Modulation of RuO2 Nanocrystals with Facile Annealing Method for Enhancing the Electrocatalytic Activity on Overall Water Splitting in Acid Solution

RuO2-based materials are considered an important kind of electrocatalysts on oxygen evolution reaction and water electrolysis, but the reported discrepancies of activities exist among RuO2 electrocatalysts prepared via different processes. Herein, a highly efficient RuO2 catalysts via a facile hydrolysis-annealing approach is reported for water electrolysis. The RuO2 catalyst dealt with at 200 °C (RuO2-200) performs the highest activities on both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acid with overpotentials of 200 mV for OER and 66 mV for HER to reach a current density of 100 mA cm-2 as well as stable operation for100 h. The high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) characterizations show that the activities of as-prepared RuO2 rely on the hydroxide group/lattice oxygen (OH-/O2-) ratio, size, and crystalline of RuO2. The density functional theory (DFT) calculation also reveal that the OH- would enhance the activities of RuO2 for HER and OER via modifying the electronic structure to facilitate intermediate adsorption, thereby reducing the energy barrier of the rate-determining step. The water electrolysis by using RuO2-200 as the catalyst on both anode and cathode demonstrates a stable generation of hydrogen and oxygen with high Faradic efficiency at a current density of ≈30 mA cm-2 and a potential of below 1.47 V.