Co-doped RuIr nanoparticles for enhanced activity and stability in alkaline overall water splitting

Developing highly active and stable bifunctional electrocatalysts for overall water splitting is critical for sustainable hydrogen production. Herein, the introduction of Co dopants into RuIr alloys resulted in a comprehensive enhancement of both HER and OER activities and stability. Co dopants tuned the electronic structure of Ru/Ir, optimizing the hydrogen binding energy and weakening the OH adsorption ability on Ru/Ir active sites, thereby enhancing HER performance. Co-Ru_0.55Ir_0.45O_x required only a 21.2 mV overpotential to achieve 10 mA cm⁻², with a Tafel slope of 27.9 mV dec⁻¹ and a TOF of 7.18 H₂ per s (at −0.15 V vs. RHE) in the alkaline HER. Additionally, the electrochemical dissolution of Co and the increase in oxygen vacancies promoted the formation of oxygen-deficient Ru/Ir-O_v species, which are identified as the actual active sites for the OER, thereby initiating a continuous metal site-oxygen vacancy synergistic mechanism (MS-O_vSM). In this pathway, two OH⁻ species nucleophilically attack the adjacent Ru/Ir-O_v pair and directly couple to form *O-O* intermediates, thus improving OER activity. Co-Ru_0.55Ir_0.45O_x exhibited an overpotential of 242 mV at 10 mA cm⁻², with a Tafel slope of 41.8 mV dec⁻¹, and a TOF of 3.23 O₂ per s (at 1.60 V vs. RHE) in alkaline solution. The d-d orbital interactions between Co and RuIr facilitated the electron transfer from Co to Ir and Ru, suppressing particle agglomeration and the dissolution of Ru/Ir species due to severe oxidation, thereby enhancing stability. The constructed Co-Ru_0.55Ir_0.45O_x||Co-Ru_0.55Ir_0.45O_x electrolyzer achieved 10 mA cm⁻² at a potential of 1.51 V, demonstrating its potential application in overall water splitting.