Identifying the roles of Ru single atoms and nanoclusters for energy-efficient hydrogen production assisted by electrocatalytic hydrazine oxidation

With a much lower thermodynamic reaction potential, the hydrazine oxidation reaction (HzOR) can be employed as an alternative of water oxidation reaction to integrate with the cathodic hydrogen evolution reaction (HER), accomplishing an energy-efficient H2 production. The realization of this necessitates the development of the excellent bifunctional electrocatalysts for both HER and HzOR. Herein, a common Ru complex was applied to prepare a Ru/porous N-doped carbon composite (Ru/PNC) simultaneously containing abundant Ru single atoms (SAs) and ultrafine Ru nanoclusters (1.7 nm). Firstly, the new Ru/PNC catalysts containing both metal-metal as well as metal-substrate interactions display superb HER and HzOR activities in alkaline and neutral electrolytes, both greatly surpassing the sole Ru nanoparticles or Ru SAs sample. The controlled experiments and theoretical studies unravel water dissociation and H ad-desorption occurs on Ru SAs and nanoclusters, respectively, involving the proton transfer between them during the HER process, while HzOR is mainly proceeded on Ru SAs sites. Secondly, the alkaline overall hydrazine splitting with Ru/PNC only demands a voltage of 0.19 V to achieve 100 mA cm-2, demonstrating the huge energy-saving advantage compared with conventional water splitting. Additionally, the hydrogen generation can be readily operated with the hydrazine fuel cell and commercial solar cell with the appreciable H2 production rate of 32.7 and 27.1 mL cm-2 h-1, respectively.