Dual-site OER mechanism exploration through regulating asymmetric multi-site NiOOH.

ABSTRACT

Asymmetric nickel oxyhydroxide (NiOOH) possesses multi-OH and O active sites on different surfaces, (001) and (001̄), which possibly causes a complicated catalytic process. Density functional theory (DFT) calculations reveal that the unconventional dual-site mechanism (UDSM) of the oxygen evolution reaction (OER) on NiOOH (001) and (001̄) exhibits significantly lower overpotentials of 0.80 and 0.77 V, compared to 1.24 and 1.62 V for the single-site mechanism (SSM), respectively. Through chemical doping or heterojunction modifications, the constructed NiOOH@FeOOH (001̄) heterojunction reduces the thermodynamic overpotential to 0.49 V from original 0.77 V undergoing the UDSM. Although Fe/Co-doping or physical compression yield similar or slightly higher overpotentials and are not conductive to facilitating the OER process by the UDSM, all dual-site paths exhibit obviously lower overpotentials than the SSM for pristine and regulated NiOOH (001) and (001̄) from the whole viewpoint. This work identifies a more reasonable and efficient dual-site OER mechanism, which is expected to help the rational design of highly-efficient electrocatalysts.