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).

Hydrogen production from water electrolysis is of great interest for attaining sustainable clean energy storage and conversion, but the required working voltage (>1.23 V) in water splitting limits its applications in industrial expansion. Therefore, replacing the oxygen evolution reaction (OER) with a more favorable anodic oxidation reaction, which can provide more valuable products and less working voltage, will be of great significance for the upcoming expansion of hydrogen production in industrial applications. In this report, a two-dimensional (2D) amorphous sheet-like nickel oxide encapsulated on the nitrogendoped carbon (NiO x /CN x ) composite was synthesized for the urea oxidation reaction (UOR) and ethanol oxidation reaction (EOR). Remarkably, the catalyst shows 1.647, 1.378, and 1.354 V vs. reversible hydrogen electrode (RHE) potential at 10 mA/cm 2 current density for OER, UOR, and EOR, respectively, with good stability. The overall water, urea, and ethanol electrolyses of NiO x /CN x were carried out by coupling with commercial Pt/C as a cathode which shows only 1.626, 1.43, and 1.414 V cell potential at 20 mA/cm 2 current density. The catalyst also shows excellent chronopotentiometric and dynamic stability toward all the electrolyses. The high catalytic activity of NiO x /CN x may be attributed to the synergistic interaction between the support and materials, amorphous structure, 2D sheet-like morphology, porous structure, and high electrochemical surface area. This finding shows that NiO x /CN x nanosheets can replace noble metal-based catalysts for efficient anodic oxidation reactions.

The enhancement of reaction kinetics and durability of the hydrogen evolution/oxidation reaction (HER/HOR) in basic media are necessary for the design of alkaline electrolyzers and fuel cells. In this work, an interface-engineered porous Pt–PdO–N-doped carbon (Pt–PdO/C) composite was synthesized for HER/HOR application in both the acidic and alkaline media. The Pt–PdO/C catalyst delivered an outstanding HER performance and durability in both media. It required 29 and 16 mV overpotential to reach 10 mA/cm2 HER current density in alkaline and acidic media with 36 and 22 mV/dec Tafel slope values, respectively. In addition, Pt–PdO/C showed excellent HOR performance in all pH solutions. The mass-specific exchange current density (i 0,m) of this catalyst was 463.8 mA/mgmetal in 0.1 M KOH solution, which was nearly 5.5 times better than that of commercial Pt/C. We demonstrated that both the hydrogen binding energy and OH binding energy are equal descriptors for HER/HOR in the alkaline media. We also investigated the effect of hydroxyl–metal–water species in the electrical double layer on HER/HOR kinetics in a basic medium. The excellent HER/HOR catalytic performance of Pt–PdO/C may be due to the interface engineering, strong synergistic interaction between the components, high electrochemical surface area, porous morphology, and so forth. We hope this work will provide an opportunity to design metal–metal oxide-based electrocatalysts for several renewable energy devices.

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The development of two-dimensional (2D) carbon nanosheets and microporous 2D carbon nanosheets with high specific surface area (SSA), large pore volume, and high conductivity is important for energy storage and gas storage applications. Traditional microporous carbon materials have several disadvantages such as low accessibility of active sites and poor mass transport due to large diffusion pathways. The nanometer-thick 2D microporous carbon nanosheets permit easy mass/heat transport, leading to overcoming the drawbacks of bulk porous materials. Herein, we demonstrate a facile synthesis of 2D boron carbonitride (BCN) and 2D porous BCN for energy and gas storage applications. The 2D BCN sample showed excellent supercapacitor (SC) applications with a specific capacitance (C s) of 273 F g–1 under 1 A g–1. Most importantly, 2D porous BCN (p-BCN) was prepared by KOH activation at high temperatures. The optimized 2D porous BCN with highly concentrated micropores and a considerable amount of mesopores provides a high SSA (3310.4 m2 g–1) and pore volume of 1.75 cc g–1. The combined effect of unique porous nanosheets and optimum doping of heteroatoms allows easy electrolyte/ion diffusion, electron conduction, faradic reactions, and so forth. The p-BCN-800 electrode showed superior C s of 406 and 355 F g–1 under 1 A g–1 in H2SO4 and KOH electrolytes, respectively. Moreover, the symmetric p-BCN-800//p-BCN-800 device showed high energy and power densities (17 W h Kg–1 and 4000 W kg–1) with high cycling stability. The 2D porous BCN showed excellent H2 and CO2 adsorption capacity. The H2 uptake of 2D porous BCN is 2.91 wt % at 77 K under 1 bar pressure, whereas the CO2 uptake is 3.96 and 2.39 mmol g–1 at 0 and 25 °C, respectively. This work demonstrates an efficient way to produce 2D BCN and 2D porous BCN for energy storage and gas uptake applications.

The development of earth-abundant, inexpensive, and durable noble-metal-free bifunctional electrocatalysts is important to design anion exchange membrane water electrolyzers (AEMWEs). In recent years, tremendous efforts have been carried out to prepare two-dimensional (2D) amorphous noblemetal-free catalysts for alkaline water splitting as they have unique characteristics in catalysis. In this report, a 2D amorphous cobalt oxide nanosheet/nitrogen-doped carbon composite (CoO x /CN x ) was prepared for water splitting in the base. The catalyst displays excellent oxygen evolution reaction (OER) activity with 310 mV overpotential at 10 mA/cm 2 current density and 60.7 mV/dec Tafel slope value. The CoO x /CN x also shows very good long-term OER stability in the base. The CoO x /CN x composite also shows moderate hydrogen evolution reaction (HER) activity, and the activity increases with increasing reaction time. We demonstrate that the HER activity increases with increasing HER cycle because of the surface modification of the catalyst. The CoO x /CN x also shows excellent overall water-splitting activity as well as durability. The catalyst possesses high catalytic activity because of its 2D, amorphous sheetlike morphology, strong synergistic interactions, porosity, large electrochemical surface area, and easy access to abundant active sites. Thus, this result may offer a prospect to design a noble metal-free electrocatalyst for AEMWEs and other renewable energy-based devices.