Enhanced Electrocatalytic Water Oxidation by Interfacial Phase Transition and Photothermal Effect in Multiply Heterostructured Co9S8/Co3S4/Cu2S Nanohybrids

Abstract The rational design of advanced nanohybrids (NHs) with optimized interface electronic environment and rapid reaction kinetics is pivotal to electrocatalytic schedule. Herein, we developed a multiple heterogeneous Co 9 S 8 /Co 3 S 4 /Cu 2 S nanoparticle in which Co 3 S 4 germinates between Co 9 S 8 and Cu 2 S. Using high‐angle annular‐dark‐field imaging and theoretical calculation, it was found that the integration of Co 9 S 8 and Cu 2 S tends to trigger the interface phase transition of Co 9 S 8 , leading to Co 3 S 4 interlayer due to the low formation energy of Co 3 S 4 /Cu 2 S (−7.61 eV) than Co 9 S 8 /Cu 2 S (−5.86 eV). Such phase transition not only lowers the energy barrier of oxygen evolution reaction (OER, from 0.335 eV to 0.297 eV), but also increases charge carrier density (from 7.76×10 14 to 2.09×10 15 cm −3 ), and creates more active sites. Compared to Co 9 S 8 and Cu 2 S, the Co 9 S 8 /Co 3 S 4 /Cu 2 S NHs also demonstrate notable photothermal effect that can heat the catalyst locally, offset the endothermic enthalpy change of OER, and promote carrier migrate, reaction intermediates adsorption/deprotonation to improve reaction kinetics. Profiting from these favorable factors, the Co 9 S 8 /Co 3 S 4 /Cu 2 S catalyst only requires an OER overpotential of 181 mV and overall water splitting cell voltage of 1.43 V to driven 10 mA cm −2 under the irradiation of near‐infrared light, outperforming those without light irradiation and many reported Co‐based catalysts.