Interface- and Surface-Engineered PdO-RuO Hetero-Nanostructures with High Activity for Hydrogen Evolution/Oxidation Reactions.

Active catalysts for HER/HOR are crucial to develop hydrogen-based renewable technologies. The interface of hetero-nanostructures can integrate different components into a single synergistic hybrid with high activity. Here, the synthesis of PdO-RuO -C with abundant interfaces/defects was achieved for the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). It exhibited a current density of 10 mA cm at 44 mV with a Tafel slope of 34 mV dec in 1 m KOH. The HER mass activity was 3 times higher in base and comparable to Pt/C in acid. The stability test confirmed high HER stability. The catalyst also exhibited excellent HOR activity in both media; in alkaline HOR it outperformed Pt/C. The exchange current density i of PdO-RuO /C was 522 mA mg in base, which is 58 and 3.4 times higher than those of Pd/C and Pt/C. The HOR activity of PdO-RuO /C was 22 and 300 times higher than those of PdO/C in acid and base. Improvement of HER/HOR kinetics in different alkaline electrolytes was observed in the order K <Na <Li , and increase of HER as well decrease of HOR kinetics was observed with increasing Li concentration. It was proposed that OH -M -(H O) in the double-layer region could influence HER/HOR activity in base. Based on the hard and soft acid and base (HSAB) theory, the OH -M -(H O) could help to remove more OH into the bulk, leading to increase in HER/HOR activity in alkaline electrolyte (K <Na <Li ) and increasing the HER with increasing Li concentration. The decrease of HOR activity of PdO-RuO /C with increasing M was due to M -induced OH destabilization through the bifunctional mechanism. The high HER/HOR activity of PdO-RuO /C could be attributed, among other factors, to interface engineering and strong synergistic interaction. This work provides an opportunity to design oxide-based catalysts for renewable energy technologies.