Leveraging the Synergistic Effects of Au/PANI/CuO Heterostructure for Enhanced Photoelectrochemical Water Splitting

Leveraging the Synergistic Effects of Au/PANI/CuO Heterostructure for Enhanced Photoelectrochemical Water Splitting | 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 Article Leveraging the Synergistic Effects of Au/PANI/CuO Heterostructure for Enhanced Photoelectrochemical Water Splitting Fahad Abdulaziz, Mohamed Zayed, Salman Latif, Yassin A. Jeilani, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5773977/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study explores a novel photoelectrode made from a combination of copper oxide (CuO), polyaniline (PANI), and gold nanoparticles (Au NPs) for efficient hydrogen production in photoelectrochemical (PEC) water splitting. The Au/PANI/CuO photoelectrode is fabricated using cost-effective methods, ensuring practical applications. The research evaluates the photoelectrode's morphology, structure, efficiency, and stability to optimize its performance in PEC reactions. Integrating Au, PANI, and CuO nanomaterials improves charge transfer, reduces resistivity, and minimizes charge recombination, resulting in significantly enhanced hydrogen production efficiency. Scanning electron microscopy (SEM) reveals that the CuO film has a rough texture with non-uniform particles, while the PANI/CuO film exhibits agglomerates and interconnected PANI nanofibers. The Au NPs are evenly distributed across the PANI/CuO film, with diameters ranging from 5 to 60 nm. Energy dispersive X-ray (EDX) analysis approves the presence of each element in the desired proportions, validating the successful fabrication of the Au/PANI/CuO photoelectrode. The Au/PANI/CuO photoelectrode exhibits enhanced light absorption properties due to the surface plasmon resonance (SPR) effect of Au NPs and the interaction between PANI and CuO. The Au/PANI/CuO photoelectrode demonstrates a remarkable 300-fold increase in photocurrent density (J ph ) compared to pure CuO, achieving a maximum of 15 mA/cm² at -0.39 V vs. RHE. Additionally, the Au/PANI/CuO photoelectrode maintains a constant photocurrent density for 0.5 hours, showing superior stability compared to CuO, which experiences rapid decay. It also achieves a high IPCE value of 45% at nearly 500 nm, indicating efficient light utilization. Overall, this study presents a promising approach for designing efficient and stable photoelectrodes in PEC water splitting and hydrogen generation applications. Au/PANI/CuO Water splitting Synergistic effect Optical properties Hydrogen generation ABPE IPCE Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Recently, there has been a notable focus on using solar energy to produce hydrogen through photoelectrochemical (PEC) processes [ 1 ]. Hydrogen is a sustainable solution to address the increasing energy demands since it is a renewable energy source that doesn't emit harmful substances. In PEC reactions, sunlight is absorbed by the photoelectrode material, exciting high-energy electrons. These electrons then trigger a redox chemical reaction at the electrode-electrolyte interface, converting water into hydrogen and oxygen. Desirable photocatalysts possess a range of favorable traits [ 2 ], [ 3 ]. They exhibit high light absorption, suitable band gap, low recombination rate, fast charge transfer, high surface area, high crystallinity, stability, recyclability, industrial compatibility, cost-effectiveness, non-toxicity, and easy fabrication. These characteristics enable them to efficiently absorb a wide spectrum of light, match the energy of incident light, minimize electron-hole recombination, and facilitate rapid charge transfer. A high surface area promotes faster reaction rates, while high crystallinity enhances stability and charge transport. Photocatalysts should also be stable, corrosion-resistant, and capable of being recycled multiple times without significant activity loss. They should be compatible with existing industrial processes, made from low-cost and abundant materials, and be safe for human health and the environment. Ultimately, these combined properties enable efficient and sustainable photocatalytic processes. CuO is a type of transition metal oxide (TMO) semiconductor that has garnered attention in PEC applications [ 4 ], [ 5 ]. CuO naturally exhibits p-type conductivity due to copper vacancies in its structure. It possesses desirable characteristics, including its abundance in nature, cost-effectiveness in production, non-toxicity, biosafety, thermal conductivity, and chemical stability [ 6 ], [ 7 ]. CuO nanostructures have found applications in various modern technologies such as lithium-ion batteries, solar cells, sensors, photocatalysis, transistors, diodes, supercapacitors, and hydrogen production. CuO shows promise as a photoelectrode material in PEC cells due to its high physical stability, broad optical absorption range, and narrow direct band gap [ 8 ]. The conduction band (CB) edge of CuO is positioned at a more negative potential than the redox potential of H 2 O/H 2 , making it suitable for the water reduction reaction (from H + to H 2 ) [ 9 ]. Previous studies have utilized CuO as a photocatalyst in PEC reactions. However, a drawback of cuprous oxide is its relatively high resistance, which hinders the movement of the majority of photon-excited electrons to the electrode-electrolyte interface during the PEC reaction. This poor carrier conductivity leads to the rapid recombination of excited electrons with holes, limiting the efficiency of hydrogen conversion [ 10 ]. Moreover, CuO demonstrates poor stability against photo corrosion in the presence of aqueous electrolytes during PEC reactions, resulting in a decline in the amount of generated hydrogen over time. Additionally, CuO exhibits a relatively low photovoltage, necessitating a significant external bias to facilitate water splitting in PEC cells due to the energetic mismatch between the semiconductor and electrolyte interface [ 11 ]. On the other hand, polyaniline (PANI) is a highly significant material driving technological advancements [ 12 ]. It is an electrically conductive polymer (CP) with excellent carrier mobilities. Its structure comprises a conjugated backbone consisting of alternating single and double bonds, resulting in a low electronic band gap and semiconductor behavior [ 13 ]. PANI functions as a p-type organic semiconductor, with holes serving as the primary charge carriers. Notably, PANI can exhibit different oxidation states, including emeraldine, leucoemeraldine, and pernigraniline forms [ 14 ], [ 15 ]. The PANI structure consists of ordered semicrystalline regions dispersed within disordered amorphous regions, creating a quasi-metallic island surrounded by nonmetallic amorphous regions. PANI possesses various desirable properties, such as ease of synthesis, cost-effectiveness, lightweight nature, high processability, tunable conductivity, favorable optical properties, biocompatibility, fast redox activity, and good mechanical properties [ 16 ]. Additionally, it exhibits good operational stability under various thermal, chemical, and electrochemical conditions. PANI nanostructures find extensive applications in LEDs, supercapacitors, and chemical sensors, offering unique advantages in these fields. In recent years, plasmonic metals, specifically Au NPs, have attracted significant attention for their application in PEC systems [ 17 ][ 18 ]. This is thanks to their exceptional optical properties arising from excited SPR [ 19 ], [ 20 ]. SPR occurs when the collective oscillations of free electrons in Au NPs are stimulated by an oscillating electric field from incident light. When integrated into photoactive semiconductors, Au NPs exhibit a wide range of optical and electronic effects that prove useful for PEC. These effects include hot electron generation, near-field enhancement, suppression of charge recombination, improved light absorption, modification of the electronic band structure, and the formation of a Schottky junction at the semiconductor/gold interface [ 21 ], [ 22 ]. Also, the thermal dissipation of energy during SPR relaxation is advantageous for PEC activity, as it enables photothermal heating that promotes heat-assisted reactions, facilitates catalyst regeneration, and enhances reactant mobility [ 23 ]. Furthermore, Moreover, co-catalysts such as Au NPs on semiconductor surfaces can increase redox processes at the electrolyte/semiconductor interface. Additionally, Au NPs possess advantageous features including low toxicity, high electrical conductivity, chemical stability, and a large surface area. These properties collectively enhanced charge generation and transfer, and contributed to enhancing the performance of PEC water splitting [ 24 ], [ 25 ]. Expanding on the provided background, the study focuses on enhancing the performance of hydrogen production in PEC systems by leveraging the synergistic effects of PANI, CuO, and Au in a specifically designed photoelectrode. The Au/PANI/CuO photoelectrode is fabricated by cost-effective and straightforward methods, ensuring its practical applications. The study thoroughly evaluates the efficiency and stability of the photoelectrode to achieve optimal performance in PEC reactions. The integration properties of Au, PANI, and CuO nanomaterials enhance charge transfer, reduce resistivity, and minimize charge recombination. Consequently, there is a significant improvement in the efficiency of hydrogen production. 2. Materials and methods 2.1 Raw materials Copper chloride (CuCl 2 . 2 H 2 O) and ammonium hydroxide (NH 4 OH) were provided by Panreac in Spain. Loba Chemie in India supplied the aniline monomer (C 6 H 5 NH 2 ) and ammonium persulfate (APS, (NH 4 ) 2 S 2 O 8 ). The gold target (99.99%) was acquired from Sigma-Aldrich in the USA. Al Nasr Company in Egypt supplied hydrochloric acid (HCl) and sulfuric acid (H 2 SO 4 ). 2.2 Synthesis of pure CuO nanostructured thin film A pure CuO thin film was prepared by utilizing the successive ionic layer adsorption and reaction (SILAR) technique on a commercially available glass substrate. This method is known for its simplicity and cost-effectiveness, as it does not necessitate complex equipment [ 26 ]. The synthesis process was comprised of four distinct steps, with each cycle of the SILAR process being accomplished through these steps. To begin, the glass substrate was vertically submerged in a cationic precursor solution for 25 seconds. This solution consisted of 50 mL of CuCl 2 .2H 2 O with a concentration of 60 mM, which was adjusted to a pH of 9 using an ammonia solution. Following this, in the second step, the glass substrate was washed with distilled water (DW) water at room temperature (RT) for 25 seconds. In the third step, the glass substrate was subjected to an ultrasonic bath for 25 minutes. This step aimed to eliminate weakly bonded molecules. Subsequently, in the fourth step, the glass substrate was immersed in hot DW at a temperature of 80°C for 40 seconds. This heated DW acted as the anionic precursor required for the synthesis process. After every five cycles, both the cationic and anionic precursor solutions were replaced. A high-quality CuO film was successfully obtained after a total of 40 SILAR cycles. Finally, the synthesized CuO film underwent annealing at a temperature of 450°C for 2 hours, further improving its properties. 2.3 Fabrication of PANI/CuO To fabricate PANI/CuO, the PANI film was applied onto the previously prepared CuO/glass substrate using the oxidative polymerization technique [ 27 ]. Initially, aniline (0.1 M) was dissolved in 0.5 M HCl and stirred for thirty minutes. Similarly, 0.1 M of APS was dissolved in DW. Subsequently, the APS oxidant solution was mixed with the aniline solution in the presence of the CuO/glass substrate. This combination facilitated the formation of the PANI film, which underwent a reaction for 20 minutes at RT. Following the reaction, the resulting PANI/CuO/glass composite was dried at 60°C for six hours. 2.4 Decoration of PANI/CuO/glass with Au NPs The PANI/CuO/glass was decorated by Au NPs using DC sputtering (Ardenne LA 440 S equipment from Dresden, Germany). The Au NPs were sputtered onto the PANI/CuO/glass at a conventional deposition angle, with the PANI/CuO/glass placed 8 cm away from the Au target. The deposition process utilized a current of 15 mA and a pressure of 2 Torr. The growth rate of the Au NP layer was estimated to be around 5 nm/min. To achieve different thicknesses of the Au NPs layer, the sputtering time was varied within a range of 1 to 4 minutes. 2.5 Characterization Various techniques were employed to analyze the films. The Rigaku D/Max 2500 instrument was used for X-ray diffractogram (XRD) analysis. The ZEISS EVOMA10 instrument was utilized for FE-SEM to examine the shape and structure of the samples. For elemental composition determination, energy dispersive analysis of X-ray (EDAX) was performed using a unit attached to the SEM. The UV-VIS-NIR spectrophotometer (PerkinElmer Lambda 950) was used to measure the optical transmittance of the films across a wavelength range of 200–1200 nm, under normal incidence. The German-made Bruker-Vertex 70 device was employed for the Fourier transform infrared spectrometer (FTIR) was used for the determination of the bonds generated throughout the preparation process. 2.6 PEC measurements The PEC measurements were carried out using the OrigaLys device (Potentiostat/Galvanostat, Flex-OGA 01 A, France) in a setup consisting of three electrodes. The working electrode was prepared with films of CuO, PbS/CuO, and Au/PbS/CuO. To establish an ohmic electrical contact, a thin film coated with silver paste was used. The counter electrode was made of platinum. A silver chloride (Ag/AgCl) reference electrode was employed. The electrolyte employed was a 0.3 M Na 2 S 2 O 3 aqueous solution with a pH of 7.0. The response of J ph was recorded while subjecting the system to simulated solar light irradiation from a Xenon lamp (Newport Model 66902, UK), applying a scanning voltage (V) ranging from − 0.34 to 0 V compared to the reversible hydrogen electrode (RHE) reference. Additionally, an AM1.5 solar filter was employed to investigate monochromatic wavelengths. A black mask was used to block light and obtain the dark J-V curve. All PEC characteristics were assessed at RT. 3. Results and discussions 3.1 SEM topography Figure 1 presents the SEM topography of a CuO film on glass, demonstrating uniform deposition without cracks or gaps. The surface exhibits a rough texture and features an interesting overlapping shrub-like structure. Upon closer inspection of the high-magnification SEM image (Fig. 1 (b)), numerous non-uniform particles can be observed, intertwining with each other. Following the deposition of the PANI film, the resulting PANI/CuO film showcases agglomerates / interconnected PANI nanofibers randomly distributed over the CuO film. The average diameter of nanofibers is approximately 42.5 nm. The interconnected nanofibers form a dense network structure, as shown in Fig. 1 (c,d). This structure provides a high surface area for potential applications. In Fig. 1 (e,f), the distribution of Au nanoparticles across the PANI/CuO film is evident. These nanoparticles are attached to the surface of the PANI network, indicating the successful preparation of the ternary films. The diameter of Au NPs changes from 5 to 60 nm. Based on these observations, the Au/PANI/CuO structure could be a promising choice for PEC applications. 3.2 EDAX analysis EDAX was employed to analyze the chemical composition of prepared films. The patterns observed for CuO, PANI/CuO, and Au/PANI/CuO films are presented in Fig. 2 . In Fig. 2 (a), the EDX analysis of the CuO film revealed weight percentages of 36.88% for Cu and 40.90% for O. Additionally, signals from Ca, Si, and Al were detected on the surface of the glass substrate, indicating that the thickness of the CuO nanostructured film was smaller than the area examined by the EDAX. Moving on to PANI/CuO (Fig. 2 (b), peaks C, O, and N, were observed which are characteristic of PANI. Carbon and nitrogen peaks located at 0.15 keV and 0.20 keV, respectively. The presence of an Au peak in Fig. 2 (c) confirmed the formation of Au/PANI/CuO. 3.3 XRD and FTIR Figure 3 (a) illustrates the XRD patterns of PANI and CuO films. XRD data was analyzed using JCPDS cards 01-080-0076 and 53-1891 [ 28 ], [ 29 ]. The PANI film was semi-crystalline in structure. Two separate peaks were found at 2θ = 20.77° and 25.54°, corresponding to the diffraction planes (021) and (200), respectively. The parallel arrangement of the PANI polymer chains is indicated by the peak at 2 \(\:{\theta\:}\) = 25.54°. The average crystallite size of PANI was calculated to be 24.67 nm. The CuO film was poly-oriented and had a monoclinic phase. The XRD pattern displayed two prominent peaks at 2 \(\:{\theta\:}\) = 35.11° (002) and 2 \(\:{\theta\:}\) = 38.64° (111). CuO crystallite size was determined to be about 25.78 nm on average. Figure 3 (b) depicts the FTIR spectra of the CuO and PANI/CuO films. A broad band at 3400.1 cm − 1 is found in the CuO spectra, which is attributable to hydroxyl functional groups (OH) formed by water molecules adsorbed from the surrounding air. Additionally, bands at 559.6 cm − 1 and 465.3 cm − 1 correspond to Cu-O vibrational modes, showing the presence of the monoclinic phase of CuO [ 30 ]. Moving on to the CuO/PANI FTIR spectra, a band is seen about 3374.2 cm − 1 and 1114.6 cm − 1 , which correspond to the vibrational modes of the N-H and -NH- groups, respectively. Furthermore, the C = N vibrational mode of the PANI rings produces a peak at 1456.1 cm − 1 , which accords with previous studies [ 31 ]–[ 33 ]. The existence of N-H and Cu-O bond bands verifies the contact between the CuO NPs and the PANI matrix, demonstrating that the CuO/PANI was successfully fabricated. 3.4 Optical studies The optical characteristics of nanostructured semiconductors are highly valued in the field of photocatalysis. The optical properties of various films were examined within a range of 250–1000 nm (Fig. 4 ), revealing notable distinctions among them. Figure 4 (a) demonstrated that the CuO thin film displayed a strong absorption peak centered in the ultraviolet (UV) region. This peak is attributed to the electron transition process within the CuO material, where photons can elevate electrons to higher energy levels. Furthermore, the CuO thin film exhibited low absorbance in the visible range, indicating limited photoactivity of CuO. Comparatively, the PANI/CuO film demonstrated higher absorption than the CuO film. The absorption spectrum of PANI/CuO exhibited peak absorptions at 652 nm, resulting from the molecular transition of PANI from benzenoid to quinoid states [ 34 ]. This confirms the successful formation of a PANI film on the CuO film. The increased absorbance of PANI/CuO films can be ascribed to the electronic interaction between PANI and CuO, leading to the formation of a new chemical category and free-carrier absorption [ 35 ], [ 36 ]. The strong interaction between the CuO surface and PANI results in charge transfer from PANI to CuO, which enhances surface electric charge [ 37 ]. Upon deposition of Au nanoparticles (NPs), the Au/PANI/CuO film exhibited the highest absorbance across the entire wavelength range, surpassing the absorption of PANI/CuO and CuO films. This is owing to the strong light-scattering abilities of Au nanoparticles and their SPR effect [ 38 ]. Au NPs can enhance the multiple scattering of photons, resulting in an increased optical path length and, consequently, an increase in absorbance. This increased absorption of Au/PANI/CuO can promote the generation of photo-charge carriers, which is advantageous for photocatalytic applications. The absorbance of Au/PANI/CuO decreased as the wavelength transitioned from the UV range to the NIR range. Additionally, a new absorption peak characteristic of the SPR of Au NPs was observed at 570 nm. SPR originates from the coherent oscillation of the free conduction electrons within Au NPs induced by photons of a specific energy. The SPR generates an electric field on the Au nanoparticles, significantly enhancing the optical properties of Au/PANI/CuO films. The absorbance edge slightly shifted towards shorter wavelengths, indicating a wider band gap compared to CuO and PANI/CuO films. Using the Tauc model, Fig. 4 (b-d), the direct energy band gap (Eg) values of the thin films were determined. Eg values were found to be 1.82, 2.19, and 2.56 eV for the CuO, PANI/CuO, and Au/PANI/CuO thin films, respectively. CuO exhibited a measured band gap value lower than those reported in the literature, possibly due to structural and morphological variations [ 39 ], [ 40 ]. PANI/CuO films displayed a high band gap compared to CuO, which could be attributed to alterations in electronic and structural properties. The interfacial interactions between CuO and PANI might influence the dihedral/torsional angle between adjacent aromatic rings within the PANI macromolecular chain [ 41 ]. Previous research has shown an expansion of the optical band gap of CuO when combined with polyaniline [ 42 ]. Following the Au sputter coating, the band gap of PANI/CuO increased due to changes in the Fermi level. 4. Water-splitting measurements 4.1 Linear sweep voltammetry (LSV) test The PEC water-splitting properties of the films prepared were assessed using the linear sweep voltammetry (LSV) in a solution containing 0.3 M Na 2 S 2 O 3 . Figure 5(a) expresses the CuO film's photocurrent density (J ph )-applied potential curve under both dark and simulated solar irradiation (AM 1.5 G, 100 mW/cm 2 ). In the PEC system, CuO serves as a photocathode and demonstrates typical p-type behavior, resulting in a cathodic photocurrent [43]. At a voltage of − 0.39 V vs. RHE, the dark current for the CuO film is approximately 0.01 mA/cm 2 , while the J ph reaches approximately 0.05 mA/cm 2 . Hence, the contribution of dark current to the overall current is very small compared to the J ph . This indicates the significant influence of light exposure. When the CuO film is exposed to light, it generates electron-hole pairs. The high surface area and good crystallinity of CuO film enhance the efficient transport of these electron-hole pairs within the film. As a result, water molecules are split, and hydrogen is produced as a consequence. The deposition of PANI to the CuO film leads to a significant increase in the J ph , reaching 0.15 mA/cm 2 at 0.39 V vs. RHE. This improvement can be ascribed to the synergistic effect between PANI and CuO, resulting in reducing the electrical resistivity of CuO [44], [45]. The presence of PANI in the film plays a crucial role in enhancing the electrical conductivity of the blended films as a result of charge transfer from CP to CuO [37]. The elevated electrical conductivity of the PANI/CuO film is anticipated to boost the mobility of charge carriers, decrease the recombination rate of charge carriers, and extend the lifetime of photo-generated charge carriers [42], [46]. The energy level difference between PANI and CuO allows for the formation of a p-p heterojunction at their interface [46]. This heterojunction structure plays a crucial role in generating hot electrons and facilitating efficient charge transport to reach the electrolyte solution. This facilitates the production of hydrogen in the PEC process and contributes to the observed increase in J ph density in the PANI/CuO film. The Au/PANI/CuO photoanode demonstrated a significantly higher J ph across the full potential window. This enhancement in photocurrent can be attributed to the presence of the SPR effect caused by the Au nanoparticles (AuNPs) on PANI/CuO. The catalytic enhancement factor (f) of the Au/PANI/CuO photoanode is obtained by dividing the J ph of the Au/PANI/CuO photoanode by the J ph of the CuO photoanode. It can be expressed as: The resulting value of f = 300 indicates a larger catalytic enhancement for the Au/PANI/CuO photoanode compared to the CuO photoanode. At the semiconductor/metal interface, energy band bending occurs due to the differing electronic structures of the semiconductor and the metal. This results in the redistribution of charges within the interface, establishing an equilibrium Fermi level. The interface is also characterized by a Schottky barrier, which affects the injection and extraction of carriers across the interface. Plasmon-induced hot electrons in Au nanoparticles are introduced into the adjacent semiconductor's CB, surpassing the Schottky barrier [47]. This process generates additional charge carriers for the PEC process [48]. The Au/PANI/CuO interface facilitates charge transfer and enables the absorption of light in the visible and near-infrared range. Also, plasmonic Au NPs act as sensitizers and greatly enhance the stability of the system [49]. Additionally, the deposition of Au nanoparticles on the surface of CuO creates active sites that accelerate the reduction reaction of H + . All these factors contribute to the improvement of hydrogen production. In Fig. 5(b), it was observed that increasing the deposition time of Au nanoparticles from 1 to 4 minutes led to an increase in the J ph of the PEC system. This can be attributed to the greater deposition of Au nanoparticles on the PANI/CuO surface as the deposition time increased. The increased nanoparticle deposition results in a larger surface area, which enhances both light absorption and catalytic activity, ultimately leading to the observed increase in J ph [50]. 4.2 Stability The stability of the photocurrent response for CuO and Au/PANI/CuO films was evaluated using chronoamperometry, specifically by analyzing the J ph -t curve. This test is necessary for assessing the long-term viability of PEC solar systems. The chronoamperometric curves were recorded for 0.5 hours at -0.39 V vs. RHE. Figure 6(a) shows that the J ph of the CuO film decreased over time, indicating poor stability. In contrast, the J ph of the Au/PANI/CuO film reached a constant value of 4.5 mA/cm 2 over a relatively long period, as shown in Fig. 6(b). Importantly, no significant decay in J ph was observed for the Au/PANI/CuO film. These findings suggest that the Au/PANI/CuO electrode exhibits excellent long-term stability in terms of PEC performance, thanks to the synergistic effect and the chemical stability of Au. The hydrogen bubbles were seen on the surface of the photoelectrode during the PEC reaction. The rate of hydrogen production was calculated based on the number of electrons passing through the circuit under continuous light irradiation for 0.5 hours, employing Faraday's law. The time-dependent hydrogen production rates for the CuO and Au/PANI/CuO photoelectrodes are illustrated in Fig. 6(d). The relationship between time and hydrogen production displayed a nearly linear trend, indicating that the amount of hydrogen generated increased as the PEC reaction progressed. The bare CuO electrode exhibited a low H 2 gas evolution rate of 0.0004 µmole/s.cm 2 under light irradiation due to the rapid recombination of electron-hole pairs (Fig. 6(e)). In contrast, the Au/PANI/CuO electrode demonstrated a significant improvement in the photocatalytic H 2 evolution rate, reaching 140 µmole/s.cm 2 . This enhancement can be attributed to the layered structure of PANI and the presence of Au nanoparticles, which facilitate efficient charge separation and act as effective co-catalysts for H 2 generation compared to CuO alone. Additionally, the presence of the Au promotes increased field confinement, leading to enhanced generation of hot holes and further boosting the gas evolution reaction [49]. The J ph response was examined under chopped light illumination, where the light was cyclically turned on and off, at -0.39 V vs. RHE. The obtained results are presented in Figs. 6(c, f). Upon light exposure, there was a rapid increase in the J ph , which subsequently decreased when the light was turned off. For the CuO film, the J ph ranged from 0.015 to 0.045 mA/cm² during the off/on light cycle. In contrast, the Au/PANI/CuO film exhibited a wider range, with the J ph varying from 0.50 (off) to 14.8 (on) mA/cm 2 . Compared to CuO alone, the photocurrent response of Au/PANI/CuO showed an approximately 320-fold increase when illuminated. These transient photocurrent findings agree well with the results obtained from the LSV measurements. The Au/PANI/CuO electrode exhibited the highest photo-response in terms of current density, indicating its great potential for PEC water-splitting applications. The significant increase in photocurrent density observed with the Au/PANI/CuO electrode underscores its excellent photo-response, further suggesting its suitability for efficient PEC water-splitting processes. 4.3 Tafel plot The Tafel equation is an important tool for analyzing the kinetics of electrochemical reactions [51]. It examines the relationship between potential and the logarithm of current, using a logarithmic scale to create a linear plot. Tafel relation for anodic and cathodic curves can be given by the equation $$\:\text{V}=\:{\beta\:}\text{log}\:\left({\text{J}}_{\text{p}\text{h}}\right)+\text{C}$$ 2 Figure 1S illustrates Tafel plots for CuO, CuO/PANI, and Au/PANI/CuO photoelectrodes. Table 1 provides calculated values for the anodic Tafel slope (\(\:{{\beta\:}}_{\text{a}}\)), cathodic Tafel slope (\(\:{{\beta\:}}_{\text{c}}\)), corrosion potential (E corr ), and corrosion current (I corr ). For Au/PANI/CuO, the values of βa and βc are 0.264 and 0.477 mV/dec, respectively, compared to 0.458 and 0.476 mV/dec for CuO. Lower values of βa and βc indicate a faster reaction rate and a more efficient PEC reaction [52]. Additionally, Au/PANI/CuO exhibits a smaller corrosion current (3.89 mA/cm 2 ) compared to CuO (5.974 mA/cm 2 ). The corrosion rate is directly proportional to I corr [53]. Consequently, this suggests that Au/PANI/CuO experiences less photocorrosion. The corrosion potential represents the potential of a film in the presence of an electrolyte without any external current. A higher corrosion potential indicates a greater ability of the film to resist corrosive damage. This is desirable for maintaining the functionality of photoelectrodes over a long time. The corrosion potential of Au/PANI/CuO (172 mV) is higher than that of CuO (141 mV). Table 1. Values of Tafel parameters of all photoelectrode. CuO PANI/ CuO Au/PANI/CuO V corr (mV) - 141 - 179 - 172 I corr (mA/cm 2 ) - 5.974 - 5.348 - 3.89 β a (mV/dec) 0.458 0.413 0.264 β c (mV/dec) 0.476 0.652 0.477 4.4 PEC water-splitting performance Efficiency measurements play a critical role in evaluating the practical applicability of photoelectrodes by providing valuable insights into their performance and effectiveness. One key parameter for evaluation is the incident photon-to-current efficiency (IPCE). The IPCE quantifies the ratio of produced electrons to the number of incident photons. It offers valuable information about the photoelectrode's ability to generate electron-hole pairs when exposed to specific light wavelengths. Consequently, IPCE measurements aid in optimizing the design of photoelectrodes and selecting suitable materials for the photoanode, particularly within specific wavelength ranges. It can be presented by the expression [54]: Where \(\:\left|{\text{J}}_{\text{p}\text{h}}\:(\text{m}\text{A}/{\text{c}\text{m}}^{2})\right|\) represents the absolute value of photocurrent measured at a specific wavelength of incident light. \(\:{\lambda\:}\:\left(\text{n}\text{m}\right)\) denotes the wavelength of a photon being incident. P \(\:(\text{m}\text{W}/{\text{c}\text{m}}^{2})\) indicates the power density of the illuminating light. Figure 7(a) demonstrates that wavelength-dependent IPCE measurements were carried out at -0.39 VRHE for the Au/PANI/CuO film. The IPCE values are high in the \(\:{\lambda\:}\) range of 300 to 636 nm, indicating a favorable photo response for the Au/PANI/CuO film. The higher rate of hydrogen evolution corresponds to a larger magnitude of photocurrent. The maximum IPCE peak value of 45% occurs at 500 nm, confirming the predominant influence of hot electron generation and utilization in the PEC reaction. By applying an external bias, the J ph of a photoanode increases, leading to improved efficiency in the PEC process. To quantify the impact of the external bias, the applied bias photon-to-current efficiency (ABPE) is used as an important measure of PEC water-splitting performance. ABPE value is derived from the \(\:{\text{J}}_{\text{p}\text{h}}\:\)- V plot and can be expressed as [55], [56]: In this equation, \(\:{\text{E}}_{\text{r}\text{e}\text{v}}\) represents the standard reversible potential (1.23 V vs. RHE). \(\:\left|{\text{V}}_{\text{a}\text{p}\text{p}}\right|\) is the absolute value of the applied bias potential vs. RHE. Figure 7(b) illustrates the plot of the ABPE as a function of the applied bias potentials at different incident wavelengths of Au/PANI/CuO photoanode. Under illumination with photons at a wavelength of 500 nm, this photoanode achieves a maximum ABPE value of about 2.5% at an applied bias potential of 1.4 V vs. RHE. The obtained results represent a significant improvement in the ABPE and IPCE values compared to different materials reported in the literature [57]–[60]. 5. Conclusions In conclusion, this study successfully investigated the combined effects of PANI, CuO, and Au NPs in a photoelectrode for enhanced hydrogen production in photoelectrochemical (PEC) water splitting. The Au/PANI/CuO photoelectrode exhibited a unique morphology and structure, along with enhanced light absorption. By integrating Au, PANI, and CuO nanomaterials, the photoelectrode achieved improved efficiency, stability, and light utilization compared to bare CuO. The significant 300-fold increase in J ph , superior stability, and efficient light utilization highlight the potential of this approach for designing efficient and stable photoelectrodes in clean and sustainable hydrogen production. Declarations Acknowledgment: This research has been funded by the Scientific Research Deanship at the University of Ha’il - Saudi Arabia through project number <> Contributions: Project administration, F. A, S. L, Y. A. J., and R. R. D. P.; Supervision, F. A., H. A. E., M. S., A. M. A., and S. L.; Software, M. R.; Visualization, Y. A. J., and S. L., A. M.; Writing—review & editing, F. A., H. A. E., R. R. D. P., and Y. A. J.; Writing—original draft, A. M. A., M. R., and M. Z.; Methodology, M. Z., M. R., and M. S.; Data curation, M. S., F. A., S. L., R. R. D. P., and M. S.; All authors have read and agreed to the published version of the manuscript. Availability of data and material: Requests should be addressed to the corresponding author on a reasonable request. References M. Ahmed and I. Dincer, “A review on photoelectrochemical hydrogen production systems: Challenges and future directions,” Int. J. Hydrogen Energy, vol. 44, no. 5, pp. 2474–2507, Jan. 2019, doi: 10.1016/J.IJHYDENE.2018.12.037. M. El ouardi et al., “Review of photoelectrochemical water splitting: From quantitative approaches to effect of sacrificial agents, oxygen vacancies, thermal and magnetic field on (photo)electrolysis,” Int. J. 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magnifications.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/4f36aa8795f8260cfaf5dcd2.png"},{"id":73685186,"identity":"a3117d66-58ea-4506-95fc-c17d91a076d7","added_by":"auto","created_at":"2025-01-13 14:39:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":193886,"visible":true,"origin":"","legend":"\u003cp\u003eEDAX for CuO, PANI/CuO, and Au/PANI/CuO.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/b71366e6c23dae8218d26b08.png"},{"id":73685179,"identity":"c43b087e-34b7-4bed-828c-7e40b61522f5","added_by":"auto","created_at":"2025-01-13 14:39:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":210633,"visible":true,"origin":"","legend":"\u003cp\u003eXRD and FTIR for CuO and PANI/CuO samples.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/e78649df5719e105910af644.png"},{"id":73686377,"identity":"e808754a-0e18-4f18-8144-f25bd4b9ea6d","added_by":"auto","created_at":"2025-01-13 14:47:19","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":264779,"visible":true,"origin":"","legend":"\u003cp\u003eOptical for CuO, PANI/CuO, and Au/PANI/CuO.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/8e102eda9ac8f61887de0c5a.png"},{"id":73685251,"identity":"02ab8389-b873-4b07-96e8-8a030a9310c4","added_by":"auto","created_at":"2025-01-13 14:39:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":158595,"visible":true,"origin":"","legend":"\u003cp\u003eLSV measurements at a scan rate of 50 mV/s for (a) CuO, and PANI/CuO, and (b)Au/PANI/CuO.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/699b8114b9d9824073f79e7c.png"},{"id":73685243,"identity":"e108f607-c779-4e3b-813a-09fb08b66c1e","added_by":"auto","created_at":"2025-01-13 14:39:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":225803,"visible":true,"origin":"","legend":"\u003cp\u003eJ\u003csub\u003eph\u003c/sub\u003e-t measurement, H\u003csub\u003e2\u003c/sub\u003e gas evolution rate, and on/off chopped J\u003csub\u003eph\u003c/sub\u003e for pure CuO and Au/PANI/CuO.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/c805785adb7cbe3464dd3f7c.png"},{"id":73685187,"identity":"50b903fb-69d7-44a9-aa4f-8d6470617364","added_by":"auto","created_at":"2025-01-13 14:39:17","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":182303,"visible":true,"origin":"","legend":"\u003cp\u003eEfficiency measurements for Au/PANI/CuO (a) IPCE and (b) ABPE.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/2a46bc701917c3a4d0ef41ae.png"},{"id":73844120,"identity":"f5ef39f0-89b2-4701-8dff-25536d837360","added_by":"auto","created_at":"2025-01-15 08:47:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":10221282,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/3a8c6e17-076c-4236-94ab-e2d898ab5d81.pdf"},{"id":73685279,"identity":"1f817589-4c22-467d-925e-6eb3d2c53a08","added_by":"auto","created_at":"2025-01-13 14:39:21","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":146767,"visible":true,"origin":"","legend":"","description":"","filename":"AuPANICuOSupp18.docx","url":"https://assets-eu.researchsquare.com/files/rs-5773977/v1/d0a302e357400a9c5357449d.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Leveraging the Synergistic Effects of Au/PANI/CuO Heterostructure for Enhanced Photoelectrochemical Water Splitting","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eRecently, there has been a notable focus on using solar energy to produce hydrogen through photoelectrochemical (PEC) processes [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Hydrogen is a sustainable solution to address the increasing energy demands since it is a renewable energy source that doesn't emit harmful substances. In PEC reactions, sunlight is absorbed by the photoelectrode material, exciting high-energy electrons. These electrons then trigger a redox chemical reaction at the electrode-electrolyte interface, converting water into hydrogen and oxygen. Desirable photocatalysts possess a range of favorable traits [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. They exhibit high light absorption, suitable band gap, low recombination rate, fast charge transfer, high surface area, high crystallinity, stability, recyclability, industrial compatibility, cost-effectiveness, non-toxicity, and easy fabrication. These characteristics enable them to efficiently absorb a wide spectrum of light, match the energy of incident light, minimize electron-hole recombination, and facilitate rapid charge transfer. A high surface area promotes faster reaction rates, while high crystallinity enhances stability and charge transport. Photocatalysts should also be stable, corrosion-resistant, and capable of being recycled multiple times without significant activity loss. They should be compatible with existing industrial processes, made from low-cost and abundant materials, and be safe for human health and the environment. Ultimately, these combined properties enable efficient and sustainable photocatalytic processes.\u003c/p\u003e \u003cp\u003eCuO is a type of transition metal oxide (TMO) semiconductor that has garnered attention in PEC applications [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. CuO naturally exhibits p-type conductivity due to copper vacancies in its structure. It possesses desirable characteristics, including its abundance in nature, cost-effectiveness in production, non-toxicity, biosafety, thermal conductivity, and chemical stability [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. CuO nanostructures have found applications in various modern technologies such as lithium-ion batteries, solar cells, sensors, photocatalysis, transistors, diodes, supercapacitors, and hydrogen production. CuO shows promise as a photoelectrode material in PEC cells due to its high physical stability, broad optical absorption range, and narrow direct band gap [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The conduction band (CB) edge of CuO is positioned at a more negative potential than the redox potential of H\u003csub\u003e2\u003c/sub\u003eO/H\u003csub\u003e2\u003c/sub\u003e, making it suitable for the water reduction reaction (from H\u003csup\u003e+\u003c/sup\u003e to H\u003csub\u003e2\u003c/sub\u003e) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Previous studies have utilized CuO as a photocatalyst in PEC reactions. However, a drawback of cuprous oxide is its relatively high resistance, which hinders the movement of the majority of photon-excited electrons to the electrode-electrolyte interface during the PEC reaction. This poor carrier conductivity leads to the rapid recombination of excited electrons with holes, limiting the efficiency of hydrogen conversion [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Moreover, CuO demonstrates poor stability against photo corrosion in the presence of aqueous electrolytes during PEC reactions, resulting in a decline in the amount of generated hydrogen over time. Additionally, CuO exhibits a relatively low photovoltage, necessitating a significant external bias to facilitate water splitting in PEC cells due to the energetic mismatch between the semiconductor and electrolyte interface [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOn the other hand, polyaniline (PANI) is a highly significant material driving technological advancements [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. It is an electrically conductive polymer (CP) with excellent carrier mobilities. Its structure comprises a conjugated backbone consisting of alternating single and double bonds, resulting in a low electronic band gap and semiconductor behavior [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. PANI functions as a p-type organic semiconductor, with holes serving as the primary charge carriers. Notably, PANI can exhibit different oxidation states, including emeraldine, leucoemeraldine, and pernigraniline forms [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The PANI structure consists of ordered semicrystalline regions dispersed within disordered amorphous regions, creating a quasi-metallic island surrounded by nonmetallic amorphous regions. PANI possesses various desirable properties, such as ease of synthesis, cost-effectiveness, lightweight nature, high processability, tunable conductivity, favorable optical properties, biocompatibility, fast redox activity, and good mechanical properties [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Additionally, it exhibits good operational stability under various thermal, chemical, and electrochemical conditions. PANI nanostructures find extensive applications in LEDs, supercapacitors, and chemical sensors, offering unique advantages in these fields.\u003c/p\u003e \u003cp\u003eIn recent years, plasmonic metals, specifically Au NPs, have attracted significant attention for their application in PEC systems [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e][\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. This is thanks to their exceptional optical properties arising from excited SPR [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. SPR occurs when the collective oscillations of free electrons in Au NPs are stimulated by an oscillating electric field from incident light. When integrated into photoactive semiconductors, Au NPs exhibit a wide range of optical and electronic effects that prove useful for PEC. These effects include hot electron generation, near-field enhancement, suppression of charge recombination, improved light absorption, modification of the electronic band structure, and the formation of a Schottky junction at the semiconductor/gold interface [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Also, the thermal dissipation of energy during SPR relaxation is advantageous for PEC activity, as it enables photothermal heating that promotes heat-assisted reactions, facilitates catalyst regeneration, and enhances reactant mobility [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Furthermore, Moreover, co-catalysts such as Au NPs on semiconductor surfaces can increase redox processes at the electrolyte/semiconductor interface. Additionally, Au NPs possess advantageous features including low toxicity, high electrical conductivity, chemical stability, and a large surface area. These properties collectively enhanced charge generation and transfer, and contributed to enhancing the performance of PEC water splitting [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eExpanding on the provided background, the study focuses on enhancing the performance of hydrogen production in PEC systems by leveraging the synergistic effects of PANI, CuO, and Au in a specifically designed photoelectrode. The Au/PANI/CuO photoelectrode is fabricated by cost-effective and straightforward methods, ensuring its practical applications. The study thoroughly evaluates the efficiency and stability of the photoelectrode to achieve optimal performance in PEC reactions. The integration properties of Au, PANI, and CuO nanomaterials enhance charge transfer, reduce resistivity, and minimize charge recombination. Consequently, there is a significant improvement in the efficiency of hydrogen production.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Raw materials\u003c/h2\u003e \u003cp\u003eCopper chloride (CuCl\u003csub\u003e2\u003c/sub\u003e.\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eO) and ammonium hydroxide (NH\u003csub\u003e4\u003c/sub\u003eOH) were provided by Panreac in Spain. Loba Chemie in India supplied the aniline monomer (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e) and ammonium persulfate (APS, (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e). The gold target (99.99%) was acquired from Sigma-Aldrich in the USA. Al Nasr Company in Egypt supplied hydrochloric acid (HCl) and sulfuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of pure CuO nanostructured thin film\u003c/h2\u003e \u003cp\u003eA pure CuO thin film was prepared by utilizing the successive ionic layer adsorption and reaction (SILAR) technique on a commercially available glass substrate. This method is known for its simplicity and cost-effectiveness, as it does not necessitate complex equipment [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The synthesis process was comprised of four distinct steps, with each cycle of the SILAR process being accomplished through these steps. To begin, the glass substrate was vertically submerged in a cationic precursor solution for 25 seconds. This solution consisted of 50 mL of CuCl\u003csub\u003e2\u003c/sub\u003e.2H\u003csub\u003e2\u003c/sub\u003eO with a concentration of 60 mM, which was adjusted to a pH of 9 using an ammonia solution. Following this, in the second step, the glass substrate was washed with distilled water (DW) water at room temperature (RT) for 25 seconds. In the third step, the glass substrate was subjected to an ultrasonic bath for 25 minutes. This step aimed to eliminate weakly bonded molecules. Subsequently, in the fourth step, the glass substrate was immersed in hot DW at a temperature of 80\u0026deg;C for 40 seconds. This heated DW acted as the anionic precursor required for the synthesis process. After every five cycles, both the cationic and anionic precursor solutions were replaced. A high-quality CuO film was successfully obtained after a total of 40 SILAR cycles. Finally, the synthesized CuO film underwent annealing at a temperature of 450\u0026deg;C for 2 hours, further improving its properties.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Fabrication of PANI/CuO\u003c/h2\u003e \u003cp\u003eTo fabricate PANI/CuO, the PANI film was applied onto the previously prepared CuO/glass substrate using the oxidative polymerization technique [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Initially, aniline (0.1 M) was dissolved in 0.5 M HCl and stirred for thirty minutes. Similarly, 0.1 M of APS was dissolved in DW. Subsequently, the APS oxidant solution was mixed with the aniline solution in the presence of the CuO/glass substrate. This combination facilitated the formation of the PANI film, which underwent a reaction for 20 minutes at RT. Following the reaction, the resulting PANI/CuO/glass composite was dried at 60\u0026deg;C for six hours.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Decoration of PANI/CuO/glass with Au NPs\u003c/h2\u003e \u003cp\u003eThe PANI/CuO/glass was decorated by Au NPs using DC sputtering (Ardenne LA 440 S equipment from Dresden, Germany). The Au NPs were sputtered onto the PANI/CuO/glass at a conventional deposition angle, with the PANI/CuO/glass placed 8 cm away from the Au target. The deposition process utilized a current of 15 mA and a pressure of 2 Torr. The growth rate of the Au NP layer was estimated to be around 5 nm/min. To achieve different thicknesses of the Au NPs layer, the sputtering time was varied within a range of 1 to 4 minutes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Characterization\u003c/h2\u003e \u003cp\u003eVarious techniques were employed to analyze the films. The Rigaku D/Max 2500 instrument was used for X-ray diffractogram (XRD) analysis. The ZEISS EVOMA10 instrument was utilized for FE-SEM to examine the shape and structure of the samples. For elemental composition determination, energy dispersive analysis of X-ray (EDAX) was performed using a unit attached to the SEM. The UV-VIS-NIR spectrophotometer (PerkinElmer Lambda 950) was used to measure the optical transmittance of the films across a wavelength range of 200\u0026ndash;1200 nm, under normal incidence. The German-made Bruker-Vertex 70 device was employed for the Fourier transform infrared spectrometer (FTIR) was used for the determination of the bonds generated throughout the preparation process.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 PEC measurements\u003c/h2\u003e \u003cp\u003eThe PEC measurements were carried out using the OrigaLys device (Potentiostat/Galvanostat, Flex-OGA 01 A, France) in a setup consisting of three electrodes. The working electrode was prepared with films of CuO, PbS/CuO, and Au/PbS/CuO. To establish an ohmic electrical contact, a thin film coated with silver paste was used. The counter electrode was made of platinum. A silver chloride (Ag/AgCl) reference electrode was employed. The electrolyte employed was a 0.3 M Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e aqueous solution with a pH of 7.0. The response of J\u003csub\u003eph\u003c/sub\u003e was recorded while subjecting the system to simulated solar light irradiation from a Xenon lamp (Newport Model 66902, UK), applying a scanning voltage (V) ranging from \u0026minus;\u0026thinsp;0.34 to 0 V compared to the reversible hydrogen electrode (RHE) reference. Additionally, an AM1.5 solar filter was employed to investigate monochromatic wavelengths. A black mask was used to block light and obtain the dark J-V curve. All PEC characteristics were assessed at RT.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussions","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 SEM topography\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the SEM topography of a CuO film on glass, demonstrating uniform deposition without cracks or gaps. The surface exhibits a rough texture and features an interesting overlapping shrub-like structure. Upon closer inspection of the high-magnification SEM image (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b)), numerous non-uniform particles can be observed, intertwining with each other. Following the deposition of the PANI film, the resulting PANI/CuO film showcases agglomerates / interconnected PANI nanofibers randomly distributed over the CuO film. The average diameter of nanofibers is approximately 42.5 nm. The interconnected nanofibers form a dense network structure, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c,d). This structure provides a high surface area for potential applications. In Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(e,f), the distribution of Au nanoparticles across the PANI/CuO film is evident. These nanoparticles are attached to the surface of the PANI network, indicating the successful preparation of the ternary films. The diameter of Au NPs changes from 5 to 60 nm. Based on these observations, the Au/PANI/CuO structure could be a promising choice for PEC applications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 EDAX analysis\u003c/h2\u003e \u003cp\u003eEDAX was employed to analyze the chemical composition of prepared films. The patterns observed for CuO, PANI/CuO, and Au/PANI/CuO films are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a), the EDX analysis of the CuO film revealed weight percentages of 36.88% for Cu and 40.90% for O. Additionally, signals from Ca, Si, and Al were detected on the surface of the glass substrate, indicating that the thickness of the CuO nanostructured film was smaller than the area examined by the EDAX. Moving on to PANI/CuO (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b), peaks C, O, and N, were observed which are characteristic of PANI. Carbon and nitrogen peaks located at 0.15 keV and 0.20 keV, respectively. The presence of an Au peak in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c) confirmed the formation of Au/PANI/CuO.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 XRD and FTIR\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) illustrates the XRD patterns of PANI and CuO films. XRD data was analyzed using JCPDS cards 01-080-0076 and 53-1891 [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The PANI film was semi-crystalline in structure. Two separate peaks were found at 2θ\u0026thinsp;=\u0026thinsp;20.77\u0026deg; and 25.54\u0026deg;, corresponding to the diffraction planes (021) and (200), respectively. The parallel arrangement of the PANI polymer chains is indicated by the peak at 2\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}\\)\u003c/span\u003e\u003c/span\u003e = 25.54\u0026deg;. The average crystallite size of PANI was calculated to be 24.67 nm. The CuO film was poly-oriented and had a monoclinic phase. The XRD pattern displayed two prominent peaks at 2 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}\\)\u003c/span\u003e\u003c/span\u003e = 35.11\u0026deg; (002) and 2 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}\\)\u003c/span\u003e\u003c/span\u003e = 38.64\u0026deg; (111). CuO crystallite size was determined to be about 25.78 nm on average.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b) depicts the FTIR spectra of the CuO and PANI/CuO films. A broad band at 3400.1 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is found in the CuO spectra, which is attributable to hydroxyl functional groups (OH) formed by water molecules adsorbed from the surrounding air. Additionally, bands at 559.6 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 465.3 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to Cu-O vibrational modes, showing the presence of the monoclinic phase of CuO [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Moving on to the CuO/PANI FTIR spectra, a band is seen about 3374.2 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1114.6 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which correspond to the vibrational modes of the N-H and -NH- groups, respectively. Furthermore, the C\u0026thinsp;=\u0026thinsp;N vibrational mode of the PANI rings produces a peak at 1456.1 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which accords with previous studies [\u003cspan additionalcitationids=\"CR32\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The existence of N-H and Cu-O bond bands verifies the contact between the CuO NPs and the PANI matrix, demonstrating that the CuO/PANI was successfully fabricated.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Optical studies\u003c/h2\u003e \u003cp\u003eThe optical characteristics of nanostructured semiconductors are highly valued in the field of photocatalysis. The optical properties of various films were examined within a range of 250\u0026ndash;1000 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), revealing notable distinctions among them. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a) demonstrated that the CuO thin film displayed a strong absorption peak centered in the ultraviolet (UV) region. This peak is attributed to the electron transition process within the CuO material, where photons can elevate electrons to higher energy levels. Furthermore, the CuO thin film exhibited low absorbance in the visible range, indicating limited photoactivity of CuO.\u003c/p\u003e \u003cp\u003eComparatively, the PANI/CuO film demonstrated higher absorption than the CuO film. The absorption spectrum of PANI/CuO exhibited peak absorptions at 652 nm, resulting from the molecular transition of PANI from benzenoid to quinoid states [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. This confirms the successful formation of a PANI film on the CuO film. The increased absorbance of PANI/CuO films can be ascribed to the electronic interaction between PANI and CuO, leading to the formation of a new chemical category and free-carrier absorption [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The strong interaction between the CuO surface and PANI results in charge transfer from PANI to CuO, which enhances surface electric charge [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUpon deposition of Au nanoparticles (NPs), the Au/PANI/CuO film exhibited the highest absorbance across the entire wavelength range, surpassing the absorption of PANI/CuO and CuO films. This is owing to the strong light-scattering abilities of Au nanoparticles and their SPR effect [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Au NPs can enhance the multiple scattering of photons, resulting in an increased optical path length and, consequently, an increase in absorbance. This increased absorption of Au/PANI/CuO can promote the generation of photo-charge carriers, which is advantageous for photocatalytic applications. The absorbance of Au/PANI/CuO decreased as the wavelength transitioned from the UV range to the NIR range. Additionally, a new absorption peak characteristic of the SPR of Au NPs was observed at 570 nm. SPR originates from the coherent oscillation of the free conduction electrons within Au NPs induced by photons of a specific energy. The SPR generates an electric field on the Au nanoparticles, significantly enhancing the optical properties of Au/PANI/CuO films. The absorbance edge slightly shifted towards shorter wavelengths, indicating a wider band gap compared to CuO and PANI/CuO films.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUsing the Tauc model, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b-d), the direct energy band gap (Eg) values of the thin films were determined. Eg values were found to be 1.82, 2.19, and 2.56 eV for the CuO, PANI/CuO, and Au/PANI/CuO thin films, respectively. CuO exhibited a measured band gap value lower than those reported in the literature, possibly due to structural and morphological variations [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. PANI/CuO films displayed a high band gap compared to CuO, which could be attributed to alterations in electronic and structural properties. The interfacial interactions between CuO and PANI might influence the dihedral/torsional angle between adjacent aromatic rings within the PANI macromolecular chain [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Previous research has shown an expansion of the optical band gap of CuO when combined with polyaniline [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Following the Au sputter coating, the band gap of PANI/CuO increased due to changes in the Fermi level.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Water-splitting measurements","content":"\u003cdiv id=\"Sec15\"\u003e\n \u003ch2\u003e4.1 Linear sweep voltammetry (LSV) test\u003c/h2\u003e\n \u003cp\u003eThe PEC water-splitting properties of the films prepared were assessed using the linear sweep voltammetry (LSV) in a solution containing 0.3 M Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. Figure 5(a) expresses the CuO film\u0026apos;s photocurrent density (J\u003csub\u003eph\u003c/sub\u003e)-applied potential curve under both dark and simulated solar irradiation (AM 1.5 G, 100 mW/cm\u003csup\u003e2\u003c/sup\u003e). In the PEC system, CuO serves as a photocathode and demonstrates typical p-type behavior, resulting in a cathodic photocurrent [43].\u003c/p\u003e\n \u003cp\u003eAt a voltage of \u0026minus;\u0026thinsp;0.39 V vs. RHE, the dark current for the CuO film is approximately 0.01 mA/cm\u003csup\u003e2\u003c/sup\u003e, while the J\u003csub\u003eph\u003c/sub\u003e reaches approximately 0.05 mA/cm\u003csup\u003e2\u003c/sup\u003e. Hence, the contribution of dark current to the overall current is very small compared to the J\u003csub\u003eph\u003c/sub\u003e. This indicates the significant influence of light exposure. When the CuO film is exposed to light, it generates electron-hole pairs. The high surface area and good crystallinity of CuO film enhance the efficient transport of these electron-hole pairs within the film. As a result, water molecules are split, and hydrogen is produced as a consequence.\u003c/p\u003e\n \u003cp\u003eThe deposition of PANI to the CuO film leads to a significant increase in the J\u003csub\u003eph\u003c/sub\u003e, reaching 0.15 mA/cm\u003csup\u003e2\u003c/sup\u003e at 0.39 V vs. RHE. This improvement can be ascribed to the synergistic effect between PANI and CuO, resulting in reducing the electrical resistivity of CuO [44], [45]. The presence of PANI in the film plays a crucial role in enhancing the electrical conductivity of the blended films as a result of charge transfer from CP to CuO [37]. The elevated electrical conductivity of the PANI/CuO film is anticipated to boost the mobility of charge carriers, decrease the recombination rate of charge carriers, and extend the lifetime of photo-generated charge carriers [42], [46]. The energy level difference between PANI and CuO allows for the formation of a p-p heterojunction at their interface [46]. This heterojunction structure plays a crucial role in generating hot electrons and facilitating efficient charge transport to reach the electrolyte solution. This facilitates the production of hydrogen in the PEC process and contributes to the observed increase in J\u003csub\u003eph\u003c/sub\u003e density in the PANI/CuO film.\u003c/p\u003e\n \u003cp\u003eThe Au/PANI/CuO photoanode demonstrated a significantly higher J\u003csub\u003eph\u003c/sub\u003e across the full potential window. This enhancement in photocurrent can be attributed to the presence of the SPR effect caused by the Au nanoparticles (AuNPs) on PANI/CuO. The catalytic enhancement factor (f) of the Au/PANI/CuO photoanode is obtained by dividing the J\u003csub\u003eph\u003c/sub\u003e of the Au/PANI/CuO photoanode by the J\u003csub\u003eph\u003c/sub\u003e of the CuO photoanode. It can be expressed as:\u003c/p\u003e\n \u003cdiv id=\"Equ1\"\u003e\n \u003cdiv id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eThe resulting value of f\u0026thinsp;=\u0026thinsp;300 indicates a larger catalytic enhancement for the Au/PANI/CuO photoanode compared to the CuO photoanode. At the semiconductor/metal interface, energy band bending occurs due to the differing electronic structures of the semiconductor and the metal. This results in the redistribution of charges within the interface, establishing an equilibrium Fermi level. The interface is also characterized by a Schottky barrier, which affects the injection and extraction of carriers across the interface. Plasmon-induced hot electrons in Au nanoparticles are introduced into the adjacent semiconductor\u0026apos;s CB, surpassing the Schottky barrier [47]. This process generates additional charge carriers for the PEC process [48]. The Au/PANI/CuO interface facilitates charge transfer and enables the absorption of light in the visible and near-infrared range. Also, plasmonic Au NPs act as sensitizers and greatly enhance the stability of the system [49]. Additionally, the deposition of Au nanoparticles on the surface of CuO creates active sites that accelerate the reduction reaction of H\u003csup\u003e+\u003c/sup\u003e. All these factors contribute to the improvement of hydrogen production. In Fig. 5(b), it was observed that increasing the deposition time of Au nanoparticles from 1 to 4 minutes led to an increase in the J\u003csub\u003eph\u003c/sub\u003e of the PEC system. This can be attributed to the greater deposition of Au nanoparticles on the PANI/CuO surface as the deposition time increased. The increased nanoparticle deposition results in a larger surface area, which enhances both light absorption and catalytic activity, ultimately leading to the observed increase in J\u003csub\u003eph\u003c/sub\u003e [50].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\"\u003e\n \u003ch2\u003e4.2 Stability\u003c/h2\u003e\n \u003cp\u003eThe stability of the photocurrent response for CuO and Au/PANI/CuO films was evaluated using chronoamperometry, specifically by analyzing the J\u003csub\u003eph\u003c/sub\u003e-t curve. This test is necessary for assessing the long-term viability of PEC solar systems. The chronoamperometric curves were recorded for 0.5 hours at -0.39 V vs. RHE. Figure 6(a) shows that the J\u003csub\u003eph\u003c/sub\u003e of the CuO film decreased over time, indicating poor stability. In contrast, the J\u003csub\u003eph\u003c/sub\u003e of the Au/PANI/CuO film reached a constant value of 4.5 mA/cm\u003csup\u003e2\u003c/sup\u003e over a relatively long period, as shown in Fig. 6(b). Importantly, no significant decay in J\u003csub\u003eph\u003c/sub\u003e was observed for the Au/PANI/CuO film. These findings suggest that the Au/PANI/CuO electrode exhibits excellent long-term stability in terms of PEC performance, thanks to the synergistic effect and the chemical stability of Au. The hydrogen bubbles were seen on the surface of the photoelectrode during the PEC reaction. The rate of hydrogen production was calculated based on the number of electrons passing through the circuit under continuous light irradiation for 0.5 hours, employing Faraday\u0026apos;s law. The time-dependent hydrogen production rates for the CuO and Au/PANI/CuO photoelectrodes are illustrated in Fig. 6(d). The relationship between time and hydrogen production displayed a nearly linear trend, indicating that the amount of hydrogen generated increased as the PEC reaction progressed. The bare CuO electrode exhibited a low H\u003csub\u003e2\u003c/sub\u003e gas evolution rate of 0.0004 \u0026micro;mole/s.cm\u003csup\u003e2\u003c/sup\u003e under light irradiation due to the rapid recombination of electron-hole pairs (Fig. 6(e)). In contrast, the Au/PANI/CuO electrode demonstrated a significant improvement in the photocatalytic H\u003csub\u003e2\u003c/sub\u003e evolution rate, reaching 140 \u0026micro;mole/s.cm\u003csup\u003e2\u003c/sup\u003e. This enhancement can be attributed to the layered structure of PANI and the presence of Au nanoparticles, which facilitate efficient charge separation and act as effective co-catalysts for H\u003csub\u003e2\u003c/sub\u003e generation compared to CuO alone. Additionally, the presence of the Au promotes increased field confinement, leading to enhanced generation of hot holes and further boosting the gas evolution reaction [49].\u003c/p\u003e\n \u003cp\u003eThe J\u003csub\u003eph\u003c/sub\u003e response was examined under chopped light illumination, where the light was cyclically turned on and off, at -0.39 V vs. RHE. The obtained results are presented in Figs. 6(c, f). Upon light exposure, there was a rapid increase in the J\u003csub\u003eph\u003c/sub\u003e, which subsequently decreased when the light was turned off. For the CuO film, the J\u003csub\u003eph\u003c/sub\u003e ranged from 0.015 to 0.045 mA/cm\u0026sup2; during the off/on light cycle. In contrast, the Au/PANI/CuO film exhibited a wider range, with the J\u003csub\u003eph\u003c/sub\u003e varying from 0.50 (off) to 14.8 (on) mA/cm\u003csup\u003e2\u003c/sup\u003e. Compared to CuO alone, the photocurrent response of Au/PANI/CuO showed an approximately 320-fold increase when illuminated. These transient photocurrent findings agree well with the results obtained from the LSV measurements. The Au/PANI/CuO electrode exhibited the highest photo-response in terms of current density, indicating its great potential for PEC water-splitting applications. The significant increase in photocurrent density observed with the Au/PANI/CuO electrode underscores its excellent photo-response, further suggesting its suitability for efficient PEC water-splitting processes.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\"\u003e\n \u003ch2\u003e4.3 Tafel plot\u003c/h2\u003e\n \u003cp\u003eThe Tafel equation is an important tool for analyzing the kinetics of electrochemical reactions [51]. It examines the relationship between potential and the logarithm of current, using a logarithmic scale to create a linear plot. Tafel relation for anodic and cathodic curves can be given by the equation\u003c/p\u003e\n \u003cdiv id=\"Equ2\"\u003e\n \u003cdiv id=\"FileID_Equ2\" name=\"EquationSource\"\u003e$$\\:\\text{V}=\\:{\\beta\\:}\\text{log}\\:\\left({\\text{J}}_{\\text{p}\\text{h}}\\right)+\\text{C}$$\u003c/div\u003e\n \u003cdiv\u003e2\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eFigure 1S illustrates Tafel plots for CuO, CuO/PANI, and Au/PANI/CuO photoelectrodes. Table 1 provides calculated values for the anodic Tafel slope (\\(\\:{{\\beta\\:}}_{\\text{a}}\\)), cathodic Tafel slope (\\(\\:{{\\beta\\:}}_{\\text{c}}\\)), corrosion potential (E\u003csub\u003ecorr\u003c/sub\u003e), and corrosion current (I\u003csub\u003ecorr\u003c/sub\u003e). For Au/PANI/CuO, the values of \u0026beta;a and \u0026beta;c are 0.264 and 0.477 mV/dec, respectively, compared to 0.458 and 0.476 mV/dec for CuO. Lower values of \u0026beta;a and \u0026beta;c indicate a faster reaction rate and a more efficient PEC reaction [52]. Additionally, Au/PANI/CuO exhibits a smaller corrosion current (3.89 mA/cm\u003csup\u003e2\u003c/sup\u003e) compared to CuO (5.974 mA/cm\u003csup\u003e2\u003c/sup\u003e). The corrosion rate is directly proportional to I\u003csub\u003ecorr\u003c/sub\u003e [53]. Consequently, this suggests that Au/PANI/CuO experiences less photocorrosion. The corrosion potential represents the potential of a film in the presence of an electrolyte without any external current. A higher corrosion potential indicates a greater ability of the film to resist corrosive damage. This is desirable for maintaining the functionality of photoelectrodes over a long time. The corrosion potential of Au/PANI/CuO (172 mV) is higher than that of CuO (141 mV).\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Values of Tafel parameters of all photoelectrode.\u003c/p\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 84px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCuO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePANI/\u003c/strong\u003e\u003cstrong\u003eCuO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 144px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAu/PANI/CuO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eV\u003csub\u003ecorr\u0026nbsp;\u003c/sub\u003e(mV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e- 141\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e- 179\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e- 172\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eI\u003csub\u003ecorr\u0026nbsp;\u003c/sub\u003e(mA/cm\u003csup\u003e2\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e- 5.974\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e- 5.348\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e- 3.89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026beta;\u003csub\u003ea\u0026nbsp;\u003c/sub\u003e(mV/dec)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.458\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0.413\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e0.264\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026beta;\u003csub\u003ec\u0026nbsp;\u003c/sub\u003e(mV/dec)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.476\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0.652\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 144px;\"\u003e\n \u003cp\u003e0.477\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\"\u003e\n \u003ch2\u003e4.4 PEC water-splitting performance\u003c/h2\u003e\n \u003cp\u003eEfficiency measurements play a critical role in evaluating the practical applicability of photoelectrodes by providing valuable insights into their performance and effectiveness. One key parameter for evaluation is the incident photon-to-current efficiency (IPCE). The IPCE quantifies the ratio of produced electrons to the number of incident photons. It offers valuable information about the photoelectrode\u0026apos;s ability to generate electron-hole pairs when exposed to specific light wavelengths. Consequently, IPCE measurements aid in optimizing the design of photoelectrodes and selecting suitable materials for the photoanode, particularly within specific wavelength ranges. It can be presented by the expression [54]:\u003c/p\u003e\n \u003cdiv id=\"Equ3\"\u003e\n \u003cdiv id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere \\(\\:\\left|{\\text{J}}_{\\text{p}\\text{h}}\\:(\\text{m}\\text{A}/{\\text{c}\\text{m}}^{2})\\right|\\) represents the absolute value of photocurrent measured at a specific wavelength of incident light. \\(\\:{\\lambda\\:}\\:\\left(\\text{n}\\text{m}\\right)\\) denotes the wavelength of a photon being incident. P \\(\\:(\\text{m}\\text{W}/{\\text{c}\\text{m}}^{2})\\) indicates the power density of the illuminating light. Figure 7(a) demonstrates that wavelength-dependent IPCE measurements were carried out at -0.39 VRHE for the Au/PANI/CuO film. The IPCE values are high in the \\(\\:{\\lambda\\:}\\) range of 300 to 636 nm, indicating a favorable photo response for the Au/PANI/CuO film. The higher rate of hydrogen evolution corresponds to a larger magnitude of photocurrent. The maximum IPCE peak value of 45% occurs at 500 nm, confirming the predominant influence of hot electron generation and utilization in the PEC reaction.\u003c/p\u003e\n \u003cp\u003eBy applying an external bias, the J\u003csub\u003eph\u003c/sub\u003e of a photoanode increases, leading to improved efficiency in the PEC process. To quantify the impact of the external bias, the applied bias photon-to-current efficiency (ABPE) is used as an important measure of PEC water-splitting performance. ABPE value is derived from the \\(\\:{\\text{J}}_{\\text{p}\\text{h}}\\:\\)- V plot and can be expressed as [55], [56]:\u003c/p\u003e\n \u003cdiv id=\"Equ4\"\u003e\n \u003cdiv id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eIn this equation, \\(\\:{\\text{E}}_{\\text{r}\\text{e}\\text{v}}\\) represents the standard reversible potential (1.23 V vs. RHE). \\(\\:\\left|{\\text{V}}_{\\text{a}\\text{p}\\text{p}}\\right|\\) is the absolute value of the applied bias potential vs. RHE. Figure 7(b) illustrates the plot of the ABPE as a function of the applied bias potentials at different incident wavelengths of Au/PANI/CuO photoanode. Under illumination with photons at a wavelength of 500 nm, this photoanode achieves a maximum ABPE value of about 2.5% at an applied bias potential of 1.4 V vs. RHE. The obtained results represent a significant improvement in the ABPE and IPCE values compared to different materials reported in the literature [57]\u0026ndash;[60].\u003c/p\u003e\n\u003c/div\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eIn conclusion, this study successfully investigated the combined effects of PANI, CuO, and Au NPs in a photoelectrode for enhanced hydrogen production in photoelectrochemical (PEC) water splitting. The Au/PANI/CuO photoelectrode exhibited a unique morphology and structure, along with enhanced light absorption. By integrating Au, PANI, and CuO nanomaterials, the photoelectrode achieved improved efficiency, stability, and light utilization compared to bare CuO. The significant 300-fold increase in J\u003csub\u003eph\u003c/sub\u003e, superior stability, and efficient light utilization highlight the potential of this approach for designing efficient and stable photoelectrodes in clean and sustainable hydrogen production.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThis research has been funded by the Scientific Research Deanship at the University of Ha\u0026rsquo;il - Saudi Arabia through project number \u0026lt;\u0026lt;RG-24 062\u0026gt;\u0026gt;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eContributions:\u0026nbsp;\u003c/strong\u003eProject administration, F. A, S. L, Y. A. J., and R. R. D. P.; Supervision, F. A., H. A. E., M. S., A. M. A., and S. L.; Software, M. R.; Visualization, Y. A. J., and S. L., A. M.; Writing\u0026mdash;review \u0026amp; editing, F. A., H. A. E., R. R. D. P., and Y. A. J.; Writing\u0026mdash;original draft, A. M. A., M. R., and M. Z.; Methodology, M. Z., M. R., and M. S.; Data curation, M. S., F. A., S. L., R. R. D. P., and M. S.; All authors have read and agreed to the published version of\u0026nbsp;the\u0026nbsp;manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAvailability of data and material:\u0026nbsp;\u003c/strong\u003eRequests should be addressed to the corresponding author on a reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eM. Ahmed and I. Dincer, \u0026ldquo;A review on photoelectrochemical hydrogen production systems: Challenges and future directions,\u0026rdquo; Int. J. 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Mustafa et al., \u0026ldquo;Efficient CuO/Ag\u003csub\u003e2\u003c/sub\u003eWO\u003csub\u003e4\u003c/sub\u003e photoelectrodes for photoelectrochemical water splitting using solar visible radiation,\u0026rdquo; RSC Adv., vol. 13, no. 17, pp. 11297\u0026ndash;11310, Apr. 2023, doi: 10.1039/D3RA00867C.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Au/PANI/CuO, Water splitting, Synergistic effect, Optical properties, Hydrogen generation, ABPE, IPCE","lastPublishedDoi":"10.21203/rs.3.rs-5773977/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5773977/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study explores a novel photoelectrode made from a combination of copper oxide (CuO), polyaniline (PANI), and gold nanoparticles (Au NPs) for efficient hydrogen production in photoelectrochemical (PEC) water splitting. The Au/PANI/CuO photoelectrode is fabricated using cost-effective methods, ensuring practical applications. The research evaluates the photoelectrode's morphology, structure, efficiency, and stability to optimize its performance in PEC reactions. Integrating Au, PANI, and CuO nanomaterials improves charge transfer, reduces resistivity, and minimizes charge recombination, resulting in significantly enhanced hydrogen production efficiency.\u003c/p\u003e \u003cp\u003eScanning electron microscopy (SEM) reveals that the CuO film has a rough texture with non-uniform particles, while the PANI/CuO film exhibits agglomerates and interconnected PANI nanofibers. The Au NPs are evenly distributed across the PANI/CuO film, with diameters ranging from 5 to 60 nm. Energy dispersive X-ray (EDX) analysis approves the presence of each element in the desired proportions, validating the successful fabrication of the Au/PANI/CuO photoelectrode. The Au/PANI/CuO photoelectrode exhibits enhanced light absorption properties due to the surface plasmon resonance (SPR) effect of Au NPs and the interaction between PANI and CuO. The Au/PANI/CuO photoelectrode demonstrates a remarkable 300-fold increase in photocurrent density (J\u003csub\u003eph\u003c/sub\u003e) compared to pure CuO, achieving a maximum of 15 mA/cm\u0026sup2; at -0.39 V vs. RHE. Additionally, the Au/PANI/CuO photoelectrode maintains a constant photocurrent density for 0.5 hours, showing superior stability compared to CuO, which experiences rapid decay. It also achieves a high IPCE value of 45% at nearly 500 nm, indicating efficient light utilization. Overall, this study presents a promising approach for designing efficient and stable photoelectrodes in PEC water splitting and hydrogen generation applications.\u003c/p\u003e","manuscriptTitle":"Leveraging the Synergistic Effects of Au/PANI/CuO Heterostructure for Enhanced Photoelectrochemical Water Splitting","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-13 14:38:11","doi":"10.21203/rs.3.rs-5773977/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"95176b90-647b-40ee-b7b9-61cd079bb04e","owner":[],"postedDate":"January 13th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-01-15T08:38:57+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-13 14:38:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5773977","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5773977","identity":"rs-5773977","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}