Morphological evolution of carnation flower-like Cu2CoSnS4 battery-type electrodes

Transition metal sulfides are the most reliable type of battery electrode material for supercapacitors. Herein, the morphological evolution of Cu2CoSnS4 has been enhanced with different time-varied temperature processes through a one-step solvothermal route. Promoted by its unique carnation flower-like morphology with excellent petals, it achieves an elevated 132.08 mA h g−1 specific capacity at 0.5 A g−1 current density and long lasting stability with only 22.33% loss over 5000 cycles at 5 A g−1. Moreover, a full-cell asymmetric solid-state supercapacitor (ASSC) device has been constructed to demonstrate its practical applications. The fabricated Cu2CoSnS4//AC ASSC device delivers a 131.90 W h kg−1 high energy density for 749.98 W kg−1 power density with an improved stability of 70% and a Coulombic efficiency of 97.98% after 20 000 charge–discharge cycles, demonstrating its potential as a gifted electrode for high-performance supercapacitor applications.publishedVersio

Neodymium-Doped Novel Barium Tungstate Nanospindles for the Enhanced Oxygen Evolution Reaction

In this work, pristine, 0.02, 0.04, and 0.06 M neodymium (Nd)-doped barium tungstate nanostructures were synthesized via a simple co-precipitation method for the water oxidation process. The obtained X-ray diffraction high-intensity peak at a 2θ value of 26.4° corresponding to the (112) lattice plane confirmed the formation of a tetragonal structure of BaWO4. Moreover, the BaWO4 morphology was examined by scanning electron microscopy, which showed the existence of nanospindles. An energy-dispersive X-ray spectrum confirmed the subsistence of the produced materials, for example, barium (Ba), tungsten (W), oxide (O), and neodymium (Nd), with weight percentages of 28.58, 46.63, 16.64, and 8.16%, respectively. The 0.04 M Nd-doped BaWO4 product was explored to attain a high surface area of 18.18 m2/g, a pore volume of 0.079 cm3/g, and a pore diameter of 2.215 nm. Compared to the other prepared electrodes, the 0.04 M Nd-doped BaWO4 product exhibited low overpotential values of 330 mV and 450 mV to deliver current densities of 10 mA/cm2 and 50 mA/cm2, respectively. In addition, the optimized electrode achieved a small Tafel slope value of 158 mV dec–1 and followed the Volmer–Heyrovsky mechanism. Moreover, the electrical conductivity of BaWO4 was tuned due to the addition of a rare-earth metal dopant, and it exhibited the charge-transfer resistance and solution resistance values of 0.98 and 1.01 Ω, respectively. The prepared electrocatalyst was further studied by using cyclic voltammetry, and it exhibited a high double-layer capacitance value of 29.3 mF/cm2 and high electrochemically active surface areas of 1.465 cm2. The electrochemical performance was greatly improved depending on the concentration of the doping agent, and it was well consistent with the obtained results. The best electrocatalyst was subjected to a chronoamperometry test, which exhibited excellent stability even after 20 h. Hence, this work suggests that alkaline metal tungstates have a cost-effective, efficient, and promising electrocatalyst, and it is a new approach for the water oxidation process.publishedVersio

CoNiSe2 Nanostructures for Clean Energy Production

Comparative investigation of the electrochemical oxygen evolution reaction (OER) activity for clean energy production was performed by fabricating three different electrodes, namely, NiSe2, CoSe2, and CoNiSe2, synthesized by hydrothermal treatment. Cubic, orthorhombic, and hexagonal structures of NiSe2, CoSe2, and CoNiSe2 were confirmed by X-ray diffraction (XRD) and also by other characterization studies. Perfect nanospheres, combination of distorted nanospheres and tiny nanoparticles, and sharp-edge nanostructures of NiSe2, CoSe2, and CoNiSe2 were explored by surface morphological images. Higher OER activity of the binary CoNiSe2 electrode was achieved as 188 mA/g current density with a comparatively low overpotential of 234 mV along with higher conductivity and low charge transfer resistance when compared to its unary NiSe2 and CoSe2 electrodes. A low Tafel slope value of 82 mV/dec was also achieved for the same binary CoNiSe2 electrode in a half-cell configuration. The overall 100% retention achieved for all of the fabricated electrodes in a stability test of OER activity suggested that the excellent optimum condition was obtained during the synthesis. This could definitely be a revelation in the synthesis of novel binary combinations of affordable metal selenides for clean energy production.publishedVersio

Exploration of Bifunctionality in Mn, Co Codoped CuO Nanoflakes for Overall Water Splitting

Herein, bimetal (Mn, Co) codoping on a CuO host is aimed at enhancing oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity. Codoping of Mn and Co on CuO to enhance bifunctional action in electrochemical water splitting has not yet been investigated to the best of our knowledge. Literatures are focused on unary Mn-doped CuO or Co-doped CuO nanostructures. Mn, Co codoped CuO through an easy chemical coprecipitation method has been successfully attempted and is more beneficial which is the novelty of the present work. Defect-enriched ample active sites (Mn2+/Mn3+ and Co2+/Co3+) along with Cu2+ in the host CuO achieved high current density (100 mA/cm2 ) in OER and HER with low overpotential such as 468 mV and 271 mV, respectively. Faster charge transfer and diffusion ability was stimulated by the bimetal codoping CuO. Reasonable Tafel plot values (OER: 199 mV/dec, and HER: 21 mV/dec) with improved water-splitting reaction kinetics were achieved for the Mn, Co codoped CuO nanoflakes. The double-layer capacitance (Cdl) value of 27.5 mF/cm2 for Mn, Co codoped CuO nanoflakes was achieved. Similarly, the increasing order of an electrochemically active surface area (EASA) was exhibited by the consequent addition of bimetal doping on CuO, denoted as Mn, Co/CuO > Co/CuO > Mn/CuO > CuO. The evidence shows that the codoping strategy could facilitate rapid reaction kinetics to develop overall water splitting. The charge transfer resistances (Rct) of 3.6Ω and 1.2Ω for the Mn, Co codoped CuO nanostructure corresponding to the OER and HER, respectively, were reported. The long-term stability over 16 h with negligible loss was reported for both the OER and the HER performance. Thus, this work contributes to better insight and analysis of the successful codoping of bimetal elements in earth-abundant electrocatalysts to enhance and make practical the electrocatalytic water-splitting activitypublishedVersio