Active catalysts for HER/HOR are crucial to develop hydrogenbased renewable technologies. The interface of hetero-nanostructures can integrate different components into a single synergistic hybrid with high activity. Here, the synthesis of PdOÀ RuO 2 À 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 À 2 at 44 mV with a Tafel slope of 34 mV dec À 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 PdOÀ RuO 2 /C was 522 mA mg À 1 in base, which is 58 and 3.4 times higher than those of Pd/C and Pt/C. The HOR activity of PdOÀ RuO 2 /C was 22 and 300 times higher than those of PdO/C in acid and base. Improve-ment 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 ad -M + -(H 2 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 + -(H 2 O) x could help to remove more OH ads 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 PdOÀ RuO 2 /C with increasing M + was due to M + -induced OH ads destabilization through the bifunctional mechanism. The high HER/HOR activity of PdOÀ RuO 2 /C could be attributed, among other factors, to interface engineering and strong synergistic interaction. This work provides an opportunity to design oxidebased catalysts for renewable energy technologies.

Development of active catalysts for the electrochemical hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are of prime importance for the commercialization of the proton-exchange membrane (PEM)/ anion-exchange membrane (AEM) water electrolyzer. Here, we report synthesis of an IrO 2 -modified RuO 2 nanowires/nitrogendoped carbon composite for overall water splitting at all pH. This catalyst exhibits excellent OER activity in 0.5 M H 2 SO 4 solution with a low overpotential of 188 mV at 10 mA/cm 2 current density, a low Tafel slope value of 42 mV/dec, and ∼96% faradic efficiency. The OER of this catalyst in neutral and base media is also higher than that of commercial RuO 2 and IrO 2 . IrO 2 −RuO 2 /C also showed very good HER activity with 10 mA/cm 2 current density at 82 and 75 mV overpotential in acid and base, respectively. The HER performance of this catalyst is better than that of commercial Pt/C in base and slightly lower in neutral and acid. The catalyst shows excellent OER and HER stability compared to the state-of-art catalysts. In addition, the overall water-splitting performance of IrO 2 −RuO 2 /C was also studied, which shows 10 mA/cm 2 current density at 1.52 and 1.51 V cell voltage in 1.0 M KOH and 0.5 M H 2 SO 4 , respectively. The outstanding activity of the IrO 2 −RuO 2 /C catalyst can be attributed to a unique one-dimensional nanowire structure, synergistic interaction, high surface area, high oxophilicity, and high mass and electron transportation between IrO 2 , RuO 2 , and the carbon support. This work may provide an opportunity to design and synthesize a highly durable and efficient electrocatalyst for renewable energy conversion.

Development of highly active, durable, bifunctional electrocatalysts for overall water splitting is of great importance to enhance the use of hydrogen energy. Herein, we synthesize a porous and interfaces-rich Fe3O4/RuO2-C composite from the Metal organic frameworks (MOF) material for overall water splitting in alkaline media. The Fe3O4/RuO2-C catalyst showed superior oxygen evolution reaction (OER) with high faradic efficacy. It requires 268 mV overpotential to achieve the current density of 20 mA/cm2. The catalyst also exhibited good hydrogen evolution reaction (HER) with a current density of 10 mA/cm2 at an overpotential of 94 mV. The stability test confirmed a remarkable long-term OER and HER stability of this catalyst in alkaline media. In addition, the Fe3O4/RuO2-C catalyst was also used as cathode and anode material for overall water splitting. It showed superior activity and stability in alkaline media with 10 mA/cm2 current density at 1.595 V cell potential. The excellent electrocatalytic activity of the Fe3O4/RuO2-C catalyst can be attributed to its porous structure, synergistic interaction between the components, the presence of hetero-interfaces, high electrochemical surface area etc. This work may provide an opportunity to design a bifunctional electrocatalyst for the development of anion exchange membrane water electrolyzers (AEMWEs).