A Robust Nonprecious CuFe Composite as a Highly Efficient Bifunctional Catalyst for Overall Electrochemical Water Splitting

To generate hydrogen, which is a clean energy carrier, a combination of electrolysis and renewable energy sources is desirable. In particular, for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in electrolysis, it is necessary to develop nonprecious, efficient, and durable catalysts. A robust nonprecious copper–iron (CuFe) bimetallic composite is reported that can be used as a highly efficient bifunctional catalyst for overall water splitting in an alkaline medium. The catalyst exhibits outstanding OER and HER activity, and very low OER and HER overpotentials (218 and 158 mV, respectively) are necessary to attain a current density of 10 mA cm−2. When used in a two-electrode water electrolyzer system for overall water splitting, it not only achieves high durability (even at a very high current density of 100 mA cm−2) but also reduces the potential required to split water into oxygen and hydrogen at 10 mA cm−2 to 1.64 V for 100 h of continuous operation

Nanoflake NiMoO<inf>4</inf> based smart supercapacitor for intelligent power balance monitoring

A supercapacitor is well recognized as one of emerging energy sources for powering electronic devices in our daily life. Although various kind of supercapacitors have been designed and demonstrated, their market aspect could become advanced if the utilisation of other physicochemical properties (e.g. optical) is incorporated in the electrode. Herein, we present an electrochromic supercapacitor (smart supercapacitor) based on a nanoflake NiMoO4 thin film which is fabricated using a facile and well-controlled successive ionic layer adsorption and reaction (SILAR) technique. The polycrystalline nanoflake NiMoO4 electrode exhibits a large electrochemically active surface area of ~ 96.3 cm2. Its nanoporous architecture provides an easy pathway for the intercalation and de-intercalation of ions. The nanoflake NiMoO4 electrode is dark-brown in the charged state and becomes transparent in the discharged state with a high optical modulation of 57%. The electrode shows a high specific capacity of 1853 Fg–1 at a current rate of 1 Ag–1 with a good coloration efficiency of 31.44 cm2/C. Dynamic visual information is obtained when the electrode is charged at different potentials, reflecting the level of energy storage in the device. The device retains 65% capacity after 2500 charge-discharge cycles compared with its initial capacity. The excellent performance of the nanoflake NiMoO4 based smart supercapacitor is associated with the synergetic effect of nanoporous morphology with a large electrochemically active surface area and desired chemical composition for redox reaction

Influence of operating temperature on Li<inf>2</inf>ZnTi<inf>3</inf>O<inf>8</inf> anode performance and high-rate charging activity of Li-ion battery

The temperature-dependent performance of a Li2ZnTi3O8 (LZTO) anode and the ultrafast-charging activity of a Li-ion battery were investigated. The LZTO anode operates at different temperatures between − 5 and 55 °C and in this work its sustainability is discussed in terms of storage performance. It delivered a discharge capacity of 181.3 mA h g−1 at 25 °C, which increased to 227.3 mA h g−1 at 40 °C and 131.2 mA h g−1 at − 5 °C. The variation in the discharge capacity with temperature is associated with the reaction kinetics and the change in internal resistance. It showed a capacity retention of 64% and a coulombic efficiency of 98% over 500 cycles. Exhibiting a discharge capacity of 107 mA h g−1, the LZTO anode was sustainable over 100 charge-discharge cycles at an ultra-high charging rate of 10 Ag−1. The reaction kinetics estimated from a cyclic voltammetry analysis at high scan rates revealed a capacitive-type storage mechanism

Self-Assembled Nanostructured CuCo<inf>2</inf>O<inf>4</inf> for Electrochemical Energy Storage and the Oxygen Evolution Reaction via Morphology Engineering

CuCo2O4 films with different morphologies of either mesoporous nanosheets, cubic, compact-granular, or agglomerated embossing structures are fabricated via a hydrothermal growth technique using various solvents, and their bifunctional activities, electrochemical energy storage and oxygen evolution reaction (OER) for water splitting catalysis in strong alkaline KOH media, are investigated. It is observed that the solvents play an important role in setting the surface morphology and size of the crystallites by controlling nucleation and growth rate. An optimized mesoporous CuCo2O4 nanosheet electrode shows a high specific capacitance of 1658 F g−1 at 1 A g−1 with excellent restoring capability of ≈99% at 2 A g−1 and superior energy density of 132.64 Wh kg−1 at a power density of 0.72 kW kg−1. The CuCo2O4 electrode also exhibits excellent endurance performance with capacity retention of 90% and coulombic efficiency of ≈99% after 5000 charge/discharge cycles. The best OER activity is obtained from the CuCo2O4 nanosheet sample with the lowest overpotential of ≈290 mV at 20 mA cm−2 and a Tafel slope of 117 mV dec−1. The superior bifunctional electrochemical activity of the mesoporous CuCo2O4 nanosheet is a result of electrochemically favorable 2D morphology, which leads to the formation of a very large electrochemically active surface area

Ultrathin Ni-Mo oxide nanoflakes for high-performance supercapacitor electrodes

Supercapacitors based on nanomaterial electrodes exhibit great potential as power sources for advanced electronic devices. From a practical viewpoint, it is desirable to fabricate highly active and sustainable nanomaterial electrodes consisting of non-precious elements using a simple technique in a controllable way. In this work, we report the synthesis of a self-assembled ultra-thin porous nanoflake Ni-Mo oxide (NMO) film using the successive ionic layer adsorption and reaction (SILAR) technique. The nanoflake NMO thin film electrode with a large electrochemically active surface area of ∼108 cm−2 exhibits a high specific capacitance of 1180 Fg−1 at a current density of 1 Ag−1 and excellent rate capability, with a negligible capacity loss of 0.075% per cycle. Even at a high current rate of 10 A g−1 it retains a capacity of 600 Fg−1. The highest energy and power densities obtained are 119 Whkg−1 and 15.7 kWkg−1, respectively. Electrochemical impedance spectroscopy analyses reveal that the electrode has considerably low charge transfer resistance. The observed excellent electrochemical energy storage performance of the nanoflake NMO electrode with a nanoporous surface is due to the synergetic effects of the large electrochemically active surface area, enhanced ion diffusion, and improved electrical conductivity

Facile electrodeposition of high-density CuCo<inf>2</inf>O<inf>4</inf> nanosheets as a high-performance Li-ion battery anode material

High-density CuCo2O4 nanosheets are grown on Ni foam using electrodeposition followed by air annealing for a Li-ion battery anode. The anode exhibits a high discharge capacity of 1244 mAh/g at 0.1 A/g (82% coulombic efficiency) and excellent high-rate performance with 95% capacity retention (1100 mAh/g after 200 cycles at 1 A/g). The outstanding battery performance of the CuCo2O4 anode is attributed to its binder-free direct contact to the current collector and high-density nanosheet morphology. The present experimental findings demonstrate that the electrodeposited binder-free CuCo2O4 material may serve as a safe, low-cost, long-cycle life anode for Li-ion batteries