Interface- and Surface-Engineered PdO-RuO₂ Hetero-Nanostructures with High Activity for Hydrogen Evolution/Oxidation...

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-RuO₂ -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^-2 at 44 mV with a Tafel slope of 34 mV dec^-1 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_0,m of PdO-RuO₂ /C was 522 mA mg^-1 in base, which is 58 and 3.4 times higher than those of Pd/C and Pt/C. The HOR activity of PdO-RuO₂ /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⁺ + + , and increase of HER as well decrease of HOR kinetics was observed with increasing Li⁺ concentration. It was proposed that OH_ad -M⁺ -(H₂ O)_x 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_ads -M⁺ -(H₂ O)_x could help to remove more OH_ads into the bulk, leading to increase in HER/HOR activity in alkaline electrolyte (K⁺ + + ) and increasing the HER with increasing Li⁺ concentration. The decrease of HOR activity of PdO-RuO₂ /C with increasing M⁺ was due to M⁺ -induced OH_ads destabilization through the bifunctional mechanism. The high HER/HOR activity of PdO-RuO₂ /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.