Uncovering The Role of Oxygen in Ni-Fe(OxHy) Electrocatalysts using In situ Soft X-ray Absorption Spectroscopy during the Oxygen Evolution Reaction

Dorian Drevon,Kathrin M Lange,Petko Chernev,Mikaela Görlin,Lifei Xi,Holger Dau

doi:10.1038/s41598-018-37307-x

Abstract

In-situ X-ray absorption spectroscopy (XAS) at the oxygen K-edge was used to investigate the role of oxygen during the oxygen evolution reaction (OER) in an electrodeposited Ni-Fe(OxHy) electrocatalyst in alkaline pH. We show the rise of a pre-peak feature at 529 eV in the O K-edge spectra, correlated to the appearance of a shoulder at the Ni L3-edge and formation of oxidized Ni3+/4+-O. Then, for the first time, we track the spectral changes in a dynamic fashion in both the soft and hard X-ray regimes during cyclic voltammetry (in situ CV-XAS) to obtain a fine-tuned resolution of the potential-related changes. The pre-peak feature at the O K-edge likely signifies formation of an electron deficient oxygen site. The electrophilic oxygen species appears and disappears reversibly in correlation with the Ni2+ ↔ Ni3+/4+ process, and persists during OER catalysis as long the metal is oxidized. Our study provides new insight into OER electrocatalysis: Before onset of the O-O bond formation step, the catalytic oxyhydroxide has accumulated electron deficiencies by both, oxidation of transition metal ions and formation of partially oxidized oxygen sites.

Highlights

Reducing global carbon emissions will require efficient catalysts for use in solar-to-fuel conversion processes, where electrochemical water oxidation is the key to approach zero emissions[1]
The oxygen evolution reaction (OER) overpotential is assumed to be restricted by scaling relations between surface bound OER intermediates (O*, OH*, OOH*) that includes four proton-coupled electron transfer (PCET) steps resulting in high overpotential[25]
An electrodeposited Ni-Fe oxyhydroxide (OxHy) catalyst was investigated for the oxygen evolution reaction using in situ X-ray absorption spectroscopy in the soft and hard X-ray regimes

Summary

Introduction

Reducing global carbon emissions will require efficient catalysts for use in solar-to-fuel conversion processes, where electrochemical water oxidation is the key to approach zero emissions[1]. We present the first in situ measurements in both the soft and the hard X-ray regimes under OER catalytic conditions at the O K-edge and the metal (Ni, Fe) L- and K- edges of an electrodeposited Ni-Fe(OxHy) oxygen evolution electrocatalyst in alkaline electrolyte.

Results

Conclusion