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

Abstract

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 RuO2-based electrocatalysts, commercial RuO2, self-synthesized RuO2, and self-synthesized RuO2/MoO3 composite are annealed at 150, 300, 500, and 700 °C in a hydrogen atmosphere, respectively. It's found that RuO2 is gradually deduced at 150 °C, ultimately, completely reduced to Ru under 300 °C. Meanwhile, the content of RuO2 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/RuO2 ratio. Density functional theory (DFT) calculations reveal that significant electron transfer across the Ru/RuO2 interface, thereby optimizing the adsorption free energy of H on Ru and RuO2, ultimately resulting in Ru/RuO2 catalyst exhibiting better HER activity than bare Ru and RuO2. The study provides guidance on the preparation of RuO2-based electrocatalysts for achieving efficient hydrogen evolution.