Cu dopants as electron buffers for stabilizing Ru-based active layers for hydrogen evolution

There is an urgent need for development of efficient and long-term stable catalytic electrodes for the hydrogen evolution reaction (HER) via alkaline water electrolysis (AWE) to enable economically competitive hydrogen energy production. In this work, a facile air pyrolysis treatment is used to fabricate RuO2 coatings on a Ti substrate (RuO2/TF), and the surface state of the active coatings during HER was investigated. It was observed that the original RuO2 surface transforms into a partially reduced form composed of mixed valence states (0/+4). Although the newly-formed surface has higher activity than RuO2, the Ru state and current efficiency fluctuate with the electrolysis conditions, and the HER activity will be limited by the final reduced state (i.e., Ru0). To stabilize and improve the active Ru surface, Cu, which experiences a polyvalence change around the HER potential, is doped into the RuO2 coating as an electron buffer. This modification with Cu electron buffers results in an active Ru surface that exhibits stable chemical states with excellent activity, rapid responsivity, and excellent stability under the fluctuating operation conditions of alkali electrolyzers. The AWE system with optimized RCO/TF as cathodes exhibits a lower voltage (2.07 V) and higher current efficiency (95.25%) at a current density of 1 A cm−2 than RuO2/TF (2.40 V, 80.97%). This study unveils the origin of the activity of Ru coatings for HER and proposes an approach to composition design for other multicomponent electrodes and electrochemical applications.