Single Cell Proton Exchange Membrane Fuel Cells Research Articles

Synthesis of low cost cathode electrocatalyst Pt‐Ni/CAB using DMSO as a solvent for low temperature proton exchange membrane fuel cell application

AbstractIn the present study, low cost platinum based bimetallic electrocatalyst Pt‐Ni/CAB with varying Pt to Ni atomic ratios 3:1, 1:1, and 1:3 were successfully synthesized for oxygen reduction reaction (ORR) of the developed proton exchange membrane fuel cell (PEMFC). The solvothermal process was adopted for the synthesis of Pt‐Ni(3:1)/CAB, Pt‐Ni(1:1)/CAB, and Pt‐Ni(1:3)/CAB using dimethyl sulfoxide (DMSO) as solvent at a temperature of 190°C which is very close to the boiling point. The Pt‐Ni/CAB exhibited the highest activity for the ORR in half‐cell and single cell PEMFC performance. The electrocatalysts Pt‐Ni(1:3)/CAB appeared with smallest crystalline FCC structures having crystallite size of 8.33 nm. The transmission electron microscopy (TEM) analysis also show that the Pt‐Ni(1:3)/CAB has smallest particle size of 1.67 ± 0.45 nm. The cyclic voltammetry (CV) analysis shows Pt‐Ni(1:3)/CAB electrocatalyst offers less activation loss at ORR peak at a potential of 0.16 V as compared to Pt‐Ni(3:1)/CAB (ORR peak – 0.12) and Pt‐Ni(1:1)/CAB (ORR peak – 0.11). The synthesized Pt‐Ni(1:3)/CAB produced a maximum power density of 18.86 mW/cm2 at a maximum current density of 44.8 mA/cm2 with an open‐circuit voltage of 0.914 V at a room temperature of 33°C. The power density improved around 1.34 times when the cell temperature was raised from 33 to 70°C. The Pt‐Ni(1:3)/CAB cathode electrocatalyst could be used as economical to substitute costly commercial pure platinum based electrocatalyst.

Bio-inspired sinusoidally-waved flow fields with exchange channels to enhance PEMFC performance

Wave-shaped structures inspired by cuttlefish fins have been applied to the design of flow fields for proton exchange membrane fuel cells (PEMFCs). However, the wave structures often cause high parasitic power. Herein, we intend to address this issue by introducing exchange channels (ECs) between neighboring wave channels. First, the performances of bio-inspired sinusoidally-waved flow fields (BSWFFs) of different sinusoidal parameters are compared to identify the optimal sinusoidal structure. Subsequently, ECs are introduced into BSWFFs with the optimal sinusoidal structure to obtain EC-BSWFFs, and EC-BSWFFs with different numbers of ECs are compared. The introduction of ECs improves the distribution of reactant gases, pressure distribution, water management and reduces parasitic power density. Specifically, the maximum net power density of the single-cell PEMFC with EC-12 is enhanced by 10.26% compared to that of the conventional parallel flow field. Moreover, as the number of ECs in EC-BSWFFs increases, the uniformity of pressure distribution gradually increases and the pressure drop becomes smaller, suggesting a balance between performance and durability. Therefore, this work affords valuable insights to solve the difficulties of excessive pressure drop and inhomogeneous reactant distribution for waved flow fields.

Scalable Synthesis of Stable Electrocatalyst for Oxygen Reduction Reaction

Carbon-based materials have been widely recognized as support material of choice for the oxygen reduction reaction due to their intriguing properties, such as high electrical conductivity, structural flexibility, and low cost. Platinum and its alloys supported on carbon are currently considered the benchmark catalysts for the oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cells (PEMFCs). Confining platinum within the pore system of mesoporous carbon prepared by hard-templating has proven to be an effective way to mitigate catalyst degradation in PEMFCs.[1] However, the challenge of template removal and the limited yield have hindered its practical application in industry. As a remedy, we establish a simple synthesis of carbon gels through sol-gel polymerization of resorcinol (R) and formaldehyde (F), ultimately resulting in graphitic mesoporous carbons.The synthesis process involves mixing resorcinol and formaldehyde in the presence of a basic catalyst, followed by heating for a certain period of time to obtain crosslinked gels.[2] Specific metal salts can be incorporated into the reaction to synthesize mesoporous and highly graphitic carbon spheres (GRF-Sphere) in a straightforward manner, without the need for hydrothermal steps, solvent exchanges, supercritical drying, or post-activation techniques. While conventional carbonized RF spheres are typically non-graphitic and microporous (Fig. 1.), modification of the synthesis route allows for the production of mesoporous, highly graphitic carbon spheres (GRF-Sphere) by taking advantage of the porogenic and graphitization effect of Fe(acac)2. Platinum nanoparticles with an average size of ca. 3 nm were deposited into the pores of GRF-spheres by incipient wetness impregnation followed by annealing at 750 °C. The specific activity of the Pt/GRF-Sphere catalyst for the ORR was found to be greater than 0.45 mA cm-2 Pt at 0.9 V vs. RHE, which in comparison with the literature indicates high catalytic activity.[3] The confinement of the active phase within the pores of the GRF-Spheres contributed to enhancing the stability of the catalyst, as confirmed by an accelerated stress test performed within the typical operating range of a PEMFC (0.6 - 1.0 VRHE). The Pt/GRF-Sphere was found to retain a significantly higher proportion of active surface area when compared to a reference Pt/Vulcan catalyst with similar platinum particle size (Fig. 1.).Furthermore, increasing the concentrations of resorcinol and formaldehyde by 25-fold resulted in the synthesis of a mesoporous and highly graphitic gel, namely GRF-Gel, at a substantial volume yield of70 g L-1, which underlines the potential for this process to be scaled up for industrial application. The ORR activity and stability of GRF-Gel in RDE are currently being investigated. Moreover, the electrochemical performance of this material will be evaluated in a single-cell PEMFC in collaboration with the group of Prof. Hubert Gasteiger (TU Munich).Overall, this research provides a promising and straightforward approach to synthesize highly graphitic mesoporous carbon materials using iron acetylacetonate as a porogen and graphitization catalyst. The method is based on the established preparation of RF-gels but includes iron salts. We have demonstrated that Pt/GRF-Sphere, which is produced by depositing Pt nanoparticles into the pore system of the GRF-Sphere, exhibits high activity and stability for the ORR. Given the simplicity and scalability of our synthesis procedure and the tailored morphology of these carbon materials, we believe that Pt/GRF-Sphere and Pt/GRF-Gel have great potential for industrial applications. Acknowledgement: We acknowledge the financial support from the German Federal Ministry for Economic Affairs and Energy (BMWi) in the framework of POREForm (project number 03ETB027F).

Investigating the Suitability of Printed Circuit Components for Fuel Cells

Flexible electrochemical energy sources using non-traditional cell materials and topologies have attracted growing attention because they offer unique design opportunities that are still being explored. They also offer potential advantages such as conformability, high power density, high specific power, and low cost through the adoption of electronics manufacturing techniques. This study examines the feasibility of using flexible printed circuits boards (PCBs) as the anode and cathode current collectors (CCs) of single cell Proton Exchange Membrane Fuel Cell (PEMFCs). In this work, we determine the best anode and cathode interfaces at which to embed flexible CCs to obtain the highest power, as illustrated in Figure 1. The flexible anode and cathode CCs are embedded A) inside the PEM|Catalyst Layer (CL) interface, B) between the CL|Micro Porous Layer (MPL) interface and C) between the Gas Diffusion Layer (GDL)| Flow field (FF) interface. The performance of the single cell PEMFC with the embedded flexible anode and cathode CCs at the different interfaces described in Figure 1 is investigated by using I-V polarization curves, electrochemical impedance spectroscopy (EIS), and thermal imaging. The performance of the cells tested with the embedded flexible CCs is compared to the performance of a standard cell. This study also investigates the effect of varying the anode and cathode CC geometry (square shape vs. circular) and opening ratio (20%, 30%, 40%, 50% and 60%) on the cell performance. Figure 1

Accelerated Stress Tests to Project PEM Fuel Cell Durability

One of the major degradation mechanisms limiting the long-term durability of proton exchange membrane fuel cells (PEMFCs) is the loss of platinum electrochemically active surface area (ECSA) of the carbon-supported platinum (Pt/C) cathode catalyst, caused by Pt dissolution that is followed by both Ostwald ripening of the Pt nanoparticles and loss of Pt into the ionomer phase [1]. The Pt ECSA loss is accelerated when subjecting PEMFCs to extended load-cycling inducing concomitant cycling of the cathode potential. To this end, accelerated stress tests (ASTs) can be conducted either by controlling the cell/stack current (“load-cycling” AST) under H2/air (anode/cathode) or the potential (“voltage-cycling” AST) under H2/N2 (anode/cathode).Most of the experiments studying the effect of load-cycling on catalyst durability have been based on voltage-cycling in a H2/N2 configuration, showing that Pt ECSA loss is aggravated with increasing upper potential limit (UPL), temperature, and relative humidity (RH) [2, 3, 4]. Comparing voltage-cycling induced degradation under H2/N2 versus H2/air, a recent study has found an essentially identical Pt ECSA loss, but a slightly higher H2/air performance decay when cycling under H2/N2 [4]. This study by General Motors Corporation indicates that Pt ECSA loss may not be a unique descriptor for H2/air performance loss, contrary to what was observed in recent work by Toyota Motor Corporation and Kyushu University [5] as well as in our own studies [6].In this talk, we will discuss the correlation between H2/air performance loss and Pt ECSA loss during voltage-cycling ASTs at different conditions (UPL, RH, and gas-feed) conducted in 5 cm2 active area single-cell PEMFCs, complemented by a voltage-loss analysis to deconvolute oxygen reduction reaction (ORR) activity losses and mass transport losses (due to oxygen mass transport and proton conduction in the cathode catalyst layer). We will also discuss whether the H2/air performance loss is governed by the Pt ECSA loss (independent of catalyst loading) or, as we had proposed previously, by the cathode electrode roughness factor (rf) loss (in cm2 Pt/cm2 cathode, i.e., the product of ECSA and Pt loading) [7]. As roughly 100,000 [8] or even more voltage-cycles are expected for heavy-duty applications, requiring very long measurement times, an approach to relate the degradation under harsh AST conditions with those under application-relevant conditions will be discussed. Experiments are conducted with cathode catalysts based on different carbon supports (Vulcan, Ketjenblack, or so-called accessible carbon supports [9, 10]), on catalysts with different initial Pt ECSAs (i.e., different Pt nanoparticle sizes) and with different initial Pt-loadings (i.e. different initial rf). Finally, exploratory experiments to evaluate the effect of start-up/shut-down on the correlation between electrode rf and H2/air performance decay will be discussed.

ORR Activity and Voltage-Cycling Stability of a Carbon-Supported PtxY Alloy Catalyst Evaluated in a PEM Fuel Cell

Platinum-yttrium alloys (PtxY) are suggested to have superior oxygen reduction reaction (ORR) activity and long-term stability in proton exchange membrane fuel cells (PEMFCs). However, the actual ORR activity and stability of a PtxY catalyst with a high electrochemically active surface area (ECSA) in a PEMFC remains uncertain. Here, a Ketjen black (KB) carbon supported PtxY/KB catalyst with a high ECSA (∼60 m2/g) was synthesized using a carbon nitride precursor. Based on elemental analysis, XRD, electron microscopy, and a mass-balance based model, it was shown that the acid-leached PtxY nanoparticles of the catalyst consist of a ∼0.7 nm thick Pt-shell and a Pt3Y core. Rotating disk electrode (RDE) and 5 cm2 single-cell PEMFC measurements indicated that the ORR activity of the acid-leached PtxY/KB catalyst is similar to an analogously synthesized Pt/KB reference catalyst with the same ECSA. Voltage-cycling accelerated stress tests (ASTs) between 0.6−1.0 V (in H2/N2 at 80 °C/95% RH) in 5 cm2 single-cells showed that the ORR activity and durability of the PtxY/KB catalyst is similar to that of the Pt/KB reference catalyst. Thus, the high durability of Pt-rare Earth alloys that has been claimed on the basis of RDE measurements is not observed in actual PEMFCs.

Impact of Accelerated Stress Tests on the Cathodic Catalytic Layer in a Proton Exchange Membrane (PEM) Fuel Cell Studied by Identical Location Scanning Electron Microscopy

Platinum is the most used electrocatalyst in proton exchange membrane fuel cells (PEMFCs). Nonetheless, it suffers from various types of degradation. Identical location electron microscopy has previously been used to observe local catalyst changes under accelerated stress tests (ASTs), giving insight into how individual catalyst particles degrade. However, it is important that such studies are carried out under relevant reaction conditions, as these can differ substantially between liquid half-cells and real PEMFC conditions. In this work, a single cell PEMFC was used to study the degradation of a commercial Pt-catalyzed membrane electrode assembly by performing square wave voltage ASTs in a potential range of 0.6 to 1.0 V. Identical location scanning electron microscopy (IL-SEM) was used to follow the degradation of the cathodic catalytic layer (CL) throughout 14,000 AST cycles. From the IL-SEM, we can conclude that the Pt nanoparticles degrade via Ostwald ripening, crystal migration, and coalescence. Small Pt nanoparticles agglomerate to larger particles or dissolve and redeposit to more stable particles, increasing the average particle size during the ASTs. In addition, cross-sectional TEM images show thinning of the ionomer layer during the AST procedure. The IL-SEM technique facilitates observation of local degradation of the CL in real PEMFCs, which will help to understand different degradation mechanisms, allowing for better solutions to be designed.

VALIDATION OF SEMI-EMPIRICAL TEMPERATURE MODEL OF PEMFC USING ATOM SEARCH OPTIMIZATION ALGORITHM

Proton Exchange Membrane Fuel Cell (PEMFC) has unique thermal characteristics. The change in PEMFC temperature directly effects the PEMFC performance. The voltage and temperature of PEMFC at different loading/ambient conditions is not easy to predict. In this work a newly developed semi-empirical model is used and the parameters of the model are optimized for single cell PEMFC (base-case) by using atom search optimization. The semi-empirical model was developed and tested for stack PEMFC system but any model developed for PEMFC cannot be validated unless it is effective for single-cell PEMFC system. The new parameters show promising results and hence the model works is considered as good model. Previously due to unknown base-case parameters the ranges selected for parameters are extremely large. In this model by considering the base-case parameters and previously extracted parameters the new short ranges for parameters are given so that in future the optimization of parameters will take less time and this increases the chances of this model to be used in online prediction of PEMFC temperature.

ORR Activity and Stability of a Carbon-Supported Ptxy Alloy Catalyst Evaluated in a PEM Fuel Cell

The application of proton exchange membrane fuel cells (PEMFCs) in light-duty vehicles (LDV) has dominated the fuel cell research field for the past decades. To reduce the LDV FC system cost to 30 $/kW by 2025 has driven the search for highly active cathode catalysts that could substitute the costly state-of-the-art Pt-alloy catalysts or reduce the cathode loadings to < 0.125 mgPt/cm2.1, 2 As novel ORR catalyst continue to emerge, theoretical calculations have turned the attention on Pt-rare earth (RE) alloys, such as platinum-yttrium alloys that were suggested to have superior activity for the oxygen reduction reaction (ORR) and superior long-term stability compared to conventional carbon-supported platinum catalyst (Pt/C). 3 Based on these findings, many attempts have been made to produce high electrochemical surface area (ECSA) Pt-RE alloy catalysts.4 In recent years, Hu, et al. introduced a new synthesis procedure that utilizes a carboiimide-assisted synthesis for the preparation of Pt-RE/C catalysts with an unprecedentedly high ECSAs in the range of ~50-60 m2/gPt.5 With such high ECSA PtxY/C catalysts, good PEMFC performance would be expected, but to date the ORR activity and stability of such PtxY/C catalysts has not been demonstrated in a PEMFC environment.In view of this, we reproduced the synthesis reported by Hu et al. using a Ketjen Black (KB) carbon support. The resulting PtxY/KB catalyst was characterized by X-ray diffraction, X-ray spectroscopy (EDS) in scanning transmission electron microscopy (STEM), and elemental analysis, indicating the formation of a Pt-richshell/Pt3Ycore structure that was caused by the acid washing procedure introduced before the electrochemical characterization.5 In our present study, two different Pt/KB catalysts were selected as reference materials: i) a Johnson Matthey reference catalyst consisting of small well-dispersed Pt nanoparticles on a KB support (Pt/KB-JM); ii) an in-house synthesized Pt/KB catalyst (Pt/KB-syn.) with a similar particle size distribution and ECSA as the in-house synthesized PtxY/KB catalyst (PtxY/KB-syn.). The ECSA (via CO-stripping voltammetry) and the ORR mass activity at 0.9 V vs. RHE (imass 0.9 V) of these three catalysts were first evaluated by rotating disk electrode (RDE) measurements in 0.1 M HClO4 at 25 °C. The catalysts were also incorporated as cathode catalysts in membrane electrode assemblies (MEAs), first determining their ECSA (by CO-stripping) and then their H2/O2 and H2/air performance in a 5 cm2 single-cell PEMFC hardware at 80 °C under differential flow conditions, including a quantification of the ORR mass activity at 0.9 V vs. RHE at 100 kPa O2.As can be seen in Figure 1, the relative ECSA and ORR mass activity values of the three different catalysts obtained in the RDE and the PEMFC configuration were essentially identical when evaluated at the same ionomer to carbon ratio (I/C = 0.7, g/g). Furthermore, a comparison of the RDE ORR activity at two different I/C ratios showed that the PtxY/KB-syn. and Pt/KB-syn. catalysts were more susceptible to ionomer poisoning when compared to the Pt/KB-JM catalyst. Following the approach taken in our previous publications, the voltage-cycling stability of the synthesized catalysts was also evaluated using an accelerated stress test (AST) consisting of a triangular potential scan between 0.6 and 1.0 VRHE at 50 mV/s up to 30000 cycles.5 Overall, the RDE and PEMFC data showed that the here synthesized carbon-supported Pt-richshell/Pt3Ycore catalyst does not shown an enhanced ORR activity nor a long-term stability benefit when compared to a Pt/KB catalyst with the same ECSA, contrary to what had been hypothesized earlier.3 References R. L. Borup, A. Kusoglu, K. C. Neyerlin, R. Mukundan, R. K. Ahluwalia, D. A. Cullen, K. L. More, A. Z. Weber and D. J. Myers, Current Opinion in Electrochemistry, 21, 192–200 (2020).M. Escudero-Escribano, K. D. Jensen and A. W. Jensen, Current Opinion in Electrochemistry, 8, 135–146 (2018).J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff and J. K. Nørskov, Nature Chemistry, 1(7), 552–556 (2009).J. N. Schwämmlein, G. S. Harzer, P. Pfändner, A. Blankenship, H. A. El-Sayed, and H. A. Gasteiger, Journal of the Electrochemical Society(165 (15)), J3173-J3185 (2018).Y. Hu, J. O. Jensen, L. N. Cleemann, B. A. Brandes and Q. Li, Journal of the American Chemical Society, 142, 953–961 (2020). Acknowledgment This work has been supported by the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No. 826097 (GAIA). This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe Research. Figure 1

Investigation of IrO2 Stability As a Cell-Reversal Mitigation Catalyst in PEMFC Anodes

In the recent years, the use of fuel cells for the propulsion of passenger vehicles and heavy-duty vehicles has gained renewed interest as alternative to internal combustion engine-powered vehicles. Particularly for the latter, the long-term durability of proton-exchange-membrane fuel cells (PEMFCs) is still a concern, which in part is governed by the catalyst layer durability during system operating conditions.1 During the operation of a PEM fuel cell system, certain transient conditions can occur that can lead to rapid degradation of the catalyst layers. On one hand, the widely studied start-up/shut-down (SUSD) phenomenon leads to significant degradation of the cathode catalyst layer due to the exposure of the cathode electrode to high potentials (>>1.0 V vs the reversible hydrogen electrode potential (VRHE)) that results from a H2/air-front passing through the anode flow field.2 On the other hand, an intermittent under-supply of hydrogen to one or several cells of a PEMFC stack can lead to a so-called cell-reversal (CR) event, resulting in the oxidation of the carbon support of the anode catalyst and in the subsequent collapse of the anode catalyst layer structure. The latter can be mitigated by the addition of an anode co-catalyst that facilitates the oxygen evolution reaction (OER) at much lower potentials than the carbon-supported platinum catalyst (Pt/C) that serves as anode catalyst for the hydrogen oxidation reaction (HOR).3 However, as shown by our recent study, the stability of the anode co-catalyst for the OER during SUSD events must be considered.4 In the present study, we examine different accelerated stress tests (ASTs) for single-cell PEMFCs that are designed to assess the stability of an anode co-catalyst for the OER in a PEMFC that is subjected to cell-reversal and SUSD events. Thus, we evaluated the stability of an anode co-catalyst under four conditions: i) subjecting the cell to extended SUSD cycles; ii) a cell-reversal protocol where a constant current is being drawn when feeding N2/air to the anode/cathode until a given cut-off cell potential is reached; iii) a protocol where cell-reversal cycling is induced by switching the anode feed gas between hydrogen and nitrogen while applying a constant current and supplying air to the cathode (later on referred as CR cycling); and, iv) an anode potential cycling protocol where the anode is supplied with N2, and its potential is cycled potentiostatically to different upper potential limits, with the cathode purged with air and serving as a counter electrode. With these ASTs, we examine the effect of the different anode potential cycles during SUSD and CR transients in order to elucidate the dependence of the IrO2 dissolution rate on operating potential.The stability of the IrO2 based anode co-catalyst is investigated by electrochemical measurements (cyclic voltammetry and polarization curves) and additionally via ex-situ XPS analysis. For example, Figure 1 shows the ex-situ XPS analysis of pristine and aged membrane electrode assemblies (MEAs). The upper two panels show the XPS data in the Pt 4f (BE>67 eV) and the Ir 4f (BE<67 eV) regions of the pristine Pt/C anode with an IrO2-based anode co-catalyst (Figure 1a) as well as the pristine Pt/C cathode (Figure 1b). The lower two panels show the cathode XPS data of the MEAs after 500 SUSD cycles (Figure 1c) and after 500 CR cycles (Figure 1d). In the case of the SUSD degraded MEA, a higher amount of Ir is observed on the cathode when compared to the CR degraded MEA. The mechanistic implications of these data will be discussed. References USDRIVE Fuel Cell Technical Team Roadmap (2017): https://www.energy.gov/eere/vehicles/downloads/us-drive-fuel-cell-technical-team-roadmap (accessed on 28.10.2021).T. Mittermeier, A. Weiß , F.Hasché, G. Hübner, H. A. Gasteiger. Journal of The Electrochemical Society, 164 (2), F127-F137 (2016).T. R. Ralph, S. Hudson, and D. P. Wilkinson, ECS Transactions, 1 (8), 67-84 (2006).M. Fathi Tovini, A. M. Damjanović, 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

Three-Dimensional Numerical Study of the inlet Temperature Effects on the Performance of Planar PEMFCs

In the present study, a CFD (computational fluid dynamics) three-dimensional model is performed to investigate the effects of the inlet temperature on the power density, pressure and local transport phenomena of a single cell PEMFC (proton exchange membrane fuel cell) with straight channels. Deferent inlet temperatures of the reactants (333, 343 and 353 K) have been investigated using ANSYS-FLUENT. The interest of our work is focused on obtaining I-P and I-V curves as well as the pressure, hydrogen, oxygen and water mass fraction profiles to analyze the effect of the oxygen and hydrogen inlet temperature on the current, voltage and power densities of the studied PEMFC. From the results obtained its appears that the variation in the inlet temperature values of the PEMFC has a significant influence on the cell performances at medium and higher current density. Therefore, the results analysis of the three-dimensional and single-phase model indicates that the increase in the reactants’ inlet temperature of the studied PEMFC shows a negative impact on the generated power densities, which have an inversely proportional effect.

Impact of Carbon N-Doping and Pyridinic-N Content on the Fuel Cell Performance and Durability of Carbon-Supported Pt Nanoparticle Catalysts.

Cathode catalyst layers of proton exchange membrane fuel cells (PEMFCs) typically consist of carbon-supported platinum catalysts with varying weight ratios of proton-conducting ionomers. N-Doping of carbon support materials is proposed to enhance the performance and durability of the cathode layer under operating conditions in a PEMFC. However, a detailed understanding of the contributing N-moieties is missing. Here, we report the successful synthesis and fuel cell implementation of Pt electrocatalysts supported on N-doped carbons, with a focus on the analysis of the N-induced effect on catalyst performance and durability. A customized fluidized bed reduction reactor was used to synthesize highly monodisperse Pt nanoparticles deposited on N-doped carbons (N-C), the catalytic oxygen reduction reaction activity and stability of which matched those of state-of-the-art PEMFC catalysts. Operando high-energy X-ray diffraction experiments were conducted using a fourth generation storage ring; the light of extreme brilliance and coherence allows investigating the impact of N-doping on the degradation behavior of the Pt/N-C catalysts. Tests in liquid electrolytes were compared with tests in membrane electrode assemblies in single-cell PEMFCs. Our analysis refines earlier views on the subject of N-doped carbon catalyst supports: it provides evidence that heteroatom doping and thus the incorporation of defects into the carbon backbone do not mitigate the carbon corrosion during high-potential cycling (1-1.5 V) and, however, can promote the cell performance under usual PEMFC operating conditions (0.6-0.9 V).

A novel approach for predicting PEMFC in varying ambient conditions by using a transient search optimization algorithm based on a semi-empirical model

&lt;abstract&gt; &lt;p&gt;Proton exchange membrane fuel cell (PEMFC) is an alternate energy source that produces electricity without any adverse effects on the environment. The drawbacks of PEMFC are its short life and its non-linear voltage with loading current. Also, PEMFC is prone to ambient conditions, and its performance varies with different ambient conditions. In this work, the semi-empirical modeling approach has been used to predict the PEMFC voltage accurately. However, when the ambient condition varies, the voltage of PEMFC varies accordingly and consequently the previous parameters of the EMI-empirical model don't produce good results. Previously the voltage variation due to changes in ambient has been predicted with the help of ambient conditions and load resistance, but this model isn't sui for all PEMFCs. In this work, a new method has been proposed where fast and accurate optimization technique such as Transient search optimization (TSO) has been used to optimize parameters when ambient condition varies and predicts the PEMFC voltage accurately and doesn't consume a lot of time. The proposed method will be very helpful in future research for predicting the PEMFC voltage for various PEMFC systems at different ambient conditions. The proposed method has been validated experimentally by performing experiments on n single-cell PEMFC system at normal and high ambient temperature.&lt;/p&gt; &lt;/abstract&gt;

Loading Impact of a PGM-Free Catalyst on the Mass Activity in Proton Exchange Membrane Fuel Cells

Platinum-group-metal-free (PGM-free) catalysts are currently considered as potential oxygen-reduction-reaction (ORR) catalysts to replace costly and supply-limited platinum at the cathode side of proton exchange membrane fuel cells (PEMFCs). Extensive research efforts have led to substantial progress with regards to the ORR activity of PGM-free ORR catalysts, but there is uncertainty about the dependence of the mass activity on the catalyst loading. In this study, the effect of catalyst loading on the mass activity is investigated by means of rotating disk electrode measurements as well as single cell PEMFC tests using a commercial PGM-free ORR catalyst. Single cell tests with a wide range of loadings (0.4–4.0 mgcat cm−2 MEA) are compared to rotating disk electrode measurements with low loadings of 40–600 μgcat cm−2 disk. In contrast to indications in the literature that the ORR activity depends on catalyst loading, our results reveal an independence of the ORR mass activity from the catalysts loading in both RDE and PEMFC tests, if corrections for the voltage losses in H2/O2 single cell tests are considered. Moreover, no clear relation of the stability to the catalyst loading was found in H2/O2 PEMFCs.

From Zn-N-C to Fe-N-C: Active-Site Imprinting As a New Method for the Synthesis of Highly Active PGM-Free Catalysts for PEMFC

The high cost and the restricted availability of Platinum-Group-Metals (PGM) used in current catalysts is one of the major hurdles for the large-scale commercialization of Proton Exchange Membrane Fuel Cells (PEMFCs). In the last decade, great efforts have been made to develop efficient PGM-free catalysts for the oxygen reduction reaction (ORR), especially metal-nitrogen-doped carbons (M-N-Cs, with M = Fe, Co). The activity gap towards Pt has successfully been narrowed, now reaching the activity requirements for practical applications.1-3 For this class of catalysts, the active site is a MN4 moiety, as known from molecules such as phthalocyanines and porphyrins.4 Due to the metastability of the MN4 sites at the temperature of their pyrolytic formation, the final transition metal loading is currently limited and significant amounts of inorganic byproducts are formed. Although synthesis protocols have been successfully optimized, multiple processing steps are required, making the preparation time-consuming.In this contribution we will show that Zn2+ ions can be utilized in our novel concept of active-site imprinting, where Zn is used as template-ion in a pyrolytic process to form Zn-N-C precursor materials.5 The Zn-N-C materials presented in this work are nitrogen-doped carbons comprising ZnN4 sites, obtained with high yield and from inexpensive precursors. The active-site imprinted carbon supports possess high surface area and hierarchical porosity, which makes them structurally advantageous for catalytic applications in terms of mass transport and high accessibility of the active sites. Through a zinc-to-iron ion exchange reaction, Fe-N-C catalysts with high Fe loading are obtained at only 170 °C. Since the active-site formation by the Zn-to-Fe exchange reaction can be conducted at low temperatures, the structural properties of the Zn-N-C precursor material are retained.6 Moreover, this synthetic procedure assures the absence of the otherwise obtained harmful side-phases (e.g., iron carbide). Cryo-Mössbauer and X-ray adsorption spectroscopy, supported by calculations of the extended X-ray absorption fine structure, reveal an exclusive presence of Fe as single atoms coordinated to four nitrogen atoms, i.e., in form of the desired FeN4 moieties.Identical-location scanning transmission electron microscopy with atomic resolution is further employed to visualize the trans-metalation event. The herein obtained catalysts match the state-of-the-art electrocatalytic activity for Fe-N-C catalyts, both in a rotating disk electrode and in single cell PEMFC measurements. The novel synthesis method will be discussed regarding its advantages and disadvantages compared to the conventional pyrolytic M-N-C catalyst syntheses, with a focus on the potential to surpass the current limitations of restricted active-site density and catalyst stability.ACKNOWLEDGEMENTS:The German Federal Ministry of Economic Affairs and Energy (BMWi) is acknowledged for funding within the Verbundproject innoKA (Project No.: 03ET6096A)REFERENCES: M. Lefèvre, E. Proietti, F. Jaouen and J.-P. Dodelet, Science, 2009, 324, 71-74.R. Bashyam and P. Zelenay, Nature, 2006, 443, 63-66. H. A. Gasteiger, S. S. Kocha, B. Sompalli and F. T. Wagner, Applied Catalysis B, 2005, 56, 9-35. Q. Jia, N. Ramaswamy, U. Tylus, K. Strickland, J. Li, A. Serov, K. Artyushkova, P. Atanassov, J. Anibal, C. Gumeci, S. C. Barton, M.-T. Sougrati, F. Jaouen, B. Halevi and S. Mukerjee, Nano Energy, 2016, 29, 65-82.A. Mehmood, J. Pampel, G. Ali, H. Y. Ha, F. Ruiz-Zepeda and T.-P. Fellinger, Advanced Energy Materials, 2018, 8.D. Menga, F. Ruiz-Zepeda, L. Moriau, M. Šala, F. Wagner, B. Koyutürk, M. Bele, U. Petek, N. Hodnik, M. Gaberšček and T.-P. Fellinger, Advanced Energy Materials, 2019, 9, 1902412. Figure 1

(Invited) Benchmarking Carbon-Supported Pt-Based Oxygen Reduction Reaction Electrocatalysts for PEMFC Cathodes

The present performance of state-of-the-art proton exchange membrane fuel cells (PEMFC) enable their commercialization, as demonstrated by the recent release of fuel-cell powered vehicles (forklifts by Plug Power, FCEV Miraï by Toyota, etc.). Now, all PEMFC manufacturers need to reduce the PEMFC systems initial cost and to enhance their durability and reliability in operation to reach the market requirements and industrial sustainability. To this goal, one must develop highly-efficient oxygen reduction reaction (ORR) electrocatalysts, which was claimed to be obtained by numerous groups in a recent past [1-6]. Unfortunately, the scientific community still struggles to obtain the best performance of these materials in operating PEFMCs: their practical performance in membrane electrode assembly (MEA) do not approach those expected from an analytical approach performed using the rotating disk electrode setup, RDE (the most widely-used setup to assess a material’s ORR performance).There are several reasons that may explain why RDE data are not relevant to account for MEA data. Firstly, in RDE, the O2 reactant is fed as gas dissolved in the electrolyte (slow diffusivity and solubility), hence the mass-transfer rate and related limiting current density are ca. 3 orders of magnitude lower than in real PEMFC conditions. Secondly, the activity data is only extracted at high potential values in RDE (E > 0.85 V vs RHE), although PEMFC optimal performance is reached in the 0.6 – 0.8 V vs RHE cathode potential range. Thirdly, the proton conduction can be limiting in the thin layer of ionomer covering the electrocatalyst nanoparticles in MEA, which could limit their operation, especially at the high current densities at stake in MEA. In essence, one is not sure that the electrocatalysts are used in optimized conditions in MEA, as emphasized mass-transport of reactants (both H+ and O2) to the catalytic sites is not granted for present ionomers and MEA structure [7, 8]. Recent results obtained in newly-developed electrochemical characterization setups like the floating electrode (FE) [9], the gas-diffusion electrode (GDE) [10] or differential cell (DC), could enable to reach much higher ORR current densities at the lab scale and therefore better match MEA data, a prerequisite for relevant benchmarking.In the present contribution, these setups will be used to characterize three state-of-the-art ORR electrocatalysts (50 wt% Pt/Vulcan XC72, 50 wt% Pt3Co/Vulcan XC72 and 30 wt% Pt/graphitized carbon black), and comparison will be made with large single-cell PEMFC data in automotive conditions. We will show whether the “RDE promises” of alloyed electrocatalysts (measured in RDE configuration) do maintain in FE, GDE and DC, and whether the “advanced electrocatalysts” still exhibit their plain potential in real PEMFC catalytic layer configuration.

Highly-performing and low-cost nanostructured membranes based on Polysulfone and layered doubled hydroxide for high-temperature proton exchange membrane fuel cells

The low cost, reduced fuel crossover and ease of preparation make sulfonated Polysulfone (sPSU) a potential candidate to replace Nafion electrolyte in proton exchange membrane fuel cells (PEMFCs). To reach a satisfactory proton conductivity the general strategy involves the preparation of macromolecules with high ion exchange capacity (IEC), even at the cost of sacrificing their mechanical properties. In this study, sPSU with relatively low IEC was used as polymer matrix for the preparation of nanocomposite electrolytes by dispersing Mg/Al–NO3- Layered Double Hydroxides (LDH). sPSU-LDH membranes were prepared by solution intercalation method and characterized by XRD, TGA and DMA, whereas water dynamics and proton conductivity were investigated by NMR (PFG and T1) and EIS spectroscopies, respectively. The complete exfoliation and nanodispersion of the LDH platelets into the polymer enhance the thermo-mechanical resistance, the dimensional stability and the water retention capacity of the electrolytes. The formation of highly connected ion channels promotes an effective Ghrotthus-type mechanism for the proton transport also under dehydrating environment. Such features allowed proton conductivity values and electrochemical performances in single cell PEMFC distinctly higher than the Nafion recast, demonstrating the possibility to prepare cost-effective and high performing sPSU-based membranes able to operate under low-humidification and high temperatures conditions.

Development of a Current Collector with a Graphene Thin Film for a Proton Exchange Membrane Fuel Cell Module.

This paper constructs planar-type graphene thin film current collectors for proton exchange membrane fuel cells (PEMFCs). The present planar-type current collector adopts FR-4 as the substrate and coats a copper thin film using thermal evaporation for the electric-conduction layer. A graphene thin film is then coated onto the current collector to prevent corrosion due to electrochemical reactions. Three different coating techniques are conducted and compared: Spin coating, RF magnetron sputtering, and screen printing. The corrosion rates and surface resistances are tested and compared for the different coating techniques. Single cell PEMFCs with the developed current collectors are assembled and tested. A PEMFC module with two cells is also designed and constructed. The cell performances are measured to investigate the device feasibility.

Ionic Liquid-Modified Microporous ZnCoNC-Based Electrocatalysts for Polymer Electrolyte Fuel Cells

Non-platinum group metal (non-PGM) oxygen reduction reaction (ORR) catalysts have been widely reported, but their application in proton exchange membrane fuel cells (PEMFCs) is challenging because of their poor performance in acidic environments. Here, [BMIM][NTf₂] ionic liquid (IL) modification of microporous ZnCoNC catalysts (derived from ZIF-ZnCo) is investigated to study their behavior in PEMFCs and to elucidate the catalytic mechanisms in practical operation. The high O₂ solubility of ILs enhances the utilization of active sites with porous ZnCoNC, and their hydrophobic nature facilitates the water transport during fuel cell operation. The half-cell measurement in aqueous HClO₄ shows that with the 20 wt % IL modification, the electron-transfer number increases from 2.58 to 3.88, approaching the desired 4-electron-transfer ORR. The power density obtained shows 140% improvement in single-cell PEMFC tests. The catalyst also yields an interesting performance in alkaline anion-exchange membrane fuel cells.

Planar current collector design and fabrication for proton exchange membrane fuel cell

This paper proposes a novel planar type lightweight current collector for proton exchange membrane fuel cells (PEMFC) designed for low power portable applications. The proposed lightweight current collector, which is composed of a substrate, electrical conduction layer and corrosion resistance layer, combines the conventional metal sheet/mesh for current collecting and substrate together to reduce the possible distortion during operation caused by the mismatch due to large different mechanical properties between components. The current collector adopts FR-4 as the substrate material. The electrical conduction layer is made via coating a copper thin film using a thermo-evaporation layer. The corrosion resistance layer is made via coating a graphene thin film using spin coating and a vacuum oven process. Fabricated current collector sheet resistance measurements are conducted. The complete current collectors are assembled into a single cell PEMFC with both forced convection air-breathing cathode and self-air-breathing cathode. The related performance and stability experiments were conducted to investigate the feasibility for further applications.