/C8TA02838A\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWan L, Song P, Liu J, Chen D, Xiao R, Zhang Y, Chen J, Xie M, Du C (2019) Facile synthesis of nitrogen self-doped hierarchical porous carbon derived from pine pollen via MgCO\u003csub\u003e3\u003c/sub\u003e activation for high-performance supercapacitors. Journal of Power Sources 438:227013. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jpowsour.2019.227013\u003c/span\u003e\u003cspan address=\"10.1016/j.jpowsour.2019.227013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu Y, An Z, Wu M, Yuan A, Zhao H, Zhang J, Xu J (2020) Peony pollen derived nitrogen-doped activated carbon for supercapacitor application. Chinese Chemical Letters 31(6):1644\u0026ndash;1647. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ccl\u003c/span\u003e\u003cspan address=\"10.1016/j.ccl\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Pine pollen, activated carbon, supercapacitor electrodes, energy storage","lastPublishedDoi":"10.21203/rs.3.rs-5742394/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5742394/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCarbon-containing materials are vital for supercapacitor electrodes. Activated porous carbons are especially attractive due to their high surface area, conductivity, and porous structure, making them ideal for double-layer supercapacitors. Recently, researchers have turned to biological materials like bacteria, algae, fungi, and pollen to create porous carbon structures. Among these, pine pollen stands out for its abundance and ease of collection.\u003c/p\u003e \u003cp\u003eThis study focused on converting pine pollen into porous carbon using hydrothermal carbonization in water, followed by activation with different agents. The carbonized pollen was activated with KOH and CuCl\u003csub\u003e2\u003c/sub\u003e at various ratios to form nanostructured porous carbons. Scanning electron microscope images showed that activation with KOH and CuCl\u003csub\u003e2\u003c/sub\u003e partially altered the pollen morphology. The sample with a 1:2 pollen-to-KOH ratio had the highest surface area at 2030.32 m\u0026sup2;/g.\u003c/p\u003e \u003cp\u003eTo evaluate their electrochemical performance, supercapacitor electrodes were created using two types of activated carbons. The specific capacitance of KOH-activated carbon (KAC) was 230 F/g, while CuCl\u003csub\u003e2\u003c/sub\u003e-activated carbon (CuAC) showed 175.9 F/g, both at 5 A/g. After 5000 charge-discharge cycles, KAC retained 76% of its capacitance, and CuAC retained 93%. These results demonstrate pine pollen's potential as a precursor for high-performance porous carbons.\u003c/p\u003e","manuscriptTitle":"Pine Pollen-Derived Activated Carbon for High-Performance Supercapacitor Electrodes: A Comparative Study of KOH and CuCl 2 Activation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-08 19:54:48","doi":"10.21203/rs.3.rs-5742394/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-02-24T01:43:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-02-22T04:54:13+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-02-01T12:33:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"143033089444327414935457922932500245551","date":"2025-02-01T07:58:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"50725254292398998626753605653714154755","date":"2025-01-31T15:56:40+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-01-29T15:08:08+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-01-06T14:15:59+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-01-06T14:12:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2024-12-31T14:00:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4f80967c-4349-4bce-81e1-d8bfec2c9a70","owner":[],"postedDate":"January 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-07-14T04:08:14+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-08 19:54:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5742394","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5742394","identity":"rs-5742394","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}