A novel fuel cell design for operando energy-dispersive x-ray absorption measurements

A S Leach,R Jervis,M Amboage,J Hack,M Wilding,A E Russell,D J L Brett,P L Cullen,S Diaz-Moreno,E Magliocca,H Huang,P F Mcmillan,C A Howard,P R Shearing,T S Miller

doi:10.1088/1361-648x/ac0476

Abstract

A polymer electrolyte fuel cell has been designed to allow operando x-ray absorption spectroscopy (XAS) measurements of catalysts. The cell has been developed to operate under standard fuel cell conditions, with elevated temperatures and humidification of the gas-phase reactants, both of which greatly impact the catalyst utilisation. X-ray windows in the endplates of the cell facilitate collection of XAS spectra during fuel cell operation while maintaining good compression in the area of measurement. Results of polarisation curves and cyclic voltammograms showed that the operando cell performs well as a fuel cell, while also providing XAS data of suitable quality for robust XANES analysis. The cell has produced comparable XAS results when performing a cyclic voltammogram to an established in situ cell when measuring the Pt LIII edge. Similar trends of Pt oxidation, and reduction of the formed Pt oxide, have been presented with a time resolution of 5 s for each spectrum, paving the way for time-resolved spectral measurements of fuel cell catalysts in a fully-operating fuel cell.

Highlights

Comparing the PtPt membrane electrode assembly (MEA), it was found that the performance of the cell during lab-based testing exceeded that of an MEA with identical electrode loadings tested on the beamline, with a higher cut-off current density of mA cm-2 compared with 437 mA cm-2, respectively
The reason for the lower performance is attributed to higher Ohmic losses, despite the higher OCV of the cell tested on the beamline
The cell’s performance as a fuel cell in the idealised laboratory environment and on the beamline has been demonstrated, illustrating the effects of the reduced humidification available at the beamline on the cell performance. This novel cell has been compared to an established three-electrode aqueous cell, and it has been shown to provide similar quality X-ray absorption spectroscopy (XAS) data and cyclic voltammetry performance

Summary

Introduction

When using this arrangement, spectra can be collected in fluorescence detection mode, enabling experiments in dilute samples with second time resolution. When benchmarking the characteristics of fuel cell catalysts using a classical three-electrode approach, it is not clear how the aqueous environment compares to a realistic triple-phase boundary involving the gas-phase reactants in contact with a solid membrane electrolyte and catalyst surface in a fuel cell set-up.[17] For example, in some aqueous-phase three-electrode based measurements under load cycle conditions, degradation mechanisms associated with particle migration and coalescence have been observed.[18] This contrasts with membrane electrode assembly (MEA) tests that have only reported Pt dissolution, but not migration or coalescence.[19] This highlights the fact that it is of the utmost importance to perform characterisation of the electrocatalyst behaviour under realistic operando conditions, as the electrode layer in an aqueous rotating disc electrode, or even a model MEA environment, differs substantially from that experienced by a real working fuel cell electrode. It is important to move towards the evaluation of catalysts in real working fuel cells (or as close as possible), by employing gas diffusion electrodes and truly operando environments.[21]

Methods

Results

Conclusion