The Structure-Performance Relation for Alkaline OER Electrocatalyst Investigated Using Analytical Electron Microscopy

Abstract

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.