Effect and mechanism of hydrogen annealing temperature on the HER performance of RuO2-based catalysts in acid media.

Annealing as an experimental means is often used to treat various electrocatalysts for improving their hydrogen evolution reaction (HER) performance. Herein, in order to investigate the effect of hydrogen annealing temperature on the HER performance of RuO 2 -based electrocatalysts, commercial RuO 2 , self-synthesized RuO 2 , and self-synthesized RuO 2 /MoO 3 composite are annealed at 150, 300, 500, and 700 °C in a hydrogen atmosphere, respectively. It's found that RuO 2 is gradually deduced at 150 °C, ultimately, completely reduced to Ru under 300 °C. Meanwhile, the content of RuO 2 at the samples surface is gradually decreases as the annealing temperature increase to 700 °C. However, for all samples, the 500 °C annealed sample shows the best HER performance in acid solutions, including the lowest over potential, the smallest Tafel slope, and the largest double-layer capacitance. We inferred that the optimal HER performance of the 500 °C annealed samples maybe attributed to their appropriate Ru/RuO 2 ratio. Density functional theory (DFT) calculations reveal that significant electron transfer across the Ru/RuO 2 interface, thereby optimizing the adsorption free energy of H on Ru and RuO 2 , ultimately resulting in Ru/RuO 2 catalyst exhibiting better HER activity than bare Ru and RuO 2. The study provides guidance on the preparation of RuO 2 -based electrocatalysts for achieving efficient hydrogen evolution. [Display omitted] • Various commercial and self synthesized RuO 2 -based catalysts have been studied. • The annealing temperature of RuO 2 -based catalysts covers a wide range of 150–700 °C. • The adsorption free energies of H on different ratio of Ru/RuO 2 were calculated. • The effect mechanism of annealing temperature on HER activity of RuO 2 was analyzed. [ABSTRACT FROM AUTHOR]