Lithium-ion Battery Waste as a Robust Oxygen Evolution Reaction Electrocatalyst for Seawater Splitting

Lithium-ion Battery Waste as a Robust Oxygen Evolution Reaction Electrocatalyst for Seawater 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 Lithium-ion Battery Waste as a Robust Oxygen Evolution Reaction Electrocatalyst for Seawater Splitting Magdalena Warczak, Katarzyna Belka, Weronika Urbańska, Monika Michalska, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5975431/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 12 Jan, 2026 Read the published version in Scientific Reports → Version 1 posted 11 You are reading this latest preprint version Abstract Electrocatalytic seawater splitting seems to be the most promising and urgent demand strategy for clean hydrogen energy production. Utilizing low-cost electrocatalysts is pivotal in the hydrogen economy, as seawater splitting can be made highly efficient and more economical. To meet these expectations, we proposed using lithium-ion battery waste, the black carbon mass left over from hydrometallurgical metal recovery, as an efficient and stable electrocatalyst for oxygen evolution reaction (OER) performed in alkaline media. The SEM-EDS, XPS, XRD, XRF, and Raman analyses revealed that the composition and structure of the post-leached battery powders depend on the hydrometallurgical waste recycling conditions, which in turn affects their OER electrocatalytic activity. The electrochemical tests proved that Li-ion battery waste has remarkable OER catalytic performance with an overpotential of 344 mV and 239 mV, reaching 10 mA cm -2 in water splitting and in seawater splitting, respectively, which is only less than 85 mV and 100 mV higher than for benchmark RuO 2 in water splitting and seawater splitting, respectively. Lithium-ion battery waste electrocatalysis oxygen evolution seawater splitting Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Highlights Li-ion battery waste is a valuable source of metals and carbon-based materials. The structure and composition of the post-leached battery waste strongly depend on the leaching process conditions. Li-ion battery waste exhibits remarkable electrocatalytic activity towards OER in alkaline electrolytes. The Li-ion battery waste has an exceptionally low OER overpotential of 344 mV and 239 mV, delivering 10 mA cm -2 in water splitting and in seawater splitting, respectively. The OER overpotential for battery waste is only 85 mV and 100 mV higher than for benchmark RuO 2 in water splitting and seawater splitting, respectively. INTRODUCTION Achieving net-zero emissions is increasingly being realized through the widespread adoption of electric vehicles (EVs). However, effective end-of-life (EOL) management of lithium-ion batteries (LIBs) remains a significant challenge 1 , 2 , 3 . It is expected that the end of life of millions of LIBs will soon be in sight, with projections for the EV market to be 530 million vehicles by 2040 [ 4 ]. Besides, this challenging issue is exacerbated by the rising incidence of excessive use of portable electronics. The cathode component of these LIBs contains useful elements, including critical raw materials like Ni, Mn, Co and Li, which can be recovered via recycling [ 5 , 6 ]. The lack of effective recycling poses a serious environmental and health risk, with less than 0.2 million tonnes of LIB waste recycled globally in 2019, most of which comes from portable electronics rather than electric vehicles [ 5 , 6 ]. Inappropriate disposal, for example in landfills, may cause toxic metals like cobalt to leach into the environment and contaminate soil and water, endangering human health. To maximize the recovery and reuse of raw materials, the development of a sustainable battery value chain that includes efficient EOL recycling is urgently needed. Although various efforts have been made to recover Li, Ni, Mn and Co (Li-NMC) from spent LIB cathodes, reusing the recycled form in new LIBs is technologically challenging [ 6 , 7 , 8 ]. Due to its environmentally friendly, efficient and sustainable nature, electrochemical water splitting, involving hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode has received a lot of attention [ 9 , 10 ]. However, the significant use of fresh water in the large-scale electrolysis of water is a cause for concern for water resources. Harnessing green hydrogen from seawater electrolysis is a key strategy for achieving dual-carbon goals, as seawater accounts for 96.5% of the world's water resources [ 11 , 12 ]. Direct seawater splitting streamlines the process by direct hydrogen production from seawater, unlike indirect seawater electrolysis, which requires desalination. However, the significant challenge at the anode in direct seawater electrolysis is oxidation of the high concentration of chlorine ions (Cl − ) to hypochlorite (ClO − ) [ 13 , 14 ], which poses a threat to electrode durability due to the corrosive nature of these products. The energy efficiency of the seawater splitting process would be significantly reduced by the electrode corrosion and poisoning caused by the byproducts of the aforementioned anodic reactions. From a thermodynamic point of view, OER is more favorable over the entire pH range, especially in alkaline media where the difference of standard electrode potential between OER and hypochlorite formation remains a constant value of 480 mV. However, the kinetics of chlorine evolution reaction/hypochlorite evolution reaction (ClER/HCER) makes it more facile than OER. Therefore, the approach of designing the electrocatalysts for alkaline seawater splitting should be focused on materials that exhibit OER overpotential lower than 480 mV, leading to HCER suppression [ 15 , 16 ]. In addition, seawater is a complex medium that contains a variety of inorganic salts, bacteria, microplastics, and dissolved gasses that can poison electrodes and hamper their long-term stability and durability, as well as that of electrocatalysts, membranes, and other materials in the seawater electrolyzer. To overcome these issues, a number of strategies are utilized, including the electrocatalysts’ structure and composition design, their surface modification engineering, as well as the local environment customization, ensuring high catalyst performance, stability, and selectivity [ 15 , 17 ]. To date, noble metal-based compounds like ruthenium and iridium have been thought to be the most efficient and selective OER electrocatalysts in seawater splitting [ 18 ]. However, their scarceness and elevated cost restrict their widespread technological use. Therefore, non-noble metal-based materials like transition metal oxides, carbides, phosphides, sulfides, selenides, chalcogenides are widely exploited as OER electrocatalysts [ 19 , 20 , 21 , 22 ]. And the combination of transition metal compounds and carbon-based materials leads to improved dispersion of active sites and enhanced catalytic activity of such composites [ 23 ]. Therefore, the exploration of such low-cost, stable, and highly active carbon-based transition metal compounds seems to be the reasonable approach for designing not only OER electrocatalysts in seawater splitting but also in general in energy conversion systems. Following this strategy, recently, we demonstrated that lithium-ion battery waste has excellent electrocatalytic activity for ORR to H 2 O 2 generation. [ 24 ]. Furthermore, we revealed the impact of the structure and composition of the battery waste on its ORR catalytic capabilities [ 25 ]. And, in this work, we showed the electrocatalytic performance of battery waste toward OER in the water splitting process. Moreover, to the best of our knowledge, this study shows the first evidence that battery waste (the carbon black mass left over from the leaching process) could be a potential OER electrocatalyst in seawater splitting. EXPERIMENTAL SECTION Chemicals. Nafion 117 solution (∼5% in a mixture of lower aliphatic alcohols and water), RuO 2 powder, LiCoO 2 powder, sodium chloride (NaCl), and glutaric acid (C 5 H 8 O 4 ) (analytical grade), (Merck KGaA) were purchased from Sigma Aldrich. KOH (analytical grade) was supplied by POCH, H 2 O 2 (30% analytical grade), and H 2 SO 4 (96% analytical grade) were received from STANLAB (Lublin, Poland). Deionized water purified with HYDROLAB (Gliwice, Poland) with ion columns was used to prepare solutions for the electrochemical studies. Acid-leaching Method for Metals’ Recovery from Spent Li-ion Batteries. Acid-leaching Method for Metals’ Recovery from Spent Li-ion Batteries. First, spent LiBs collected from laptops of various manufacturers (including Toshiba, Samsung, and Asus) were mechanically dismantled, and the anodes and the cathodes were separated from other fractions before being crushed and ground into powder. Then, the powders were washed with distilled water, and dried in an oven overnight at 90°C. The battery waste powders were then treated under different conditions, where the samples were named BAT 1, BAT 2, and BAT 3, see Table 1 . To prepare BAT 1 sample, the powder was treated with 1.5 M sulfuric acid (H 2 SO 4 ) with a mass ratio of 1:10 (solid residue:liquid) for 120 min with the mechanical stirring of about 500 rpm. In the case of material BAT 2: the solid residue was treated with 5 M formic acid (CH 2 O 2 ) at 55°C for 3 min with magnetic stirring at 500 rpm and then 5 g of glutaric acid (C 5 H 8 O 4 ) and 3 mL of 30% aq hydrogen peroxide (H 2 O 2 ) were added with continuous stirring for an additional 120 min. Then, the residue was filtered to separate the solid residue from the leaching bath. The post-leaching residue (the carbon black mass) was then rinsed with deionized water until neutralization, dried at 50°C overnight, mechanically ground, and then used for electrochemical studies. In the case of material BAT 3: instead of 5 M formic acid (CH₂O₂), lactic acid (C 3 H 6 O 3 ) was used with the same procedure. Figure S1 displays the rate of metals recovery from battery waste as a result of leaching process operating under various conditions leading to producing black carbon battery waste masses: BAT 1–3 (see Table 1 ). Characterization . The morphology analysis was performed using ZEISS Crossbeam 350 scanning electron microscope (SEM) equipped with X-ray Electron Dispersive Spectroscopy (EDS), Zeiss, Germany. The SPECS PHOIBOS 100 hemispherical analyzer with a 5-channel detector and a SPECS XR50/FOCUS 500 monochromatic X-ray source equipped with an Al and Ag dual anode was used to analyze the samples’ surface composition and the chemical state of the elements. The Al anode at E pass 40 eV and 10 eV was used for survey and high-resolution spectra, respectively. The spectra were collected in a normal direction and a sample charge was compensated by the SPECS FG22 flood gun during the measurements. The analyzer was set to work in Fixed Analyzer Transmission mode and Medium Area (Magnification M = 5) settings with an entrance slit of 7 × 20 mm 2 and Iris diameter of 35 mm, thus the measured area is about 1.4 × 4 mm 2 . The pressure was kept under 7 × 10 − 7 Pa during the measurements. The acquired data were processed in CasaXPS software with a Shirley background profile and built-in RSF was used for the calculation of the elemental composition. X-ray fluorescence spectroscopy (XRF) was conducted on the wave-dispersive XRF spectrometer Rigaku Primus IV using standardless SQX analysis based on the fundamental parameters method. This spectrometer enables the measurement of element concentration across the range from F to U, with a concentration range of 1 ppm to 100%. The X-ray diffractometry (XRD) was performed on a Panalytical X’Pert Pro MPD (Multipurpose Difractometer). Data collection was performed over a range from 10 to 90° with a scanning rate of 1.5° (2θ)/min with CuKα radiation (45 kV, 40 mA, λ = 1.5406 nm). The crystal phases were identified by referencing diffraction patterns in a licensed library from the International Centre for Diffraction Data (ICDD). The Raman spectra were acquired on a DXR Raman microscope (Thermo Scientific) with a 32-two-second scan, laser 532 nm (3 mW) under a 10 × objective of an Olympus microscope. The content of heavy metal ions in the solution after the leaching to determine the recovery rate was investigated using inductively coupled plasma mass spectrometer (ICP-MS) NexION 5000 Perkin Elmer (USA). Electrocatalytic Activity Measurements. Linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronopotentiometry (CP) were conducted with an Ivium potentiostat (Ivium Technologies, Netherlands) in a three-electrode cell. The static glassy carbon (GC) disc electrode (0.0314 cm 2 , Mineral, Poland) was employed as a working electrode, while the Hg/HgO electrode (Mineral, Poland) and Pt wire (Mineral, Poland) served as a reference electrode and a counter electrode, respectively. All potentials were recalculated vs. the RHE electrode referring to the Nernst equation where E 0 Hg/HgO = 0.098 V [ 26 ]. The GC electrodes were modified with a suspension of 2.5 mg battery waste powder in 10 µL of 5% Nafion solution. Electrochemical experiments were conducted in 0.1 M KOH solution (pH 13.16) or 0.1 M KOH + 1 M NaCl (1:1 vol., pH 12.56) under ambient conditions. RESULTS AND DISCUSSION The morphology and composition analysis . Morphology analysis using scanning electron microscopy revealed differences in the battery waste powders leached under various experimental conditions (Table 1 ). As can be seen in Fig. 1 a, the BAT 1 sample has a highly porous surface differing from the other samples, where layered particles are stacked on top of each other, also containing fine particles with a non-uniform shape on the surface. The fine structures can be attributed to the presence of cobalt oxide-based structures, while the surrounding larger structures are derived from carbon. The following BAT 2 sample (Fig. 1 b) has a heterogeneous structure in which flat, flake-like, multilayered clusters are visible along with granular nanostructures surrounding larger flakes on the micron-scale carbon grains. Elemental mapping using EDS indicates that the granules can be attributed to a carbon-based matrix in which larger structures containing cobalt oxide-based structures can be distinguished. The presence of granules may be related to the different leaching conditions. The morphology of the BAT 3 sample is granular, where one can see clumped, flat structures covered with numerous, finer objects with irregular shapes and porous surfaces; see Fig. 1 c. The EDS map shows the aggregates of the cobalt-based compounds randomly dispersed onto the carbon-based matrix. Among these three samples, BAT 1 shows the most porous and complex structure that can be related to the promising catalytic properties. Upon completion of the SEM-EDS analysis, the X-ray fluorescence (XRF) technique was employed to ascertain the metals' contents (in mass percentages) in the post-leached battery waste powders BAT 1–3. The XRF study reveals that cobalt is the main metal in all tested materials (Fig. 2 a). Its mass percentage ranges from 74.8% for BAT 1 up to 92.6% and 95% for BAT 2 and BAT 3, respectively. While nickel, manganese, and copper were also found, their mass percentages in the tested samples were below a few percent (Fig. 2 a). As BAT 1 was leached with sulfuric acid, a signal from possible sulfur compounds, e.g. CoSO 4 , is evident in this sample. Given that the XRF analysis is only an elemental technique, the samples were subjected to the following further examinations. The crystallinity of BAT 1–3 samples was studied by X-ray diffraction (XRD). The XRD patterns in Fig. 2 b show only slight changes in peak intensity, indicating that leaching under different experimental conditions slightly affects the battery waste powder. It can be seen that the peaks located at 2θ = 18.54, 35.9, 37.6, 45.3, 59.5, 65.2̊ can be ascribed to the Co-based materials, in particular LiCoO 2 [ 2 7 , 2 8 ] assigned to the (103), (101), (012), (104), (107), (018), (110) (JC-PDS 00-075-0532 for LiCoO 2 ) and/or cobalt oxides like Co 3 O 4 ascribed to the (111), (311), (222), (400), (511), (440) (JC-PDS 00-042-1467 for Co 3 O 4 ) [ 2 7 , 2 8 ], respectively. The peaks located at 2θ = 26.6, 49.6, 54.7, 77.6, and 83.9̊ can be ascribed to the graphitic carbon, where the lowest intensity is recorded for BAT 2 among the BAT 1–3 samples. This effect relates to the leaching conditions, where the application of the mild organic acids instead of strong inorganic acids leach metals like cobalt with the various yield. The Raman spectroscopy analysis clearly shows the differences in the stoichiometry between the peaks for the particular ingredients including graphitic carbon, cobalt oxides, and pristine LiCoO₂ that was not fully leached. The highest peaks intensity relating to the carbon is recorded for the sample BAT 3. The presence of pristine LiCoO₂ is observed in BAT 2 and BAT 3, where a peak at 583 cm⁻¹, attributed to the E g mode of LiCoO₂, is detected (see Fig. 2 c) [ 29 ]. These findings are in accordance with the results of the X-ray diffraction (XRD) studies. However, due to the high noise-to-signal ratio in the Raman spectra, the expected peak at approximately 483 cm⁻¹, ascribed to the A 1g mode of LiCoO₂ in the literature, is barely discernible. The signal observed in the range of 590–800 cm − 1 , which is associated with M-O vibrations, may be attributed to delithiated LiCoO 2 [ 29 ] and/or Co 3 O 4 [ 30 , 31 ]. It can thus be inferred that the samples contain a mixture of delithiacted and pristine LiCoO₂ as well as cobalt oxide. The peaks with the highest intensities, at approximately 1347, 1575, 2322, and 2712 cm − 1 , are attributed to the D, G, 2D, and D + G bands of graphitic carbon. The observed peaks at 848 and 1026 cm − 1 are likely attributed to electrolyte residues that may have been trapped within the pore structures of the materials. These findings are consistent with those reported elsewhere [ 32 , 33 ]. Furthermore, the presence of other metals, such as Mn and Ni, in BAT 1–3 may also contribute to the observed signals, given the potential for these elements to form oxides. It was observed that the surface of the BAT 1–3 samples differed in composition from the bulk. In order to determine the leaching effect on the chemical composition of the battery waste powders, X-ray photoelectron spectroscopy (XPS) was employed. XPS survey spectra performed for BAT 1–3 materials (Fig. 2 d) confirmed the presence of carbon, oxygen, cobalt, and fluorine in all tested samples as well as additional sulfur for BAT 1 which was leached using sulfuric acid. The high-resolution spectra reveal distinct peaks corresponding to C = C, C-C, C-O, and O = C-O bands in the materials, as shown in the C 1s spectrum (Fig. 2 e). While the C 1s spectra are generally similar across the samples, a slight variation is observed in BAT 2, where the peak for C = C is lower compared to BAT 1 and BAT 3. The C 1s peaks within the binding energy range of 284 eV to 291 eV are characteristic of graphite, the primary constituent of the anodes in Li-ion batteries [ 34 ]. The peak at 284 eV, which exhibits the highest intensity, is attributed to C-C bonds in the graphite sheets, which are sp 2 hybridized [ 35 ]. Peaks between 285 eV and 287 eV are indicative of carbon with sp³ hybridization, bonded to heteroatoms such as C- H, C-O, or C-N [ 36 ]. Additionally, the peak at 291 eV suggests the presence of carbonates and/or C-F bonds, which may arise from trace amounts of the LiPF 6 electrolyte [ 37 , 38 ], or potentially from O = C-O bonds formed by the creation of –COOH groups on the carbon surface during acid leaching [ 39 , 40 , 41 ]. Figure 2 f presents the valence spectrum for a Co-based compound, where spin-orbit coupling results in two distinct Co 2p 3/2 and Co 2p 1/2 peaks for BAT 1 and BAT 3. However, the peaks for BAT 3 are notably broader and shifted toward higher binding energies. The deconvolution spectra reveal two prominent peaks, which are attributed to compounds such as CoO, Co₃O₄, Co(OH)₂, and Co₂O₃ in the BAT 1 and BAT 2 samples [ 42 , 43 ]. For BAT 3, these peaks are shifted to binding energies of approximately 785 eV and 800 eV, corresponding to the Co 2p 3/2 and Co 2p 1/2 orbitals, respectively. This shift suggests the presence of Co²⁺ and Co³⁺ ions, likely originating from CoSO₄, CoO, and Co₃O₄ compounds [ 42 ]. The deconvolution curves for BAT 2 further indicate an additional pair of peaks, which may imply the coexistence of both Co³⁺ and Co²⁺ in the sample [ 44 ]. Additionally, the formation of CoF₂ can also be inferred [ 45 ]. The supplementary material presents the high-resolution spectra for O 1s, F 1s, and S 2p spectra, as shown in Figure S2 , respectively. The O 1s XPS spectra reveal peaks at 531–534 eV that can be attributed to the C = O bonding and to the graphite C-O surface groups resulting from surface modification by the leaching process [ 37 ]. The appearance of F 1s peaks at approximately 688–689 eV indicates the presence of C-F bonds and LiFP 6 [ 37 ] in the BAT 1–3 samples. Additionally, the S 2p peaks observed in BAT 3 between 169 and 173 eV are likely associated with S-F bonds or CoSO 4 [ 42 ]. As BAT 3 is the only sample subjected to leaching with sulfuric acid, the sulfur-based peak is observed exclusively in this sample. Electrochemical characterization. Water splitting . The electrocatalytic OER activity of GC electrodes modified with different post-leached battery waste was assessed using linear sweep voltammetry (LSV) and cyclic voltammetry (CV) techniques. For comparison, the OER activity of benchmark LiCoO 2 and RuO 2 catalysts was also evaluated. As shown in Fig. 3 a, the LSV curves revealed that the battery waste material BAT 1 demonstrated superior OER activity compared to BAT 2, BAT 3, and the commercially available LiCoO₂, which is commonly used in Li-ion battery production. The onset potential ( E onset ) required for reaching 10 mA cm − 2 was 1.57 V for BAT 1 (Fig. 3 a) which is significantly lower than either for BAT 2 (569 mV), BAT 3 (444 mV) or LiCoO 2 (504 mV) (Fig. 3 a, b) and is only of 344 mV higher than theoretical thermodynamic potential for water splitting (1.23 V vs. RHE). Moreover, OER onset potential for BAT 1 is just 85 mV and 21 mV higher than the benchmark RuO 2 (Fig. 3 b, Figure S3 ) and IrO 2 [ 46 ] (Fig. 3 a,b) but lower than for Co 3 O 4 (440 mV) [ 47 ]. Furthermore, BAT 1 demonstrated superior OER catalytic performance, with an overpotential of 344 mV to reach 10 mA cm − 2 , outperforming graphite-based materials recycled from spent Li-ion batteries (506 mV and 436 mV) [ 48 ]. These materials had undergone additional chemical oxidation and N-doping post-recycling, which enhanced their catalytic properties [ 49 ]. A comparison of the electrocatalytic properties of the battery waste materials under investigation reveals that BAT 1 exhibits the highest OER performance, while BAT 2 shows the lowest catalytic activity, with OER overpotentials of 344 mV and 569 mV at 10 mA cm − 2 , respectively (Fig. 3 b). Additionally, BAT 1 displays the lowest Tafel slope (101 mV dec − 1 ) among the battery waste materials studied (Fig. 3 c ) , which is comparable to that of RuO 2 ( Figure S3 ), suggesting a faster reaction rate. In contrast, LiCoO 2 , identified as a benchmark material, exhibits a relatively high overpotential at 10 mA cm − 2 and a higher Tafel slope (151 mV dec − 1 ) (Fig. 3 c), indicating the slowest OER reaction rate. Additionally, the noticeable anodic peak that appears at about 1.1 V on the CV curve for BAT 1 indicates the presence of a significant number of redox-active cobalt compounds (Co 2+ /Co 3+ ) at its surface as compared to other tested battery waste, which probably contain fewer bulk cobalt compounds. This conclusion aligns with the findings of Raman and XRD investigations, which show a predominance of Co-based compounds in BAT 1 compared to the other battery waste materials. The superior OER catalytic activity of BAT 1, in comparison to other battery waste materials and several non-precious cobalt- and carbon-based catalysts, as illustrated in Fig. 4 b, can be attributed to the structure and composition of the battery waste. This suggests that BAT 1 has a higher density of active sites and that its more porous structure facilitates enhanced electron transfer. In order to verify this, the double layer capacitance C dl was determined using CV recorded at different scan rates in the non-faradaic potential region (ΔE) ( Figure S5 ). C dl was calculated from the equation: Δj = (j a -j c )/2ν, where j a and j c are the anodic and cathodic current densities at ΔE and ν is the scan rate in mV s − 1 [ 50 ]. Out of all the battery waste materials that were evaluated, BAT 1 has the highest C dl (19.2 mF cm − 2 ), as shown in Fig. 4 a. Since the double layer capacitance is directly proportional to the electrochemically active surface area (ECSA) (ECSA = C dl /C s , where C s is a specific capacitance of the electrode) [ 50 ] and as we compared similarly compositional battery waste materials (based on carbon black mass with slightly different metal contents), it can be concluded that the ECSA values for battery waste materials changing in the following manner: BAT 1 > BAT 3 > BAT 2, which is reflected in their electrocatalytic activity towards OER (Fig. 3 ). Furthermore, all tested materials demonstrated robust durability with no significant increase in electrode potential observed during long-term stability measurements conducted in 0.1 M KOH (Fig. 3 d). A slight increase in the electrode potential is caused by the formation of an oxygen bubble that becomes trapped on the surface, thereby reducing the active surface area of the electrode. Seawater splitting. Following the confirmation of the robust OER electrocatalytic activity of Li-ion battery waste in alkaline freshwater electrolyte, its OER performance was further explored in an alkaline simulated seawater electrolyte (1 M KOH : 1 M NaCl, 1:1 vol.). As shown in Fig. 5 , the OER performance of different battery waste materials (BAT 1–3) exhibited slight variations. BAT 2 demonstrated the lowest OER performance, consistent with findings from freshwater splitting studies. It exhibited an overpotential of 319 mV at 10 mA cm − 2 , along with a higher Tafel slope, indicating slower OER kinetics compared to the other battery waste materials. In contrast, BAT 1 showed the lowest overpotential (239 mV) to achieve 10 mA cm − 2 , while BAT 3 required 279 mV of overpotential for the same current density. BAT 1 exhibited a lower Tafel slope (153 mV dec − 1 ) compared to BAT 3 (168 mV dec − 1 ), suggesting that the OER is more facile with BAT 1. Two benchmark materials, RuO 2 and LiCoO 2 , demonstrated lower overpotentials for the OER, with values of 139 mV and 159 mV, respectively (see Fig. 5 and Figure S4 ). However, the relatively poor OER kinetics of LiCoO 2 and RuO 2 in seawater splitting is evidenced by higher Tafel slope values (225 mV dec − 1 and 212 mV dec − 1 , respectively) than for all tested battery waste. In general, the Tafel slopes determined for tested battery waste Materials as well as the benchmark catalysts differ and have higher values than for those obtained in 0.1 M KOH electrolyte, indicating different rate-determining steps within a given pathway [ 55 , 56 ]. The OH − electrosorption on the electrocatalyst surface initiates a typical oxygen generation in the water/seawater splitting process. Therefore, a high affinity for adsorbed OH-intermediates is a necessary feature of an effective catalyst with high OER performance. Then, the subsequent steps of oxygen generation will become rate-determining steps if the formation and equilibrium coverage of OH-intermediates are rapidly reached, leading to a smaller Tafel slope [ 56 ]. Additionally, the LSV curves for BAT 1 (at 1.1 V, Fig. 5 a) clearly show an anodic peak corresponding to the redox Co²⁺/Co³⁺ couple, similar to that observed in 0.1 M KOH electrolyte. The benchmark LiCoO₂ material also exhibits an anodic peak at 1.24 V (Fig. 5 a) in the LSV curve, which may be associated with the Co³⁺/Co⁴⁺ redox couple. These anodic peaks are more visible than that observed in 0.1 M KOH which may results from the chloride ions present in alkaline electrolyte that enhance the cobalt oxidation reaction [ 57 ]. The chronopotentiometry experiments conducted at a current density of 10 mA cm − 2 (Fig. 5 d) did not reveal any discernible/increase in activity following 3600 s stability tests. Only a few notable potential increases/decays related to the oxygen bubble formation were observed, which remained/adhered to the surface and detach from it. Figure 6 a shows the double layer capacitance C dl determined for battery waste materials tested in the simulated seawater medium according to the same procedure as previously utilized for OER in KOH electrolyte. As can be seen, the same trend is observed: BAT 1 exhibits the highest C dl (69.2 mF cm − 2 ), while BAT 2 - the lowest (3.6 mF cm − 2 ). That means the ESCA for the tested materials changes as follows: BAT 1 > BAT 3 > BAT 2. As depicted in Fig. 6 b, the OER performance of BAT 1 is superior to that of the majority of recently explored seawater OER catalysts, including carbon-transition metal-based composites. However, it exhibits slightly inferior OER characteristics in comparison to noble metal oxides and composites demonstrating an overpotential of 100 mV and 80 mV higher than that observed for RuO 2 and LiCoO 2 , respectively. CONCLUSIONS This study represents a significant advancement in our understanding of the catalytic potential of post-leached battery waste powders, specifically the residual black carbon mass that remains after metal recovery. Our findings demonstrate that these powders can drive the oxygen evolution reaction (OER) for seawater splitting with remarkable low overpotential. The structure, morphology, and composition of the spent BAT 1–3 powders were found to be markedly influenced by the leaching conditions. It is noteworthy that the leaching process using sulfuric acid resulted in the lowest recovery rate of cobalt, yet the highest efficiency in the catalytic process for the OER, both in water and seawater splitting. This highlights the crucial role of cobalt-based materials in this reaction. Moreover, the recovery process undergone with sulfuric acid has resulted in a more developed battery waste structure exhibiting a higher electrochemical surface active area than obtained after recovery with organic acids. These findings indicate that a well-developed surface structure is a key factor in enhancing the efficiency of electrocatalytic water splitting in saline environments. The results of electrochemical tests, coupled with compositional and structural analyses, revealed that the presence of LiCoO₂ and other cobalt-based compounds, as well as a highly porous surface structure (electrochemical active surface area), are critical factors influencing the OER catalytic performance of battery waste. Conversely, higher levels of crystallinity were found to contribute less significantly to catalytic activity. It is noteworthy that the post-leached battery waste powders exhibited remarkable OER electrocatalytic activity in seawater splitting, exceeding that of a widely studied carbon–transition metal-based material. These powders demonstrated an OER overpotential that was only 100 mV higher than that of the benchmark RuO₂ catalyst. These findings highlight the potential of waste-derived, low-cost electrocatalysts in advancing the hydrogen economy. In summary, the electrocatalytic performance of spent lithium-ion batteries (LiBs) is determined not only by the cobalt-based compound content but also by the material's morphology, particularly the development of the carbon-based matrix. This study provides valuable insights into the role of these factors in energy conversion processes and represents a significant step toward the reuse of spent LiBs. The findings emphasize the critical importance of recycling battery waste powders for electrocatalytic applications, contributing to a circular economy and the sustainable utilization of resources. Declarations ACKNOWLEDGEMENTS M. Warczak would like to acknowledge the National Science Center (NCN, Poland) for financial support through grant SONATA No. 2022/47/D/ST4/01421. M. Michalska would like to acknowledge for the financing support through the European Union under the REFRESH - Research Excellence For REgion Sustainability and High-tech Industries (project no. CZ.10.03.01/00/22_003/0000048) via the Operational Programme Just Transition, and MATUR - Materials and Technologies for Sustainable Development project number CZ.02.01.01/00/22_008/0004631 funded by European Union and the state budget of the Czech Republic within the framework of the Jan Amos Komensky Operational Program. M. Michalska would like to thank for the assistance provided by the Research Infrastructure NanoEnviCz, supported by the Ministry of Education, Youth and Sports of the Czech Republic under Project No. LM2023066. M. Warczak would like to thank Natalia Sławkowska from Bydgoszcz University of Science and Technology for her help in the laboratory. M. Osial would like to thank Piotr Jenczyk from the IPPT PAN for the morphology studies and valuable consultations and prof. Michael Giersig for the laboratory access. DATA AVAILABILITY The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. References Heath, G. A., Ravikumar, D., Hansen, B. & Kupets, E. A critical review of the circular economy for lithium-ion batteries and photovoltaic modules – status, challenges, and opportunities. J. Air Waste Manag. Assoc. 72 , 478–539 (2022). Nurdiawati, A. & Agrawal, T. K. 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CoSe2 nanocrystals embedded into carbon framework as efficient bifunctional catalyst for alkaline seawater splitting. Inorg. Chem. Commun. 146 , 110170 (2022). Additional Declarations No competing interests reported. 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(b) overpotential at 10 mA cm\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e; (c) Tafel plots; (d) CP curves recorded in 0.1 M KOH at 10 mA cm\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-5975431/v1/302f64593d5131cf04ad3349.png"},{"id":75909600,"identity":"5dd6b432-26b0-4630-b3e9-44edae96aba6","added_by":"auto","created_at":"2025-02-10 12:25:27","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":8896989,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) Average current density (Dj=(ja-jc)/2) versus the scan rate presenting the double-layer capacitance (Cdl) taken from the corresponding CVs; (b) A comparison of the selected cobalt and carbon based catalysts for OER in KOH electrolyte [\u003c/strong\u003e\u003csup\u003e51\u003c/sup\u003e\u003cstrong\u003e,\u003c/strong\u003e\u003csup\u003e52\u003c/sup\u003e\u003cstrong\u003e,\u003c/strong\u003e\u003csup\u003e53\u003c/sup\u003e\u003cstrong\u003e,\u003c/strong\u003e\u003csup\u003e54\u003c/sup\u003e\u003cstrong\u003e].\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure4ab.png","url":"https://assets-eu.researchsquare.com/files/rs-5975431/v1/5872d9ea952fb9ae62da2018.png"},{"id":75909584,"identity":"75148c6f-e2e7-42b5-af50-1d59b30d4e17","added_by":"auto","created_at":"2025-02-10 12:25:27","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":6050102,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe electrochemical OER performance of battery waste BAT 1-3 and benchmark catalysts: (a) LSV curves; (b) overpotential at 10 mA cm\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e; (c) Tafel plots; (d) CP curves recorded in 1 M KOH + 1 M NaCl (1:1 vol.).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-5975431/v1/e7f6d00a8ce68d460d73eaa8.png"},{"id":75909588,"identity":"87bcc7b2-cc07-4436-8f54-71d7d93314fe","added_by":"auto","created_at":"2025-02-10 12:25:27","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":6396043,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) Average current density (Dj=(ja-jc)/2) versus the scan rate presenting the double-layer capacitance (Cdl) taken from the corresponding CVs; (b) A comparison of OER overpotential for reaching of 10 mA cm\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e of various catalysts in KOH + NaCl (or KOH + seawater) solution [\u003c/strong\u003e\u003csup\u003e58\u003c/sup\u003e\u003cstrong\u003e,\u003c/strong\u003e\u003csup\u003e59\u003c/sup\u003e\u003cstrong\u003e,\u003c/strong\u003e\u003csup\u003e60\u003c/sup\u003e\u003cstrong\u003e,\u003c/strong\u003e\u003csup\u003e61\u003c/sup\u003e\u003cstrong\u003e,\u003c/strong\u003e\u003csup\u003e62\u003c/sup\u003e\u003cstrong\u003e, \u003c/strong\u003e\u003csup\u003e63\u003c/sup\u003e\u003cstrong\u003e].\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure6ab.png","url":"https://assets-eu.researchsquare.com/files/rs-5975431/v1/26629bcfc4def5c0511a4b8a.png"},{"id":100616075,"identity":"1af9bf0d-f573-4b19-8504-91cdeba3fe86","added_by":"auto","created_at":"2026-01-19 17:39:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":22454848,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5975431/v1/5f47915b-7ca7-4b93-bd9a-628c34acc8d2.pdf"},{"id":75911134,"identity":"98834f08-dfbf-4522-96ae-122b6dd5a5ff","added_by":"auto","created_at":"2025-02-10 12:41:27","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3101612,"visible":true,"origin":"","legend":"","description":"","filename":"SupplemSeawatersplitting20250124MW.docx","url":"https://assets-eu.researchsquare.com/files/rs-5975431/v1/a5aaac1a207c3a606579a4a0.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Lithium-ion Battery Waste as a Robust Oxygen Evolution Reaction Electrocatalyst for Seawater Splitting","fulltext":[{"header":"Highlights","content":"\u003cp\u003eLi-ion battery waste is a valuable source of metals and carbon-based materials.\u003c/p\u003e\n\u003cp\u003eThe structure and composition of the post-leached battery waste strongly depend on the leaching process conditions.\u003c/p\u003e\n\u003cp\u003eLi-ion battery waste exhibits remarkable electrocatalytic activity towards OER in alkaline electrolytes.\u003c/p\u003e\n\u003cp\u003eThe Li-ion battery waste has an exceptionally low OER overpotential of 344 mV and 239 mV, delivering 10 mA cm\u003csup\u003e-2\u003c/sup\u003e in water splitting and in seawater splitting, respectively.\u003c/p\u003e\n\u003cp\u003eThe OER overpotential for battery waste is only 85 mV and 100 mV higher than for benchmark RuO\u003csub\u003e2\u003c/sub\u003e in water splitting and seawater splitting, respectively.\u003c/p\u003e"},{"header":"INTRODUCTION","content":"\u003cp\u003eAchieving net-zero emissions is increasingly being realized through the widespread adoption of electric vehicles (EVs). However, effective end-of-life (EOL) management of lithium-ion batteries (LIBs) remains a significant challenge\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. It is expected that the end of life of millions of LIBs will soon be in sight, with projections for the EV market to be 530\u0026nbsp;million vehicles by 2040 [\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e]. Besides, this challenging issue is exacerbated by the rising incidence of excessive use of portable electronics. The cathode component of these LIBs contains useful elements, including critical raw materials like Ni, Mn, Co and Li, which can be recovered via recycling [\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e]. The lack of effective recycling poses a serious environmental and health risk, with less than 0.2\u0026nbsp;million tonnes of LIB waste recycled globally in 2019, most of which comes from portable electronics rather than electric vehicles [\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e]. Inappropriate disposal, for example in landfills, may cause toxic metals like cobalt to leach into the environment and contaminate soil and water, endangering human health. To maximize the recovery and reuse of raw materials, the development of a sustainable battery value chain that includes efficient EOL recycling is urgently needed. Although various efforts have been made to recover Li, Ni, Mn and Co (Li-NMC) from spent LIB cathodes, reusing the recycled form in new LIBs is technologically challenging [\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e]. Due to its environmentally friendly, efficient and sustainable nature, electrochemical water splitting, involving hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode has received a lot of attention [\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e]. However, the significant use of fresh water in the large-scale electrolysis of water is a cause for concern for water resources. Harnessing green hydrogen from seawater electrolysis is a key strategy for achieving dual-carbon goals, as seawater accounts for 96.5% of the world's water resources [\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, \u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e]. Direct seawater splitting streamlines the process by direct hydrogen production from seawater, unlike indirect seawater electrolysis, which requires desalination. However, the significant challenge at the anode in direct seawater electrolysis is oxidation of the high concentration of chlorine ions (Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e) to hypochlorite (ClO\u003csup\u003e\u0026minus;\u003c/sup\u003e) [\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e], which poses a threat to electrode durability due to the corrosive nature of these products. The energy efficiency of the seawater splitting process would be significantly reduced by the electrode corrosion and poisoning caused by the byproducts of the aforementioned anodic reactions. From a thermodynamic point of view, OER is more favorable over the entire pH range, especially in alkaline media where the difference of standard electrode potential between OER and hypochlorite formation remains a constant value of 480 mV. However, the kinetics of chlorine evolution reaction/hypochlorite evolution reaction (ClER/HCER) makes it more facile than OER. Therefore, the approach of designing the electrocatalysts for alkaline seawater splitting should be focused on materials that exhibit OER overpotential lower than 480 mV, leading to HCER suppression [\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e]. In addition, seawater is a complex medium that contains a variety of inorganic salts, bacteria, microplastics, and dissolved gasses that can poison electrodes and hamper their long-term stability and durability, as well as that of electrocatalysts, membranes, and other materials in the seawater electrolyzer. To overcome these issues, a number of strategies are utilized, including the electrocatalysts\u0026rsquo; structure and composition design, their surface modification engineering, as well as the local environment customization, ensuring high catalyst performance, stability, and selectivity [\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e].\u003c/p\u003e \u003cp\u003eTo date, noble metal-based compounds like ruthenium and iridium have been thought to be the most efficient and selective OER electrocatalysts in seawater splitting [\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e]. However, their scarceness and elevated cost restrict their widespread technological use. Therefore, non-noble metal-based materials like transition metal oxides, carbides, phosphides, sulfides, selenides, chalcogenides are widely exploited as OER electrocatalysts [\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e]. And the combination of transition metal compounds and carbon-based materials leads to improved dispersion of active sites and enhanced catalytic activity of such composites [\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e]. Therefore, the exploration of such low-cost, stable, and highly active carbon-based transition metal compounds seems to be the reasonable approach for designing not only OER electrocatalysts in seawater splitting but also in general in energy conversion systems.\u003c/p\u003e \u003cp\u003eFollowing this strategy, recently, we demonstrated that lithium-ion battery waste has excellent electrocatalytic activity for ORR to H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e generation. [\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e]. Furthermore, we revealed the impact of the structure and composition of the battery waste on its ORR catalytic capabilities [\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e]. And, in this work, we showed the electrocatalytic performance of battery waste toward OER in the water splitting process. Moreover, to the best of our knowledge, this study shows the first evidence that battery waste (the carbon black mass left over from the leaching process) could be a potential OER electrocatalyst in seawater splitting.\u003c/p\u003e"},{"header":"EXPERIMENTAL SECTION","content":"\u003cp\u003e\u003cstrong\u003eChemicals.\u003c/strong\u003e Nafion 117 solution (\u0026sim;5% in a mixture of lower aliphatic alcohols and water), RuO\u003csub\u003e2\u003c/sub\u003e powder, LiCoO\u003csub\u003e2\u003c/sub\u003e powder, sodium chloride (NaCl), and glutaric acid (C\u003csub\u003e5\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) (analytical grade), (Merck KGaA) were purchased from Sigma Aldrich. KOH (analytical grade) was supplied by POCH, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (30% analytical grade), and H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e (96% analytical grade) were received from STANLAB (Lublin, Poland). Deionized water purified with HYDROLAB (Gliwice, Poland) with ion columns was used to prepare solutions for the electrochemical studies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcid-leaching Method for Metals\u0026rsquo; Recovery from Spent Li-ion Batteries. Acid-leaching Method for Metals\u0026rsquo; Recovery from Spent Li-ion Batteries.\u003c/strong\u003e First, spent LiBs collected from laptops of various manufacturers (including Toshiba, Samsung, and Asus) were mechanically dismantled, and the anodes and the cathodes were separated from other fractions before being crushed and ground into powder. Then, the powders were washed with distilled water, and dried in an oven overnight at 90\u0026deg;C. The battery waste powders were then treated under different conditions, where the samples were named BAT 1, BAT 2, and BAT 3, see Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. To prepare BAT 1 sample, the powder was treated with 1.5 M sulfuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e) with a mass ratio of 1:10 (solid residue:liquid) for 120 min with the mechanical stirring of about 500 rpm. In the case of material BAT 2: the solid residue was treated with 5 M formic acid (CH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) at 55\u0026deg;C for 3 min with magnetic stirring at 500 rpm and then 5 g of glutaric acid (C\u003csub\u003e5\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) and 3 mL of 30%\u003csub\u003eaq\u003c/sub\u003e hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) were added with continuous stirring for an additional 120 min. Then, the residue was filtered to separate the solid residue from the leaching bath. The post-leaching residue (the carbon black mass) was then rinsed with deionized water until neutralization, dried at 50\u0026deg;C overnight, mechanically ground, and then used for electrochemical studies. In the case of material BAT 3: instead of 5 M formic acid (CH₂O₂), lactic acid (C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) was used with the same procedure. \u003cstrong\u003eFigure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/strong\u003e displays the rate of metals recovery from battery waste as a result of leaching process operating under various conditions leading to producing black carbon battery waste masses: BAT 1\u0026ndash;3 (see Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/122228_c8a1650c59388082/122228_custom_files/img1739189575.png\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization\u003c/strong\u003e. The morphology analysis was performed using ZEISS Crossbeam 350 scanning electron microscope (SEM) equipped with X-ray Electron Dispersive Spectroscopy (EDS), Zeiss, Germany.\u003c/p\u003e\n\u003cp\u003eThe SPECS PHOIBOS 100 hemispherical analyzer with a 5-channel detector and a SPECS XR50/FOCUS 500 monochromatic X-ray source equipped with an Al and Ag dual anode was used to analyze the samples\u0026rsquo; surface composition and the chemical state of the elements. The Al anode at E\u003csub\u003epass\u003c/sub\u003e 40 eV and 10 eV was used for survey and high-resolution spectra, respectively. The spectra were collected in a normal direction and a sample charge was compensated by the SPECS FG22 flood gun during the measurements. The analyzer was set to work in Fixed Analyzer Transmission mode and Medium Area (Magnification M\u0026thinsp;=\u0026thinsp;5) settings with an entrance slit of 7 \u0026times; 20 mm\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e and Iris diameter of 35 mm, thus the measured area is about 1.4 \u0026times; 4 mm\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The pressure was kept under 7 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e Pa during the measurements. The acquired data were processed in CasaXPS software with a Shirley background profile and built-in RSF was used for the calculation of the elemental composition.\u003c/p\u003e\n\u003cp\u003eX-ray fluorescence spectroscopy (XRF) was conducted on the wave-dispersive XRF spectrometer Rigaku Primus IV using standardless SQX analysis based on the fundamental parameters method. This spectrometer enables the measurement of element concentration across the range from F to U, with a concentration range of 1 ppm to 100%.\u003c/p\u003e\n\u003cp\u003eThe X-ray diffractometry (XRD) was performed on a Panalytical X\u0026rsquo;Pert Pro MPD (Multipurpose Difractometer). Data collection was performed over a range from 10 to 90\u0026deg; with a scanning rate of 1.5\u0026deg; (2\u0026theta;)/min with CuK\u0026alpha; radiation (45 kV, 40 mA, \u0026lambda;\u0026thinsp;=\u0026thinsp;1.5406 nm). The crystal phases were identified by referencing diffraction patterns in a licensed library from the International Centre for Diffraction Data (ICDD).\u003c/p\u003e\n\u003cp\u003eThe Raman spectra were acquired on a DXR Raman microscope (Thermo Scientific) with a 32-two-second scan, laser 532 nm (3 mW) under a 10 \u0026times; objective of an Olympus microscope.\u003c/p\u003e\n\u003cp\u003eThe content of heavy metal ions in the solution after the leaching to determine the recovery rate was investigated using inductively coupled plasma mass spectrometer (ICP-MS) NexION 5000 Perkin Elmer (USA).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrocatalytic Activity Measurements.\u003c/strong\u003e Linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronopotentiometry (CP) were conducted with an Ivium potentiostat (Ivium Technologies, Netherlands) in a three-electrode cell. The static glassy carbon (GC) disc electrode (0.0314 cm\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, Mineral, Poland) was employed as a working electrode, while the Hg/HgO electrode (Mineral, Poland) and Pt wire (Mineral, Poland) served as a reference electrode and a counter electrode, respectively. All potentials were recalculated vs. the RHE electrode referring to the Nernst equation where E\u003csup\u003e0\u003c/sup\u003e\u003csub\u003eHg/HgO\u003c/sub\u003e = 0.098 V [\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e]. The GC electrodes were modified with a suspension of 2.5 mg battery waste powder in 10 \u0026micro;L of 5% Nafion solution. Electrochemical experiments were conducted in 0.1 M KOH solution (pH 13.16) or 0.1 M KOH\u0026thinsp;+\u0026thinsp;1 M NaCl (1:1 vol., pH 12.56) under ambient conditions.\u003c/p\u003e"},{"header":"RESULTS AND DISCUSSION","content":"\u003cp\u003e \u003cb\u003eThe morphology and composition analysis\u003c/b\u003e. Morphology analysis using scanning electron microscopy revealed differences in the battery waste powders leached under various experimental conditions (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). As can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, the BAT 1 sample has a highly porous surface differing from the other samples, where layered particles are stacked on top of each other, also containing fine particles with a non-uniform shape on the surface. The fine structures can be attributed to the presence of cobalt oxide-based structures, while the surrounding larger structures are derived from carbon. The following BAT 2 sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) has a heterogeneous structure in which flat, flake-like, multilayered clusters are visible along with granular nanostructures surrounding larger flakes on the micron-scale carbon grains. Elemental mapping using EDS indicates that the granules can be attributed to a carbon-based matrix in which larger structures containing cobalt oxide-based structures can be distinguished. The presence of granules may be related to the different leaching conditions. The morphology of the BAT 3 sample is granular, where one can see clumped, flat structures covered with numerous, finer objects with irregular shapes and porous surfaces; see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec. The EDS map shows the aggregates of the cobalt-based compounds randomly dispersed onto the carbon-based matrix. Among these three samples, BAT 1 shows the most porous and complex structure that can be related to the promising catalytic properties.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUpon completion of the SEM-EDS analysis, the X-ray fluorescence (XRF) technique was employed to ascertain the metals' contents (in mass percentages) in the post-leached battery waste powders BAT 1\u0026ndash;3. The XRF study reveals that cobalt is the main metal in all tested materials (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Its mass percentage ranges from 74.8% for BAT 1 up to 92.6% and 95% for BAT 2 and BAT 3, respectively. While nickel, manganese, and copper were also found, their mass percentages in the tested samples were below a few percent (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). As BAT 1 was leached with sulfuric acid, a signal from possible sulfur compounds, e.g. CoSO\u003csub\u003e4\u003c/sub\u003e, is evident in this sample. Given that the XRF analysis is only an elemental technique, the samples were subjected to the following further examinations.\u003c/p\u003e \u003cp\u003eThe crystallinity of BAT 1\u0026ndash;3 samples was studied by X-ray diffraction (XRD). The XRD patterns in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb show only slight changes in peak intensity, indicating that leaching under different experimental conditions slightly affects the battery waste powder. It can be seen that the peaks located at 2θ\u0026thinsp;=\u0026thinsp;18.54, 35.9, 37.6, 45.3, 59.5, 65.2̊ can be ascribed to the Co-based materials, in particular LiCoO\u003csub\u003e2\u003c/sub\u003e [\u003csup\u003e2\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e2\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e] assigned to the (103), (101), (012), (104), (107), (018), (110) (JC-PDS 00-075-0532 for LiCoO\u003csub\u003e2\u003c/sub\u003e) and/or cobalt oxides like Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e ascribed to the (111), (311), (222), (400), (511), (440) (JC-PDS 00-042-1467 for Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) [\u003csup\u003e2\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e2\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e], respectively.\u003c/p\u003e \u003cp\u003eThe peaks located at 2θ\u0026thinsp;=\u0026thinsp;26.6, 49.6, 54.7, 77.6, and 83.9̊ can be ascribed to the graphitic carbon, where the lowest intensity is recorded for BAT 2 among the BAT 1\u0026ndash;3 samples. This effect relates to the leaching conditions, where the application of the mild organic acids instead of strong inorganic acids leach metals like cobalt with the various yield.\u003c/p\u003e \u003cp\u003eThe Raman spectroscopy analysis clearly shows the differences in the stoichiometry between the peaks for the particular ingredients including graphitic carbon, cobalt oxides, and pristine LiCoO₂ that was not fully leached. The highest peaks intensity relating to the carbon is recorded for the sample BAT 3. The presence of pristine LiCoO₂ is observed in BAT 2 and BAT 3, where a peak at 583 cm⁻\u0026sup1;, attributed to the E\u003csub\u003eg\u003c/sub\u003e mode of LiCoO₂, is detected (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec) [\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e]. These findings are in accordance with the results of the X-ray diffraction (XRD) studies. However, due to the high noise-to-signal ratio in the Raman spectra, the expected peak at approximately 483 cm⁻\u0026sup1;, ascribed to the A\u003csub\u003e1g\u003c/sub\u003e mode of LiCoO₂ in the literature, is barely discernible.\u003c/p\u003e \u003cp\u003eThe signal observed in the range of 590\u0026ndash;800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is associated with M-O vibrations, may be attributed to delithiated LiCoO\u003csub\u003e2\u003c/sub\u003e [\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e] and/or Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e [\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e]. It can thus be inferred that the samples contain a mixture of delithiacted and pristine LiCoO₂ as well as cobalt oxide. The peaks with the highest intensities, at approximately 1347, 1575, 2322, and 2712 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, are attributed to the D, G, 2D, and D\u0026thinsp;+\u0026thinsp;G bands of graphitic carbon. The observed peaks at 848 and 1026 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are likely attributed to electrolyte residues that may have been trapped within the pore structures of the materials. These findings are consistent with those reported elsewhere [\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e]. Furthermore, the presence of other metals, such as Mn and Ni, in BAT 1\u0026ndash;3 may also contribute to the observed signals, given the potential for these elements to form oxides.\u003c/p\u003e \u003cp\u003eIt was observed that the surface of the BAT 1\u0026ndash;3 samples differed in composition from the bulk. In order to determine the leaching effect on the chemical composition of the battery waste powders, X-ray photoelectron spectroscopy (XPS) was employed. XPS survey spectra performed for BAT 1\u0026ndash;3 materials (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) confirmed the presence of carbon, oxygen, cobalt, and fluorine in all tested samples as well as additional sulfur for BAT 1 which was leached using sulfuric acid.\u003c/p\u003e \u003cp\u003eThe high-resolution spectra reveal distinct peaks corresponding to C\u0026thinsp;=\u0026thinsp;C, C-C, C-O, and O\u0026thinsp;=\u0026thinsp;C-O bands in the materials, as shown in the C 1s spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). While the C 1s spectra are generally similar across the samples, a slight variation is observed in BAT 2, where the peak for C\u0026thinsp;=\u0026thinsp;C is lower compared to BAT 1 and BAT 3. The C 1s peaks within the binding energy range of 284 eV to 291 eV are characteristic of graphite, the primary constituent of the anodes in Li-ion batteries [\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e]. The peak at 284 eV, which exhibits the highest intensity, is attributed to C-C bonds in the graphite sheets, which are sp\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e hybridized [\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e]. Peaks between 285 eV and 287 eV are indicative of carbon with sp\u0026sup3; hybridization, bonded to heteroatoms such as C- H, C-O, or C-N [\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e]. Additionally, the peak at 291 eV suggests the presence of carbonates and/or C-F bonds, which may arise from trace amounts of the LiPF\u003csub\u003e6\u003c/sub\u003e electrolyte [\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e], or potentially from O\u0026thinsp;=\u0026thinsp;C-O bonds formed by the creation of \u0026ndash;COOH groups on the carbon surface during acid leaching [\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef presents the valence spectrum for a Co-based compound, where spin-orbit coupling results in two distinct Co 2p\u003csub\u003e3/2\u003c/sub\u003e and Co 2p\u003csub\u003e1/2\u003c/sub\u003e peaks for BAT 1 and BAT 3. However, the peaks for BAT 3 are notably broader and shifted toward higher binding energies. The deconvolution spectra reveal two prominent peaks, which are attributed to compounds such as CoO, Co₃O₄, Co(OH)₂, and Co₂O₃ in the BAT 1 and BAT 2 samples [\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e]. For BAT 3, these peaks are shifted to binding energies of approximately 785 eV and 800 eV, corresponding to the Co 2p\u003csub\u003e3/2\u003c/sub\u003e and Co 2p\u003csub\u003e1/2\u003c/sub\u003e orbitals, respectively. This shift suggests the presence of Co\u0026sup2;⁺ and Co\u0026sup3;⁺ ions, likely originating from CoSO₄, CoO, and Co₃O₄ compounds [\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e]. The deconvolution curves for BAT 2 further indicate an additional pair of peaks, which may imply the coexistence of both Co\u0026sup3;⁺ and Co\u0026sup2;⁺ in the sample [\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e]. Additionally, the formation of CoF₂ can also be inferred [\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e].\u003c/p\u003e \u003cp\u003eThe supplementary material presents the high-resolution spectra for O 1s, F 1s, and S 2p spectra, as shown in \u003cb\u003eFigure S2\u003c/b\u003e, respectively. The O 1s XPS spectra reveal peaks at 531\u0026ndash;534 eV that can be attributed to the C\u0026thinsp;=\u0026thinsp;O bonding and to the graphite C-O surface groups resulting from surface modification by the leaching process [\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e]. The appearance of F 1s peaks at approximately 688\u0026ndash;689 eV indicates the presence of C-F bonds and LiFP\u003csub\u003e6\u003c/sub\u003e [\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e] in the BAT 1\u0026ndash;3 samples. Additionally, the S 2p peaks observed in BAT 3 between 169 and 173 eV are likely associated with S-F bonds or CoSO\u003csub\u003e4\u003c/sub\u003e [\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e]. As BAT 3 is the only sample subjected to leaching with sulfuric acid, the sulfur-based peak is observed exclusively in this sample.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eElectrochemical characterization.\u003c/b\u003e \u003cb\u003eWater splitting\u003c/b\u003e. The electrocatalytic OER activity of GC electrodes modified with different post-leached battery waste was assessed using linear sweep voltammetry (LSV) and cyclic voltammetry (CV) techniques. For comparison, the OER activity of benchmark LiCoO\u003csub\u003e2\u003c/sub\u003e and RuO\u003csub\u003e2\u003c/sub\u003e catalysts was also evaluated. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, the LSV curves revealed that the battery waste material BAT 1 demonstrated superior OER activity compared to BAT 2, BAT 3, and the commercially available LiCoO₂, which is commonly used in Li-ion battery production. The onset potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eonset\u003c/sub\u003e) required for reaching 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was 1.57 V for BAT 1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) which is significantly lower than either for BAT 2 (569 mV), BAT 3 (444 mV) or LiCoO\u003csub\u003e2\u003c/sub\u003e (504 mV) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b) and is only of 344 mV higher than theoretical thermodynamic potential for water splitting (1.23 V vs. RHE). Moreover, OER onset potential for BAT 1 is just 85 mV and 21 mV higher than the benchmark RuO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, \u003cb\u003eFigure S3\u003c/b\u003e) and IrO\u003csub\u003e2\u003c/sub\u003e [\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea,b) but lower than for Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (440 mV) [\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e]. Furthermore, BAT 1 demonstrated superior OER catalytic performance, with an overpotential of 344 mV to reach 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, outperforming graphite-based materials recycled from spent Li-ion batteries (506 mV and 436 mV) [\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e]. These materials had undergone additional chemical oxidation and N-doping post-recycling, which enhanced their catalytic properties [\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA comparison of the electrocatalytic properties of the battery waste materials under investigation reveals that BAT 1 exhibits the highest OER performance, while BAT 2 shows the lowest catalytic activity, with OER overpotentials of 344 mV and 569 mV at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Additionally, BAT 1 displays the lowest Tafel slope (101 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) among the battery waste materials studied (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec\u003cb\u003e)\u003c/b\u003e, which is comparable to that of RuO\u003csub\u003e2\u003c/sub\u003e (\u003cb\u003eFigure S3\u003c/b\u003e), suggesting a faster reaction rate. In contrast, LiCoO\u003csub\u003e2\u003c/sub\u003e, identified as a benchmark material, exhibits a relatively high overpotential at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and a higher Tafel slope (151 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), indicating the slowest OER reaction rate.\u003c/p\u003e \u003cp\u003eAdditionally, the noticeable anodic peak that appears at about 1.1 V on the CV curve for BAT 1 indicates the presence of a significant number of redox-active cobalt compounds (Co\u003csup\u003e2+\u003c/sup\u003e/Co\u003csup\u003e3+\u003c/sup\u003e) at its surface as compared to other tested battery waste, which probably contain fewer bulk cobalt compounds. This conclusion aligns with the findings of Raman and XRD investigations, which show a predominance of Co-based compounds in BAT 1 compared to the other battery waste materials.\u003c/p\u003e \u003cp\u003eThe superior OER catalytic activity of BAT 1, in comparison to other battery waste materials and several non-precious cobalt- and carbon-based catalysts, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, can be attributed to the structure and composition of the battery waste. This suggests that BAT 1 has a higher density of active sites and that its more porous structure facilitates enhanced electron transfer. In order to verify this, the double layer capacitance C\u003csub\u003edl\u003c/sub\u003e was determined using CV recorded at different scan rates in the non-faradaic potential region (ΔE) (\u003cb\u003eFigure S5\u003c/b\u003e). C\u003csub\u003edl\u003c/sub\u003e was calculated from the equation: Δj = (j\u003csub\u003ea\u003c/sub\u003e-j\u003csub\u003ec\u003c/sub\u003e)/2ν, where j\u003csub\u003ea\u003c/sub\u003e and j\u003csub\u003ec\u003c/sub\u003e are the anodic and cathodic current densities at ΔE and ν is the scan rate in mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e]. Out of all the battery waste materials that were evaluated, BAT 1 has the highest C\u003csub\u003edl\u003c/sub\u003e (19.2 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. Since the double layer capacitance is directly proportional to the electrochemically active surface area (ECSA) (ECSA\u0026thinsp;=\u0026thinsp;C\u003csub\u003edl\u003c/sub\u003e/C\u003csub\u003es\u003c/sub\u003e, where C\u003csub\u003es\u003c/sub\u003e is a specific capacitance of the electrode) [\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e] and as we compared similarly compositional battery waste materials (based on carbon black mass with slightly different metal contents), it can be concluded that the ECSA values for battery waste materials changing in the following manner: BAT 1\u0026thinsp;\u0026gt;\u0026thinsp;BAT 3\u0026thinsp;\u0026gt;\u0026thinsp;BAT 2, which is reflected in their electrocatalytic activity towards OER (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFurthermore, all tested materials demonstrated robust durability with no significant increase in electrode potential observed during long-term stability measurements conducted in 0.1 M KOH (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). A slight increase in the electrode potential is caused by the formation of an oxygen bubble that becomes trapped on the surface, thereby reducing the active surface area of the electrode.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eSeawater splitting.\u003c/b\u003e Following the confirmation of the robust OER electrocatalytic activity of Li-ion battery waste in alkaline freshwater electrolyte, its OER performance was further explored in an alkaline simulated seawater electrolyte (1 M KOH : 1 M NaCl, 1:1 vol.). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the OER performance of different battery waste materials (BAT 1\u0026ndash;3) exhibited slight variations. BAT 2 demonstrated the lowest OER performance, consistent with findings from freshwater splitting studies. It exhibited an overpotential of 319 mV at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, along with a higher Tafel slope, indicating slower OER kinetics compared to the other battery waste materials. In contrast, BAT 1 showed the lowest overpotential (239 mV) to achieve 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, while BAT 3 required 279 mV of overpotential for the same current density. BAT 1 exhibited a lower Tafel slope (153 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) compared to BAT 3 (168 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), suggesting that the OER is more facile with BAT 1. Two benchmark materials, RuO\u003csub\u003e2\u003c/sub\u003e and LiCoO\u003csub\u003e2\u003c/sub\u003e, demonstrated lower overpotentials for the OER, with values of 139 mV and 159 mV, respectively (see Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cb\u003eFigure S4\u003c/b\u003e). However, the relatively poor OER kinetics of LiCoO\u003csub\u003e2\u003c/sub\u003e and RuO\u003csub\u003e2\u003c/sub\u003e in seawater splitting is evidenced by higher Tafel slope values (225 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 212 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively) than for all tested battery waste. In general, the Tafel slopes determined for tested battery waste Materials as well as the benchmark catalysts differ and have higher values than for those obtained in 0.1 M KOH electrolyte, indicating different rate-determining steps within a given pathway [\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e,\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e]. The OH\u003csup\u003e\u0026minus;\u003c/sup\u003e electrosorption on the electrocatalyst surface initiates a typical oxygen generation in the water/seawater splitting process. Therefore, a high affinity for adsorbed OH-intermediates is a necessary feature of an effective catalyst with high OER performance. Then, the subsequent steps of oxygen generation will become rate-determining steps if the formation and equilibrium coverage of OH-intermediates are rapidly reached, leading to a smaller Tafel slope [\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e].\u003c/p\u003e \u003cp\u003eAdditionally, the LSV curves for BAT 1 (at 1.1 V, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) clearly show an anodic peak corresponding to the redox Co\u0026sup2;⁺/Co\u0026sup3;⁺ couple, similar to that observed in 0.1 M KOH electrolyte. The benchmark LiCoO₂ material also exhibits an anodic peak at 1.24 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) in the LSV curve, which may be associated with the Co\u0026sup3;⁺/Co⁴⁺ redox couple. These anodic peaks are more visible than that observed in 0.1 M KOH which may results from the chloride ions present in alkaline electrolyte that enhance the cobalt oxidation reaction [\u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe chronopotentiometry experiments conducted at a current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed) did not reveal any discernible/increase in activity following 3600 s stability tests. Only a few notable potential increases/decays related to the oxygen bubble formation were observed, which remained/adhered to the surface and detach from it.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea shows the double layer capacitance C\u003csub\u003edl\u003c/sub\u003e determined for battery waste materials tested in the simulated seawater medium according to the same procedure as previously utilized for OER in KOH electrolyte. As can be seen, the same trend is observed: BAT 1 exhibits the highest C\u003csub\u003edl\u003c/sub\u003e (69.2 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), while BAT 2 - the lowest (3.6 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). That means the ESCA for the tested materials changes as follows: BAT 1\u0026thinsp;\u0026gt;\u0026thinsp;BAT 3\u0026thinsp;\u0026gt;\u0026thinsp;BAT 2.\u003c/p\u003e \u003cp\u003eAs depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, the OER performance of BAT 1 is superior to that of the majority of recently explored seawater OER catalysts, including carbon-transition metal-based composites. However, it exhibits slightly inferior OER characteristics in comparison to noble metal oxides and composites demonstrating an overpotential of 100 mV and 80 mV higher than that observed for RuO\u003csub\u003e2\u003c/sub\u003e and LiCoO\u003csub\u003e2\u003c/sub\u003e, respectively.\u003c/p\u003e"},{"header":"CONCLUSIONS","content":"\u003cp\u003eThis study represents a significant advancement in our understanding of the catalytic potential of post-leached battery waste powders, specifically the residual black carbon mass that remains after metal recovery. Our findings demonstrate that these powders can drive the oxygen evolution reaction (OER) for seawater splitting with remarkable low overpotential. The structure, morphology, and composition of the spent BAT 1\u0026ndash;3 powders were found to be markedly influenced by the leaching conditions. It is noteworthy that the leaching process using sulfuric acid resulted in the lowest recovery rate of cobalt, yet the highest efficiency in the catalytic process for the OER, both in water and seawater splitting. This highlights the crucial role of cobalt-based materials in this reaction. Moreover, the recovery process undergone with sulfuric acid has resulted in a more developed battery waste structure exhibiting a higher electrochemical surface active area than obtained after recovery with organic acids. These findings indicate that a well-developed surface structure is a key factor in enhancing the efficiency of electrocatalytic water splitting in saline environments.\u003c/p\u003e \u003cp\u003eThe results of electrochemical tests, coupled with compositional and structural analyses, revealed that the presence of LiCoO₂ and other cobalt-based compounds, as well as a highly porous surface structure (electrochemical active surface area), are critical factors influencing the OER catalytic performance of battery waste. Conversely, higher levels of crystallinity were found to contribute less significantly to catalytic activity. It is noteworthy that the post-leached battery waste powders exhibited remarkable OER electrocatalytic activity in seawater splitting, exceeding that of a widely studied carbon\u0026ndash;transition metal-based material. These powders demonstrated an OER overpotential that was only 100 mV higher than that of the benchmark RuO₂ catalyst. These findings highlight the potential of waste-derived, low-cost electrocatalysts in advancing the hydrogen economy.\u003c/p\u003e \u003cp\u003eIn summary, the electrocatalytic performance of spent lithium-ion batteries (LiBs) is determined not only by the cobalt-based compound content but also by the material's morphology, particularly the development of the carbon-based matrix. This study provides valuable insights into the role of these factors in energy conversion processes and represents a significant step toward the reuse of spent LiBs. The findings emphasize the critical importance of recycling battery waste powders for electrocatalytic applications, contributing to a circular economy and the sustainable utilization of resources.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eACKNOWLEDGEMENTS\u0026nbsp;\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eM. Warczak would like to acknowledge the National Science Center (NCN, Poland) for financial support through grant SONATA No. 2022/47/D/ST4/01421. M. Michalska would like to acknowledge for the financing support through the European Union under the REFRESH - Research Excellence For REgion Sustainability and High-tech Industries (project no. CZ.10.03.01/00/22_003/0000048) via the Operational Programme Just Transition, and MATUR - Materials and Technologies for Sustainable Development project number CZ.02.01.01/00/22_008/0004631 funded by European Union and the state budget of the Czech Republic within the framework of the Jan Amos Komensky Operational Program. M. Michalska would like to thank for the assistance provided by the Research Infrastructure NanoEnviCz, supported by the Ministry of Education, Youth and Sports of the Czech Republic under Project No. LM2023066.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eM. Warczak would like to thank Natalia Sławkowska from Bydgoszcz University of Science and Technology for her help in the laboratory. M. Osial would like to thank Piotr Jenczyk from the IPPT PAN for the morphology studies and valuable consultations and prof. Michael Giersig for the laboratory access.\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eDATA AVAILABILITY\u0026nbsp;\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHeath, G. A., Ravikumar, D., Hansen, B. \u0026amp; Kupets, E. A critical review of the circular economy for lithium-ion batteries and photovoltaic modules \u0026ndash; status, challenges, and opportunities. \u003cem\u003eJ. Air Waste Manag. 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Commun.\u003c/em\u003e \u003cstrong\u003e146\u003c/strong\u003e, 110170 (2022).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Lithium-ion battery, waste, electrocatalysis, oxygen evolution, seawater splitting","lastPublishedDoi":"10.21203/rs.3.rs-5975431/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5975431/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectrocatalytic seawater splitting seems to be the most promising and urgent demand strategy for clean hydrogen energy production. Utilizing low-cost electrocatalysts is pivotal in the hydrogen economy, as seawater splitting can be made highly efficient and more economical. To meet these expectations, we proposed using lithium-ion battery waste, the black carbon mass left over from hydrometallurgical metal recovery, as an efficient and stable electrocatalyst for oxygen evolution reaction (OER) performed in alkaline media. The SEM-EDS, XPS, XRD, XRF, and Raman analyses revealed that the composition and structure of the post-leached battery powders depend on the hydrometallurgical waste recycling conditions, which in turn affects their OER electrocatalytic activity. The electrochemical tests proved that Li-ion battery waste has remarkable OER catalytic performance with an overpotential of 344 mV and 239 mV, reaching 10 mA cm\u003csup\u003e-2\u003c/sup\u003e\u0026nbsp;in water splitting and in seawater splitting, respectively, which is only less than 85 mV and 100 mV higher than for benchmark RuO\u003csub\u003e2\u003c/sub\u003e\u0026nbsp;in water splitting and seawater splitting, respectively.\u003c/p\u003e","manuscriptTitle":"Lithium-ion Battery Waste as a Robust Oxygen Evolution Reaction Electrocatalyst for Seawater Splitting","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-10 12:25:22","doi":"10.21203/rs.3.rs-5975431/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-28T15:52:43+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-13T02:18:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"97199201951672000371210557839650939239","date":"2025-06-03T11:56:38+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-02T13:01:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"315439301563210650921893722678893058474","date":"2025-02-20T10:53:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"260413569659468558973713836905043099376","date":"2025-02-20T10:24:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-02-20T10:18:22+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-02-11T16:54:38+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-02-11T06:49:27+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-02-07T09:34:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-02-06T17:04:49+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"fb3f21ac-267a-4cd9-99eb-517d9bc4847a","owner":[],"postedDate":"February 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-01-19T17:03:25+00:00","versionOfRecord":{"articleIdentity":"rs-5975431","link":"https://doi.org/10.1038/s41598-025-34856-w","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-01-12 16:28:45","publishedOnDateReadable":"January 12th, 2026"},"versionCreatedAt":"2025-02-10 12:25:22","video":"","vorDoi":"10.1038/s41598-025-34856-w","vorDoiUrl":"https://doi.org/10.1038/s41598-025-34856-w","workflowStages":[]},"version":"v1","identity":"rs-5975431","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5975431","identity":"rs-5975431","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}