  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.
