Electronic modulation and vacancy engineering of Ni9S8 to synergistically boost efficient water splitting: Active vacancy-metal pairs

Developing easy-to-make and excellent bifunctional electrocatalysts for water splitting over a wide pH range is a challenging yet appealing topic. Herein, based on integration of vacancy engineering and electronic modulation, a high-performance v s -Ru-Ni 9 S 8 electrocatalyst for water splitting was constructed via a cost-effective one-step hydrothermal method. Under the synergistic regulation of Ru-doping and sulfur vacancies, the v s -Ru-Ni 9 S 8 exhibited the outstanding electrocatalytic performance and long-time durability, along with ultra-low OER overpotentials of 218 and 268 mV at 100 and 300 mA cm −2 in alkaline electrolyte and low HER overpotentials of 56, 131, 94 mV at 10 mA cm −2 in acidic, neutral, alkaline electrolyte. Impressively, 1.47 and 1.68 V of voltages were needed to achieve 10 and 300 mA cm −2 for the v s -Ru-Ni 9 S 8 (+, -) cell. Our DFT results revealed that the doping Ru atom played a crucial role in regulating electron density in OER, rather than served as a catalytic active site. More importantly, we corroborated the active Ni-vacancy pair composed of Ni atom and sulfur vacancy, as an active site, and its catalytic synergy in OER. Especially, a vacancy-metal synergetic mechanism for OER was suggested to correctly describe the OER process and the role of vacancy in catalytic process. Our work provides a simple and effective strategy for fabricating high-performance catalysts and an in-depth understanding of OER. ● A high-performance nickel-based sulfide electrocatalyst for overall water splitting was constructed. ● Improving synergistically the catalytic activity via electronic modulation and vacancy engineering was revealed. ● An active Ni-vacancy pair as an active site and its catalytic synergy in OER were corroborated. ● A vacancy-metal synergetic mechanism for OER was suggested.