Electrochemical Investigations of Double Perovskite M2NiMnO6 (Where M = Eu, Gd, Tb) for High-Performance Oxygen Evolution Reaction.

Double perovskites are known for their special structures which can be utilized as catalyst electrode materials for electrochemical water splitting to generate carbon-neutral hydrogen energy. In this work, we prepared lanthanide series metal-doped double perovskites at the M site such as M2NiMnO6 (where M = Eu, Gd, Tb) using the solid-state reaction method, and they were investigated for an oxygen evolution reaction (OER) study in an alkaline medium. It is revealed that the catalyst with a configuration of Tb2NiMnO6 has outstanding OER properties such as a low overpotential of 288 mV to achieve a current density of 10 mAcm-2, a lower Tafel slope of 38.76 mVdec-1, and a long cycling stability over 100 h of continuous operation. A-site doping causes an alteration in the oxidation or valence states of the NiMn cations, their porosity, and the oxygen vacancies. This is evidenced in terms of the Mn4+/Mn3+ ratio modifying electronic properties and the surface which facilitates the OER properties of the catalyst. This is discussed using electrochemical impedance spectroscopy (EIS) and electrochemical surface area (ECSA) of the catalysts. The proposed work is promising for the synthesis and utilization of future catalyst electrodes for high-performance electrochemical water splitting.

One-Pot Synthesized Biomass C-Si Nanocomposites as an Anodic Material for High-Performance Sodium-Ion Battery.

Aiming at materializing an excellent anodic source material of the high-performance sodium-ion battery (SIB), we fabricated the biomass carbon-silicon (C-Si) nanocomposites by the one-pot synthesis of facile magnesiothermic reduction using brown rice husk ashes. The C-Si nanocomposites displayed an aggregated morphology, where the spherical Si nanoparticles (9 nm on average) and the C nanoflakes were encapsulated and decorated with each other. When utilizing the nanocomposites as an SIB anode, a high initial discharge capacity (i.e., 378 mAh/g at 100 mA/g) and a high reversible capacity (i.e., 122 mAh/g at 200 mA/g) were achieved owing to their enhanced electronic and ionic conductivities. Moreover, the SIB device exhibited a high cyclic stability in its Coulombic efficiency (i.e., 98% after 100 charge-discharge cycles at 200 mA/g). These outstanding results depict that the one-pot synthesized biomass C-Si nanocomposites are beneficial for future green energy-storage technology.

Activated Carbon-Decorated Spherical Silicon Nanocrystal Composites Synchronously-Derived from Rice Husks for Anodic Source of Lithium-Ion Battery.

The nanocomposites of activated-carbon-decorated silicon nanocrystals (ACAC) were synchronously derived in a single step from biomass rice husks, through the simple route of the calcination method together with the magnesiothermic reduction process. The final product, ACAC, exhibited an aggregated structure of activated-carbon-encapsulated nanocrystalline silicon spheres, and reveals a high specific surface area (498.5 m2/g). Owing to the mutualization of advantages from both silicon nanocrystals (i.e., low discharge potential and high specific capacity) and activated carbon (i.e., high porosity and good electrical conductivity), the ACAC nanocomposites are able to play a substantial role as an anodic source material for the lithium-ion battery (LIB). Namely, a high coulombic efficiency (97.5%), a high discharge capacity (716 mAh/g), and a high reversible specific capacity (429 mAh/g after 100 cycles) were accomplished when using ACAC as an LIB anode. The results advocate that the simultaneous synthesis of biomass-derived ACAC is beneficial for green energy-storage device applications.

Self-Assembled Nanostructured CuCo2 O4 for Electrochemical Energy Storage and the Oxygen Evolution Reaction via Morphology Engineering.

CuCo2 O4 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 CuCo2 O4 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 CuCo2 O4 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 CuCo2 O4 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 CuCo2 O4 nanosheet is a result of electrochemically favorable 2D morphology, which leads to the formation of a very large electrochemically active surface area.