The Structure-Performance Relation for Alkaline OER Electrocatalyst Investigated Using Analytical Electron Microscopy
Authors: Yu Haoran , Osmieri Luigi , Kariuki Nancy N. , Myers Deborah J. , Hermann Raphael P. , Serov Alexey , Zelenay Piotr , Cullen David A. 
Published: September 2023

Water electrolysis technology plays a key role in reducing carbon emission by converting renewable energy to clean hydrogen. Among various types of electrolyzers, anion exchange membrane water electrolyzer (AEMWE) receives growing effort of research due to its potential of comparable power density as its counterpart, proton exchange membrane water electrolyzer (PEMWE), while offering less corrosive environment on the oxygen evolution electrode which permits the use of non-noble metal catalysts [1].

Nickel-iron oxides/hydroxides are among the most active electrocatalysts for oxygen evolution reaction (OER) in alkaline environment [2]. Recently, aerogel-like Ni-Fe oxides developed at Los Alamos National Laboratory have shown promising performance in AEMWE. The modified sol-gel approach followed by drying under supercritical condition produces high-surface-area oxides which likely contributes to high OER activity with enhanced number of active sites compared to other synthesis methods [3].

In this work, we aim to elucidate the structure-performance relation for aerogel-like Ni-Fe oxides. Analytical electron microscopy methods, namely, energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) are used to investigate the distribution of Fe in the oxides and the oxidation states of Ni and Fe. The effect of annealing temperature in air on the oxide structure and OER activity has been investigated. Moreover, the structural changes before and after catalyst activation and long-term operation at OER potentials have been studied. Finally, results from analytical electron microscopy have been correlated with X-ray absorption spectroscopy and 57Fe Mossbauer spectroscopy to obtain a comprehensive picture of the oxide composition, especially the chemical environment of Fe.

References

[1] C Santoro et al., ChemSusChem, 15 (2022), p.e202200027.

[2] MB Stevens, et al., J. Am. Chem. Soc., 139 (2017) p.11361.

[3] W Moschkowitsch et al., ACS Catal., 12 (2022), p.12162.

[4] This material is based on work performed by the Electrocat 2.0 Consortium, which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office. Electron microscopy research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy (DOE). The U.S. government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).