Applicability of Graphite as Anodic Counter Electrode for Electrocatalyst Evaluation

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Learn More CiteCitationCitation and abstractCitation and referencesMore citation options ShareShare onFacebookX (Twitter)WeChatLinkedInRedditEmailJump toExpandCollapse ViewpointAugust 26, 2024Applicability of Graphite as Anodic Counter Electrode for Electrocatalyst EvaluationClick to copy article linkArticle link copied!Weiran Zheng*Weiran ZhengDepartment of Chemistry, Guangdong Technion-Israel Institute of Technology, Shantou 515063, ChinaTechnion-Israel Institute of Technology, Haifa 32000, IsraelGuangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion, Guangdong Technion-Israel Institute of Technology, Shantou 515063, China*[email protected]More by Weiran Zhenghttps://orcid.org/0000-0002-9915-6982Lijie DuLijie DuDepartment of Chemistry, Guangdong Technion-Israel Institute of Technology, Shantou 515063, ChinaMore by Lijie DuOpen PDFSupporting Information (1)ACS Energy LettersCite this: ACS Energy Lett. 2024, 9, XXX, 4581–4586Click to copy citationCitation copied!https://pubs.acs.org/doi/10.1021/acsenergylett.4c01869https://doi.org/10.1021/acsenergylett.4c01869Published August 26, 2024 Publication History Received 10 July 2024Accepted 14 August 2024Published online 26 August 2024article-commentary© 2024 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissionsThis publication is licensed for personal use by The American Chemical Society. ACS Publications© 2024 American Chemical SocietySubjectswhat are subjectsArticle subjects are automatically applied from the ACS Subject Taxonomy and describe the scientific concepts and themes of the article.Anode materialsCarbonElectrochemical cellsElectrolytesOxidationGraphite rod is a popular counter electrode (CE) material due to its affordability, ease of use, and relatively stable chemical and electrochemical properties. (1−3) As suggested by the literature survey (Figure S1), it is generally favored over Pt CE (67% vs 29%) when serving as the anode (e.g., as CE for hydrogen evolution reaction (HER) catalyst evaluation) due to the Pt dissolution, (4,5) yet several issues arise. The primary concern is carbon corrosion, causing graphite particle detachment and CO/CO2 production (Figure 1). (6) These byproducts can harm the accuracy and reliability of electrocatalyst evaluations. Lee et al. and Ji et al. demonstrated that carbon fiber paper and graphite are susceptible to oxidation in acidic conditions and can deactivate Pt electrodes via CO poisoning. (7,8) Separating the CE compartment from the working electrode (WE) can minimize byproduct diffusion, as demonstrated by Sheng et al. using a graphite CE housed in a glass tube in acidic conditions. (9) These suggestions offer a general judgment on the applicability of graphite CE. However, the behavior of the CE depends significantly on factors such as the electrolyte (acidic or basic), the electrochemical methods (e.g., polarization, steady state), and the electrochemical parameters (e.g., scan rate, scan range, and CE area). Therefore, a comprehensive analysis and guidance on the applicability of graphite CE is needed. This Viewpoint aims to provide such guidance by offering a fundamental analysis of graphite CE followed by best practice recommendations.Figure 1Figure 1. Potential/current relationship in a three-electrode cell and possible interferents generated from the CE diffusing to the WE. ϕWE: WE potential; ϕCE: CE potential; ϕREF: reference electrode potential; EWE: WE voltage; ECE: CE voltage; ECELL: cell voltage; i, iCELL, iWE, and iCE: identical currents in the circuit, cell, WE, and CE; QWE, QCE: charge input/output at WE and CE.High Resolution ImageDownload MS PowerPoint Slide Role of the CEFirst, we need to revisit the role of the CE. In a three-electrode cell, the current flows between the WE and CE (Figure 1). The WE hosts the electrochemical reaction of interest with a precisely controlled voltage (EWE), while the CE completes the circuit by matching the charge requirements. The charge at the WE (QWE) equals the charge at the CE (QCE) at all times, meaning the current at the WE (iWE = QWE/t) always equals the current at the CE (iCE = QCE/t). This current determines the potential applied by the potentiostat on the CE (ECE) (Figure 2A). As the demand for iWE or QWE increases, ECE is increased to drive the corresponding iCE or QCE through Faradaic and/or non-Faradaic processes. Yet, the instrument's compliance voltage (12 V in our case) limits the applicable range of ECE and EWE.Figure 2Figure 2. (A) Changes in ϕWE, Q, i, and ϕCE during an HER polarization study: as ϕWE exceeds the HER onset potential, Q (and i) rises, requiring an increase in ϕCE to produce matching Q and i, involving OER. (B) Potential drops across WE and CE (from EDL of WE, bulk electrolyte, to EDL of CE) in two cases: top, rising i (blue: low current; red: high current); bottom, less active CE (blue: high activity; red: low activity). Ru: solution resistance between WE and REF; EDL: electric double layer.High Resolution ImageDownload MS PowerPoint SlideAlthough some suggest that a slow kinetic process on the CE (i.e., a less active CE) can limit the current on the WE, (7) this is fundamentally unlikely in a three-electrode cell. The iWE is determined exclusively by the EWE (ϕWE – ϕREF) and the nature of the reaction. Regardless of the CE's activity, the potentiostat will increase or decrease the ECE to achieve the required current at the specific EWE. (10) Assuming the same WE and CE, an increase in i results in a larger potential drop across the bulk electrolyte between the WE and CE (Figure 2B, top), while for a less active CE, a higher ECE within the electric double layer (EDL) of the CE is required to meet the same i requirement (Figure 2B, bottom). (10,11) Therefore, to maximize the i and EWE range, especially with potentiostats having low compliance voltage (e.g., 6 V for many compact models), a shorter WE–CE distance and a CE with faster kinetics (i.e., more active) are recommended.For accurate WE analysis, electrochemical processes at the CE must not interfere with the reaction at the WE. Acceptable scenarios include confined species production (the iCE or QCE is generated by electrochemical processes at the CE that produce species confined to the CE surface or separated from the WE) and nonreactive species production (the iCE or QCE results from electrochemical processes at the CE that produce diffusible but nonreactive species concerning the WE). Inevitably, non-Faradaic charging/discharging at the CE contributes to iCE or QCE, but this contribution is minor and does not interfere with the WE. Anodic Behavior of Graphite CETo analyze how graphite as a CE provides QCE, we used a graphite rod as the WE and another as the CE (cell configuration denoted as C|C). In an acidic electrolyte (0.5 M H2SO4), the current increases around 0 V (all potential values in this contribution are calibrated against a reversible hydrogen electrode (RHE), see Supporting Information) and rises rapidly from ∼1.52 V (Figure 3A), due to sulfate ion intercalation. (12) In an alkaline electrolyte (1.0 M KOH), noticeable current onset occurs at ∼1.70 V. Charge accumulation (Figure 3B) shows that the graphite electrode contributes more charge in acidic conditions than in alkaline ones, indicating a smaller ECE requirement in acid for the same QCE. Differential electrochemical mass spectra (DEMS) (Figure 3C) reveal that in acidic conditions, CO and O2 evolve from ∼2.02 V and CO2 from ∼1.61 V. In comparison, only O2 is produced in alkaline conditions from ∼1.79 V (CO2 is undetectable due to carbonation), which agrees with the DEMS study by Schuhmann et al. that OER can hinder carbon corrosion in alkaline. (6) After a few cycles, black particles appear from ∼1.50 V in the acidic electrolyte, indicating graphite exfoliation and detachment. (12) The cycled graphite surface is rougher in acidic electrolytes than in alkaline ones (Figure S2), suggesting more intense exfoliation in acidic conditions.Figure 3Figure 3. (A) Cyclic voltammograms of graphite electrodes in Ar-saturated 0.5 M H2SO4 (orange) and 1.0 M KOH (blue) electrolytes (scan rate: 10 mV s–1). (B) Corresponding charge plots. (C) DEMS signals of O2, CO, and CO2 as a function of potential. (D) Schematic representation of the anodic polarization processes of graphite electrodes.High Resolution ImageDownload MS PowerPoint SlideFigure 3D outlines the anodic polarization processes on the graphite CE, (6,13) including anion adsorption/intercalation, exfoliation, particle detachment, surface oxidation, OER, and complete oxidation to CO/CO2. Although most processes are surface-bound, released particles and CO/CO2 can diffuse to the WE, potentially interfering with the desired reaction. Thus, the suitability of graphite as a CE depends on the applied ECE and the durations of these processes, which vary with different electrochemical methods. We will focus the discussion on two key methods: cyclic voltammetry (CV) and steady-state electrolysis. CV Using Graphite CE: One vs Two CompartmentsA two-compartment cell (H-cell) is often recommended to mitigate corrosion product diffusion from a carbon CE. (9) We start by analyzing the electrochemical response of Pt WE and graphite CE in two cell configurations under acidic and alkaline conditions.Figures 4A and 4B show the evolution of EWE, ECE, and i in acidic and alkaline conditions within a one-compartment cell (denoted as Pt|C) during 100 cycles of CV study. In the first cycle (insets), as EWE decreases from 0 to −0.20 V, i increases due to HER catalyzed by Pt, requiring a matching iCE from the graphite CE, causing ECE to rise. Two major kinetic zones are identified in both conditions, indicating that graphite CE undergoes at least two processes to provide the matching iCE or QCE (Figure S3). Since ECE exceeds 2.50 V, all anodic processes of graphite are present, producing exfoliated particles and O2 (acid and base) and CO/CO2 (acid). When EWE returns to 0 V, ECE drops to ∼1.50 V, indicating irreversible graphite oxidation as it remains higher than the reduction potentials of surface oxidation species (Figure 3A). Notably, the initial ECE (∼1.07 V) at i = 0 A is never achieved again, as i returns to 0 A in each cycle (ECE ≈ 1.62 V), suggesting a permanent change in the graphite CE surface after the first cycle. Continuous cycling leads to a decline in i and QCE (Figure S3) at EWE = 0.20 V, resulting in a lower ECE demand.Figure 4Figure 4. (A, B) EWE (blue), ECE (orange), and i (green) correlation during CV analysis (100 cycles) in (A) H2-saturated 0.5 M H2SO4 and (B) H2-saturated 1.0 M KOH electrolytes (scan rate: 10 mV s–1; EWE range: 0 ∼ −0.20 V). (C) Correlation between the i and ECE at EWE = −0.20 V of each cycle in H2SO4 (blue) and KOH (red) electrolytes with (square) and without (circle) involving IEM.High Resolution ImageDownload MS PowerPoint SlideTo verify if the decline is caused by anodic corrosion products (such as CO, a well-known poisoning species for Pt) (14) of the graphite CE, we separated the Pt WE and graphite CE in an H-cell (denoted as Pt|IEM|C) using a Nafion-117 ion exchange membrane (IEM) to minimize product diffusion (Figure S4). Cycling data and the ECE–QCE correlation (Figures S5 and S6) show similar graphite CE behavior to Pt|C cells. Figure 4C compares ECE and i at EWE = −0.2 V in both configurations. In acidic conditions, the current decline is significantly reduced, from 82% (Pt|C) to 21% (Pt|IEM|C) after 100 cycles, indicating a major negative impact of the unseparated graphite CE on Pt-based HER catalyst benchmarking, likely due to overwhelming CO production and poisoning at Pt WE when ECE > 2.5 V. In alkaline conditions, adding IEM does not affect the current decline (51% for Pt|IEM|C, 55% for Pt|C), suggesting a minor contribution from the graphite CE in Pt|C, which is reasonable because no noticeable CO production of graphite is observed in alkaline electrolyte. The deactivation of polycrystalline Pt in alkaline electrolytes may relate to surface/crystalline structure changes during cycling, (15) though this is beyond our current focus.However, using an IEM has drawbacks. Cells with IEM show smaller currents in the initial 5 cycles due to hindered ion transport between the WE and CE, as indicated by the higher WE-CE resistance (RWE-CE) in the electrochemical impedance spectra (EIS) (Figure S7). Since iR compensation only corrects RWE-REF (∼0.3 ohms for all cells), (16) the activity of the Pt WE can be underestimated (by ∼15% from first cycle data). Additionally, the extra voltage loss requires a higher ECE to achieve the same current, limiting the usable EWE range. (17) As shown in Figure 4C, the IEM increases ECE by ∼0.32 V in alkaline conditions and 0.05 V in acidic conditions.Therefore, separating the graphite CE from the Pt WE is generally preferred for long-term cycling analysis, such as stability evaluation, especially in acidic electrolytes. For accurate Pt activity assessment, the Pt WE and graphite CE should share the same compartment to minimize cell voltage loss. In these cases, using single-run linear sweep voltammetry (LSV) or CV with fewer cycles (<5 in our study) is recommended to avoid the accumulation of oxidation products from the graphite, particularly in acidic conditions. Impact of CV Scan Range and Scan Rate on Graphite CEThe cycle number reflects the total charge associated with the anodic corrosion of the graphite CE under varying ECE, influenced by CV parameters such as scan range (EWE range) and scan rate.Figure 5A compares the highest current in each cycle (imax) and the required ECE at different EWE ranges. Lower EWE results in higher current and higher ECE on the graphite. For instance, cycling between 0 and −0.30 V generally requires an ECE higher than 3.0 V (ECELL > 3.3 V). In alkaline electrolytes, ECE is generally higher than in acidic ones, likely due to sulfate ion intercalation in H2SO4 contributing to iCE at lower potentials.Figure 5Figure 5. (A) Correlation between the max i and ECE of each cycle in H2-saturated H2SO4 (blue) and KOH (red) electrolytes with different EWE range: 0.1 V (0 ∼ −0.10 V), 0.2 V (0 ∼ −0.20 V), 0.3 V (0 ∼ −0.30 V). (B) Correlation between the i and ECE of each cycle at EWE = −0.2 V with different WE/CE ratios: 1:5 and 1:2 (cell configuration: Pt|IEM|C; scan rate: 10 mV s–1).High Resolution ImageDownload MS PowerPoint SlideA smaller EWE range (lower i) can significantly improve stability, as supported by data with (Figure 5A) and without IEM (Figure S8). Higher scan rates in CV result in higher currents due to increased electron transfer reactions and double-layer capacitive charging, (18) requiring higher ECE (Figure S9). However, higher scan rates also shorten the duration of extensive anodic corrosion on the graphite CE, leading to a lower current decline rate.Overall, while adjusting the scan rate and range is often necessary to obtain electrochemical properties, it is important to consider their impact on the graphite CE. A small scan range and high scan rate with IEM can minimize current decline due to accumulated graphite corrosion products in stability evaluations. However, high scan rates and IEM increase ECE on graphite to achieve the same current as in one-compartment cells, reducing the usable EWE range and potentially reaching the compliance voltage limit. Impact of Graphite CE Properties: Surface Area and Surface StateTwo frequently mentioned suggestions for a good CE are high surface area and activity. (9) Since the CE's sole function is to provide a matching current, a higher surface area offers more charge transfer sites, and a more active CE enables faster charge transfer (i.e., higher current) at the same ECE.The geometric surface area ratio between WE and CE in the previous discussion is fixed at 1:5. Herein, we decrease the CE area, and Figure 5B compares cyclic performance with WE/CE ratios of 1:2 and 1:5. Smaller CE area does not significantly impact iWE, suggesting CE is not limiting WE kinetics. However, ECE increases by ∼0.4 V (acid) and ∼0.5 V (base) with a 60% reduction in graphite area, indicating that the potentiostat compensates areal loss by increasing ECE to match i. The ECE trend is noisier with a 1:2 ratio, indicating higher instability with a smaller CE.In principle, a larger CE area improves charge transport between WE and CE due to a larger liquid projection containing more charge carriers (Figure 6A), allowing for a lower and more stable ECE demand, enabling a wider ECE and i range. While a WE/CE ratio of 1:10 is widely suggested in the literature, (7,9) our results show no significant differences between 1:5 and 1:10 (Figure S10), likely due to the larger electrochemical surface area (ECSA) of graphite compared to its geometrical area (GA), which is 3.6:1 for ECSA/GA according to our study, meaning that the actual ECSA ratio of WE/CE is 1:18.Figure 6Figure 6. (A) Impact of WE/CE ratio on the RWE-CE: smaller CE leads to larger RWE-CE and lower i allowance. (B) Current profile during 10h-CA analysis in an alkaline electrolyte with different WE/CE ratios (cell configuration: Pt|IEM|C; EWE = −0.20 V).High Resolution ImageDownload MS PowerPoint SlideDuring cycling, the graphite CE undergoes varying ECE (1.75–2.50 V), leading to reversible (charging/discharging) and irreversible (surface oxidation, particle detachment, full oxidation) anodic behavior. Irreversibility from surface oxidation is evident as ECE never returns to the initial ∼1.0 V at i = 0 A (insets of Figures 4A, 4B, S5A, and S5B). DEMS results (Figure S11) show that cycling alters the graphite CE surface state and anodic behavior. In acidic conditions, overwhelming CO production starts at a lower potential after just 3 cycles, likely due to the oxidized graphite surface being more prone to further oxidation into CO. To avoid significant CO production in initial cycles, it is necessary to remove the oxide layer formed in previous experiments. Polishing the graphite rod with sandpaper to achieve a smooth surface can effectively remove the oxide layer and increase the onset potential of graphite corrosion. (Figures S12 and S13, more details in the Experimental Section of Supporting Information) Steady-State Analysis Using Graphite CESteady-state analysis examines a system under constant conditions. In chronoamperometry (CA), EWE is fixed to monitor changes in i, with the potentiostat adjusting ECE. As the catalyst deactivates, i decreases, resulting in a lower ECE (i.e., a smaller ECELL) (Figure 6B). In chronopotentiometry (CP), i is fixed to monitor changes in EWE. If the CE maintains its activity, EWE remains constant. However, as the catalyst deactivates, EWE increases, leading to a larger ECELL. In this regard, using a larger and more active CE benefits wider i and EWE ranges.For graphite CE, unlike in CV studies, non-Faradaic i from charging/discharging is negligible since ECE does not vary rapidly. Complete oxidation of the graphite surface can be quickly achieved. Thus, during long-term steady-state analysis, iCE or QCE is sustained by exfoliation, OER, and full oxidation to CO/CO2. In alkaline conditions, the electrolyte initially turns brown due to the production of few-layer graphene. In acidic conditions, black particles from the graphite CE settle at the bottom. The graphite surface becomes significantly rougher after 10 h of CA testing (Figure S14) compared to 100 cycles of CV (Figure S2). Similar to CV treatment, irreversible surface changes in graphite after electrolysis are evident (Figure S15), highlighting the importance of polishing the graphite surface to ensure a reproducible experimental setup.To avoid WE surface contamination, using an IEM is essential in steady-state studies. However, some particles may attach to the IEM, potentially reducing ion exchange efficiency. A CE with a larger surface area can mitigate this issue since a lower ECE is needed, decreasing the exfoliation rate. Beyond Pt-Based ElectrocatalystsThe above discussions are based on Pt WE, known to be poisoned by CO. (14) For the CV analysis of other HER catalysts (e.g., MoS2) that do not suffer from CO and significant structural evolution, (8,19) it is expected that graphite CE can still be usable without IEM. Figure S16 confirms that no major current decrement occurs within 100 cycles with and without IEM (by ∼1.8% over 100 cycles). Similar to the previous comparison between Pt|C and Pt|IEM|C, using IEM increases the ECE by ∼170 mV. Therefore, if the graphite corrosion species are known as non-interfering species for the WE reaction, IEM is not essential. However, in reality, such information is mostly unknown, and using IEM is generally suggested despite the higher iR and cell voltage. Best Practices with Graphite CEIn summary, using a Pt WE, we have explored the applicability of graphite as an anodic CE in both acidic and alkaline conditions for HER activity evaluation. We examined several aspects related to two fundamental electrochemical methods, CV and steady-state analysis, focusing on the anodic behavior of the graphite CE and its impact on current and cell voltage. Although the specific WE and condition of the graphite CE may vary from lab to lab, making exact current and potential values less universally applicable, we can draw a few general best practice guidelines:1)Separate graphite CE from WE for long-term cycling and steady-state analysis in acidic conditions: In acidic conditions, aged graphite CE generates lots of CO/CO2 and large particles. Using an H-cell minimizes contamination and ensures accuracy. In alkaline conditions, OER and graphite exfoliation dominate, and while the impact is less distinguishable, a separator prevents unknown interferences. However, a separator can also introduce additional resistance between the WE and CE, lowering the i and EWE–ECE range. A larger CE and shorter WE–CE distance can reduce the resistance.2)Use a shared compartment for accurate activity assessment with single-run LSV or limited CV cycles: The WE and graphite CE should share the same compartment to minimize cell voltage loss introduced by the separator and to ensure precise evaluation. However, the test duration should be as short as possible (<5 cycles) to prevent the accumulation of oxidation products from the graphite in the electrolyte, especially in acidic conditions.3)Perform large current and high potential tests on a potentiostat with large compliance voltage: In principle, the activity of the CE does not matter if sufficient ECE can be provided to meet the current demand. However, the data becomes meaningless if the instrumental compliance voltage is reached. Therefore, researchers need to check the cell voltage regularly. A potentiostat with a larger compliance voltage is generally recommended, as it enables a wider EWE–ECE range.4)Reduce the WE–CE distance to enable a larger current range for testing: A shorter WE–CE distance can reduce the RWE-CE resistance, therefore decreasing the potential drop in the bulk electrolyte between the WE and CE. For a fixed iRWE-CE limited by the compliance voltage, lower RWE-CE means higher i allowance.5)Choose scan range and scan rate wisely: A larger scan range and higher scan rate often lead to increased ECE, while a smaller scan rate prolongs graphite corrosion. Therefore, when selecting CV parameters, a pre-experimental evaluation of the graphite anodic behavior is necessary.6)Use a WE/CE ratio of 1:5 or lower: A larger CE area can decrease the ECE demand and RWE-CE, allowing a wider EWE range and higher current for testing. A WE/CE ratio lower than 1:5 is preferred for graphite CE, especially when using a potentiostat with a small compliance voltage.7)Polish graphite CE before and after each experiment: Graphite CE undergoes irreversible surface oxidation as an anode, making it more susceptible to oxidation in subsequent tests. For reproducible analysis, the surface should be polished with sandpaper to achieve a smooth surface before and after each test to ensure a similar open circuit potential (OCV, i.e., similar surface state). Furthermore, we also recommend storing graphite CE in ion-free water to release the intercalated species from previous experiments.8)Replace the graphite CE regularly: Based on the above discussion, changes (oxidation and intercalation) in the graphite CE can gradually accumulate, leading to permanent deterioration. Researchers should replace the graphite CE if a consistent OCV cannot be achieved or if the ECE becomes abnormally high and unstable compared to a new graphite CE.Supporting InformationClick to copy section linkSection link copied!The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsenergylett.4c01869.Experimental details; Literature survey; Graphite morphology before and after CV study; ECE–QCE correlation during the first and 100th cycles in Pt|C and Pt|IEM|C cells; H-cell configuration; CV profile in Pt|IEM|C cell; Resistance introduced by IEM; Impact of CV scan rate/scan range on ECE and i in Pt|C and Pt|IEM|C cells; Impact of WE/CE ratio: from 1:5 to 1:10; DEMS results of repeated staircase voltammetry: aging of graphite surface; Aged graphite surface treatment; ECE–i correlation using MoS2 as WE and graphite as CE (PDF)nz4c01869_si_001.pdf (14.34 MB) Terms & Conditions Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html. Author InformationClick to copy section linkSection link copied!Corresponding AuthorWeiran Zheng - Department of Chemistry, Guangdong Technion-Israel Institute of Technology, Shantou 515063, China; Technion-Israel Institute of Technology, Haifa 32000, Israel; Guangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion, Guangdong Technion-Israel Institute of Technology, Shantou 515063, China; https://orcid.org/0000-0002-9915-6982; Email: [email protected]AuthorLijie Du - Department of Chemistry, Guangdong Technion-Israel Institute of Technology, Shantou 515063, ChinaNotesViews expressed in this Viewpoint are those of the author and not necessarily the views of the ACS.The authors declare no competing financial interest.AcknowledgmentsClick to copy section linkSection link copied!W.Z. is grateful for the support of the Guangdong Basic and Applied Basic Research Foundation (Grant Number: 2023A1515012277) and the Guangdong Technion-Israel Institute of Technology (Grant Number: ST2200002).ReferencesClick to copy section linkSection link copied! This article references 19 other publications. 1McCrory, C. C.; Jung, S.; Ferrer, I. M.; Chatman, S. M.; Peters, J. C.; Jaramillo, T. F. Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices. J. Am. Chem. Soc. 2015, 137 (13), 4347– 4357, DOI: 10.1021/ja510442p Google Scholar1Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting DevicesMcCrory, Charles C. L.; Jung, Suho; Ferrer, Ivonne M.; Chatman, Shawn M.; Peters, Jonas C.; Jaramillo, Thomas F.Journal of the American Chemical Society (2015), 137 (13), 4347-4357CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society) Objective comparisons of electrocatalyst activity and stability using std. methods under identical conditions are necessary to evaluate the viability of existing electrocatalysts for integration into solar-fuel devices as well as to help inform the development of new catalytic systems. Herein, the authors use a std. protocol as a primary screen for evaluating the activity, short-term (2 h) stability, and electrochem. active surface area (ECSA) of 18 electrocatalysts for the H evolution reaction (HER) and 26 electrocatalysts for the O evolution reaction (OER) under conditions relevant to an integrated solar H2O-splitting device in aq. acidic or alk. soln. The primary figure of merit is the overpotential necessary to achieve a magnitude c.d. of 10 mA cm-2 per geometric area, the approx. c.d. expected for a 10% efficient solar-to-fuels conversion device under 1 sun illumination. The specific activity per ECSA of each material is also reported. Among HER catalysts, several could operate at 10 mA cm-2 with overpotentials <0.1 V in acidic and/or alk. solns. Among OER catalysts in acidic soln., no nonnoble metal based materials showed promising activity and stability, whereas in alk. soln. many OER catalysts performed with similar activity achieving 10 mA cm-2 current densities at overpotentials of ∼0.33-0.5 V. Most OER catalysts showed comparable or better specific activity per ECSA when compared to Ir and Ru catalysts in alk. solns., while most HER catalysts showed much lower specific activity than Pt in both acidic and alk. solns. For select catalysts, addnl. secondary screening measurements were conducted including faradaic efficiency and extended stability measurements. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=AC