Cathode Catalyst Loading Research Articles

The Influence of Membrane Thickness and Catalyst Loading on Performance of Proton Exchange Membrane Fuel Cells

This paper explores the influence of membrane thickness and catalyst loading on fuel cell performance of commercially relevant membrane electrode assemblies (MEAs). A systematic study was carried out with MEAs comprised of commercially available Pt/C electrocatalysts and reinforced PFSA membranes to better understand the practical limitations of incorporating low platinum loadings and ultra-thin membranes in commercially viable MEA designs. Three different MEA configurations were compared where membrane thickness was either 15 or 10 μm and cathode catalyst loading was either 0.4 or 0.1 mgPt cm−2. Extensive in situ electrochemical characterization was carried out to extract the relevant physical and electrochemical parameters of each MEA configuration. By changing only one variable at a time, i.e., either thickness or catalyst loading, it was possible to deconvolute the specific contributions of membrane thickness and catalyst loading on fuel cell performance. Interestingly, as membrane thickness was reduced below 15 μm, no significant changes in fuel cell performance were observed as membrane interfacial effects begin to dominate compared to bulk transport effects. Conversely, reducing catalyst layer loading from 0.4 to 0.1 mgPt cm−2 introduces significant polarization losses attributed to a combination of kinetic and mass transport effects.

Influence of Current Collector Design and Combination on the Performance of Passive Direct Methanol Fuel Cells

In this work, an anode current collector with a scaled step-hole structure (called SF-type) and a cathode current collector with a perforated cross-tilt structure (called X-type) were designed and fabricated for application in passive direct methanol fuel cells (DMFCs). A whole-cell test showed that the combination of an anode SF-type current collector and cathode conventional current collector increased the optimal methanol concentration from 6 M to 8 M and the maximum power density to 5.40 mW cm−2, which improved the cell performance by 51.6% compared to that of the conventional design under ambient testing conditions. The combination of the anode conventional current collector and cathode X-type current collector achieved a maximum power density of 5.65 mW cm−2 with a 58.7% performance improvement, while the optimal methanol concentration was increased to 10 M. Furthermore, the combination of anode SF-type and cathode X-type obtained the highest power density at 6.22 mW cm−2. Notably, the anode and cathode catalyst loadings used in this study were 2.0 mg cm−2, which is lower than the commonly used loading, thus reducing the fuel cell cost.

Nickel adsorbed algae biochar based oxygen reduction reaction catalyst

Lately, the bio electrochemical systems are emerging as an efficient wastewater treatment and energy conversion technology. However, their scaling-up is considerably restrained by slow-rate of cathodic oxygen reduction reaction (ORR) or otherwise by the high cost associated with the available efficient ORR catalysts. In this investigation, a cost-effective and eco-friendly approach for synthesizing Ni based ORR catalyst utilizing biosorption property of microalgae is accomplished. The synthesised Ni adsorbed algal biochar (NAB) served as an efficient cathode catalyst for enhancing ORR in a microbial carbon-capture cell (MCC). On increasing the initial concentration of Ni2+ in the aqueous medium from 100 mgL−1 to 500 mgL−1, the biosorption capacity was found to increase from 3 mgg−1 to 32 mgg−1 of algae cell. The MCC operated with NAB based cathode catalyst loading of 2 mgcm-2 exhibited 3.5 times higher power density (4.69 Wm−3) as compared to the one with commercial activated carbon. A significant organic matter removal (82 %) in the anodic chamber with simultaneous algal biomass productivity in the cathodic chamber was attained by MCC with cathode loaded with 2 mgcm−2 of NAB. Hence, this easily synthesised low-cost catalyst, out of waste stream, proved its ability to improve the performance of MCC.

Platinum Group Metal-Free Catalyst Loading Optimization for Dry Cathode Operation in Anion Exchange Membrane Water Electrolysis

With an increasing interest for green hydrogen as an important fuel for the global energy transition and as a raw material for green chemistry, extensive research efforts are currently devoted to increase the performance of water electrolysis technologies. In this frame work, Anion Exchange Water Electrolysis (AEMWE) has a strategic role promising to boost electrolytic hydrogen production without relying on scarce resources as AEMWE does not need Iridium or other Platinum group metals (PGM) catalysts, unlike Proton Exchange Membrane Water Electrolysis (PEMWE), to reach high power density [1].In this work, the focus is on electrode optimization for dry cathode operation. Operating without a liquid feed on the cathode reduces the extent of the drying of hydrogen gas and simplifies the balance of the plant. However, water must be transported from the anode to the cathode where it is consumed by the hydrogen evolution reaction (HER) [2]. Also, ionic connection from the membrane to catalyst surface must be provided by the ionomer without a supporting electrolyte which is generally employed in AEMWE to improve performance [1]. Under these premises, it is clear that using high catalyst loading to compensate for the intrinsic low activity of Platinum group metals-free (PGM-free) catalysts will result in lower utilization of the catalyst layer as a function of the electrode thickness [3].To study how transport limitations hinder cathode performance, we manufactured catalyst coated membranes (CCMs) via decal transfer method and varied the cathode catalyst loading thereby adjusting catalyst layer (CL) thickness. RaneyTM Nickel served as the cathode catalyst and Super PTM Carbon as the conductive additive. It was found that increasing the catalyst loading between 0.65 mg/cm2 and 1.65 mg/cm2 greatly improved cell performance (Figure 1). However, cell voltage proved to be less sensitive to cathode loading for higher loadings. In fact, to reasonably improve the performance further, a loading of 4.55 mg/cm2 was necessary. Noticeably, the high frequency resistance (HFR) was found to be independent of catalyst loading (i.e. CL thickness) due to the high electronic conductivity of the cathode CL with carbon additive.This works sheds light on how AEMWE performance are related to cathode catalyst loading when the cathode is dry operated. It is found that performance improvement is limited at high loading (above 1.65 mg/cm2). This shows how the ionic conductivity of the electrode should be improved to mitigate the low mass activity of PGM-free catalyst.[1] Ayers, Katherine, Nemanja Danilovic, Ryan Ouimet, Marcelo Carmo, Bryan Pivovar, and Marius Bornstein. “Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale.” Annual Review of Chemical and Biomolecular Engineering 10, no. 1 (June 7, 2019): 219–39.[2] Koch, Susanne, Joey Disch, Sophia K. Kilian, Yiyong Han, Lukas Metzler, Alessandro Tengattini, Lukas Helfen, Michael Schulz, Matthias Breitwieser, and Severin Vierrath. “Water Management in Anion-Exchange Membrane Water Electrolyzers under Dry Cathode Operation.” RSC Advances 12, no. 32 (2022): 20778–84.[3] Liu, Jiangjin, Zhenye Kang, Dongguo Li, Magnolia Pak, Shaun M. Alia, Cy Fujimoto, Guido Bender, Yu Seung Kim, and Adam Z. Weber. “Elucidating the Role of Hydroxide Electrolyte on Anion-Exchange-Membrane Water Electrolyzer Performance.” Journal of The Electrochemical Society 168, no. 5 (May 1, 2021): 054522.Figure 1 Polarization curve of CCMs with different cathode catalyst loading. The cathode contains 65 % catalyst (RaneyTM Nickel), 10% ionomer and 25% Super PTM Carbon. NiFe nanoparticles are used in the anode with 5% ionomer (AP-1-HNN5-00-X). The measurements are conducted at 60 °C feeding 1 M KOH to anode. Figure 1

Understanding Charge, Mass, and Heat Transfer in Fuel Cells for Transport Applications – Insights from the Camelot Project

Proton Exchange Membrane Fuel Cells (PEMFCs) are a promising solution for zero-emission vehicle propulsion owing to their high energy density, low operating temperature, and high efficiency. The overall aim of the CAMELOT project is to improve the power density of fuel cells by understanding the limitations on the performance of state-of-the-art (SoA) and beyond SoA PEMFC membrane electrode assemblies (MEAs). To achieve this, the CAMELOT project has diagnosed the fundamental transport properties that limit performance of these MEAs and materials. Not only has the CAMELOT project produced MEAs with features that have the potential to enable disruptive performance increases but have further developed leading open-source models to enable accurate simulations validated through experimental work. In-depth parametrisation of fuel cell components through extensive ex-situ and in-situ characterisation has been performed to provide input to the modelling activities. The two major modelling advances achieved by the CAMELOT project are i) the improvement of water uptake and transport models, especially concerning ultra-thin PEMs, and ii) extending a leading open-source model (FAST-FC) to enable accurate simulation of beyond SoA fuel cell performance and voltage loss breakdown. CAMELOT has developed a series of beyond-SoA fuel cell components to ensure that the modelling inputs are representative of SoA component properties. A series of membranes with varying thicknesses were prepared and a range of ex-situ experiments were carried out to gather water uptake and permeability properties for the water transport models. Additional in-situ electrochemical characterisation was carried out on a series of catalyst coated membranes (CCMs) to extract important properties of the catalyst and membrane components as inputs to improve the physics-based fuel cell performance model.Significant results from the project to be highlighted in this presentation include the development of a water transport model with improved description of water uptake and transport in thin ionomeric layers, the development of a predictive modelling framework from which we can identify the most important material parameters to tune to reach our MEA performance targets of 2.7 A/cm2 at >0.67 V with total catalyst loadings <0.08 mgPt/cm2, the development of ultrathin (< 10 µm) proton exchange membranes and ultra-low loading cathode catalyst loadings (0.08 mgPt/cm2), the development of catalyst coated membranes (CCMs) with in-plane catalyst and ionomer gradients, and extensive in-situ fuel cell characterization of the SoA CAMELOT CCMs/MEAs.The CAMELOT project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under grant agreement No 875155. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research.

Visualization of Hydrogen Bubbles Using Synchrotron X-Ray CT inside Porous Transport Layer of Direct Toluene Electro-Hydrogenation Electrolyzers

Toluene is a highly versatile solvent commonly used in many industries due to its high energy density and effective hydrogen carrier properties. It can store a considerable amount of hydrogen in a relatively small volume, making it a promising hydrogen carrier for various applications. Toluene's high volumetric energy density also makes it one of the best hydrogen carriers available. Additionally, toluene is easy to handle and transport as it is a liquid at room temperature, and it can be stored and transported like any other liquid fuel. Furthermore, toluene is a safer alternative for hydrogen storage compared to other hydrocarbons due to its low toxicity.Direct toluene-electro hydrogenation electrolyzer is a promising method that enables the simultaneous performance of water electrolysis and toluene hydrogenation in a single system. However, during the toluene direct electrolytic hydrogenation process, the formation of hydrogen bubbles from the electrolysis of water hinders the toluene hydrogenation reaction, leading to a reduced conversion rate of methylcyclohexane (MCH) and Faraday efficiency.In this study, we aimed to understand the conditions for hydrogen bubble generation and transport. We quantitatively evaluated the generation amount and distribution of hydrogen bubbles by visualizing them in an operating electrochemical cell using Synchrotron X-ray CT. Figure 1 displays the distribution of hydrogen bubbles along the porous transport layer (PTL) of the electrochemical cell. These bubbles were visualized using the raw images obtained from Spring-8 and subsequently reconstructed. The cell was operating at a current density of 200 mA/cm2 for a period of 30 minutes with pure water supplied to the anode side. Darker areas in the images indicate regions with hydrogen bubbles, which have a lower density and atomic weight than other substances in the PTL. Therefore, they are more transparent to X-rays and appear darker in the image. Higher current values and longer operation times led to increased hydrogen bubble generation, with a significant increase observed at 30 minutes. By visualizing these hydrogen bubbles, we were able to evaluate the generation distribution, amount, and transport of hydrogen, which can help improve the direct toluene-electro hydrogenation electrolyzer system. Acknowledgement This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Nagasawa K, Sugita Y, Atienza-Márquez A, Kuroda Y, Mitsushima S. Effect of the cathode catalyst loading on mass transfer in toluene direct electrohydrogenation. Journal of Electroanalytical Chemistry 2023:117431. https://doi.org/10.1016/J.JELECHEM.2023.117431.Shigemasa, A. Atienza-Márquez, K. Inoue, S. Jang, F. Reyna-Peña, T. Araki, “Visualization of dragged water and generated hydrogen bubbles in a direct toluene electro-hydrogenation electrolyzer,” J. Power Sources 2023; 554:232304. https://doi.org/10.1016/j.jpowsour.2022.232304.Nagasawa, A. Kato, Y. Nishiki, Y. Matsumura, M. Atobe, S. Mitsushima, “The effect of flow-field structure in toluene hydrogenation electrolyzer for energy carrier synthesis system. Electrochemical Acta 2017; 246:459-65. https://doi.org/10.1016/j.electacta.2017.06.081. Nagasawa, K. Tanimoto, J. Koike, K. Ikegami, S. Mitushima, “Toluene permeation through solid polymer electrolyte during toluene direct electro-hydrogenation for energy carrier synthesis”, Journal of Power Sources, Vol.439, (2019) 22707. https://doi.org/10.1016/j.jpowsour.2019.227070. Figure 1 SPring-8 CT Visualization Reconstructed image after 30 minutes of operation at 200 mA/cm². Figure 1

Highly durable platinum group metal-free catalyst fiber cathode MEAs for proton exchange membrane fuel cells

Fe-based platinum group metal (PGM)-free catalysts were incorporated into electrospun fiber mat or powder cathode membrane-electrode-assemblies (MEAs) with a Nafion 211 membrane and a Pt/C powder anode. Fabrication and characterization tests were performed on MEAs with: (1) a conventional powder cathode with a neat Nafion binder, (2) a fiber mat cathode with a Nafion/polyethylene oxide (PEO) binder, where PEO was extracted before MEA testing, (3) a powder cathode with a blended binder of Nafion and polyvinylidene fluoride (PVDF), and (4) a series of fiber mat cathodes with different Nafion/PVDF binder weight ratios. Cathode degradation occurred, with a loss in power output, in MEAs with a neat Nafion powder cathode or with a Nafion fiber cathode. In contrast, little or no power loss was observed for powder or fiber cathodes when the binder was a blend of Nafion and PVDF. The presence of hydrophobic PVDF drove water and electrogenerated peroxide out of the cathode, away from catalyst particles, which improved cathode durability, but PVDF also decreased the binder conductivity and slowed oxygen reduction kinetics, resulting in lower power densities. A 75:25 w:w Nafion:PVDF fiber cathode MEA was the best compromise for maximizing power and minimizing catalyst degradation. For such a cathode, with a PGM-free cathode catalyst loading of 3.0 mg cm−2, a power density of 88 mW cm−2 at 0.5 V, 80 °C, and 200 kPaabs pressure was maintained for 80 h of continuous operation.

(Digital Presentation) Synthesis of Proton Exchange Membrane Fuel Cell Catalyst and Optimization of Membrane Electrode Assembly Preparation Parameters

Reducing platinum content in proton exchange membrane fuel cells (PEMFCs) is one of the most essential development directions to secure the economic viability of PEMFC. Efforts are being made to synthesise new, more active catalysts and to optimise PEMFC assembly parameters. (1–4)The study aimed to synthesise 60 wt% Pt/C catalyst and optimise catalyst loading on the electrodes, gasket thickness and coating strategy.The catalyst was synthesised by depositing Pt nanoparticles on carbon black (Ketjenblack EC-300J) using ethylene glycol as a reducing agent and solvent (5–7). The studied catalyst was characterised by thermogravimetric analysis, X-ray diffraction and N2 sorption analysis. The synthesized catalyst material contained approximately 60 wt% of Pt, and the average platinum crystallite size was under 3 nm. The catalyst had a micro-mesoporous structure with a specific surface area of 320 m2 g−1.For electrochemical characterisation, the measurements were performed in H2/air PEMFC. Using an ultrasonic coating system, the catalyst was deposited on the Nafion membrane or gas diffusion layer. A suitable gasket thickness was found using electrochemical measurements. The catalyst loading was varied on the anode between 0.05 and 0.50 mg cm−2 and on the cathode between 0.40 and 1.00 mg cm−2, leaving the catalyst loading constant on the non-variable electrode. Electrodes thickness depended linearly on the catalyst loading. The results showed that electrochemically active surface area does not depend on catalyst loading. Varying catalyst loading on the anode did not show a decrease in electrochemical activity; thus, the anode catalyst loading could be reduced to 0.05 mg cm−2. However, the electrochemical activity decreased at low cathode catalyst loadings. It was found that the cathode catalyst loading can be reduced to 0.60 mg cm−2.Under optimised conditions, the electrochemical activity of the investigated material was excellent. The PEMFC current density was 0.81 A cm−2 at 670 mV, the maximum achieved power density 0.80 W cm−2 and the electrochemically active surface area 56 mPt 2 gPt −1. Acknowledgements This work was supported by the EU through the European Regional Development Fund TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011) and the Estonian Research Agency project (personal research support group grant project No. PRG676). References R. Alink, R. Singh, P. Schneider, K. Christmann, J. Schall, R. Keding, and N. Zamel, Molecules, 25, E1523 (2020).Á. Kriston, T. Xie, D. Gamliel, P. Ganesan, and B. N. Popov, Journal of Power Sources, 243, 958 (2013).J. Lee, C. Seol, J. Kim, S. Jang, and S. M. Kim, Energy Technol., 9, 2100113 (2021).H. A. Gasteiger, J. E. Panels, and S. G. Yan, Journal of Power Sources, 127, 162 (2004).Y. Shao, S. Zhang, R. Kou, X. Wang, C. Wang, S. Dai, V. Viswanathan, J. Liu, Y. Wang, and Y. Lin, Journal of Power Sources, 195, 1805 (2010).W. Li, C. Liang, W. Zhou, J. Qiu, Zhou, G. Sun, and Q. Xin, J. Phys. Chem. B, 107, 6292 (2003).R. Kou, Y. Shao, D. Mei, Z. Nie, D. Wang, C. Wang, V. V. Viswanathan, S. Park, I. A. Aksay, Y. Lin, Y. Wang, and J. Liu, J. Am. Chem. Soc., 133, 2541 (2011).

Optimization of the Cathode Catalyst Layer for Boosting Direct Ammonia Fuel Cell Performance by Orthogonal Tests

The design of the cathode catalyst layer (CCL) for the oxygen reduction reaction is critical to improving the performance of anion-exchange membrane-based direct ammonia fuel cells (AEM-DAFCs) due to the impact of ammonia crossover. Herein, the effects of three factors (cathode catalyst loading, binder type, and binder content) and their corresponding three levels on the CCL have been investigated to achieve optimal cell performance by the orthogonal test for the first time. CCLs are characterized by scanning electron microscopy, mercury intrusion porosimetry, and contact angle measurements, which further verify the reliability of the orthogonal test results. The results show the following order of influence on the cell performance: binder type > binder content > cathode catalyst loading. These factors affect the mass transport and the number of three-phase interfaces in the CCL by changing its thickness, surface morphology, pore structure, and hydrophobicity, thus affecting the cell performance. An AEM-DAFC with a champion peak power density (PPD) of 158.6 mW cm–2 has been achieved under the optimal combination of cathode catalyst loading (2 mg cm–2), binder type (poly(tetrafluoroethylene) (PTFE)), and binder content (15 wt %). This work provides an alternative avenue to improve the performance of AEM-DAFCs using state-of-the-art catalysts and binders through rapid optimization of the CCL structure in the future.

(Digital Presentation) Synthesis of Proton Exchange Membrane Fuel Cell Catalyst and Optimization of Membrane Electrode Assembly Preparation Parameters

The oxygen reduction catalyst was synthesized by depositing Pt nanoparticles on carbon black using ethylene glycol as a reducing agent. The synthesized catalyst material contained approximately 60 wt% of Pt, and the average Pt crystallite size was under 3 nm. The catalyst had a micro-mesoporous structure with a specific surface area of 320 m2 g−1. Electrochemical characterization was performed in H2/air fuel cell. The catalyst was deposited on the Nafion membrane or gas diffusion layer using an ultrasonic coating system. The thickness of Teflon gaskets as well as hot pressing conditions were optimized. Lowering catalyst loading on the anode did not show a decrease in electrochemical activity up to 0.05 mg cm−2. However, it was found that the cathode catalyst loading can be reduced only up to 0.60 mg cm−2.

Effect of the cathode catalyst loading on mass transfer in toluene direct electrohydrogenation

Toluene (TL)-methylcyclohexane (MCH) organic hydride is one of the most promising carrier candidates for the large-scale transport and storage of hydrogen. TL Direct electrohydrogenation electrolyzers based on solid polymer electrolyte membrane technology exhibit significant advantages in terms of energy efficiency compared with the conventional TL hydrogenation method. Mass transfer in the catalyst layer is a crucial aspect of the performance of these electrochemical devices. In this study, experiments were conducted using catalyst-coated membranes with various thicknesses to control the catalyst loading (carbon-supported platinum/ruthenium alloy) and investigate its influence on the mass transfer properties and electrolytic performance of a TL direct electrohydrogenation electrolyzers. The current efficiency was also evaluated for TL concentrations between 1% and 100% in the cathode reactant. The results indicated than an optimum thickness of the cathode catalyst layer corresponding to catalyst loadings of 1.4–1.6 mg cm−2 could maximize the current efficiency of the electrolyzer. The presence of hydrogen gas generated as a side reaction in the high-TL concentration range and high MCH concentrations in the low-TL concentration range are the main factors contributing to a decrease in current efficiency.

Alternative and facile production pathway towards obtaining high surface area PtCo/C intermetallic catalysts for improved PEM fuel cell performance.

The design of catalysts with stable and finely dispersed platinum or platinum alloy nanoparticles on the carbon support is key in controlling the performance of proton exchange membrane (PEM) fuel cells. In the present work, an intermetallic PtCo/C catalyst is synthesized via double-passivation galvanic displacement. TEM and XRD confirm a significantly narrowed particle size distribution for the catalyst particles compared to commercial benchmark catalysts (Umicore PtCo/C). Only about 10% of the mass fraction of PtCo particles show a diameter larger than 8 nm, whereas this is up to or even more than 35% for the reference systems. This directly results in a considerable increase in electrochemically active surface area (96 m2 g-1 vs. >70 m2 g-1), which confirms the more efficient usage of precious catalyst metal in the novel catalyst. Single-cell tests validate this finding by improved PEM fuel cell performance. Reducing the cathode catalyst loading from 0.4 mg cm-2 to 0.25 mg cm-2 resulted in a power density drop at an application-relevant 0.7 V of only 4% for the novel catalyst, compared to the 10% and 20% for the commercial benchmarks reference catalysts.

Optimization of graded catalyst layer to enhance uniformity of current density and performance of high temperature-polymer electrolyte membrane fuel cell

The optimal use of catalyst materials is essential to improve the performance, durability and reduce the overall cost of the fuel cell. The present study is related to spatial distributions of current and overpotential for various graded catalyst structures in a high temperature-polymer electrolyte membrane fuel cell (HT-PEMFC). The effect of catalyst gradient across the catalytic layer (CL) thickness and along the channel and their combination on cell performance and catalyst utilization is investigated. The graded catalytic structure comprises two, three, or multiple layers of catalyst distribution. For a total cathode catalyst loading of 0.35 mg/cm2, higher loading near the membrane presents improved cell performance and catalyst utilization due to reduced limitations caused by oxygen and ion diffusions. However, non-uniformity in the current distribution is significantly increased. The increase in the catalyst loading along the reactant flow provides a substantially uniform current density but lower cell performance. The synergy of varying catalytic profiles across the CL thickness and along the cathode flow direction is investigated. The results emphasize the importance of a rational design of cathode structure and mathematical functions as a strategic tool for functional grading of a CL towards improved uniform current distribution and catalyst utilization.

Dense Pt Nanowire Electrocatalyst for Improved Fuel Cell Performance Using a Graphitic Carbon Nitride-Decorated Hierarchical Nanocarbon Support.

An innovative strategy is presented to engineer supported-Pt nanowire (NW) electrocatalysts with a high Pt content for the cathode of hydrogen fuel cells. This involves deposition of graphitic carbon nitride (g-CN) onto 3D multimodal porous carbon (MPC) (denoted as g-CN@MPC) and using the g-CN@MPC as an electrocatalyst support. The protective coating of g-CN on the MPC provides good stability for the electrocatalyst support against electrochemical oxidation, and also enhances oxygen adsorption and provides additional active sites for the oxygen reduction reaction. Compared with commercial carbon black Vulcan XC-72R (denoted as VC) support material, the larger hydrophobic surface area of the g-CN@MPC enables the supported high-content Pt NWs to disperse uniformly on the support. In addition, the unique 3D interconnected pore networks facilitate improved mass transport within the g-CN@MPC support material. As a result, the g-CN@MPC-supported high-content Pt catalysts show improved performance with respect to their counterparts, namely, MPC, VC, and g-CN@VC-supported Pt NW catalysts and the conventional Pt nanoparticle (NP) catalyst (i.e., Pt(20wt%)NPs/VC (Johnson Matthey)) used as the benchmark. More importantly, the g-CN-tailored high-content Pt NW (≈60wt%) electrocatalyst demonstrates high PEM fuel cell power/performance at a very low cathode catalyst loading (≈0.1mgPt cm-2 ).

The Influence of Porous Co/CeO1.88-Nitrogen-Doped Carbon Nanorods on the Specific Capacity of Li-O2 Batteries

Li-O2 batteries are attracting considerable attention as a promising power source for electric vehicles as they have the highest theoretical energy density among reported rechargeable batteries. However, the low energy density and efficiency of Li-O2 batteries still act as limiting factors in real cell implementations. This study proposes the cathode structure engineering strategy by tuning the thickness of a catalyst layer to enhance the Li-O2 battery performance. The construction of the Li-O2 battery with a thinner porous cathode leads less parasitic reactions at the solid electrolyte interface, maximization of the catalyst utilization, and facile transport of oxygen gas into the cathode. A remarkably high specific capacity of 33,009 mAh g-1 and the extended electrochemical stability for 75 cycles at a 1000 mAh g-1 limited capacity and 100 mA g-1 were achieved when using the porous Co/CeO1.88-nitrogen-doped carbon nanorod cathode. Further, a high discharge capacity of 20,279 mAh g-1 was also achieved at a relatively higher current density of 300 mA g-1. This work suggests the ideal cathode structure and the feasibility of the Co/CeO1.88-nitrogen-doped carbon nanorod as the cathode material, which can minimize the areal cathode catalyst loading and maximize the gravimetric energy density.

Para-Polybenzimidazole for High Temperature Alklaine Water Electrolysis

Due to limited storage capacity and environmental resources is a trend of increasing interest in new energy sources. Among various new energy source, Hydrogen has attracted attention as a future energy source because it emits very little environmental pollutants. In addition, hydrogen has high energy density per mass of 143 kJ/g, which is about 3 times higher than of fossil fuels. So, hydrogen is widely used in energy production, storage, utilization. Hydrogen production methods include reforming using fossil fuels, and using non-fossil fuels such as electricity and heat. Reforming emits many environmental pollutants but the method using electricity, heat, and etc. don’t emit environmental pollutants. However, other methods, except electricity, are still need to research. The method using electricity is largely divided into alkaline water electrolysis (AWE), polymer electrolyte water electrolysis (PEMWE), anion exchange membrane water electrolysis (AEMWE). The PEMWE has advantages such as various operating conditions, small cell design, and high performance, but has a large disadvantage of expensive due to using high cost component. The anion exchange membrane water electrolysis has advantages of other water electrolysis and complements disadvantages. But anion exchange membrane has low stability and conductivity, so it needs to research. AWE has advantages such as non-PGM catalyst, low price and long-term stability. However, there is a disadvantage in that gas crossover, and low current densities are easier than other water electrolysis. But, zero gap assembly can compensate for the disadvantages of the AWE.At present, there are anion exchange membranes used in water electrolysis which is PBI, PEEK, PVA, and etc. Especially, PBI showed a high performance and stability in high temperature, alkaline condition. In addition, it showed excellent stability even at high temperature. Therefore, PBI is expected to be applied to high temperature steam process due to its excellent high temperature stability.In this study, the water uptake, thickness changes were measured in 10 wt% potassium hydroxide (KOH) to make the chemical stability of the PBI. It was measured for about a month, and there was no significant change in water uptake and thickness, but it was confirmed that cracks occurred on the surface. PBI was used to develop electrolytic MEAs that can operate in high temperature and alkaline conditions. Electrodes were fabricated catalyst slurry. Catalyst slurry were prepared by catalyst, H2O, ionomer and IPA. The catalyst used was IrO2 as anode and Pt/C as cathode, respectively. Both anode and cathode were used PFTE as ionomer. The catalyst to ionomer ratio was 0.091 to 1. The resulting catalyst slurry was sonicated in water bath for 40 min. Electrodes were fabricated by catalyst coated substrate (CCS) method on porous transport layers (PTLs). The cathode catalyst loading as 0.95 to 1 mg/cm2 and anode catalyst loading as 2 mg/cm2, respectively. The prepared electrode was heated at 350 oC for 10 min to disperse PTFE. The electrode size was 6.25 cm2. Single cell tests were operated 80, and 120 ℃, 1.5 bar. Electrolyte was 10 wt% Potassium hydroxide (KOH) which was injected into the anode side. The flow rate was 20 ml/min. Electrochemical analysis was performed using LSV, and EIS. LSV was measured by increasing 10 mV per second from 1.0 to 2.0 V, and EIS was measured in the range of 50 kHz to 50 mHz at 1.6 V. MEA containing PBI membrane is showed about 700 mA/cm2 at 2.0 V. Compared to the previous research results (80 oC), it was applied to high temperature alkaline water electrolysis and exhibited high performance. In addition, high stability of the PBI membrane was maintained even in long term operation for more than 200 h in 120 ℃, 1.5 bar.

(Invited) Fuel Cells for Heavy Duty Vehicles

The commercialization of fuel cell products for a variety of applications including forklifts, buses, cars and heavy duty trucks is well underway. Particularly in the heavy duty fuel cell market, recent studies suggest that in Europe, fuel cell electric buses (FCEB) total cost of ownership (TCO) will breakeven with battery electric buses (BEB) by 2023, and with internal combustion engine buses (ICEB) by 20241. For applications such as long-distance and heavy-duty transportation, the hydrogen route appears the decarbonisation option of choice, and can become cost competitive with internal combustion engines by 20302.Over the past 30 years, Ballard has developed a wide array of technology “building blocks” for Fuel Cell stacks components. The application requirements (duty cycle, speed, vehicle weight, lifetime and environmental exposure) will determine the key stack features and result in customization of components where economically viable. In contrast with fuel cell stacks developed for passenger cars, Fuel Cells for heavy duty vehicles are particularly challenged by high durability requirements3, with MEA attributes such as catalyst loading and peak efficiency point significantly affecting stack and fuel costs.Building on proven and demonstrated stack durability in the field of more than 35,000 hours in heavy duty vehicles4 Ballard’s MEA development activities draw from extensive field experience to support step changes in durability with each subsequent product iteration. The use of an accelerated testing and modeling approach developed and validated over numerous product iterations enables continuous cost decreases and gains in power density, operational robustness and reliability, with a calculated risk tolerance for new technology introduction.Those MEA durability prediction models along with a good understanding of failure mechanisms are a cornerstone to developing the next generation of Fuel Cells for heavy duty vehicles. Of particular importance is the use of the voltage degradation model to evaluate the time to reach the degradation target for heavy duty applications (USDOE Ultimate target of 10% degradation at 30,000 hours5). Simulation results as a function of the electrode composition show the relationship between cathode catalyst loading and lifetime, and assist in making electrode design and composition choices for a successfully durable product. A sharp increase in voltage loss is observed when local oxygen transport resistance becomes limiting once the cathode reaches low surface area. Maximizing beginning-of-life catalyst electrochemical surface area (ECSA) utilization in the electrode structure, as well as optimizing surface area retention, can have significant benefits for lifetime. A combination of design choices or processing parameters during catalyst layer fabrication can be effective ways to optimize the electrode6.The same voltage degradation model is used to demonstrate the relationship between lifetime and the peak operating current density of the product, which limits the stack design power density within the allocated voltage degradation constraints of heavy-duty vehicles.The simulation results demonstrate that the ideal Fuel Cell stack for heavy duty applications is the result of complex trade-offs between cost, stack design attributes (e.g. catalyst loading), active area sizing (peak efficiency point) and durability, with the ultimate goal to achieve an attractive TCO for wide acceptance of the technology. References Deloitte and Ballard. (2020). Fueling the Future of Mobility: Hydrogen and fuel cell solutions for transportation. Volume 1 [White paper]. Deloitte China. https://www2.deloitte.com/content/dam/Deloitte/cn/Documents/finance/deloitte-cn-fueling-the-future-of-mobility-en-200101.pdf McKinsey & Company and Hydrogen Council. (2020). Path to hydrogen competitiveness: A cost perspective. https://www.hydrogen.energy.gov/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdfMacauley, N., Lauritzen, M., Knights, S. and Kjeang, E., J. Electrochem. Soc., 165(10), F780 (2018).https://www.ballard.com/about-ballard/newsroom/news-releases/2020/01/27/ballard-powers-fuel-cell-electric-vehicles-for-unprecedented-30-million-kilometers-enough-to-circle-the-globe-750-timesUSDOE Hydrogen Class 8 Long Haul Truck Targets https://www.hydrogen.energy.gov/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdf M. Dutta, A. Young, V. Colbow, J. Bellerive, S. Knights, Examining Catalyst Layer Design Strategies for Improved Fuel Cell Performance and Durability, ECS PRiME 2020

Durable Hybrid Electrocatalysts for Proton Exchange Membrane Fuel Cells

Developing transition metal and nitrogen co-doped carbon (Me-N-C) catalysts with comparable ORR activity is a feasible approach to addressing the material cost issue of proton exchange membrane fuel cells (PEMFCs).1-3 However, the low durability of Me-N-C hinders their practical application. It was found that the half-wave potential of Fe-N-C catalysts decreased significantly (16-30 mV) only after 10000 cycles between 0.6 and 1.0 V in acidic electrolytes,4-5 and above 50% current density loss only after 20 h at 0.4 V in sing cell tests.6-7Herein, we rationally designed a hybrid Pt-Fe-N-C electrocatalyst consisting of abundant Pt and Fe single atoms homogeneously dispersed on the nitrogen-doped carbon support and a small amount of Pt-Fe alloy nanoparticles. The distributions of single atoms and morphologies of carbon framework were obtained with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The oxidation state and chemical bond information was characterized by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The optimized Pt-Fe-N-C consisting of 0.21wt.% Pt and 2.4 wt.% Fe demonstrated unprecedented durability upon potential cycling with no change in the half-wave potential after 70000 cycles between 0.6 and 1.0 V (Figure 1a). The higher durability was also confirmed in the fuel cell testing. As shown in Figure 1b, after keeping the voltage at 0.4 V for 85 h, the current density of the fuel cell using Pt-Fe-N-C as the cathode material only dropped by 20%. For comparison, the current density dropped by more than 50% after only 23 h for the fuel cell using Fe-N-C as the cathode material.This work demonstrates the feasibility of improving the durability of Fe-N-C material via ultra-low Pt doping. In addition, it highlights the importance of the synergy effect between Pt and Fe single atoms and the strong interaction between active sites and carbon support, which may shed light on improving the durability of non-precious metal catalysts via a hybrid structure.Figure 1. (a) Steady-state polarization curves of oxygen reduction reaction activity Pt-Fe-N-C after 70000 cycles in 0.1 M HClO4 electrolyte. The catalyst loading is 0.51 mg cm-2. (b) Long-term durability test of Pt-Fe-N-C and Fe-N-C catalyst at 0.4 V (1 bar H2/1 bar air; anode Pt loading: 0.1 mg cm-2; cathode catalyst loading: 3.2 mg cm-2; cell temperature 80 °C; 100% RH).References(1)Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt. Science 2011, 332, 443-447.(2)Chung, H. T.; Cullen, D. A.; Higgins, D.; Sneed, B. T.; Holby, E. F.; More, K. L.; Zelenay, P., Direct Atomic-Level Insight into the Active Sites of a High-Performance PGM-Free ORR Catalyst. Science 2017, 357, 479-484.(3)Proietti, E.; Jaouen, F.; Lefèvre, M.; Larouche, N.; Tian, J.; Herranz, J.; Dodelet, J.-P., Iron-Based Cathode Catalyst with Enhanced Power Density in Polymer Electrolyte Membrane Fuel Cells. Nat. Commun. 2011, 2, 416.(4)Xiao, F.; Xu, G.-L.; Sun, C.-J.; Xu, M.; Wen, W.; Wang, Q.; Gu, M.; Zhu, S.; Li, Y.; Wei, Z., Nitrogen-Coordinated Single Iron Atom Catalysts Derived from Metal Organic Frameworks for Oxygen Reduction Reaction. Nano Energy 2019, 61, 60-68.(5)Merzougui, B.; Hachimi, A.; Akinpelu, A.; Bukola, S.; Shao, M., A Pt-Free Catalyst for Oxygen Reduction Reaction Based on Fe–N Multiwalled Carbon Nanotube Composites. Electrochimica Acta 2013, 107, 126-132.(6)Chen, J.; Yan, X.; Fu, C.; Feng, Y.; Lin, C.; Li, X.; Shen, S.; Ke, C.; Zhang, J., Insight into the Rapid Degradation Behavior of Nonprecious Metal Fe–N–C Electrocatalyst-Based Proton Exchange Membrane Fuel Cells. ACS Appl. Mater. Interfaces 2019, 11, 37779-37786.(7)Choi, J.-Y.; Yang, L.; Kishimoto, T.; Fu, X.; Ye, S.; Chen, Z.; Banham, D., Is the Rapid Initial Performance Loss of Fe/N/C Non Precious Metal Catalysts Due to Micropore Flooding? Energy Environ. Sci. 2017, 10, 296-305. Figure 1

Interplay between PEMFC Performance, Gas Diffusion Electrode Structure and Mass Transport Properties

Due to substantial research and development in the last two decades, energy conversion systems based on proton exchange membrane fuel cell (PEMFC) technology are emerging to the market. However, cost of the fuel cells is still high compared to the conventional energy generating systems like internal combustion engines. A decrease in Pt loading is a vital requirement for cost reduction and commercialization of the fuel cell technology. Operation of low-Pt PEMFCs showed that fuel cell performance is declining with a decrease in Pt loading and the voltage drop becomes very significant at high current density due to increasing mass transfer losses [1]. Thus, it is critical to understand this voltage loss phenomenon and mitigate it. Previously we developed a method for determining the oxygen mass transfer coefficient which is based on measurements of limiting current distributions using O2 mixtures with different diluents (from He to C3H8) [2]. In this work we studied effects of gas diffusion electrodes (GDEs) composition and structure such as cathode catalyst and microporous layer (MPL) loadings on oxygen mass transport and PEMFC performance.A segmented cell and data acquisition system were operated with commercially available 100 cm2 MEAs with cathode loadings of 0.1, 0.2 and 0.4 mgPt cm-2, while the anode Pt content was kept 0.1 mg cm-2. Cathode gas diffusion layer (GDL) was also varied to separate contributions from MPL and catalyst layer. 25BA (no MPL) and 25BC (with MPL) diffusion medias from Sigracet SGL were used for the cathode electrode. The experiments were performed at 80°C, fully humidified conditions and varied back pressures. Details of experimental procedures are presented in [2].A comparison of the IV curves showed that 25BA cannot provide good water and gas management at high current operation (Fig. 1 a). At the same time, an increase in Pt loading significantly improves the performance at low and high current regimes. The high performance of the sample MEA-0.4-25BC with Pt loading of 0.4 mgPt cm-2 and 25BC cathode GDL indicates on a possibility that part of catalyst layer acts as an MPL and actively participates in water removal from electrode structure to macro-porous layer of carbon paper.Using our previously described method we separated mass transport coefficients in gas phase (km, N2 ) and a combination of Knudsen diffusion and transport through ionomer/water films in overall GDE (kK+film ). Comparing results for MEA-25BA and MEA-25BC we extracted contribution from MPL (kK, MPL ) and cathode layer (CL) (kK+film, CL ). Further variation of back pressure allowed us to eliminate impact of Knudsen diffusion in CL and extract pressure independent contribution (kfilm,CL ) which represents a diffusion through the ionomer/water films in CL.The obtained values of pressure-independent oxygen mass transfer coefficients in CL (kfilm, CL ), Knudsen diffusion in MPL (kK, MPL ) and CL (kK, CL ) and molecular diffusion in N2 media (km, N2 ) are compared at Fig. 1 b. A reduction in Pt loading leads to a decrease in kfilm, CL as it was previously reported [3-6]. Interestingly, that MEA with the highest Pt content (MEA-0.4-25BC) is characterized by the greatest value of kK, MPL as well. All samples have nearly the same values of the O2 mass transfer coefficient in gas phase varying from 0.040 to 0.043 m s-1.Performances of the studied samples in terms of cell voltage at 1.5 A cm-2 and mass transport voltage losses (permeability and diffusion) are presented at Fig. 1 c. A direct comparison of the data shows that MEA-0.4-25BC has the best performance due to the greatest values of kfilm, CL and kK, MPL insuring a good gas transport within catalyst layer and MPL as well as water transport. Detailed analysis of the PEMFC performance, voltage losses and oxygen mass transfer coefficients at various operating conditions will be presented and discussed.ACKNOWLEDGEMENTSWe gratefully acknowledge funding from ONR (N00014-19-1-2159) and ARO (W911NF-15-1-0188). The authors are thankful G. Randolf and J. Huizingh for support of the operation as well as T. Carvalho for assisting with SEM.References A. Kongkanand, M. Mathias, J. Phys. Chem. Lett. 7 (2016) 1127.T. V. Reshetenko, J. St-Pierre, J. Electrochem. Soc., 161, F1089-F1100 (2014).Y. Ono, T. Mashio, S. Takaichi, A. Ohma, H. Kanesaka, K. Shinohara, ECS Trans. 28 (27) 69-78 (2010).N. Nonoyama, S. Okazaki, A.Z. Weber, Y. Ikogi, T. Yoshida, J. Electrochem. Soc. 158 (4) B416-B423 (2011).T. Greszler, D. Caulk P. Sinha, J. Electrochem. Soc. 159 (12) F831-F840 (2012).J.P. Owejan, J.E. Owejan, W. Gu, J. Electrochem. Soc. 160 (8) F824-F839 (2013). Figure 1

Development of an Oxygen Mass Transport Coefficient Measurement and Separation Method for Proton Exchange Membrane Fuel Cells

The cost and durability of proton exchange membrane fuel cells (PEMFCs) still limit their adoption as sustainable power systems [1]. Operation at high current densities, which decreases the inventory of costly materials [2], is still considered an option [3] in addition to concurrent reductions in Pt catalyst loadings. However, these approaches intensify mass transfer losses especially at the cathode because the oxidant stream is more dilute (21 % O2 in air) than the fuel (100 % H2) and the heavier O2 molecule moves more slowly. The improvement of characterization methods able to measure and separate oxygen mass transfer coefficients is desirable for more accurate identification and localization of resistances in membrane/electrode assemblies (MEAs).Average limiting currents iave are first measured with a dilute oxidant stream for different flow rates. Subsequently, data are fitted to a mathematical model [4] to obtain the overall mass transfer coefficient k: iave =ie (1–exp(–nFkpr /RTief)) (1)with ie the inlet reactant flow rate equivalent current density, n the number of electrons exchanged in the electrochemical reaction, F the Faraday constant, pr the dry inlet reactant stream pressure, R the ideal gas constant, T the temperature, and f the inert gas to reactant fraction in the dry inlet reactant stream. The oxidant diluent is also varied (He, N2, CO2) to separate the molecular diffusion mass transfer coefficient km by extrapolating to the origin the linear correlation between the overall mass transfer resistance and the diluent molecular mass M [4]: k –1=km (M)–1+k e+K (c)–1=km (M)–1+ke (c)–1+kK –1 (2)The ionomer permeability mass transfer coefficient contribution ke was separated from 1/k e+K by taking advantage of the constant Knudsen diffusion resistance (equation 2 above and equation 7 in [5]). For that last step, the linear correlation between the lumped ionomer permeability and Knudsen diffusion mass transfer resistance 1/k e+K and the oxygen concentration c (1 to 7 %) was extrapolated to the origin, which yielded the Knudsen diffusion mass transfer coefficient kK . This approach to isolate the Knudsen contribution is novel. Other techniques are used, including temperature variations [5].Experiments were conducted with a 50 cm2 active area cell and General Motors MEAs with a commercially relevant cathode catalyst loading of 0.05 to 0.15 mg Pt cm–2 (Pt catalyst supported on a high surface area carbon). All MEA tests were duplicated and completed for several temperatures (30 to 80 °C) and relative humidities (50 to 100 %). Four diagnostic methods were employed to supplement the analysis of mass transfer data. The use of O2, 21 % O2 in He, and air enabled the derivation of overpotentials from polarization curves [6]. The high frequency cell resistance was measured with a milliohmmeter. The catalyst area was extracted from the hydrogen adsorption region of cyclic voltammograms [7]. The overall cell water balance was also calculated to assess the presence of liquid water [8].The smallest mass transfer resistance was assigned to the ionomer permeability, which supported the need for repetitive measurements and statistics for an accurate quantification. The slope of the linear correlation between the ionomer permeability and Knudsen diffusion mass transfer resistance and the oxygen concentration was dependent on the water balance. A positive slope occurred under sub-saturated streams whereas a negative slope was correlated with the wettest operating conditions, which will require a method modification to extract the Knudsen diffusion resistance. A plot of the ionomer and molecular diffusion mass transfer resistance versus the total mass transfer overpotential showed two regimes that are differentiated by the absence/presence of liquid water (see figure). Catalyst layers, only several microns thick, have a larger mass transfer resistance and overpotential under flooding conditions.[1] Y. Wang, D. F. R. Diaz, K. S. Chen, Z. Wang, X. C. Adroher, Mater. Today, 32 (2020) 178.[2] A. Kongkanand, M. F. Mathias, J. Phys. Chem. Lett., 7 (2016) 1127.[3] N. Ramaswamy, W. Gu, J. M. Ziegelbauer, S. Kumaraguru, J. Electrochem. Soc., 167 (2020) article 064515.[4] T. Reshetenko, J. St-Pierre, J. Electrochem. Soc., 161 (2014) F1089.[5] N. Nonoyama, S. Okazaki, A. Z. Weber, Y. Ikogi, T. Yoshida, J. Electrochem. Soc., 158 (2011) B416.[6] J. St-Pierre, M. Angelo, K. Bethune, J. Huizingh, T. Reshetenko, M. Virji, Y. Zhai, Modern Fuel Cell Testing Laboratory, in Springer Handbook of Electrochemical Energy, Part D, Chapter 19, Edited by C. Breitkopf, K. Swider-Lyons, Springer, 2017, p. 611.[7] R. N. Carter, S. S. Kocha, F. T. Wagner, M. Fay, H. A. Gasteiger, ECS Trans., 11(1) (2007) 403.[8] J. St-Pierre, N. Jia, M. van der Geest, A. Atbi, H. R. Haas, United States patent 7,132,179, November 7, 2006. Figure 1