Two-dimensional (2D) materials have attracted attention for electrochemical energy storage applications because of their unique physical and chemical properties. However, the facile synthesis of thin 2D sheets remains a challenge. Herein, we demonstrate the formation of 3D assembly of thin Co–Al spinel sheets and carbon composite through a facile two steps process: hydrothermal synthesis of CoAl Layered double hydroxide (LDH) followed by heating of this LDH at high temperature to form CoAl2O4/C. This composite with a high specific surface area (SSA) of 102.7 m2 g–1 showed enhanced energy storage application. The CoAl2O4/C is capable of delivering specific capacitance of 1394 F g–1 under 1 A g–1 current density with 87% capacitance retention after 5000 cycles. For asymmetric supercapacitor (ASC), the CoAl2O4/C and activated carbon (AC) were used as cathode and anode, respectively. The device CoAl2O4/C//AC exhibits a high energy density of 76.34 W h kg–1 at a power density of 750.045 W kg–1 with good cyclic durability of 79% after 10 000 cycles. The improved electrochemical activity may be due to the 3D assembly of thin 2D Co–Al spinel nanosheets that allows easy electron and mass transport, high surface area, synergistic interaction among different components, etc. for which Co–Al spinel/C composite will find application in energy storage.

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.

Proper modulation of the compositions and porosities of carbon materials is crucial for capacitive energy storage and gas adsorption of carbon materials. Herein, porous N-doped carbon was synthesized from formamide by using a sequential hydrothermal treatment followed by pyrolysis with KOH. The activation with KOH resulted in a high increase in the porosity of the carbon and in the performance. A high porosity of >3000 m2 g–1 was achieved with a low KOH/C ratio of only 2. The presence of nitrogen introduces pseudocapacitance and also enhances the electron density in the carbon framework. The obtained N-doped porous carbon exhibits a good specific capacitance value of 307 F g–1 at 1 A g–1 in 6 M KOH. Also, the fabricated symmetric supercapacitor displays excellent performance in both alkaline and neutral media. It shows a stable cycling performance (91.4% retention after 10 000 cycles), a reasonable rate performance, and a maximum energy density of 14.36 Wh kg–1 at a power density of 351 W kg–1 in 1 M Na2SO4. The prepared material shows good gas adsorption behavior, and as a H2 adsorbent at 77 K, it shows a good uptake value of 2.86 wt % at 1 bar pressure. It also shows maximum CO2 uptake values of 4.88 and 2.88 mmol g–1 at 1 bar pressure under temperatures of 0 and 25 °C, respectively, with a high CO2/N2 selectivity of 14.54. The compound also shows a methane uptake capacity of 1.67 mmol g–1 at 0 °C and 1 bar pressure with a CO2/CH4 selectivity of 3.8. Our research provides a promising material for both energy storage and gas storage through a green synthetic strategy.

Development of electrode materials for electrochemical energy storage is of great importance because of growing energy demand. Supercapacitors are one of the important energy storage devices because of their high...