Strain Controlling Catalytic Efficiency of Water Oxidation for Ni1-xFexOOH alloy

TL;DR

This study uses DFT+U simulations to show that applying strain and adjusting iron content in Ni1-xFexOOH alloys can optimize water oxidation efficiency, revealing strain as a new control parameter.

Contribution

It demonstrates that strain and iron content together influence catalytic efficiency, offering a novel approach to enhance water splitting catalysts.

Findings

Optimal efficiency at 33% Fe and 5% expansion.

Low Fe content mimics compressive strain effects.

Efficiency decreases at high Fe due to surface instability.

Abstract

A catalyst surface may be exposed to strain due to application of load or interfacing with a substrate with large lattice mismatch. In order to test the effect of strain on catalytic efficiency, we use Density Functional Theory +U (DFT+U) to model water oxidation on expanded and contracted surfaces of the Ni1-xFexOOH alloy, one of the best known catalysts for water splitting. We find that a low amount of iron content has a similar effect as of applying compressive strain. Due to high oxidation state of Fe4+ at the active site, the Fe-O bond is shorter than in pure FeOOH, which is beneficial for extracting electrons from states delocalized on Fe and Ni atoms. At 33% of Fe content the efficiency is even better since Fe3+ is at the active site and can easily change oxidation state during the reaction. However, the efficiency drops at higher iron percentages since the surface is unstable and may form FeOOH aggregates. We find that the best performance is obtained at 33% iron content and 5% expansion. Therefore, in addition to changing iron content, strain can also be used as a control handle for improving water splitting catalysis.