Origin of High OER Activity in Ni/Fe Oxyhydroxides
Operando X-ray techniques and density-functional theory (DFT) are used to understand the effect of Fe on the performance of the oxygen-evolving reaction (OER) Ni1-xFexOOH catalysts.
Significance & impact
With excellent agreement between theory and experiment, the origin of the 500-fold OER increased activity in alkaline electrolyte was investigated, demonstrating that the presence of Fe in Ni1-xFexOOH octahedral sites results in optimal adsorption energies for OER intermediates and low overpotentials.
Operando X-ray absorption spectroscopy (XAS) and high energy resolution fluorescence detection (HERFD) reveals that Fe3+ in Ni1-xFexOOH occupies octahedral sites with unusually short Fe–O bond distances, induced by edge-sharing with surrounding [NiO6] octahedra. Using computational methods, it is established that this structural motif results in near optimal adsorption energies of OER intermediates and low overpotentials at Fe sites. By contrast, Ni sites in Ni1-xFexOOH are not active sites for the oxidation of water.
- Operando X-ray spectroscopy provides local electronic structure information at Fe and Ni sites
- Mixed (Ni,Fe)OOH are up to 500-fold more active than pure NiOOH and FeOOH materials
- DFT+Hubbard U framewor is used to obtain theoretical, site-specific OER overpotentials from Gibbs free energies of intermediates