Manipulating d-d orbital hybridization induced by Mo-doped Co9S8 nanorod arrays for high-efficiency water electrolysis

Precisely refining the electronic structure of electrocatalysts represents a powerful approach to further optimize the electrocatalytic performance. Herein, we demonstrate an ingenious d-d orbital hybridization concept to construct Mo-doped Co9S8 nanorod arrays aligned on carbon cloth (CC) substrate (abbreviated as Mo-Co9S8@CC hereafter) as a high-efficiency bifunctional electrocatalyst toward water electrolysis. It has experimentally and theoretically validated that the 4d-3d orbital coupling between Mo dopant and Co site can effectively optimize the H2O activation energy and lower H* adsorption energy barrier, thereby leading to enhanced hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities. Thanks to the unique electronic and geometrical advantages, the optimized Mo-Co9S8@CC with appropriate Mo content exhibits outstanding bifunctional performance in alkaline solution, with the overpotentials of 75 and 234 mV for the delivery of a current density of 10 mA cm−2, small Tafel slopes of 53.8 and 39.9 mV dec−1 and long-term stabilities for at least 32 and 30 h for HER and OER, respectively. More impressively, a water splitting electrolylzer assembled by the self-supported Mo-Co9S8@CC electrode requires a low cell voltage of 1.53 V at 10 mA cm−2 and shows excellent stability and splendid reversibility, demonstrating a huge potential for affordable and scalable electrochemical H2 production. The innovational orbital hybridization strategy for electronic regulation herein provides an inspirable avenue for developing progressive electrocatalysts toward new energy systems.