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

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 Co9 S8 /Co3 S4 /Cu2 S nanoparticle in which Co3 S4 germinates between Co9 S8 and Cu2 S. Using high-angle annular-dark-field imaging and theoretical calculation, it was found that the integration of Co9 S8 and Cu2 S tends to trigger the interface phase transition of Co9 S8 , leading to Co3 S4 interlayer due to the low formation energy of Co3 S4 /Cu2 S (-7.61 eV) than Co9 S8 /Cu2 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 7.76×1014 to 2.09×1015 cm-3 ), and creates more active sites. Compared to Co9 S8 and Cu2 S, the Co9 S8 /Co3 S4 /Cu2 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 Co9 S8 /Co3 S4 /Cu2 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.