Proton Exchange Membrane Fuel Cell Anode Research Articles

Irreducible IrO2 Anode Co-Catalysts for PEM Fuel Cell Voltage Reversal Mitigation and Their Stability Under Start-Up/Shut-Down Conditions

IrO2 has been widely used as the anode co-catalyst for mitigating cell voltage reversal damages in proton exchange membrane fuel cells (PEMFCs). However, under the PEMFC anode operation conditions, conventionally prepared IrO2 catalysts are reduced by H2, forming metallic Ir on their surface, which is prone to dissolution during start-up/shut-down (SUSD) cycles. The dissolved Irn+ ions can permeate through the membrane to the cathode electrode, poisoning the oxygen reduction reaction (ORR) activity of the Pt/C cathode catalyst. In this study, we introduce an unprecedented approach to synthesize IrO2 catalysts (irr-IrO2) which are not reduced in the PEMFC anode environment at 80 °C over extended time. Their preparation is based on an industrially scalable procedure, consisting of a high-temperature (650 °C–1000 °C) heat treatment step, a subsequent ball milling step, and a final post-annealing step, thereby attaining catalysts with specific surface areas of ∼25 m2 g−1. The high reduction resistance of the irr-IrO2 catalysts, attributed to their highly ordered crystalline structure compared to that of typically synthesized IrO2 catalysts, is reflected by the observation that SUSD cycling of MEAs with the irr-IrO2 as anode co-catalysts does not result in iridium dissolution and the associated iridium poisoning of the Pt/C cathode catalyst.

High density iridium synergistic sites boosting CO-tolerate performance for PEMFC anode

The usage of cheap crude H2 in proton-exchange membrane fuel cells (PEMFCs) is still unrealistic to date, due to the suffering of the current Pt based nano-catalysts from impurities such as CO in anode. Recently, synergistic active sites between single atom (SA) and nanoparticle (NP) have been found to be promising for overcoming the poisoning problem. However, lengthening the nanoparticle-single atom (SA–NP) interface, i.e., constructing high density synergistic active sites, remains highly challenging. Herein, we present a new strategy based on molecular fusion strategy to create abundant SA–NP interfaces, with high density SA–NP interfaces created on a two dimensional nitrogen doped carbon nanosheets (Ir-SACs&NPs/NC). Owing to the abundance of SA–NP interface sites, the catalyst was empowered with a high tolerance towards up to 1000 ​ppm CO in H2 feed. These findings provide guidelines for the design and construction of active and anti-poisoning catalysts for PEMFC anode.

Towards bridging thermo/electrocatalytic CO oxidation: from nanoparticles to single atoms.

Proton exchange membrane fuel cells (PEMFCs), as a feasible alternative to replace the traditional fossil fuel-based energy converter, contribute significantly to the global sustainability agenda. At the PEMFC anode, given the high exchange current density, Pt/C is deemed the catalyst-of-choice to ensure that the hydrogen oxidation reaction (HOR) occurs at a sufficiently fast pace. The high performance of Pt/C, however, can only be achieved under the premise that high purity hydrogen is used. For instance, in the presence of trace level carbon monoxide, a typical contaminant during H2 production, Pt is severely deactivated by CO surface blockage. Addressing the poisoning issue necessitates for either developing anti-poisoning electrocatalysts or using pre-purified H2 obtained via a thermo-catalysis route. In other words, the CO poisoning issue can be addressed by either thermal-catalysis from the H2 supply side or electrocatalysis at the user side, respectively. In spite of the distinction between thermo-catalysis and electro-catalysis, there are high similarities between the two routes. Essentially, a reduction in the kinetic barrier for the combination of CO to oxygen containing intermediates is required in both techniques. Therefore, bridging electrocatalysis and thermocatalysis might offer new insight into the development of cutting edge catalysts to solve the poisoning issue, which, however, stands as an underexplored frontier in catalysis science. This review provides a critical appraisal of the recent advancements in preferential CO oxidation (CO-PROX) thermocatalysts and anti-poisoning HOR electrocatalysts, aiming to bridge the gap in cognition between the two routes. First, we discuss the differences in thermal/electrocatalysis, CO oxidation mechanisms, and anti-CO poisoning strategies. Second, we comprehensively summarize the progress of supported and unsupported CO-tolerant catalysts based on the timeline of development (nanoparticles to clusters to single atoms), focusing on metal-support interactions and interface reactivity. Third, we elucidate the stability issue and theoretical understanding of CO-tolerant electrocatalysts, which are critical factors for the rational design of high-performance catalysts. Finally, we underscore the imminent challenges in bridging thermal/electrocatalytic CO oxidation, with theory, materials, and the mechanism as the three main weapons to gain a more in-depth understanding. We anticipate that this review will contribute to the cognition of both thermocatalysis and electrocatalysis.

High CO and sulfur tolerant proton exchange membrane fuel cell anodes enabled by “work along both lines” mechanism of 2,6-dihydroxymethyl pyridine molecule blocking layer

Proton exchange membrane fuel cells (PEMFCs) are hindered by their poor tolerance to CO and H2S poisoning. Herein, we report an effective method, via engineering 2,6-dihydroxymethyl pyridine (DhmPy) molecule blocking layers on Pt surface, aiming to save the poisoning issue for PEMFC anode reaction. The PEMFCs assembled by this catalyst produce a power density of 1.18 W cm−2 @ 2.0 A cm−2 and 1.32 W cm−2 @ 2.0 A cm−2, far exceeding commercial Pt/C after H2/10 ppm CO poisoning and H2/5 ppm H2S poisoning tests, respectively. Density functional theory (DFT) indicates that a coronal molecule layer with a steric confinement height (1.82 Å), constructed by DhmPy, emerges more intensive adsorption energy compared to 2,6-pyridinedicarboxamide (DcaPy) and 2,6-diacetylpyridine (DAcPy), thereby more effectively inhibits the adsorption of large-sized CO and H2S on Pt surface without affecting H2 traverse. This “work along both lines” mechanism with the resistance of both CO and H2S provides a new and promising design thought for high CO and sulfur tolerant PEMFC anodes.

A hybrid combined heat and power system based on PEM fuel cell design for high-speed zero carbon service area

A combined heat and power system (CHPs) using proton exchange membrane fuel cells (PEMFC) as its primary energy output device is an attractive option due to its high electrical generation efficiency and low heat-to-power ratio. A hybrid PEMFC-based CHPs (PEMFC-CHPs) has been designed to provide both electricity and heat for a hydrogen high-speed service area. A comprehensive model of the system has been established and validated to analyze the impacts of key parameters such as PEMFC current density and anode hydrogen inlet pressure on the performance of hybrid PEMFC-CHPs. Evaluate and analyze the system from the perspectives of exergy, energy, and economy. The findings indicate that by fulfilling the service area's load demand, the thermal-led strategy can effectively prevent a waste of 670 kW of heat energy daily but exhibits a power shortage of 573.8 kW.

Anode Nitrogen Concentration Estimation Based on Voltage Variation Characteristics for Proton Exchange Membrane Fuel Cell Stacks

Hydrogen energy has become an important way to solve energy crises owing to its non-pollution, high level of efficiency, and wide application. Proton exchange membrane fuel cells (PEMFCs) have received wide attention as an energy conversion device for hydrogen energy. The hydrogen concentration in the PEMFC anode directly determines the output voltage of the stack. The performance of the PEMFC gradually decreases due to the accumulation of nitrogen. However, the continuous circulation of anode gas and the nitrogen accumulation at the anode due to transmembrane diffusion lead to difficulties in estimating the anode gas concentration. The relationship between anode nitrogen concentration and voltage variation characteristics was studied by increasing the anode hydrogen concentration through the method of increasing nitrogen concentration and conducting experiments on a 16-cell stack. In this paper, an estimation method for nitrogen concentration in the anode is proposed to evaluate the nitrogen concentration in the anode on the basis of voltage variation characteristics, and the method was recalibrated and validated using experimental data. Due to the inhomogeneity of the gas distribution within the PEMFC stack, the mean cell voltage can provide a more accurate estimation of the anode nitrogen concentration compared to a single cell voltage. It is shown that the proposed approach can offer a new method to estimate anode nitrogen concentration. Compared with the conventional method, the new method is simpler as it does not require additional equipment or complex algorithms. In this paper, the anode nitrogen concentration was estimated by applying this method with a maximum error of only 0.35%.

Effect of hydrogen impurities on hydrogen oxidation activity of Pt/C catalyst in proton exchange membrane fuel cells

AbstractHigh-purity of hydrogen is vital to the guarantee of end usage in proton exchange membrane fuel cell (PEMFC) electric vehicles (EVs) with superior durability and low expense. However, the currently employed hydrogen, primarily from fossil fuel, still contains some poisoning impurities that significantly affect the durability of PEMFCs. Here, we investigate the poisoning effect of several typical hydrogen impurities (S2–, Cl–, HCOO– and CO32–) on the hydrogen oxidation reaction (HOR) of the state-of-the-art carbon-supported platinum (Pt/C) catalyst used in the PEMFC anode. Electrochemical results indicate that the electrochemically active surface area of Pt/C is hampered by these hydrogen impurities with reduced effective Pt reactive sites due to the competitive adsorption against hydrogen at Pt sites showing the extent of the poisoning on Pt sites in the order: S2– > Cl– > HCOO– > CO32–. Density functional theory calculations reveal that the adsorption energy of S2– on Pt (111) is greater than that of Cl–, HCOO– and CO2, and the electronic structure of Pt is found to be changed due to the adsorption of impurities showing the downshift of the d-band centre of Pt that weakens the adsorption of hydrogen on the Pt sites. This work provides valuable guidance for future optimization of hydrogen quality and also emphasizes the importance of anti-poisoning anode catalyst development, especially towards H2S impurities that seriously affect the durability of PEMFCs.

Nonlinear model predictive control of PEMFC anode hydrogen circulation system based on dynamic coupling analysis

Anode hydrogen circulation system with purge valve has become one of the most effective ways for proton exchange membrane fuel cell (PEMFC) to alleviate performance degradation caused by nitrogen permeation and improve the hydrogen utilization rate. However, nonlinearity and multivariable coupling of the system make it difficult for PEMFC to achieve pressure and hydrogen supply synchronous tracking under complex operating conditions. To solve the problem, a novel nonlinear model predictive control scheme based on coupling analysis is proposed in this paper. Firstly, coupling characteristics of the hydrogen circulation system and the control pairing of the multivariable system are analyzed based on the relative gain array method. Then a novel control scheme based on an adaptive model predictive controller and a nonlinear model predictive controller is designed to keep the anode pressure stable and sufficient hydrogen supply, which use nonlinear observers to estimate the internal states online. Finally, the proposed controllers are implemented in control experiments of a 50 kW PEMFC anode hydrogen circulation system. The results demonstrate that the proposed control approach has great dynamic performance, anti-disturbance ability and can maintain a high hydrogen utilization rate under purge operation, current disturbance and uncertain intake pressure.

Intriguing H2S Tolerance of the PtRu Alloy for Hydrogen Oxidation Catalysis in PEMFCs: Weakened Pt-S Binding with Slower Adsorption Kinetics.

High quality of hydrogen is the key to the long lifetime of proton-exchange membrane fuel cell (PEMFC) vehicles, while trace H2S impurities in hydrogen significantly affect their durability and fuel expense. Herein, we demonstrate a robust PtRu alloy catalyst with an intriguing H2S tolerance as the PEMFC anode, showing a stronger antipoisoning capability toward hydrogen oxidation reaction compared with the Pt/C anode. The PtRu/C-based single PEMFC shows approximately 14.3% loss of cell voltage after 3 h operation with 1 ppm of H2S in hydrogen, significantly lower than that of Pt/C-based PEMFCs (65%). By adopting PtRu/C as the anode, the H2S limit in hydrogen can be increased to 1.7 times that of the Pt/C anode, assuming that the PEMFC runs for 5000 h, which is conductive for the cost reduction of hydrogen purification. The three-electrode electrochemical test indicates that PtRu/C exhibits a slower adsorption kinetics toward S2- species with poisoning rates of 0.02782, 0.02982, and 0.03682 min-1 at temperatures of 25, 35, and 45 °C, respectively, all lower than those of Pt/C. X-ray absorption fine structure spectra indicate the weakened Pt-S binding for PtRu/C in comparison to Pt/C with a longer Pt-S bond length. Density functional theory calculation analyses reveal that adsorption energy of sulfur on the Pt surface was reduced for PtRu/C, showing 1-10% decrease at different Pt sites for (111), (110), and (100) planes, which is ascribed to the downshifted Pt d-band center caused by the ligand and strain effects due to the introduction of second metallic Ru. This work provides a valuable guide for the development of the H2S-tolerant catalysts for long-term application of PEMFCs.

CrN Coating on 316L Stainless Steel via Inductively Coupled Plasma‐Enhanced Magnetron Sputtering as Bipolar Plates for Proton‐Exchange Membrane Fuel Cells

Herein, CrN monolayer films are deposited on 316L stainless steel (316LSS) via inductively coupled plasma (ICP)‐enhanced magnetron sputtering technology to compensate the defects of bare 316LSS in an acidic, hot, and humid proton‐exchange membrane fuel cell (PEMFC) environment. To assess the anticorrosive performance and conductivity of CrN‐coated 316LSS, the electrochemical behavior and interfacial contact resistances (ICRs) of samples are measured before and after the modification. The results of the potentiodynamic polarization test show that CrN‐coated 316LSS possesses high anticorrosion performance according to the ultralow corrosion current density of 0.094 and 0.078 μA cm−2 under the imitated PEMFC anode and cathode environments, respectively. These values are far below the USA Department of Energy's requirements of <l μA cm−2. In addition, the ICR of CrN‐coated 316LSS also satisfies the DOE's target (<10 mΩ cm2), which is obtained to be 7.8 mΩ cm2 under 140 N cm−2. Through analysis of potentiostatic polarization and electrochemical impedance spectroscopy, it suggests that CrN‐coated 316LSS combines better long‐term stability under the working voltages of two electrodes in PEMFCs with better electrochemical impedance than bare 316LSS. Consequently, CrN coating on 316LSS via ICP‐enhanced magnetron sputtering technology can be potentially suitable for bipolar plate applications in PEMFCs.

Irreducible IrO2 Anode Co-Catalysts for PEM Fuel Cell Voltage Reversal Mitigation and Their Stability Under Transient Operation Conditions

The cell voltage reversal that can occur during the transient operation of a proton exchange membrane fuel cell (PEMFC) stack leads to a substantial degradation of the anode catalyst. During cell reversal, the anode potential increases (>>1 V vs. the reversible hydrogen electrode potential (RHE)), causing severe oxidation of the anode catalyst carbon support, which leads to a collapse of the anode catalyst layer and to cell failure. One strategy to mitigate the damages of H2 starvation is the addition of a co-catalyst to the anode electrode, which catalyzes the oxygen evolution reaction (OER), so that the non-damaging OER rather than the damaging carbon oxidation reaction (COR) takes place. A commonly used anode co-catalyst to favor the OER over the COR during cell reversal events is iridium oxide (IrO2).1 Recent findings show that the near-surface layer(s) of IrO2 can be completely reduced to metallic Ir upon exposure to H2, e.g., under the operating conditions of a PEMFC anode.2, 3 Such alteration of the near-surface layer(s) of IrO2 drastically affects its stability during the anode potential transients that occur during start-up/shut-down (SUSD) events, where our recent study showed that the dissolution of metallic Ir and crossover of the dissolved Irn+ species through the membrane to the cathode electrode cause iridium deposition on the Pt/C cathode catalyst.3 Such iridium-based contamination on the cathode catalyst surface deteriorates the oxygen reduction reaction (ORR) activity of Pt and results in a significant performance loss during the normal operation of the fuel cell. At the same time, SUSD transients also cause an OER activity loss of the anode co-catalyst, which was shown to be mainly due to the redeposition of Pt dissolved from the anode hydrogen oxidation reaction (HOR) catalyst onto the reduced IrO2 anode co-catalyst, blocking its OER active sites.3 Since these degradation mechanisms are caused by the chemical reduction of the typically employed IrO2 anode co-catalysts in the PEMFC anode, a reduction-resistant OER catalyst would be required.In this contribution, we introduce an unprecedented approach to synthesize IrO2 catalysts that are not reduced in the PEMFC anode environment. The preparation of such irreducible IrO2 (Irr-IrO2) catalysts is based on an industrially scalable procedure consisting of a high-temperature (650-1000 ᵒC) heat treatment step followed by a deagglomeration step and a post annealing step to prepare catalyst powders with specific surface areas of ~25 m2/g. Figure 1 shows the thermogravimetric analysis (TGA) according to our previously proposed evaluation protocol3 under 3.3 vol.% H2/Ar of an as-received commercial benchmark catalyst (IrO2/TiO2 (Umicore)), a self-made IrO2 catalyst heat-treated near the conventional temperature of 500 °C (IrO2-500 °C), and a stabilized IrO2 catalyst prepared by a procedure introduced in this contribution (Irr-IrO2). It can be seen that the temperature that corresponds to the reduction of 20% of the IrO2 phase (α = 20%) of the Irr-IrO2 catalyst is ~38 °C and ~53 °C higher than those of the IrO2-500 °C and the IrO2/TiO2 (Umicore) catalysts, respectively. Considering the fact that all of these catalysts have a specific surface area of ~25 m2/g, the observed reductive stability improvement of Irr-IrO2 catalyst is due to its intrinsic structural distinctions from the typically synthesized IrO2 and the commercial benchmark IrO2 catalysts. As will be shown, this higher stability is reflected by the observation that SUSD cycling of MEAs with the Irr-IrO2 as anode co-catalyst does not result in iridium dissolution and the associated iridium poisoning of the ORR activity of the cathode catalyst. Furthermore, while its OER activity is lower than that of conventional IrO2 catalysts, it still dramatically increases the cell reversal tolerance time of a conventional Pt/C anode. References T. R. Ralph, S. Hudson, and D. P. Wilkinson, ECS Transactions, 1 (8), 67-84 (2006).P. J. Rheinländer and J. Durst, Journal of the Electrochemical Society, 168 (2), 024511 (2021).M. Fathi Tovini, A. M. Damjanovic, H. A. El-Sayed, J. Speder, C. Eickes, J.-P. Suchsland, A. Ghielmi, and H. A. Gasteiger, Journal of The Electrochemical Society, 168 (6), 064521 (2021). Figure 1. TGA (5 K min-1) experiments under 3.3 vol.% H2/Ar with the as-received IrO2/TiO2 (Umicore), the IrO2-500 °C, and the Irr-IrO2 catalyst powder samples (following a drying/cleaning step; see Ref. 3 for further details). The y-axis represents the fraction of the IrO2 phase in the catalyst powder samples that is reduced to metallic Ir (α). The black horizontal dashed line illustrates a reaction extent of α= 20%, to compare the stability of different samples in a H2-containing atmosphere. Figure 1

Nb–Cr–C coated titanium as bipolar plates for proton exchange membrane fuel cells

Herein, a ternary Nb–Cr–C film is successfully prepared by arc ion plating for surface modification of titanium using as proton exchange membrane fuel cell (PEMFC) bipolar plates. Film morphology, composition as well as corrosion behavior, conductivity and performance of single cell are investigated. As results revealed, the Nb–Cr–C film is about 500 nm thick without obvious defects. Compared with the bare titanium, the corrosion current density of Nb–Cr–C coated titanium lowered to 0.022 μA/cm 2 and -0.051 μA/cm 2 in simulated PEMFC cathode and anode environments, respectively, accompanied with the interfacial contact resistance lowered to 1.15 mΩ cm 2 , indicating outstanding anti-corrosion and conductivity performance. The single cell with Nb–Cr–C coated titanium bipolar plates reaches its peak power density 1.167 W/cm 2 at 2.2 A/cm 2 , which is comparable with that of graphite bipolar plates and apparently better than that of bare titanium bipolar plates. The remarkable improvements in both ex-situ tests and single cell tests suggest that the Nb–Cr–C coated titanium might be a proper material for PEMFC bipolar plates. • A novel Nb–Cr–C film is designed to modify titanium for PEMFC bipolar plates. • Corrosion current density at 0.6 V in cathode is 0.022 μA/cm 2 . • ICR with carbon paper at 1.5 MPa is 1.15 mΩ cm 2 .

Highly-integrated and Cost-efficient Ammonia-fueled fuel cell system for efficient power generation: A comprehensive system optimization and Techno-Economic analysis

Ammonia (NH3) has been considered as a promising hydrogen storage media due to the features of low saturated vapor pressure at room temperature, high hydrogen content, low costs of transportation and storage, and carbon-free emission·NH3 can decompose into a gaseous mixture compromising of 75 vol% H2 and 25 vol% N2 in an NH3 decomposition reactor, which can integrate with a proton exchange membrane fuel cell (PEMFC) into one compact system, called as an indirect ammonia PEMFC (IA-PEMFC) system. IA-PEMFC systems are applicable for distributed power systems, vehicle and marine applications. In this study, we develop a physical–chemical model of an IA-PEMFC system, and perform a comprehensive techno-economic analysis to optimize IA-PEMFC system layout and improve its energetic, exergetic and economic performance. Results indicate that using our self-developed Ru/C NH3 decomposition catalyst can reduce operating temperature to less than 500 °C with remarkable stability, at least 300 °C lower than current commercially-available Ni-based catalyst, which can help the IA-PEMFC system to save heat supply by 29%, leading to an improvement of 2 points of percentage in energy efficiency. Recycling and burning tail gas from PEMFC anode are an effective pathway for better heat integration, and can significantly enhance system efficiency by about 11% to 56.1% when average cell voltage is 0.7 V. An auto-thermal reactor integrating NH3 decomposition and H2 catalytic combustion can further improve system efficiency by 0.5 points of percentage to 56.6%, and the exergy efficiency increases to 49% correspondingly. Economic estimation reveals fuel cost of our optimized IA-PEMFC system reaches 0.13 $/kWh for power generation and 0.024 $/km for vehicle application, respectively. In contrast, a carbon-free IA-PEMFC system is more economically efficient than ones using gasoline-fueled heat engines and H2-fueled PEMFC, and highly competitive in both energy efficiency and economic feasibility to indirect methanol PEMFC system (with end-user CO2 emission).

Corrosion and interfacial contact resistance of nanocrystalline β-Nb2N coating on 430 FSS bipolar plates in the simulated PEMFC anode environment

The corrosion of metallic bipolar plates in the proton exchange membrane fuel cells (PEMFCs) anode environment would degrade the performance and shorten the lifespan of the fuel cell. Hence, it is essential to develop a conductive coating with good corrosion resistance. Herein we demonstrate a dense, defect-free, and well-adhered nanocrystalline β-Nb2N coating prepared on 430 ferritic stainless steel (430 FSS) via disproportionation of Nb(Ⅳ) species in molten salts. The corrosion mechanism of bare and β-Nb2N coated 430 FSS in the simulated PEMFC anode environment is also studied by electrochemical techniques including potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy. Results show that β-Nb2N coating can significantly improve the corrosion resistance of the steel alloy with acceptable contact resistance. In addition, no obvious degradation is observed for the β-Nb2N coating after potentiostatic polarization measurement for 500 h. This work offers a promising strategy to develop the corrosion protective coating on metallic bipolar plates for PEMFCs.

PEMFC Anode Durability: Innovative Characterization Methods and Further Insights on OER Based Reversal Tolerance

Durability is a major lever for commercial success of proton exchange membrane fuel cells (PEMFCs). The introduction of OER catalyst to the PEMFC anode has been established as a material based mitigation strategy for reversal events caused by gross fuel (i.e. H2) starvation. We investigated the degradation of two different OER based reversal tolerant anodes during short-term recurring reversal operation to mimic field occurrence of reversal events realistically. PEMFC failure during normal operation can be observed whereas OER activity during reversal operation is unaffected. This result is in contrast to findings for commonly applied prolonged reversal accelerated stress tests (ASTs) and indicates an OER catalyst recovery effect for short and recurring reversal events. Combining the developed AST with cyclic voltammetry, electrochemical impedance spectroscopy and hydrogen pump, tests failures during normal operation is mainly assigned to hydrogen oxidation mass transfer increase indicating carbon corrosion and structural change within the anode catalyst layer. Consequently, the developed combination of AST and further characterization methods enables in situ distinction between catalyst and structural degradation, highlighting to be a good basis to investigate future aspects regarding anode degradation caused by cell reversal.

(Invited) Updated Catalyst Activity Targets for Performance Parity in Hydroxide Exchange Membrane Fuel Cells

The critical importance of power density on fuel cell system cost is well-recognized within the low-temperature fuel cell community. By increasing the required active area of the stack, a low-cost, low-performance component can increase the cost of other major stack components and increase system cost. The cost of platinum-group-metal (PGM) catalysts is a substantial barrier to reaching the long-term U.S. Department of Energy cost target of $30 / kW for automotive proton exchange membrane fuel cell (PEMFC) systems. Hydroxide exchange membrane fuel cells (HEMFCs) offer a possibly pathway to PGM-free catalysis in low-temperature fuel cells, among other potential cost benefits. However, only 35% of PEMFC stack cost is due to PGMs1. Therefore, as a first approximation, we believe the appropriate target for low-PGM or PGM-free HEMFCs is performance parity with state-of-the-art PEMFCs2. Performance parity ensures that catalyst cost savings pass through to the system level, justifying investment in an unproven competitor to the incumbent PEMFC. Although PGM-free catalyst loadings may be relatively unconstrained by economics, transport still places an upper bound on the loading that can be utilized at high current densities. For high catalyst loadings, the most important considerations are ionic conduction through the electrode ionomer and reactant diffusion through the catalyst layer pores. Making reasonable baseline assumptions for effective conductivity and diffusivity, as well as the area-specific resistance, activity targets can be derived for PGM-free catalysts to enable performance-parity with PEMFCs. Comparing reported PGM-free catalysts to these targets, it is clear that progress is needed in both anode and cathode catalysts (Figure 1). Interestingly, the derived target for PGM-free cathode catalysts exceeds the performance of Pt/C considerably. To reach performance parity, any additional mV of overpotential must be compensated by reductions elsewhere. Because the PEMFC anode operates at near-zero overpotential, an unlikely feat for PGM-free catalysts, the HEMFC must compensate for this extra loss at the cathode. In the long-term, the major challenge to achieving high-performance PGM-free HEMFCs is the anode catalyst. Relatively few reports of PGM-free hydrogen oxidation reaction (HOR) catalysts have been made, although many have reported hydrogen evolution reaction (HER) catalysts. The reason for this discrepancy is the tendency of nickel-based catalysts to oxidize and become deactivated at potentials only slightly higher than RHE. In the short-term, the most urgent need for HEMFC catalyst development is a high-performance PGM-free cathode catalyst. On the anode side, PtRu/C offers volumetric activity several times higher than the target for PGM-free catalysts, making low-loading PGM anodes a viable option. Low-loading Pt-alloy cathodes are a less attractive option, given the likely challenges of local oxygen transport and catalyst stability. If only the cathode target can be met, HEMFCs can still reach the important milestone of PEMFC performance parity at equal or lower PGM loading. References B. D. James, J. M. Huya-Kouadio, C. Houchins, and D. A. DeSantis, Mass Production Cost Estimation of Direct H2 PEM Fuel Cell Systems for Transportation Applications: 2017 Update, Arlington, VA, (2017).B. P. Setzler, Z. Zhuang, J. A. Wittkopf, and Y. Yan, Nat. Nanotechnol., 11, 1020–1025 (2016). Figure 1

Carbon Corrosion in Proton-Exchange Membrane Fuel Cells: Spectrometric Evidence for Pt-Catalysed Decarboxylation at Anode-Relevant Potentials.

The carbon oxidation reaction (COR) is a critical issue in proton-exchange membrane fuel cells (PEMFCs), as carbon in various forms is the most used electrocatalyst support material. The COR is thermodynamically possible above the C/CO2 standard potential, but its rate becomes significantly important only at high overpotential (e. g. PEMFC cathode potential). Herein, using on-line differential electrochemical mass spectrometry, we show that oxygen-containing carbon surface groups present on high-surface aera carbon, Vulcan XC72 or reinforced graphite are oxidized at PEMFC anode-relevant potential (E=0.1 V vs. the reversible hydrogen electrode, RHE), but not at E=0.4 V vs. RHE. We rationalized our findings by considering a Pt-catalysed decarboxylation mechanism in which Pt nanoparticles provide adsorbed hydrogen species to the oxygen-containing carbon surface groups, eventually leading to evolution of carbon dioxide and carbon monoxide. These results shed fundamental light on an unexpected degradation mechanism and facilitate the understanding of the long-term stability of PEMFC anode nanocatalysts.

Pt/C catalyst impregnated with tungsten-oxide – Hydrogen oxidation reaction vs. CO tolerance

Hydrogen Oxidation Reaction (HOR) is anode reaction in Proton exchange membrane fuel cells (PEMFCs) and it has very fast kinetics. However, the purity of fuel (H2) is very important and can slow down HOR kinetics, affecting the overall PEMFC performance. The performance of commercial Pt/C catalyst impregnated with WOx, as a catalyst for HOR, was investigated using a set of electrochemical methods (cyclic voltammetry, linear scan voltammetry and rotating disk electrode voltammetry). In order to deepen the understanding how WOx species can contribute CO tolerance of Pt/C, a particular attention was paid to CO poisoning. In the absence of CO, HOR is under diffusion limitations and HOR kinetics is not affected by WOx species. Appreciable HOR current on the electrodes pre-saturated with COads at potentials above 0.3 V vs. RHE, which is not observed for pure Pt/C, was discussed in details. HOR liming diffusion currents for higher concentrations of W are reached at high anodic potentials. The obtained results were explained by donation of OHads by WOx phase for COads removal in the mid potential region and reduced reactivity of Pt surface sites in the vicinity of the Pt|WOx interface. The obtained results can provide guidelines for development of novel CO tolerant PEMFC anode catalysts.

Performance improvement in a proton exchange membrane fuel cell with separated coolant flow channels in the anode and cathode

Thermal management is critical for improving the performance of a proton exchange membrane fuel cell (PEMFC). Operation temperature can directly affect the saturated water vapour pressure and thus the water transport between the anode and cathode in PEMFCs. However, current researches on the effect of operation temperature on the performance are based on convenient design of a joint coolant flow channel for the anode and cathode. Consequently, the independent effect of the temperature on the anode or cathode is ignored. In this study, a single PEMFC with separated coolant flow channels in the anode and cathode is fabricated to investigate the effects of different anode and cathode operation temperatures on the performance. The results show that different anode and cathode operation temperatures could affect the performance of PEMFCs. A lower anode temperature improved the electro-osmotic drag role of water transport from anode to cathode. Hence, the PEMFC performance increased both with the increasing cathode operation temperature and the temperature differences between the cathode and anode. Higher operation temperature improves the activity of the catalyst, and water management and elevated operation pressure affect the kinetics of the electrochemical reaction. Peak performance is obtained through the balance of operation temperature, pressure and water management, particularly for different anode and cathode operation temperatures of PEMFCs.

X-Ray Absorption Study of Sputtered Pt-CeO2 Catalyst Used in PEM-FC

The proton exchange membrane fuel cell (PEMFC) is supposed to be an environmentally friendly near-future power source for mobile devices. The crucial problem in the fuel cell technology field is the finding of a stable, efficient and economical catalyst for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) at working conditions of PEMFC. The Pt catalyst, which is widely used due to fact that this catalyst is only really functional enough, is an expensive material. Moreover, unfortunately all of the less expensive Platinum bimetallic alloys as ORR catalysts enhancing the activity rapidly degrade in acidic environment and ORR condition [1]. We have already shown that Pt-CeO2sputtered catalyst exhibits high specific power (thousand-times higher power per mg of platinum and only few times lower power density in comparison with Pt reference catalyst) so such material could be an appropriate for PEMFC anode (HOR) [2,3,4]. Presented work is aimed for understanding the role of Pt and Ce chemical states and Pt-Ce interactions in HOR and ORR catalytic activity investigated in-situ using X-ray Absorption Near Edge Structure (XANES). Additionally, the performance and endurance of this catalyst obtained through direct testing in fuel cell test station are presented. Then, morphology determined by scanning electron microscopy and photoelectron spectroscopy results is shown. [1] G.-F. Wei et al., Energy Environ. Sci.,4(2011) 1268 [2] R. Fiala et al., J. Nanosci. Nanotechnol.,11 (2011) 5062–5067 [3] V. Matolin et al., Langmuir, 26 (2010) 12824–12831 [4] V. Matolin et al., Int. J. Nanotechnol., 9 (2012) 680–694 Figure 1