An Experimental Study of the Effects of Operational History on Activity Changes in a PEMFC

In this contribution, we demonstrate the presence of high-spin Fe 3+ in Fe-substituted ZrO 2 (Fe x Zr 1−x O 2−δ), as deduced from X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and 57 Fe Mössbauer spectroscopy measurements. The activity of this carbon-supported Fe x Zr 1−x O 2−δ catalyst toward the oxygen reduction reaction (ORR) was examined by both rotating (ring) disk electrode (R(R)DE) method and single-cell proton exchange membrane fuel cells (PEMFCs). DFT calculations suggest that the much higher ORR mass activity of Fe x Zr 1−x O 2−δ compared to Fe-free ZrO 2 is due to the enhanced formation of oxygen vacancies: their formation is favored after Zr 4+ substitution with Fe 3+ and the oxygen vacancies create potential adsorption sites, which act as active centers for the ORR. H 2 O and/or H 2 O 2 production observed in RRDE measurements for the Fe 0.07 Zr 0.93 O 1.97 is also in agreement with the most likely reaction paths from DFT calculations. In addition, Tafel and Arrhenius analyses are performed on Fe 0.07 Zr 0.93 O 1.97 using both RRDE and PEMFC data at various temperatures.

Section: Resultsmentioning

confidence: 95%

mentioning

confidence: 99%

Nanometric Fe-Substituted ZrO₂on Carbon Black as PGM-Free ORR Catalyst for PEMFCs

Madkikar

Menga

Harzer

et al. 2019

“…While ECSA measurement only requires electron and proton access, good access to reactant O 2 is also required for ORR. Minor changes in the ionomer distribution in the electrode have been shown to significantly affect the ORR activity as well as fuel cell performance at high current density, 3,35,[37][38][39][40][41][42] a topic of great interest in the fuel cell community. 3,43,44 Therefore, it is not a surprise that these vastly diverse methods yield slightly different performance.…”

Section: Resultsmentioning

confidence: 99%

Preparation of PEMFC Electrodes from Milligram-Amounts of Catalyst Powder

Yarlagadda

McKinney²,

Keary

et al. 2017

Development of electrocatalysts with higher activity and stability is one of the highest priorities in enabling cost-competitive hydrogen-air fuel cells. Although the rotating disk electrode (RDE) technique is widely used to study new catalyst materials, it has been often shown to be an unreliable predictor of catalyst performance in actual fuel cell operation. Fabrication of membraneelectrode assemblies (MEA) for evaluation which are more representative of actual fuel cells generally requires relatively large amounts (>1 g) of catalyst material which are often not readily available in early stages of development. In this study, we present two MEA preparation techniques using as little as 30 mg of catalyst material, providing methods to conduct more meaningful MEA-based tests using research-level catalysts amounts.

“…Hypothetically, the local resistance can be attributed to slow oxygen dissolution process at the gas/ionomer interface, 266,338 and/or strong interaction between the Pt surface and the sulfonate groups in ionomer leading to either a decrease in the effective Pt surface area, or ionomer structural changes in the thinfilms near the Pt surface that lowers oxygen permeability as discussed below. 340 Thus, the measured local resistance is a sum of three components from gas phase to the Pt surface: the interfacial resistance at the gas/ionomer interface, the bulk resistance of the ionomer film, and the interfacial resistances at ionomer/Pt interfaces. Quantification of each resistance would provide fundamental knobs to mitigate the voltage losses due to the local resistance via a combined modeling and experimental approach.…”

Section: 142mentioning

confidence: 99%

A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells

Weber

Borup

Darling³

et al. 2014

509

394

Polymer-electrolyte fuel cells are a promising energy-conversion technology. Over the last several decades significant progress has been made in increasing their performance and durability, of which continuum-level modeling of the transport processes has played an integral part. In this review, we examine the state-of-the-art modeling approaches, with a goal of elucidating the knowledge gaps and needs going forward in the field. In particular, the focus is on multiphase flow, especially in terms of understanding interactions at interfaces, and catalyst layers with a focus on the impacts of ionomer thin-films and multiscale phenomena. Overall, we highlight where there is consensus in terms of modeling approaches as well as opportunities for further improvement and clarification, including identification of several critical areas for future research. Fuel cells may become the energy-delivery devices of the 21 st century. Although there are many types of fuel cells, polymer-electrolyte fuel cells (PEFCs) are receiving the most attention for automotive and small stationary applications. In a PEFC, fuel and oxygen are combined electrochemically. If hydrogen is used as the fuel, it oxidizes at the anode releasing proton and electrons according toThe generated protons are transported across the membrane and the electrons across the external circuit. At the cathode catalyst layer, protons and electrons recombine with oxygen to generate waterAlthough the above electrode reactions are written in single step, multiple elementary reaction pathways are possible at each electrode. During the operation of a PEFC, many interrelated and complex phenomena occur. These processes include mass and heat transfer, electrochemical reactions, and ionic and electronic transport. * Electrochemical Society Active Member. z E-mail: azweber@lbl.govOver the last several decades significant progress has been made in increasing PEFC performance and durability. Such progress has been enabled by experiments and computation at multiple scales, with the bulk of the focus being on optimizing and discovering new materials for the membrane-electrode-assembly (MEA), composed of the proton-exchange membrane (PEM), catalyst layers, and diffusionmedia (DM) backing layers. In particular, continuum modeling has been invaluable in providing understanding and insight into processes and phenomena that cannot be resolved or uncoupled through experiments. While modeling of the transport and related phenomena has progressed greatly, there are still some critical areas that need attention. These areas include modeling the catalyst layer and multiphase phenomena in the PEFC porous media.While there have been various reviews over the years of PEFC modeling 1-7 and issues, [8][9][10][11][12][13][14] as well as numerous books and book chapters, there is a need to examine critically the field in terms of what has been done and what needs to be done. This review serves that purpose with a focus on transport modeling of PEFCs. This is not meant to be an exhaustive review...