Built‐In Electric Field Boosted Overall Water Electrolysis at Large Current Density for the Heterogeneous Ir/CoMoO4 Nanosheet Arrays

Abstract Advanced bifunctional electrocatalysts are essential for propelling overall water splitting (OWS) progress. Herein, relying on the obvious difference in the work function of Ir (5.44 eV) and CoMoO 4 (4.03 eV) and the constructed built‐in electric field (BEF), an Ir/CoMoO 4 /NF heterogeneous catalyst, with ultrafine Ir nanoclusters (1.8 ± 0.2 nm) embedded in CoMoO 4 nanosheet arrays on the surface of nickel foam skeleton, is reported. Impressively, the Ir/CoMoO 4 /NF shows remarkable electrocatalytic bifunctionality toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), especially at large current densities, requiring only 13 and 166 mV to deliver 10 and 1000 mA cm −2 for HER and 196 and 318 mV for OER. Furthermore, the Ir/CoMoO 4 /NF||Ir/CoMoO 4 /NF electrolyzer demands only 1.43 and 1.81 V to drive 10 and 1000 mA cm −2 for OWS. Systematical theoretical calculations and tests show that the formed BEF not only optimizes interfacial charge distribution and the Fermi level of both Ir and CoMoO 4 , but also reduces the Gibbs free energy (Δ G H* , from 0.25 to 0.03 eV) and activation energy (from 13.6 to 8.9 kJ mol −1 ) of HER, the energy barrier (from 3.47 to 1.56 eV) and activation energy (from 21.1 to 13.9 kJ mol −1 ) of OER, thereby contributing to the glorious electrocatalytic bifunctionality.