Carbon Oxidation Reaction Research Articles

Bifunctionality and Reversibility of Colloidal Pt-Ir Anode Catalyst Material for Hydrogen Starvation

Cell reversal events are based on the hydrogen starvation, that takes place during to fast load changes, blockage of flow field channels or catalyst layer pores by liquid water. During the hydrogen starvation, protons and electrons continue to be supplied to the cathode, which is why carbon oxidation reaction (COR) sets in at the anode.[1] To mitigate the carbon oxidation reaction (COR), various catalyst strategies have been reported in the literature. For instance, the addition of iridium-based co-catalysts such as IrOx promote the oxygen evolution reaction (OER) instead of the carbon oxidation reaction (COR). [1-5] Although iridium is very costly and scarce, its use can be further increased by atomically mixing it with platinum to form a Pt-Ir alloy.In this work, we have prepared atomically mixed Pt-Ir alloy catalysts that combine both functionalities (hydrogen oxidation reaction and OER) in one nanoparticle (NP) in a unique matter. A colloidal route was chosen to control the particle size and composition of Pt-Ir NPs. The adopted synthesis method is based on the “Co4Cat” concept in methanol. [6] Afterwards, the colloidal NPs with controlled size of 1 – 2 nm and atomic Pt:Ir ratio of 1:1 and 3:1 were deposited on Vulcan XC72 Carbon and characterized by TEM, XPS and XRF techniques.The electrochemical experiments were performed in a three-electrode arrangement using a thin film rotating disc electrode (TF-RDE) technique. 0.1 M HClO4 was used as electrolyte solution. The ECSA was determined by underpotential deposited hydrogen (Hupd). Linear sweep voltammetry (LSV) measurements were performed to establish the HOR and OER activity. Thereby, the electrolyte was saturated with H2 and Ar for HOR and OER measurements, respectively.The PtIr/V and Pt3Ir/V catalysts with 1 – 2 nm show values of electrochemically active surface area (ECSA) of 70 ± 2 m2 g-1 PtIr and 73 ± 3 m2 g-1 PtIr. The HOR kinetics on platinum – iridium surfaces is very fast in acidic media. Therefore, we could only compare the measured HOR polarization curves with the theoretical diffusion limiting current. Since these are always on top of each other, we can conclude that the Pt-Ir catalysts are very active for HOR. In addition, the OER polarization curves were analyzed and showed an Ir-based mass activity of 70 ± 6 A g-1 Ir for PtIr/V and 104 ± 6 A g-1 Ir for Pt3Ir/V at iR-corrected potential of 1.50 VRHE. As a comparison, commercial IrOx shows a mass activity of 47 ± 6 A g-1 Ir at 1.50 VRHE.To investigate the electrochemical reversibility of Pt-Ir alloy catalysts, we alternated between the LSV measurements in the region of HOR and OER at least five times. One cycle includes three LSV measurements under each HOR and OER conditions. The HOR and OER activities for PtIr/V and Pt3Ir/V continuously decrease within the 5 cycles between HOR and OER. In other words, after the 5th cycle the OER mass activity dropped to 28 ± 3 A g-1 Ir and 32 ± 4 A g-1 Ir for PtIr/V and Pt3Ir/V catalysts, respectively. However, the ECSA values mainly retain and are 68 ± 2 m2 g-1 PtIr for PtIr/V and 70 ± 2 m2 g-1 PtIr for Pt3Ir/V.We can sum up that the colloidal Pt-Ir catalysts show bifunctional properties towards HOR and OER and reversible behaviour, which can be helpful to improve the cell reversal tolerance during the H2 starvation.Literature:[1] R. Marić et al., Towards a Harmonized Accelerated Stress Test Protocol for Fuel Starvation Induced Cell Reversal Events in PEM Fuel Cells, Journal of Electrochemical Society (2020)167, 124520 DOI:10.1149/1945-7111/abad68, [2] E. Alizadeh et al., The experimental analysis of a dead-end H2 /O2 PEM fuel cell stack with cascade type design, International Journal of Hydrogen Energy 42 (2017)11662 -11672DOI: https./7doi.org/10.1016/j.ijhydene.2017.03.094[3]Wang et al., Ir-Pt/C composite with high metal loading as a high-performance anti-reversal anode catalyst for proton exchange membrane fuel cells, International journal of hydrogen energy 47 (2022) DOI:10.1016/j.ijhydene.2022.02.065 [4] Kim et al., Pt-IrO x catalysts immobilized on defective carbon for efficient reversal tolerant anode in proton exchange membrane fuel cell, Journal of Catalysis (2021)DOI:https://doi.org/10.1016/j.jcat.2021.01.028[5]Fang et al, Facile synthesis of Pt-decorated Ir black as bifunctional oxygen catalyst Nanoscale(2019)11,9091DOI:10.1039/c9nr00279k[6]Quinson et al., Surfactant-free synthesis of size controlled platinum nanoparticles: Insights from in situ studies;Applied Surface Science (2021)549,149263 DOI: 10.1016/j.apsusc.2021.149263

Effect of Co-Catalyst Support Toward the Cell Reversal Tolerance of IrO2 Nanosheets-Pt/C Catalyst

Introduction During the operation of a polymer electrolyte fuel cell (PEFC), certain parts of the anode flow channel may not receive sufficient supply of hydrogen due to water blockage or sluggish diffusion. This can lead to hydrogen starvation, which further causes a shortage of protons during cell reaction. Such phenomenon causes an increase in anode potential, which triggers the carbon oxidation reaction (COR) and damages the catalyst layer. This destructive chained reaction is known as cell reversal degradation.Promoting the oxygen evolution reaction (OER) to alleviate the COR is a promising strategy to develop reversal-tolerant anodes (RTAs). Incorporating OER-active co-catalyst such as IrO2 is an effective way to mitigate the rise in anode potential and prevent COR [1]. We developed a new reversal tolerant anode (RTA) by directly coating a novel OER-active material, iridium oxide nanosheets (IrO2(ns)), as a co-catalyst to commercial Pt/C (c-Pt/C) [2]. With only 2.5 mass% of IrO2(ns) coating, the IrO2(ns)-c-Pt/C catalyst achieved an improved cell reversal resistance.The OER current of IrO2(ns) plays an important role in enhancing the reversal tolerance. In this study, we focus on the degradation behavior of IrO2(ns)-supporting material. IrO2(ns) supported on carbon was physically mixed with c-Pt/C (IrO2(ns)/KB+c-Pt/C) and compared with IrO2(ns) coated on c-Pt/C (IrO2(ns)-c-Pt/C). Experimental IrO2(ns) colloid was synthesized following literature [3] [4]. The directly coated catalyst, IrO2(ns)-c-Pt/C, was prepared by mixing IrO2(ns) colloid and Pt/C. The samples will be denoted as Coated-x, where x is the IrO2 mass% in the catalyst. The mixed catalyst, IrO2(ns)/KB+c-Pt/C, was prepared by physically mixing IrO2(ns) /KB, which was prepared by mixing IrO2(ns) colloid and KB (Ketjen black EC-300J), and c-Pt/C. The sample will be denoted as Mixed-x, where x is the IrO2 mass% in the catalyst.Rotating disk electrode (RDE) studies were conducted using a 3-electrode half-cell setup with 0.1 M HClO4 as the electrolyte. For hydrogen oxidation reaction (HOR) activity measurements, the electrolyte was purged with H2. For chronopotentiometry (CP) and electrochemically active Pt surface area (ECSA) measurement, the electrolyte was purged with N2. All data were accumulated at 60 oC. Results and Discussion: To simulate the degradation behavior in the fuel cell anode, accelerated stress test (AST) was conducted by applying a series of CP (178 μA/cm2, 20 mins) and CV (0.05-1.2 V, 50 mV/s, 10 cycles) tests. The HOR mass activity was measured after 5 CP-CV tests. The HOR activity was evaluated using linear sweep voltammetry (LSV) from -0.08 V to 0.5 V vs. RHE and calculated at 20 mV vs. RHE based on the Koutecky-Levich equation. After AST, the Coated-5 sample showed a decrease in HOR activity from 1575 A/g to 272 A/g (17.3 % retention). In contrast, the Mixed-4.6 sample showed a decrease in HOR from 1840 A/g to 575 A/g (31.2 % retention).Samples with higher IrO2(ns) content ratio were used for morphology observation by TEM and treated with higher AST current (CP current 1120 μA/cm2). Figures 1(A) and 1(B) show the initial state of Coated-15 and Mixed-10.7 and Figures 1(C) and 1(D) show the morphology after AST. In Coated-15 sample, agglomerated clusters were found, suggesting the dissolution/re-precipitation of Pt nearby IrO2(ns) (Figure (C)). On the other hand, in Mixed-10.7 sample, instead of forming large cluster, the damage of carbon substrate without Pt particle was found, suggesting the degradation of IrO2(ns)/KB due to high OER current (Figure (D)).According to the results above, the separate coating of IrO2(ns) onto KB helps in preventing the high OER current that damages the Pt/C structure and provides a high HOR retention after AST. Acknowledgments This work was supported in part by funds for the "R & D of novel anode catalyst project" in "Collaborative industry-academia-government R&D project for solving common challenges toward dramatically expanded use of fuel cells” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. We appreciate valuable discussions with Prof. Hiroyuki Uchida, Yamanashi University.

Concept and Advantages of Carbon/Air Secondary Battery System as a Fixed Compact Power Storage with Large Capacity

Introduction One of the critical technological isuues to constract carbon neutral society is the suppression of the impact of the volatility in power generation from inexpensive variable renewable energy power sources, such as solar cells and wind powers. It is necessary to maintain a balance between power generation, transmission, and consumption, and to maintain three types of stability in the power system: frequency stability, synchronization stability, and voltage stability. For this reason, energy storage technology is one of the most important issues for making up carbon neutral energy system. Among energy storage technologies, lithium-ion secondary batteries are superior in terms of both output density and energy density, but they present a cost challenge for large-capacity energy storage. Pumped storage power generation is the mainstay of long-term large-capacity energy storage in the current power system, but significant pumped storage expansion is subject to geopolitical constraints. Therefore, a compact, large-capacity energy storage system that can be installed in the power grid is required to expand the introduction of variable renewable energy power sources.In this research, we first describe the operating mechanism and advantages of the "Carbon/Air Secondary Battery (CASB) system" [1,2], a compact power storage system that integrates the functions of a solid oxide fuel cell that generates electricity by producing CO2 through the oxidation reaction of carbon and a solid oxide electrolytic cell that produces carbon through the electrolysis of CO2. The operating mechanism and features of the CASB system are introduced. In addition, we report the calculation results of feasible system efficiency based on thermodynamic considerations compared to power storage system using H2/H2O-solid oxide fuel cells/electrolysis cells. In addition, the advantages/disadvantages of the two types of CASBs, integrated type of CASB between carbon deposition /electrochemical reaction, and the separated type of CASBs, as well as their representative charge/discharge characteristics will be presented. Theoreticl advantage of CASB as a fixed compact power storage with large capacity The theoretical charge/discharge efficiency of CASB, which is the ΔG/ΔH of reaction “C+O2→CO2” is 100%. This means that there is no heat input and output ideally in both carbon generation and CO2 electrolysis (in charge/discharge). Therefore, temperature control is simple and a heat exchanger can be minimized, which may allow the system to be compact. The feasible charge/discharge system efficiency of CASB including possible heat exchange were estimated as 92% based on thermodynamics, which is much higher than that of power storage system using H2/H2O-solid oxide fuel cells/electrolysis cells (63%). In addition, since CO2 can be liquefied at about 6.4 MPa at 25°C, its volumetric energy density to 1.62 × 103 Wh L-1, about four times higher than the volumetric energy density of hydrogen compressed at 20 MPa at 25°C, 3.79 × 102 Wh L-1. A key technological point of CASB at its discharging , which is combination between electrochemical reaction (CO2→ CO+O2-) and thermochemical reaction (2CO→ C+CO2) by achiving at closed system The discharge reaction of the CASB is the same as that of the Rechargeable Direct Carbon Fuel Cell [3,4,5]. The reason for the first successful demonstration of the CASB is that the combining electrochemical reaction with low overpotential (CO2 →CO+O2-) with the thermochemical reaction, the Boudouard equilibrium reaction (2CO → C+CO2) were achieved at the charging by making the system a closed system. Two types of CASBs, (1) Integrated type of CASB between carbon deposition /electrochemical reaction, and (2) the separated type of CASBs Since generally, the carbon deposition on the electrode cause its degradation [6], two type of CASBs can be designed and demonstrated (as shown in Fig.1). Both types of CASBs could be demonstrated.

Mechanistic Insights into the Bifunctionality of Cell-Reversal Tolerant Pt-Ir Alloy Catalysts during HOR and OER Using Operando Quick-XANES

Hydrogen (H2) starvation, for example due to insufficient supply of H2 or nonuniform gas distribution, remains one of the major challenges for PEMFC applications.[1,2] The H2 starvation in PEMFCs results in a rapid (several milliseconds to few seconds) increases in voltage at the anode.[3] In order to continuously provide protons and electrons to the cathode during the H2 starvation, the carbon oxidation reaction (COR) commences as an alternative reaction at the anode.[4] To mitigate carbon corrosion and improve the long-term durability of PEMFCs, several material strategies can be utilized. One promising approach is the utilization of co-catalysts such as IrOx to accelerate the oxygen evolution reaction (OER) as an alternative source for protons and electrons.[3,5] The iridium can be (i) physically mixed into the platinum-based catalyst layer as IrOx, (ii) added to the same carbon support material as Pt nanoparticles (NPs) or (iii) alloyed with Pt NPs. Although several studies showed an increase in cell reversal tolerance using Pt-Ir alloys instead of physical mixing [6-9], no operando spectroscopic studies have so far been conducted to understand the surface oxidation states and electron transfer processes between the two metals and metal oxides during the cell reversal event. As this is a very dynamic process occurring within several milliseconds to few seconds, our approach is to use operando Quick-X-ray absorption near edge structure (Quick-XANES). This allows us to fundamentally understand the dynamics of structural and electronic interactions of both metals during the hydrogen oxidation reaction (HOR) and OER.In this work, alloyed Pt-Ir NPs with Pt:Ir ratios of 1:1 and 3:1 were prepared by two different synthetic routes (colloidal and wet-impregnation).[10] Very interestingly, the oxidation states of platinum and iridium as well as the particle size strongly vary depending on the synthesis route. More precisely, the wet-impregnation enables preparing Pt-Ir NPs of 3 – 4 nm size, while ~2 nm Pt-Ir NPs with amorphous IrOx species are obtained by the colloidal route. Using the RDE technique in 0.1 M HClO4, all Pt-Ir catalysts show activities close the diffusion limiting current, indicating high HOR kinetics. Despite the different oxidation states and particle sizes, the Pt-Ir NPs show considerable activity for the OER compared to pure commercial Pt/C and IrOx catalysts. Especially, the Pt-Ir NPs prepared by the colloidal route exhibit 2.5 times increase in OER mass activity (normalized to the Ir content) at 1.5 VRHE compared to commercial IrOx.To gain fundamental insights into the reversibility and catalytically active states of these bifunctional Pt-Ir catalysts under working conditions, operando Quick-XANES experiments by jumping between hydrogen evolution reaction (HER) and OER within a few seconds were conducted. Very interestingly, these jumping experiments reveal that the bifunctionality of these Pt-Ir NPs is highly reversible for several minutes independent of the Pt:Ir ratio and synthesis route. However, the oxidation state of iridium during the OER is strongly influenced by the Pt:Ir ratio as well as the synthesis route. For both synthetic routes, using a Pt:Ir ratio of 3:1 results in a higher abundance of Ir4+ species during the OER compared to using a 1:1 ratio. During the OER the content of oxidized Pt and Ir species are lower for the larger NPs (3 – 4 nm) prepared by the wet-impregnation route compared to the colloidal ones (2 nm). In addition, we reveal the influence of electronic effects between alloyed and non-alloyed NPs during the electrochemical reactions, especially for OER. During the HER, independent from the synthetic route the Pt-Ir NPs show a reduction of Ptz+ species to metallic platinum within a few seconds, while the Ir4+ species are partially reduced to form Ir3+ species. These dynamic changes in oxidation state of both elements within Pt-Ir alloy NPs are highly reversible within seconds under the HER or OER conditions.Based on the operando Quick-XANES, our results provide new insights into the dynamic behavior of bifunctional Pt-Ir NPs during HOR and OER within a few seconds to design new cell reversal tolerant catalyst materials with low loading of the very costly and scarce iridium.

Investigations on the Corrosion Behavior of a 20 Cell PEMFC Automotive Short Stack Caused By Air/Air Start-Ups at Different Operating Conditions Utilizing a Segmented Current Mapping Board

The Polymer Electrolyte Membrane Fuel Cell (PEMFC) emerges as one of the key technologies for the future of energy and mobility landscapes by offering a clean, efficient, and sustainable power generation. To ensure the commercial viability of PEMFCs, the components, particularly the Membrane Electrode Assembly (MEA), and its operation must be designed to minimize the impact of degradation processes over their entire lifetime and to maximize durability.It is known that the oxidation or corrosion of the cathode catalyst support material resulting from the so-called reverse current decay mechanism caused by gas atmosphere changes when starting up from an inactive state (air/air situation) or shutting down from the active state (H2/air situation) is one of the most significant degradation processes. The Carbon Oxidation Reaction (COR) can lead to a detachment of the supported catalyst particles from the rest of the electrical network or to a delamination from the ionic network and therefore ultimately result in a reduction of the Effective Catalyst Surface Area (ECSA) and in increasing mechanical instability up to the collapse of the catalyst layer [1].In previous work, different approaches have been taken to simulate this degradation mechanism using accelerated stress tests, usually at half-cell or sub-scale level, with active areas <50 cm² [2][3]. The aim of this work is to investigate the effect of Air/Air Start-Ups (AASUs) on a higher integration level using a 20 cell short stack with a single full-size automotive cell active area of >200 cm². AASUs were executed after different air soak durations and under different operating conditions with focus on relative humidity, coolant inlet temperature, hydrogen concentration and inflow rate to vary the gas front residence time within the active area. The short stack is equipped with a Cell Voltage Monitoring (CVM) of each individual cell and a high-resolution segmented Current Mapping Board (CMB) next to the anode Interface Plate (IFP) to record local and internal current density changes, particularly during the passage of the gas atmosphere front, as exemplified and illustrated in Figure 1.After the fundamental investigation of the impact of different operating parameters, a specific parameter set was chosen to assess the degradative effects on an identical stack in a continuous AASU sequence operation until failure. Throughout the stress testing, the cell performances including the local current distribution as well as the ohmic resistance of the stack by Electrochemical Impedance Spectroscopy (EIS) were monitored. Furthermore, morphological investigations using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) were performed after disassembly of the stack on different cells in the stack and at different positions within the active area. The formation of degradation gradients within the active cell area and along the stack, induced by AASU stress testing, is demonstrated through changes in local current densities measured with the CMB, accompanied by a loss of overall cell performance and supported by in-depth morphological investigations.

Comparison of Galvanostatic and Potentiostatic Accelerated Stress Tests of Bifunctional Pt-Ir Alloy Anode Catalysts for H2 Starvation Using Rde Technique

One of the main challenges to overcome for the wide implementation of PEMFCs is the improvement of their long-term durability. For instance, the blockage of the diffusion pathway by liquid water or rapid changes of load can lead to hydrogen starvation.[1] Due to the hydrogen starvation, the anode potential increases and accelerates the carbon oxidation reaction (COR) to further supply electrons and protons for the cathode ORR half-cell reaction, also referred to as cell reversal event.[2] Aggregation and particle detachment associated with the carbon corrosion occur, resulting in a drastic loss of the PEMFC performance.[3] Therefore, material innovation solutions are needed to overcome the cell reversal events. In this context, fast and simple accelerated stress tests and set-ups are needed. Currently, galvanostatic accelerated stress tests (G-AST) at single cell level are often used to evaluate the cell reversal tolerance (CRT) of catalyst materials, which is extremely time-consuming, costly and slow.[4] On the other hand, the rotating disc electrode (RDE) technique is widely used, simple, less expensive and fast for catalyst screening. However, the electrochemical measurements of activity and durability are usually carried out in the potentiostatic mode. The research question arises whether the RDE technique is capable of evaluating the CRT behaviour of novel catalyst materials using galvanostatic AST.This systematic work compared both galvanostatic and potentiostatic accelerated stress tests (G-AST and P-AST) protocols to evaluate the degradation behaviour of novel bifunctional Pt-Ir alloy catalyst materials for hydrogen starvation. The Pt-Ir alloy catalysts with 1:1 and 3:1 ratios were prepared by wet-impregnation route. Here, the PtIr and Pt3Ir catalysts supported on Vulcan XC72 show a mean particle size of 3-5 nm and total metal loading of 35-50 wt.%Pt+Ir obtained from TEM, TGA and EDX data. In a RDE set-up equipped with three-electrode configuration, all electrochemical measurements were performed in 0.1 M HClO4 and room temperature. At begin-of-life (BoL), the performance of the Pt-Ir catalysts was evaluated by measuring the ECSA via Hupd and CO stripping methods, HOR and OER polarization curves. It is noted that the HOR polarization curves were only fitted with the diffusion limiting current due to the fast kinetics of the HOR on platinum and iridium surfaces in acidic media. For the G-AST protocol, a current density of 0.5 mA/cm2 geo was held for 10h with a cut off at 2 VRHE. The time it takes to reach 2 VRHE is referred to as the fail time (FT) and signifies the loss of the protection mechanism of catalyst materials, namely the OER activity. Based on the results from the G-AST protocol, the same FT was used to perform the chronoamperometric measurements by holding the potential at 1.6 VRHE during the P-AST protocol.At the BoL, the Pt-Ir catalysts with 3-4 nm size show sufficient ECSA values (45-50 m2/gPt+Ir via Hupd) and improved OER activity (PtIr: 23±6 A/gPt+Ir and Pt3Ir: 8±1 A/gPt+Ir @1.5 VRHE) compared to the commercial Pt/V catalyst (79±4 m2/gPt via Hupd, 6±1 A/gPt @1.5 VRHE) and IrOx (47±6 A/gIr). During the G-AST, we observed that the FT increases with higher Ir content. In addition, the Pt3Ir/V catalyst shows a significant improvement of FT compared to the Pt/V. More precisely, during the G-AST protocol, the potential of 2 VRHE by applying a constant current density of 0.5 mA/cmgeo was already reached after 15min, while for the Pt3Ir/V catalyst this took at least 1 hour. Furthermore, our data shows that the G-AST protocol is more aggressive compared to the P-AST to evaluate the catalyst aging processes.Altogether, we showed the influence of galvanostatic and potentiostatic ASTs for rapid benchmarking of novel bifunctional cell reversal tolerant Pt-Ir alloy catalysts using the three-electrode RDE technique. This study can be helped to improve the electrochemical results obtained from the RDE to the catalyst coated membranes.[1] Marić, R. et al.Towards a Harmonized Accelerated Stress Test Protocol for Fuel Starvation Induced Cell Reversal Events in PEM Fuel Cells: The Effect of Pulse Duration. J. Electrochem. Soc., 2020, 167, 124520.DOI: https://doi.org/10.1149/1945-7111/abad68[2] Chen W. et al.: Thickness effects of anode catalyst layer on reversal tolerant performance in proton exchange membrane fuel cell. Int. J. Hydrog. Energy, 2021, 46, 8749.DOI: https://doi.org/10.1016/j.ijhydene.2020.12.041[3] Zhou X. et al.: High-Repetitive Reversal Tolerant Performance of Proton-Exchange Membrane Fuel Cell by Designing a Suitable Anode. ACS OMEGA, 2020, 5, 10099.DOI: https://dx.doi.org/10.1021/acsomega.0c00638[4] Peng Y. et al.: Pitfalls of a commonly used accelerated stress test for reversal tolerance testing of proton exchange membrane fuel cell anode layers. J. Power Sources, 2021, 500, 229986.DOI: https://doi.org/10.1016/j.jpowsour.2024.234087

Impact of Electrode Reversal Method on Electrode Degradation By High-Potential Environment in Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are key energy conversion devices, that address global energy challenges and climate change and are prized for various applications due to their high efficiency, low operating temperature, fast startup, and low toxic emissions. Enhancing PEMFC durability is crucial for advancing commercialization. Thus, prioritizing research on Catalyst Layer (CL) degradation mechanisms of Membrane Electrode Assembly (MEA) and developing analytical methods to understand extreme degradation conditions are becoming imperative.In PEMFCs’ operational scenarios, various issues deteriorate the membrane electrode assembly (MEA) of PEMFCs, leading to irreversible performance declines. These include Pt dissolution, ionomer degradation, carbon corrosion [1], and occasional membrane mechanical issues. Of these, the electrochemical carbon oxidation reaction is particularly detrimental, causing a significant reduction in electrochemical double layer capacitance (EDLC), the formation of oxygen functional groups in carbon supports, and substantial deterioration in electrochemical surface area (ECSA) [2, 3], ultimately leading to degraded PEMFC performance.On the other hand, reversible performance degradation occurs during fuel cell operation, which specific operational recovery procedures can rectify. Mechanisms contributing to reversible voltage degradation include the platinum oxide formation, adsorption of impurity ions and contaminants on the catalyst surface, water flooding/dehydration, and oxidation of the carbon support surface to create hydrophilic oxygen-containing groups [4]. Understanding reversible degradation mechanisms and recovery strategies is important for efficient operation, improved durability, and prolonged cell lifespan. Typically, the "electrode reversal" method is practical and economical, allowing power output during recovery without additional equipment, thereby minimizing recovery operation runtime.In this study, we examine the impact of the electrode reversal method on PEMFC performance and the deterioration tendency of MEA during carbon corrosion of cathode CL (Figure 1). Accelerated stress tests (AST) were conducted at high potentials exceeding 1.0 V (vs. RHE), specifically investigating the relationship between electrode degradation behaviors, porous carbon structural properties including ionic resistance and EDLC, and overall PEMFC performance.Particularly noteworthy after the electrode reversal recovery method were the discernible variations in degradation behaviors and diverse rates of performance decline observed through electrochemical impedance spectroscopy (EIS) analysis. EIS can be used to isolate the contribution of many processes to performance loss, allowing investigation of the effect of carbon corrosion-induced catalyst layer changes on fuel cell performance [5]. The EIS data underwent evaluation via parametric fitting utilizing the transmission line model (TLM) applied to the EIS spectrum. Furthermore, relaxation time distribution (DRT) analysis was employed to directly analyze internal resistance factors as a diagnostic tool for assessing electrode degradation by enhancing the TLM-based impedance analysis results. During the ASTs, electrochemical measurements (i-V, CV, LSV, and EIS) were performed to estimate the degree of PEMFC degradation, we also conducted ex-situ surface analysis of MEA using SEM, TEM, and XPS to elucidate the specific degradation components. Fig. 1 Electrode Reversal Recovery method during Anode cycling AST of the PEMFC single cell (a) polarization curves (i-V curves); 10 A constant current test (b)-(d): (b) fresh MEA, (c) after 250 cycles, (d) after 500 cycles of Anode cycling AST References [1] Sorrentino, Antonio, Kai Sundmacher, and Tanja Vidakovic-Koch. "Polymer electrolyte fuel cell degradation mechanisms and their diagnosis by frequency response analysis methods: a review." Energies 13.21 (2020): 5825.[2] Macauley, Natalia, et al. "Carbon corrosion in PEM fuel cells and the development of accelerated stress tests." Journal of The Electrochemical Society 165.6 (2018): F3148.[3] Kwon, JunHwa, et al. "Identification of electrode degradation by carbon corrosion in polymer electrolyte membrane fuel cells using the distribution of relaxation time analysis." Electrochimica Acta (2022): 140219.[4] Yang, Wenbin, et al. "Investigation of an electrode reversal method and degradation recovery mechanisms of PEM fuel cell." Electrochimica Acta 449 (2023): 142181.[5] Kwon, JunHwa, et al. "A Comparison Study on the Carbon Corrosion Reaction under Saturated and Low Relative Humidity Conditions via Transmission Line Model-Based Electrochemical Impedance Analysis." Journal of The Electrochemical Society 168.6 (2021): 064515. Figure 1

Self-sacrificing and self-supporting biomass carbon anode–assisted water electrolysis for low-cost hydrogen production

Electrooxidation of renewable and CO2-neutral biomass for low-cost hydrogen production is a promising and green technology. Various biomass platform molecules (BPMs) oxidation assisted hydrogen production technologies have obtained noticeable progress. However, BPMs anodic oxidation is highly dependent on electrocatalysts, and the oxidation mechanism is ambiguous. Meanwhile, the complexity and insolubility of natural biomass severely constrain the efficient utilization of biomass resources. Here, we develop a self-sacrificing and self-supporting carbon anode (SSCA) using waste corncobs. The combined results from multiple characterizations reveal that the structure-property-activity relationship of SSCA in carbon oxidation reaction (COR). Theoretical calculations demonstrate that carbon atoms with a high spin density play a pivotal role in reducing the adsorption energy of the reactive oxygen intermediate (*OH) during the transition from OH- to *OH, thereby promoting COR. Additionally, the HER||COR system allows driving a current density of 400 [Formula: see text] at 1.24 V at 80 °C, with a hydrogen production electric consumption of 2.96 kWh Nm-3 (H2). The strategy provides a ground-breaking perspective on the large-scale utilization of biomass and low-energy water electrolysis for hydrogen production.

Fe(III)-cycle enhanced carbon oxidation reaction for low-energy hydrogen production via water electrolysis

Integrating the hydrogen evolution reaction (HER) with the carbon oxidation reaction (COR) is a promising method for producing H₂ with lower energy consumption. However, due to the passivation effect of oxygen functional groups (OFGs) for COR and Fe³⁺, achieving efficient and sustainable carbon oxidation to assist water electrolysis for hydrogen production remains a challenge over the past decades. This study introduced [EDTA·Fe(III)]– as a mediator to promote COR. [EDTA·Fe(III)]– effectively prevented the oxidation layer on the carbon surface from anchoring Fe (III) and reactivated the carbon that had been passivated by the oxidation layer. Density functional theory calculations indicated that the notable COR activity resulted from [EDTA·Fe(III)]– effectively lowering the vertical ionization potential of carbon, without being affected by OFGs. Notably, in the HER||COR-[EDTA·Fe(III)]– system, a cell voltage of merely 0.74 V is sufficient to reach a current density of 10 mA cm−2, with the corresponding energy consumption being 1.76 kWh Nm−3 (H2). This strategy offers new insights into achieving stable, low-energy hydrogen production via water electrolysis.

Tuning the Bifunctional Properties of Cell Reversal-Tolerant Ir-Pt Electrocatalysts for HOR and Oer

Hydrogen starvation is still a big problem in PEM fuel cells [1]. In order to provide protons and electrons to the cathode during H2 starvation, the carbon oxidation reaction (COR) takes place at the anode [2]. To solve this issue, there are three main strategies: (i) utilization of corrosion resistant support materials, (ii) integration of extensive and complex system mitigation strategies and finally (iii) the addition of co-catalyst to promote the oxygen evolution reaction(OER) instead of COR. [3, 4]In this work, platinum-iridium (PtIr) nanoparticles (NPs) have been designed as a novel bifunctional electrocatalysts to accelerate either the hydrogen oxidation reaction (HOR) or the OER depending on the reaction conditions. Our catalyst concept is the combination of both functionality (HOR and OER) in single Pt-Ir alloy nanoparticles (NPs) deposited on the same support material. The Pt-Ir NPs with Pt:Ir ratios of 1:1 and 3:1 were prepared by two different (colloidal and wet-impregnation) routes. Very interestingly, the oxidation states of platinum and iridium as well as the particle size strongly vary depending on the synthesis route. More precisely, the wet-impregnation enables preparing Pt-Ir NPs of 3 – 4 nm size and mainly in the metallic state, while strongly oxidized NPs with ~2 nm size are produced by colloidal route. Despite the different oxidation states and particle sizes, the Pt-Ir NPs show considerable activity for HOR and OER compared to pure commercial Pt/C and IrOx catalysts. Very interestingly, the bifunctionality of these Pt-Ir is highly reversible and is robust during accelerated stress tests. Operando Quick-X-ray Absorption Near Edge Structure (XANES) spectroscopy were performed to provide fundamental insights into the reversibility and catalytically active states of these bifunctional catalysts under the working conditions by jumping with the potential between HER and OER within few seconds. The combination of operando XANES, RDE and MEA data show that the bifunctional approach is a promising way to improve the cell reversal-tolerant properties of anode catalyst materials compared to the state-of-the-art Pt-IrOx catalyst materials.

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

Optimizing the Atomic Structure of Ruthenium Deposited on Pt/C Cathode Catalysts to Enhance Durability of Automotive Fuel Cell

Proton exchange membrane fuel cells (PEMFCs) for automotive applications suffer from cathode corrosion problems due to the sudden potential jump caused by unintended air leakage into the anodic flow field during start-up and shut-down (SU/SD) events. Here, we report a solution to the instantaneous potential jump issue during SU/SD events by imparting oxygen evolution reaction (OER) activity to the PEMFC cathodic catalyst to preferentially promote OER and suppress the unwanted carbon oxidation reaction at the cathode. In the newly developed Ru-on-Pt/C electrocatalyst, the small particle size of sputtered Ru and the Ru–Pt interaction significantly improve activity–stability for OER and prevent corrosion in cathode by preemptively consuming electrons related to the potential jump. Membrane electrode assemblies constructed using Ru-on-Pt/C showed an extraordinary (98 %) performance retention after repeating the SU/SD protocol test 100 times, demonstrating unprecedented state-of-the-art durability.

The development of B/Cr co-doped DLC coating by FCVA deposition system and its tribological properties at 300 °C

The diamond-like carbon (DLC) coating prepared using filtered cathodic arc deposition (FCVA) lost its promising wear resistance under high temperatures. Element-doped DLC coatings have been investigated to suppress carbon oxidation reaction and subsequently enhance the wear resistance in high-temperature environments. Previous research clarified the excellent tribological properties of boron-doped DLC (B-DLC) but identified challenge such as arc discharge extinguishment and coating declamation (under high-temperature friction test). In this study, the introduction of Argon gas (10 sccm) during the deposition process stabilized stable arc discharge, resulting in high hardness and deposition rate. Moreover, a chromium interlayer and varying concentration of Cr dopant (0.5 %, 1.0 %, 3.0 % at.) were added to B-DLC to develop a stable, co-doped DLC with low friction and high wear resistance. Raman spectroscopy and nano-indentation revealed an increase in the disordered carbon structure and reduction in hardness and Young's Modulus with Cr doping. Macroscopic ball-on-disk friction test, showed 1 % Cr-doped B-DLC (a-C:B:Cr1) coating exhibited super low friction (avg. coefficient 0.02) and a low specific wear rate (<5.0 × 10−6 mm3/Nm). Raman spectroscopy indicated that the transferred graphite-like tribo-film onto the surface of Si3N4 counterparts contributed to stable low friction. Additionally, XPS analysis on the DLC coatings' wear track suggested the rich BB bond might contribute to its high wear resistance. This successful improvement on element-doped DLC prepared by FCVA provided valuable insights for further exploration of DLC coating applied to various working situations.

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.

АНАЛІЗ РОЗВИТКУ РЕАКЦІЇ ОКИСЛЕННЯ ВУГЛЕЦЮ НИЗЬКОВУГЛЕЦЕВОЇ СТАЛІ В КОВШІ ПІД ВАКУУМОМ

The object of research is the process of vacuuming steel in a ladle. The purpose of the study is to determine the degree of approach of degassing reactions to equilibrium and removal rates by articles. Research methods - theoretical studies are based on the basic provisions of physical chemistry and the theory of metallurgical processes, thermodynamic calculations of the non-equilibrium reactions of degassing. Scientific novelty - in vacuum degassing processes, the approximation of the corresponding reactions to equilibrium plays a significant role, in industrial vacuum installations, the equilibrium between carbon and oxygen dissolved in steel is not achieved due to ex-tremely small concentrations of interacting substances, the speed of the chemical reaction decreases so much that it does not allow for processing time to even approach the state of thermodynamic equilibrium. Practical significance - to ensure a high degree of implementation of the deoxidizing ability of carbon in vacuum conditions, it is neces-sary to: apply the main lining of steel pouring ladles; maintain a high basicity of slag and a minimum content of iron oxides in it; mix the melt in the ladle with an inert gas to facilitate the conditions for the nucleation of carbon oxidation reaction products.

Research on the regulatory mechanism of pore structure in soil matrix prepared by fluidized bed calcination of coal gangue

As a bulk industrial solid waste, coal gangue has caused serious pollution to the environment, and its application in the field of soil amendments has been widely studied, but the mechanism of pore structure regulation of coal gangue as soil substrate has not been reported in the literature. In this paper, the physical and chemical properties of coal gangue are analyzed, and its particle size, element content, and occurrence state are defined. The regulation mechanism of pores and pores in preparing matrix soil with coal gangue is revealed, and an efficient and energy-saving fluidizing activation technology is proposed to prepare active matrix soil. The results show that matrix soil with optimal pore structure can be obtained by fluidized bed calcination at 700 °C for 15 min, with a porosity of 55.0 %, volumetric water content of 28.7 %, and gas phase rate of 24.8 %. The technology also removes carbon, which is prone to natural fires, and fixes sulfur, which is good for plant growth. The formation and regulation mechanism of pores structure of soil matrix prepared by fluidized calcination of coal gangue is as follows: The oxidation reaction of carbon and the decomposition of minerals in coal gangue will form pore structures. Adjusting the reaction temperature and time, controlling the rate of carbon oxidation reaction, and the rate of mineral decomposition can achieve the goal of regulating the pore structure. Large pores with a pore size greater than 0.03 mm are formed by the oxidation of carbon and the decomposition of kaolinite. The pores with a diameter of 0.0001–0.03 mm are formed by the overflow of carbon dioxide gas, which is generated by the oxidation reaction of carbon embedded in coal gangue particles and the decomposition of calcium carbonate. The results of this study will provide technical and theoretical support for promoting the comprehensive utilization of coal gangue and improving environmental protection.

Modeling of vacuuming of low-carbon steel in a ladle taking into account the approach of degasation reactions to equilibrium

The object of research is the process of vacuuming steel in a ladle. The purpose of the study is to determine the degree of approach of degassing reactions to equilibrium and removal rates by articles. Research methods - theoretical studies are based on the basic provisions of physical chemistry and the theory of metallurgical processes, thermodynamic calculations of the non-equilibrium reactions of degassing. Scientific novelty - in vacuum degassing processes, the approximation of the corresponding reactions to equilibrium plays a significant role, in industrial vacuum installations, the equilibrium between carbon and oxygen dissolved in steel is not achieved due to extremely small concentrations of interacting substances, the speed of the chemical reaction decreases so much that it does not allow for processing time to even approach the state of thermodynamic equilibrium. Practical significance - to ensure a high degree of implementation of the deoxidizing ability of carbon in vacuum conditions, it is necessary to: apply the main lining of steel pouring ladles; maintain a high basicity of slag and a minimum content of iron oxides in it; mix the melt in the ladle with an inert gas to facilitate the conditions for the nucleation of carbon oxidation reaction products.

Development of IrO2 Nanosheet–Pt/C Composite as Reversal Tolerant Anode Catalysts for Polymer Electrolyte Fuel Cell

Introduction: During the start-up and shutdown cycles of a polymer electrolyte fuel cell (PEFC), certain areas of the anode flow channel may not receive sufficient hydrogen due to water blockage or sluggish diffusion. This can lead to hydrogen starvation, which in turn causes a shortage of protons during cell reaction. The result is an increase in anode potential, which triggers the carbon oxidation reaction (COR) and damages the catalyst layer.Promoting the oxygen evolution reaction (OER) to alleviate the COR is a promising strategy to develop reversal-tolerant anodes (RTAs). Incorporating OER-active materials, such as IrO2, as a co-catalyst is an effective way to mitigate the rise in anode potential and prevent COR [1].In this study, a novel OER-active material, iridium oxide nanosheet (IrO2(ns)), was used as the co-catalysts and combined with commercial Pt/C in three different ways; mixing Pt/C with normal- and small-sized IrO2 nanosheets (IrO2(ns)/Pt/C), and Pt/C mixed with carbon supported IrO2 nanosheet (Pt/C+IrO2(ns)/KB). The OER activity and tolerance to cell reversal conditions were characterized using a 3-electrode rotating disk electrode (RDE) setup. Experiment: IrO2(ns)(250 nm) colloid was synthesized following literature [2]. The resulting IrO2(ns)(250 nm) colloid was subjected to ultrasonication to obtain small-sized nanosheets (IrO2(ns)(100 nm)) [3]. Nanosheet-carbon composite (IrO2(ns)(100 nm)/KB) was prepared by mixing IrO2(ns)(100 nm) colloid and KB (Ketjen black EC-300J) and physically mixed with Pt/C. Commercially available IrO2 nanoparticles (c-IrO2) were purchased from Tokuriki Honten Co., Ltd. and added to Pt/C (c-IrO2-Pt/C) and used as a reference sample.The composite catalyst was prepared by mixing Pt/C with different IrO2 nanomaterials and will be denoted as IrO2(ns)(x mass%)-Pt/C or c-IrO2 (x mass%)-Pt/C depending on the source of the IrO2 material used. RDE studies were conducted using a 3-electrode half-cell setup with 0.1 M HClO4 as the electrolyte. The counter electrode was carbon fiber, and a reversible hydrogen electrode (RHE) was used as the reference electrode.Except for the OER activity, the electrodes for all measurement were prepared with a Pt loading of 8.0 μg/cm2. For hydrogen oxidation reaction (HOR) activity measurements, the electrolyte was purged with H2. For chronopotentiometry (CP) and electrochemically active Pt surface area (ECSA) measurement, the electrolyte was purged with N2. For OER activity measurements, the electrolyte was purged with N2, and the working electrode was prepared with a Pt loading of 17.3 μg/cm2. Except for ECSA measurement, all data were accumulated at an electrolyte temperature of 60oC. Results and Discussion: Figure 1 shows the OER activity (10 mV/s) of Pt/C and composite catalysts prepared with c-IrO2(5 mass%), IrO2(ns)(250 nm, 5 mass%), IrO2(ns)(100 nm, 5 mass%), IrO2(ns)(100 nm, 2.5 mass%) and IrO2(ns)(100 nm, 1 mass%). At 1.5 V vs. RHE, IrO2(ns)(100 nm, 2.5 mass%)-Pt/C exhibited a 2-fold increase in OER activity compared to IrO2(ns)(250 nm, 5 mass%)-Pt/C and a 25 % increase compared to c-IrO2 (5 mass%)-Pt/C. All composite catalysts displayed significantly higher OER activity than the pristine Pt/C sample.To simulate the degradation behavior in the fuel cell anode, a series of CP tests were performed at 16, 48, 80, and 112 μA/cm2. The HOR mass activity was used as a quantitative factor to present the decay caused by cell reversal degradation. The HOR activity before and after CP was evaluated using linear sweep voltammetry (LSV) from -0.08 V to 0.5 V vs. RHE. The HOR mass activity at 20 mV vs. RHE was calculated based on the Koutecky-Levich equation. After CP, the Pt/C sample showed a decrease in HOR activity from 851 A/g to 621 A/g (72% retention). In contrast, IrO2(ns)(100 nm, 2.5 mass%)-Pt/C showed an initial HOR activity comparable to Pt/C (1420 A/g) and still retained a high HOR activity of 1400 A/g after CP (100% retention). The addition of IrO2(ns) as a co-catalyst effectively suppressed the carbon oxidation reaction under cell reversal conditions.

Synthesis of Ir Nanoparticles As Promoters for the Stabilization of Fenc-Catalysts Under Ssc Conditions

Fuel cells are promising devices for implementation in automotive propulsion. While the standard operation seems feasible, during start-up and shutdown high potentials occur on the cathodic site induced by the reverse current mode. In consequence, the carbon oxidation reaction (COR) occurs and limits the lifetime of PEMFCs. One approach suppressing carbon corrosion is the introduction of small amounts of an oxygen evolution reaction (OER) catalyst, as e.g. iridium. In our recent work we showed that in relative manner the durability was improved, however, the initial performance was less compared to the non-modified FeNC catalyst.[1 ] These NP had been prepared by a polyol approach.[2 ] However, capping agents (CA) could eventually still be present in these systems, blocking the particles in their performance.Herein, we present our results using an alternative surfactant free synthesis of Ir nanoparticles, adapted from literature,[3 ] that are then used for the modification of an FeNC catalysts. The performance of the newly prepared FeNC+Ir vs the FeNC+Ir+CA reference was evaluated employing accelerated stress tests mimicking the start-up and shut down conditions in RDE and PEMFC. It is shown that with this new approach the amount of NP on the surface can be better controlled. Beside the electrochemical testing structural characterization by X-ray-diffraction, thermogravimetric analysis and transmission-electron-microscopy was performed.It will be shown that by surfactant free synthesis Ir nanoparticles with high purity can be obtained. Due to the higher purity, an improvement of the OER activity can be achieved with the same Ir loading. In the RDE, an improvement in stability was observed by loading an FeNC catalyst with Ir nanoparticles. However, under fuel cell conditions, no improvement in stability was observed by loading Ir nanoparticles onto a FeNC catalyst.List of references[1] Prössl, C., Kübler, M., Paul, S., Ni, L., Kinkelin, S. J., Heppe, N., Eberhardt, K., Geppert, C., Jaegermann, W., Stark, R. W., Bron, M. & Kramm, U. I. (2022). Impact of Ir modification on the durability of FeNC catalysts under start-up and shutdown cycle conditions. Journal of Materials Chemistry A, 10(11), 6038-6053.[2] Prössl, C., Kübler, M., Nowroozi, M. A., Paul, S., Clemens, O., & Kramm, U. I. (2021). Investigation of the thermal removal steps of capping agents in the synthesis of bimetallic iridium-based catalysts for the ethanol oxidation reaction. Physical Chemistry Chemical Physics, 23(1), 563-573.[3] Bizzotto, F., Quinson, J., Schröder, J., Zana, A., & Arenz, M. (2021). Surfactant-free colloidal strategies for highly dispersed and active supported IrO2 catalysts: Synthesis and performance evaluation for the oxygen evolution reaction. Journal of catalysis, 401, 54-62.

Biochar and other carbonaceous materials used in steelmaking: Possibilities and synergies for power generation by direct carbon fuel cell

The objective of this study is the preliminary investigation of the feasibility of using a low-temperature molten hydroxide direct carbon fuel cell as an additional energy source for steel production by electric arc furnace. For this purpose, four carbonaceous materials related to the steel industry (electrographite, coke, torrefied biochar and hydrochar) were selected and characterized to predict their electrical behavior before their actual introduction as fuels. Special attention was paid to both the morphological effect (bulk/pellet or powder) and the chemical composition of the fuels on the electrical performance of the cell. Electrical measurements showed the positive influence of powder morphology, with coke powder having the highest peak power density value (49.6 mW/cm2). Electrographite was found to be useable only as a powder (18.7 mW/cm2), as the high chemical stability of the bulk morphology, provided by the smooth surface and the pitch used as a binder, acted as inhibitors of the carbon oxidation reaction. Although biochar appeared superior to hydrochar when inserted as powder (23.5 vs. 18.2 mW/cm2), the latter showed promising results also inserted as pellet. the latter also showed promising results when inserted as a pellet. Specifically, once inserted within the molten hydrochar, the binder used to produce the hydrochar is removed changing the morphology from pellet to sandy/powdery, negating the penalizing effect of the lower surface to volume of bulk morphology (15.8 vs. 18.2 mW/cm2) and offering the advantage of avoiding the milling process and related fine particulate production from an industrial point of view.