Effect of Interlayer Co2+ on Structure and Charge Transfer in NiFe Layered Double Hydroxides

The intercalation of Co in NiFe layered double hydroxides (LDH) significantly improves the electrocatalytic performance of the LDH for the oxygen evolution reaction. The mechanism behind the improvement and the structure of the Co-intercalated LDHs, however, is not precisely known. We use classical molecular dynamics (CMD) to study the impact of intercalated Co on the structure of NiFe LDH and the electron transfer process. CMD studies find that the Co ions form small clusters, pushing apart the surrounding hydroxide sheets to form small pockets around these clusters, disrupting the planar nature of the sheets in the absence of intercalated Co clusters. The structure of the pockets is a strong function of force field parameters and the accuracy of the LDH bulk modulus. We use umbrella sampling to study electron transfer and show that the clusters of Co in the interlayer are important for electron transfer, such that solvent molecules have greater freedom to reorient with a change in charge state, thereby reducing the barrier to electron transfer.