Carbon Corrosion Research Articles

(Invited) Operando Visualization of the Electrolyte Distribution in Vanadium Redox Flow Electrodes

Electrolyte transport losses are among the main factors that limit the performance of Vanadium Redox Flow Batteries (VRFBs)1. The electrolyte must percolate into the electrode and reach the reaction sites with minimum resistance to reduce such losses. The optimized electrolyte flow ensures that the reactants and products are transported to and away from the reaction sites freely and decreases the pumping losses of the electrochemical cell, increasing the overall efficiency of the battery system.The electrolyte distribution in a porous electrode is crucial for the stability and performance of the electrode. The presence of gas bubbles in the electrode reduces the electrochemically active surface, resulting in cell potential fluctuations. In addition, the gas bubbles cause poor contact between the electrolyte and the electrode, and the ionic conductivity could be locally blocked2. These effects lead to inhomogeneous potential distribution (spikes), accelerating the electrode material's corrosion. Gas bubbles are very common in VRFBs, and they result from parasitic side reactions, such as carbon corrosion, hydrogen evolution (HER), or incomplete electrode wetting3.Synchrotron X-ray imaging is a powerful tool for tracking these bubbles in porous carbon materials. We have designed an experimental setup resembling an operating VRFB cell to image the flow through the porous carbon electrode. With its modular structure, the setup offers excellent flexibility to evaluate different designs and operational aspects of VRFBs4, 5. The findings of our investigations over the years will be discussed in this presentation. References J. Kim and H. Park, Journal of Power Sources, 2022, 545, 231904. K. Krause, C. Lee, J. K. Lee, K. F. Fahy, H. W. Shafaque, P. J. Kim, P. Shrestha and A. Bazylak, ACS Sustainable Chemistry & Engineering, 2021, 9, 5570-5579. M.-A. Goulet, M. Skyllas-Kazacos and E. Kjeang, Carbon, 2016, 101, 390-398. L. Eifert, N. Bevilacqua, K. Köble, K. Fahy, L. Xiao, M. Li, K. Duan, A. Bazylak, P.-C. Sui and R. Zeis, ChemSusChem, 2020, 13, 3154-3165. K. Köble, L. Eifert, N. Bevilacqua, K. F. Fahy, A. Bazylak and R. Zeis, Journal of Power Sources, 2021, 492, 229660. Figure 1

Manganese Oxide Gas Diffusion Electrode Conditioning and Electrochemical Doping for Reversible Oxygen Reduction/Evolution Reactions

Developing durable and active bifunctional gas diffusion electrodes for reversible oxygen reduction/evolution (ORR/OER) reaction catalysis is crucial yet challenging in the development of numerous electrochemical energy conversion systems, including regenerative fuel cells and rechargeable metal-air batteries. This research is focused on developing manganese oxide-based gas diffusion electrodes for reversible oxygen electrodes.Core-porous shell Mn/Mn3O4 (abbreviated as MnOx) nanoparticles (QSI) demonstrated increased ORR/OER activities compared to γ-MnO2 (EMD) and b-MnO2.[1] The unique behaviour of core-shell MnOx is attributed to the charge transfer between the low-valent Mn core and the high-valent Mn3O4 shell, thereby regenerating Mn(III) active sites through comproportionation.[1]The stability of transition-metal-based reversible oxygen electrodes remains a challenge. As shown in Figure 1, the deterioration of Mn/Mn3O4 during ORR and OER cycling can be attributed to three aspects: Mn active sites oxidation (Figure 1a), less active MnOx phase formation (Figure 1b), and material loss (carbon corrosion and dissolved MnO4 - formation) (Figure 1c).[2] As a result, the QSI MnOx electrode transformed from pristine to inactive status within 15 galvanostatic ORR/OER cycles. To improve the stability of the electrode, a set of in-situ electrochemical conditioning and electric field-driven metallic cation incorporation into MnOx GDE was investigated. Among the explored metal cations, the Ni2+ incorporation showed the most significant improvement in terms of activity and cyclic stability. The Ni-MnOx GDE demonstrated excellent stability for over 120 galvanostatic cycles at ±10 mA cm-2 in O2-saturated KOH without losing OER activity, surpassing the Pt/C-IrO2 benchmark.[3]These findings position the MnOx electrodes as promising and sustainable alternatives to precious metal-based electrodes for ORR/OER catalysis and provide valuable insights into designing reversible oxygen electrodes for energy conversion and storage in alkaline systems, contributing to a green future.[1] Pei, Y., Wilkinson, D. P., & Gyenge, E. L. Insights into the electrochemical behavior of manganese oxides as catalysts for the oxygen reduction and evolution reactions: monometallic core‐shell Mn/Mn3O4. Small, 2023, 19, 2204585.[2] Pei, Y., Wilkinson, D. P., & Gyenge, E. L. Gas Diffusion Electrode Design and Conditioning with Manganese (III/IV) Oxide Catalyst for Reversible Oxygen Reduction/Evolution Reactions. ACS Energy & Fuels (2023), 37, 23, 19278–19291.[3] Pei, Y., Wu, W. Y., Wilkinson, D. P., & Gyenge, E. L. High-Performance Reversible Oxygen Reduction/Evolution Gas Diffusion Electrodes with Multivalent Cation Doped Core-Shell Mn/Mn3O4 Catalysts. ChemElectroChem, in press. Figure 1

Enhancing Anode Reversal Tolerance by Low-Carbon and Carbon-Free Anode Catalyst Layers for Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs), as the main hydrogen utilization device, are considered a powerful tool for accelerating a carbon-neutral society. However, durability and cost are the two main obstacles to the commercialization of PEMFCs. Specifically, the anode reversal has been extensively studied as a severe issue that deteriorates the performance and durability of PEMFCs and leads to cell failure. Commercially, iridium oxide (IrOx) or iridium black is intensively utilized as oxygen evolution reaction catalysts to fabricate reversal tolerant anodes (RTAs) despite the slight performance loss. However, previous studies concentrated on investigating the origin or phenomena during the cell-reversal, the key factors and mechanisms affecting the anti-reversal performance, and the interaction among the anode catalyst layer components are still yet to be explored.Hence, we systematically studied the performance using three typical carbon supports with three metal contents and different metal deposition orders by experiments and model calculations. First, we synthesized Ir outside Ir/Pt/C and Pt outside Pt/It/C with uniform nanoparticle size and distribution and characterized them comprehensively. A new parameter, “relative metal coverage”, is put forward to evaluate and predict the anti-reversal ability, showing that higher relative metal coverage results in a longer reversal time and lower polarization performance degradation rate. In addition, Ir outside Ir/Pt/C shows better reversal tolerance than Pt outside Pt/It/C, which has been rarely mentioned in previous studies. Further, the experimental results show that even though the metal coverage is high, the performance degradation caused by carbon corrosion is still inevitable. On this basis, we synthesized a high specific surface area conductive oxide Ti4O7 as the anode catalyst support to eliminate the adverse effects of carbon corrosion. Previously, the initial performance of Ti4O7-supported catalyst was obstructed by the disadvantaged electrical conductivity of Ti4O7. We obtain a comparable polarization performance after optimizing the Ti4O7-supported anode catalyst layer parameters by shortening the electron transfer pathway and increasing metal coverage. Typically, the Ir@IrOx/Pt/Ti4O7-fabricated RTA with low Ir loading displays approximately ten times longer reversal time (6 hours) and two orders of magnitude lower degradation rate than a conventional carbon-supported counterpart. The degradation origin of the Ti4O7-supported anodes is also studied by postmortem characterizations, pointing to the Pt oxidation caused by the formation of TiOx thin layers on the Pt surface. These two works aim to promote the development of highly durable and reversal tolerance anode and provide a bright perspective for practical high-performance, low-degradation, and cost-friendly RTA fabrication.

Nitrogen Doped Graphene Aerogel Inserted By Carbon Black As Novel Catalyst Support for Low Temperature Hydrogen Fuel Cells

Carbon supported Pt nanocatalysts, which are commonly used in hydrogen fuel cells, suffer from Pt degradation and carbon corrosion. That causes the high cost and limited lifetime of the fuel cell1. Developing catalyst support materials with high surface area, high electrical conductivity, stability and good interaction with catalyst is an effective solution to address this issue.To enhance the activity and durability of Pt-based catalysts for hydrogen fuel cells, graphene aerogels (GA) are a prospective material with rich porous 3D-structure, large surface area, high electrical conductivity, and good electrochemical stability. They also can improve the tolerance of catalyst CO poisoning and avoid graphene stacking by integrating 2D sheet structure into 3D aerogel structure2, 3. Some research show that the nitrogen doped on the surface of carbon materials could improve ORR activity and electronic conductivity by changing the local electronic structure as well as providing a stable anchor point for pt nanoparticles to enhance the durability of catalysts4, 5.However, most GAs are made from graphene oxide (GO) produced by Hummers method which may lead to safety and environmental issue due to the usage of highly toxic and corrosive chemicals2, 5. Also, there are few articles on the application of GA in fuel cells. It may be limited by the collapse and loss of pore structure caused by compression in a fuel cell setup.In this work, graphene oxide produced by electrochemical exfoliation (EGO) was used to prepare N-doped graphene aerogel (NGA) via hydrothermal treatment with ammonia solution as nitrogen source. Moreover, NGA was mixed with carbon black (CB) as a hybrid support material that can avoid collapse of the macropore and generate a graphene-carbon network to provide large surface area for Pt nanoparticles and improve the performance of the fuel cell. Figure1 shows preliminary characterization results of NGA and performance of NGA-CB supported Pt catalysts with different content of NGA. Rich macro-mesoporous structure of NGA can be observed in the SEM image (Figure 1 (a)). Pt catalyst with 20% NGA has a maximum power density of 838 mw cm-2 which is a 31% improvement over that of Pt/CB (Figure 1 (b)).In conclusion, this study presents a fast, efficient and environmentally friendly way to synthesize nitrogen doped GA. The introduction of NGA into CB as catalyst supports can improve the electrochemical active surface area and performance of fuel cells due to graphene aerogel's high conductivity and porosity. Besides, it is effective to enhance the utilization of Pt and durability of catalysts. This will help to reduce the cost of fuel cells and facilitate their commercialization in various fields of application.Figure 1 (a) SEM images of dried NGA. (b) Performance of Pt/NGA-CB with various content of NGA compared to Pt/CB catalyst in a hydrogen fuel cell at 60 ℃ with 100% RH. References Liu, J.; Wu, X.; Yang, L.; Wang, F.; Yin, J., Unprotected Pt nanoclusters anchored on ordered mesoporous carbon as an efficient and stable catalyst for oxygen reduction reaction. Electrochimica Acta 2019, 297, 539-544.Sarac Oztuna, F. E.; Barim, S. B.; Bozbag, S. E.; Yu, H.; Aindow, M.; Unal, U.; Erkey, C., Graphene Aerogel Supported Pt Electrocatalysts for Oxygen Reduction Reaction by Supercritical Deposition. Electrochimica Acta 2017, 250, 174-184.Wu, Z.-S.; Yang, S.; Sun, Y.; Parvez, K.; Feng, X.; Müllen, K., 3D Nitrogen-Doped Graphene Aerogel-Supported Fe3O4 Nanoparticles as Efficient Electrocatalysts for the Oxygen Reduction Reaction. Journal of the American Chemical Society 2012, 134 (22), 9082-9085.Li, O. L.; Chiba, S.; Wada, Y.; Panomsuwan, G.; Ishizaki, T., Synthesis of graphitic-N and amino-N in nitrogen-doped carbon via a solution plasma process and exploration of their synergic effect for advanced oxygen reduction reaction. Journal of Materials Chemistry A 2017, 5 (5), 2073-2082.Xie, B.; Zhang, Y.; Zhang, R., Coassembly and high ORR performance of monodisperse Pt nanocrystals with a mesopore-rich nitrogen-doped graphene aerogel. Journal of Materials Chemistry A 2017, 5 (33), 17544-17548 Figure 1

Revealing the Path-Dependence of Catalyst Degradation in Polymer Electrolyte Fuel Cells

Electro-catalyst plays a central role in many clean energy technology applications including water electrolysis for green hydrogen generation, emission free fuel cells for transportation, electrochemical CO2 reduction and combine heat and power generation. Electro-catalysts degrade via multiple mechanisms, depending on the exact operating conditions in its life cycles. In this presentation, we demonstrate the dependance of the electro-catalyst degradation in polymer electrolyte fuel cell (PEFC) on the specific “paths” that the fuel cell takes to age. Specifically, differently ordered aging protocols with the same total number of accelerated stress tests (ASTs) cycles (i.e., 31,000 total cycles including 30,000 cycles of square-wave load/unload ASTs and 1000 cycles of triangular-wave carbon corrosion ASTs) were used to degrade membrane electrode assemblies (MEAs). At the end-of-life, performances were distinct, indicating that depending on the specific aging route taken, the fuel cell catalyst layer degrades differently after same number of total AST cycles. The load/unload aging protocol led to more severe losses of performance when preceding after the carbon corrosion aging ASTs

Dynamic Oxygen Collection Efficiency: Unraveling the Effects of Perovskites on Carbon Corrosion As Composite Catalysts for Oxygen Electrode

Introduction The composite catalyst comprising perovskite and carbon has been extensively studied as a catalyst for the oxygen evolution reaction (OER) at the oxygen electrode in alkaline media. However, the competitive corrosion of carbon under harsh OER potential necessitates additional caution when determining OER activity from the overall oxidation current. The use of a rotating ring-disk electrode (RRDE) is acknowledged for its ability to quantitatively determine the faradaic efficiency of the OER. [1] However, for practical applications, the generation of oxygen bubbles can cause unpredictable disturbance, leading to the erroneous collection efficiency. In this study, we aim to establish a dynamic current-response collection efficiency during the generation of oxygen bubbles. This was achieved by modelling with an Au/Au RRDE, well-known for its electrochemical stability under harsh conditions. In addition, using this calibrated collection efficiency, we investigate the influence of perovskite catalysts on the degradation behaviors of carbon materials at OER potentials in alkaline media. Materials and electrochemical measurements Measurements of oxygen gas collection efficiency were conducted using a modeled RRDE comprising an Au disk electrode and an Au ring electrode. The RRDE served as the working electrode, with a Pt wire as the counter electrode, a reversible hydrogen electrode (RHE) as the reference electrode, and a solution of Ar-saturated 1 mol dm-3 KOH as the electrolyte. The disk electrode underwent a 5-minute chronopotentiometry with varied oxidation currents, while the ring electrode underwent chronoamperometry at 0.3 V (vs. RHE). The collection efficiency was calculated from the ring current attributed to the oxygen 2-electron reduction reaction.Two kinds of perovskite catalysts, namely Sr2Co0.8Fe0.2O3Cl[2] (hereafter SCFOC) and LaCoO3 (hereafter LCO), and two carbonaceous materials, namely graphitized carbon black (TOKABLACK#3845, hereafter TB) and ketjen black (EC-600JD, hereafter KB), were used to evaluate the influence of perovskite on the carbon degradation behavior. Four composite catalysts, each comprising perovskite and carbon with a weight ratio of 5:1, were loaded on a disk electrode of the glassy carbon disk/Au ring RRDE. A cell analogous to the aforementioned design was assembled. Electrochemical measurements were conducted through chronoamperometry, employing various potentials at the disk electrode, and maintaining a potential of 0.3 V vs. RHE at the ring electrode, for a duration of 5 minutes. Results and discussion Figure 1 illustrates a three-dimensional representation of the oxygen gas collection efficiency of the Au/Au RRDE as two functions of disk current density and measurement time. It was evident that the oxygen gas collection efficiency varied significantly from the theoretical value (25.6 %) and was dependent on the disk current density and measurement time. The constrained solubility of oxygen in aqueous solution and the hydrophobic nature of the PTFE between the ring and the disk might cause a decrease in the collection efficiency due to the partial retention of oxygen bubbles on the electrode as the oxygen generation current increased and the measurement time elapsed. This suggests that, unlike typical solution reactions, the dynamic determination of the oxygen gas collection efficiency is essential, considering current density and measurement time.Figure 2 illustrates the computation of faradaic oxygen efficiency, utilizing dynamic oxygen collection efficiency. The composite catalyst composed of TB and SCFOC was taken as an illustrative example. The variation in collection efficiency, synchronized with the shape of disk current density, was employed in determining the faradaic oxygen efficiency. This dynamic collection efficiency yielded a comparatively smooth faradaic oxygen efficiency.Utilizing the calibrated faradaic oxygen efficiency, we proceeded to assess the capacity of carbon degradation by integrating the current density of the carbon oxidation reaction (COR) calculated by subtracting the OER current from the overall current. As depicted in Figure 3, the COR capacity as a function of the potential suggested that the components of the composite catalysts had distinct impacts on carbon degradation. Specifically, SCFOC appears to enhance degradation, whereas LCO exhibits a comparatively less pronounced effect.A more comprehensive discussion of these findings will be presented at the upcoming meeting.[1] I.S. Filimonenkov et al., Electrochim. Acta 321, 134657 (2019).[2] Y. Miyahara et al., Chem. Mater. 32, 8195 (2020). Figure 1

Functionalisation of Carbon Catalyst Support By Plasma Treatment for PEMFC Cathode

Proton exchange membrane fuel cell (PEMFC) is one promising electric device to replace the combustion engine using fossil fuel especially for heavy-duty transport. One of the main issue for the widespread of this technology on the European roads is the cost and degradation of their components over time. The sluggish reduction of dioxygen at the cathode require high amount of noble metal (i.e. platinum). Under PEMFC operating conditions, carbon as catalyst support is unstable.This study presents a new approach to improve the stability of the cathode components (catalyst, carbon support and ionomer) thanks to the enhancement of the interaction between the three entities and to reduce carbon corrosion. Plasma treatment were performed on different carbon black sources (different surface area and porosity) to functionalize their surface by nitrogen function using different gas. The modified carbons were characterized by TEM, XPS, Raman spectroscopy, calorimetry, elemental analysis. The plasma treatments were reproducible and allow controlling the degree of functionalisation. The nitrogen doped carbons were catalysed by platinum nanoparticles. A better dispersion of the nanoparticles was observed by TEM showing the interest of the plasma treatment. Cyclic voltammetry were performed and a better catalytic activity toward the electrochemical reduction of O2 was observed.[1] Isothermal titration calorimetry experiments were carried out and show an improved interaction between the nitrogen functionalized carbon and the ionomer.[1] A. Parnière, P.-Y. Blanchard, S. Cavaliere, N. Donzel, B. Prelot, J. Rozière, D.J. Jones, Nitrogen Plasma Modified Carbons for PEMFC with Increased Interaction with Catalyst and Ionomer, J. Electrochem. Soc. 169 (2022) 044502. Figure 1

Janus structural TaON/Graphene-like carbon dual-supported Pt electrocatalyst enables efficient oxygen reduction reaction

Developing carbon-supported Pt-based electrocatalysts with high activity and long-durability for the oxygen reduction reaction (ORR) is an enormous challenge for their commercial applications due to the corrosion of carbon supports in acid/alkaline solution at high potential. In this work, a Janus structural TaON/graphene-like carbon (GLC) was synthesized via an in-situ molecular selfassembly strategy, which was used as a dual-carrier for platinum (Pt). The as-obtained Pt/TaON/GLC presents high half-wave potential (0.94 V vs. RHE), excellent mass (1.48 A mgPt-1) and specific (1.75 mA cmPt-2) activities at 0.9 V, and superior long-term durability with a minimal loss (8.0 %) of mass activity after 10,000 cycles in alkaline solution, outperforming those of Pt/C and other catalysts. The structural characterizations and density functional theory (DFT) calculations indicate that the Pt/TaON/GLC catalyst exhibits the maximum synergies, including enhanced interfacial electron density, improved charge transfer, enhanced O2 adsorption, andsuperimposed OO cleavage. This work shows a potential strategy for preparing the high-active and long-durable Pt-based electrocatalyst by synergism-promoted interface engineering.

Impact of fuel starvation–induced anode carbon corrosion in proton exchange membrane fuel cells on the structure of the membrane electrode assembly and exhaust gas emissions: A quantitative case study

Although the durability of proton exchange membrane fuel cells (PEMFCs) is crucial for their broad commercial applications, current durability assessments do not encompass all operational scenarios. Startup/shut-down (SUSD) are among the most significant degradation factors in the city. To bridge this gap, we examine the phenomenon of fuel starvation, which leads to the rapid and irreversible degradation of PEMFC performance, particularly during SUSD, but has not been independently examined in the context of PEMFC durability. A quantitative methodology is used to analyze anode carbon corrosion and establish correlations with critical parameters under fuel starvation conditions. In particular, we quantify carbon loss based on (i) the composition or amount of the anode outlet gas emitted under such conditions and (ii) changes in the anode thickness at three distinct locations. The corresponding carbon losses due to 10 min of fuel starvation ((i): 212.0 μg cm−2, (ii): 189.6 ± 12.9 μg cm−2) agree well with each other. The largest decrease in the anode thickness (81.3 %) is observed near the outlet. The obtained insights provide guidance for the design of high-performance PEMFCs and the development of protective measures against the detrimental effects of fuel starvation.

Corrosion of carbon steels subjected to chloride and sulfate in simulated concrete pore solutions with different pH

The present study explores low-carbon steel corrosion in simulated concrete pore solutions with varying pH, focusing on the influence of chloride and/or sulfate ions. Employing electrochemical techniques, ToF-SIMS, XRD and DFT calculations, the results reveals that higher pH strengthens the passivation film and reduces corrosion by limiting corrosive ions adsorption. Notably, sulfate triggers corrosion at higher thresholds, while chloride alone significantly elevates corrosion rates. The presence of both ions shows mitigated corrosion risk due to competitive absorption onto steel interface of sulfate. The two-stage mechanism involving competitive adsorption and catalytic corrosion is initially proposed and elucidates the interaction mechanism of chloride and sulfate during steel corrosion process.

Scanning Gas Diffusion Electrode Setup for Real-Time Analysis of Catalyst Layers.

The scanning gas diffusion electrode (S-GDE) half-cell is introduced as a new tool to improve the evaluation of electrodes used in electrochemical energy conversion technologies. It allows both fast screening and fundamental studies of real catalyst layers by applying coupled mass spectrometry techniques such as inductively coupled plasma mass spectrometry and online gas mass spectrometry. Hence, the proposed setup overcomes the limitations of aqueous model systems and full cell-level studies, bridging the gap between the two approaches. In this proof-of-concept work, standard fuel cell electrodes are investigated at elevated oxygen reduction reaction current densities, while dissolved Pt x+ ions in the electrolyte and gaseous CO2 in the outlet gas stream are detected to track platinum dissolution and carbon corrosion, respectively. Relevant current densities of up to 0.75 A cm-2 are demonstrated. The electrochemically active surface area, oxygen reduction reaction activity, and Pt dissolution rates are quantified and benchmarked to the values obtained in the conventional stationary GDE half-cell. Moreover, it is found that Pt dissolution is suppressed when O2 is purged into the catalyst layer. Overall, this work demonstrates the feasibility of fast fuel cell electrode screening obtaining, complementary to electrochemical, mass spectrometry data necessary in fundamental studies on structure/performance relationships under actual reaction conditions. While Pt/C, in relevance to its fuel cell application, is used in this study, the proposed setup can be applied in water electrolysis, CO2 conversion, metal-air batteries, and other neighbor technologies.

Lanthanum nanoparticle decorated carbon nanotubes: Facile method of synthesis and studies of their redox stability, cytotoxicity and corrosion inhibition on the magnesium alloy in 3.5 % NaCl environment

Functionalized carbon materials can act as high-temperature coatings and eco-friendly composite materials. We have studied lanthanum-doped carbon nanotube (La-CNT) material redox behavior, cytotoxicity, and corrosion inhibition efficiency. The La-CNT material has been characterized by different techniques to confirm the presence of functional groups. The Fourier transform infrared (FTIR) and Raman studies were performed to investigate the functional groups and carbon defects. Field emission scanning electron microscopy (FESEM) and tunneling electron microscopy (TEM) studies were used to investigate the carbon nanotube microstructure, La nanoparticles were shown to interact with the carbon nanotube surface. X-ray diffraction (XRD) techniques were used to confirm the crystallinity of composite material. Electrochemical methods were used to investigate corrosion inhibition and redox stabilities. After corrosion study on the Mg alloy its microstructure was analyzed to confirm the composite material inhibition efficiency. The composite material showed significant cytotoxicity, and corrosion inhibition efficiency was shown to be 82 % as compared with pristine epoxy-coated Mg alloy.XPS results are suggested that alloy oxide layer formed. The DFT study supported the experimental findings.

Improvement in ORR Durability of Fe Single-Atom Carbon Catalysts Hybridized with CeO2 Nanozyme.

FeNC catalysts are considered one of the most promising alternatives to platinum group metals for the oxygen reduction reaction (ORR). Despite the extensive research on improving ORR activity, the undesirable durability of FeNC is still a critical issue for its practical application. Herein, inspired by the antioxidant mechanism of natural enzymes, CeO2 nanozymes featuring catalase-like and superoxide dismutase-like activities were coupled with FeNC to mitigate the attack of reactive oxygen species (ROS) for improving durability. Benefiting from the multienzyme-like activities of CeO2, ROS generated from FeNC is instantaneously eliminated to alleviate the corrosion of carbon and demetallization of metal sites. Consequently, FeNC/CeO2 exhibits better ORR durability with a decay of only 5 mV compared to FeNC (18 mV) in neutral electrolyte after 10k cycles. The FeNC/CeO2-based zinc-air battery also shows minimal voltage decay over 140 h in galvanostatic discharge-charge cycling tests, outperforming FeNC and commercial Pt/C.

Hydrogen Peroxide-Induced Overoxidation of Fe-N-C Catalysts: Implications for ORR Activity.

Fe-N-C (iron-nitrogen-carbon) electrocatalysts have emerged as promising alternatives to precious metals for the oxygen reduction reaction (ORR), but they remain insufficiently stable for widespread adoption in fuel cell technologies. One plausible mechanism to explain this lack of stability, and the associated catalyst degradation, is oxidative attack on the catalyst surface by hydrogen peroxide, a non-selective byproduct of the ORR. In this work, we perform a detailed analysis of this degradation mechanism, using a combination of periodic Density Functional Theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations to probe the thermodynamics and kinetics of hydrogen peroxide activation on a series of candidate active sites for the Fe-N-C catalyst. The results demonstrate that carbon atoms neighbouring FeN4 active sites can be strongly over-oxidized via formation of hydroxyl or epoxy groups when hydrogen peroxide is present in the electrolyte. In most cases, the interaction between the over-oxidizing groups and the ORR reaction intermediates reduces the ORR activity, and we further propose that the over-oxidized sites are likely precursors to irreversible carbon corrosion and further catalyst deactivation.

Pt-decorated tantalum oxide on mesoporous carbon supports for enhanced mass activity and start-stop and load cycling durability in PEFCs

Unique Pt/TaOx/MC cathode electrocatalysts for polymer electrolyte fuel cells (PEFCs) are developed using partially-reduced TaOx decorated on mesoporous carbon (MC). An initial mass activity (MA) of more than 500 A g−1 was observed for a TaOx/MC support heat treated at 700 °C in H2 or 1300 °C in Ar, more than double that of a conventional Pt/C electrocatalyst. The durability against start-stop and load potential cycling was successfully improved compared with the reference catalysts, as verified by half-cell voltammetry and full membrane-electrode-assembly (MEA) tests. Durability against start-stop cycling was attributed to the use of a thermochemically-stable TaOx support which prevents direct contact between Pt and MC, thus minimizing carbon corrosion. Durability against load cycling was mainly attributed to the mesoporous structure, preventing the agglomeration of Pt catalyst particles. As such, the Pt/TaOx/MC cathode electrocatalysts presented in this work have the potential to achieve both high durability and high power output, which is especially attractive for heavy-duty vehicular fuel cell applications.

Operando carbon corrosion measurements in fuel cells using boron-doped carbon supports

Carbonaceous materials are the most common catalyst supports in proton exchange membrane fuel cell (PEMFCs), yet their corrosion is one of the limiting factors in achieving high durability. Herein, we doped carbon supports with boron (B) to increase the corrosion-resistance of the support. Two types of B-doped carbons were synthesized and studied as platinum support materials. They varied in their morphologies, surface areas, and the types of boron species. The durability of Pt/B-doped carbon catalysts was investigated using the US-DOE catalysts’ supports accelerated stress test (AST) and a mass-spectrometer connected to the fuel cell effluent stream to quantify the mass of corroded carbon support in operando. The addition of boron to the carbon increased the stability of Pt catalysts in long-term usage of PEMFC. After 4000 AST cycles, more than 50 % of initial current density was preserved for the boron-containing systems, while less than 30 % of it remained with Vulcan carbon (Pt/V). Also, the Pt/B-doped carbon samples demonstrated better electrochemical active surface area (ECSA) stability when compared to Pt/V. Carbon loss measurements showed that B-doped carbons have higher resistance to electrochemical corrosion than unmodified carbon. Specifically, the substitutional boron-doped carbon demonstrated an extremely high stability and low corrosion rate.

Structurally Tunable Graphitized Mesoporous Carbon for Enhancing the Accessibility and Durability of Cathode Pt‐Based Catalysts for Proton Exchange Membrane Fuel Cells

Low Pt utilization and intense carbon corrosion of cathode catalysts is a crucial issue for high‐efficiency proton exchange membrane fuel cells due to the highly demanded long‐term durability and less acquisition/application cost. Herein, structurally tunable graphitized mesoporous carbon (GMC) is obtained by direct high‐temperature pyrolysis and in situ‐controlled mesopore formation; the structure‐optimized GMC1300‐1800 exhibits a mesopore size of 7.54 nm and enhanced corrosion resistance. Functionalized GMC1300‐1800 is loaded with small‐sized Pt nanoparticles (NPs) (1.5 nm) uniformly by impregnation method to obtain Pt/GMC1300‐1800 and form an “internal platinum structure” to avoid sulfonic acid groups poisoning as well as ensure O2/proton accessibility. Hence, the electrochemically active surface area (ECSA) of Pt/GMC1300‐1800 reaches 106.1 m2 g−1Pt, while mass activity and specific activity at 0.9 V are 2.1 and 1.4 times those of commercial Pt/C, respectively. Notably, the ECSA decay is less than 17% for both 30 000 cycles’ accelerated durability tests (ADTs) of Pt attenuation and carbon attenuation. Accordingly, the optimized mesoporous structure of GMC1300‐1800 significantly decreases the coverage of sulfonic acid groups on Pt NPs, leading to the highest peak power density in the single‐cell test. Density functional theory calculations demonstrate the synergistic effect between graphitization and mesoporosity on enhancing the accessibility and durability of the catalysts.

Interfacial Insights into the Polarization Protocol: Toward Reducing Corrosion and Improving the Cycle Life of Electrochemical Capacitors.

The number of scientific publications on the impact of corrosion on current collectors on the working parameters of electrochemical capacitors is very limited. The aim of current research is to search for new, environmentally friendly chemical power sources and energy storage devices and to improve existing ones. Therefore, this article presents a simple and effective way to improve the life of a symmetric electrochemical capacitor by changing the direction of electrode polarization, which in turn inhibits the corrosion of the current collector. This slows the degradation of current collectors of positive electrode over long durations. However, activated carbon electrode corrosion also occurs. Experiments on capacitors with stainless steel and gold current collectors indicate that the lifespan of the latter is much longer than that of the former. Therefore, current collector corrosion has a distinct and detrimental impact on electrochemical capacitor operation. Moreover, the research results indicate that carbon corrosion results from current collector corrosive damage.

Impact of Carbon Corrosion and Denitrogenation on the Deactivation of Fe–N–C Catalysts in Alkaline Media

Impact of Carbon Corrosion and Denitrogenation on the Deactivation of Fe–N–C Catalysts in Alkaline Media

Carbon Corrosion Induced by Surface Defects Accelerates Degradation of Platinum/Graphene Catalysts in Oxygen Reduction Reaction.

Graphene supported electrocatalysts have demonstrated remarkable catalytic performance for oxygen reduction reaction (ORR). However, their durability and cycling performance are greatly limited by Oswald ripening of platinum (Pt) and graphene support corrosion. Moreover, comprehensive studies on the mechanisms of catalysts degradation under 0.6-1.6V versus RHE (Reversible Hydrogen Electrode) is still lacking. Herein, degradation mechanisms triggered by different defects on graphene supports are investigated by two cycling protocols. In the start-up/shutdown cycling (1.0-1.6V vs.RHE), carbon oxidation reaction (COR) leads to shedding or swarm-like aggregation of Pt nanoparticles (NPs). Theoretical simulation results show that the expansion of vacancy defects promotes reaction kinetics of the decisive step in COR, reducing its reaction overpotential. While under the load cycling (0.6-1.0V vs.RHE), oxygen containing defects lead to an elevated content of Pt in its oxidation state which intensifies Oswald ripening of Pt. The presence of vacancy defects can enhance the transfer of electrons from graphene to the Pt surface, reducing the d-band center of Pt and making it more difficult for the oxidation state of platinum to form in the cycling. This work will provide comprehensive understanding on Pt/Graphene catalysts degradation mechanisms.