Redox-Active Hydrogel Polymer Electrolytes with Different pH Values for Enhancing the Energy Density of the Hybrid Solid-State Supercapacitor

To enhance the energy density of solid-state supercapacitors, a novel solid-state cell, made of redox-active poly­(vinyl alcohol) (PVA) hydrogel electrolytes and functionalized carbon nanotube-coated cellulose paper electrodes, was investigated in this work. Briefly, acidic PVA–[BMIM]­Cl–lactic acid–LiBr and neutral PVA–[BMIM]­Cl–sodium acetate–LiBr hydrogel polymer electrolytes are used as catholyte and anolyte, respectively. The acidic condition of the catholyte contributes to suppression of the undesired irreversible reaction of Br^– and extension of the oxygen evolution reaction potential to a higher value than that of the redox potential of Br^–/Br₃^– reaction. The observed Br^–/Br₃^– redox activity at the cathode contributes to enhance the cathode capacitance. The neutral condition of the anolyte helps extend the operating voltage window of the supercapacitor by introducing hydrogen evolution reaction overpotential to the anode. The electrosorption of nascent H on the negative electrode also increases the anode capacitance. As a result, the prepared solid-state hybrid supercapacitor shows a broad voltage window of 1.6 V, with a high Coulombic efficiency of 97.6% and the highest energy density of 16.3 Wh/kg with power density of 932.6 W/kg at 2 A/g obtained. After 10 000 cycles of galvanostatic charge and discharge tests at the current density of 10 A/g, it exhibits great cyclic stability with 93.4% retention of the initial capacitance. In addition, a robust capacitive performance can also be observed from the solid-state supercapacitor at different bending angles, indicating its great potential as a flexible energy storage device

Hierarchical FeNiP@Ultrathin Carbon Nanoflakes as Alkaline Oxygen Evolution and Acidic Hydrogen Evolution Catalyst for Efficient Water Electrolysis and Organic Decomposition

Efficiency of hydrogen evolution via water electrolysis is mainly impeded by the kinetically sluggish oxygen evolution reaction (OER). Thus, it is of great significance to develop highly active and stable OER catalyst for alkaline water electrolysis or to substitute the more kinetically demanding acidic OER with a facile electron-donating reaction such that OER is no longer the bottleneck half-reaction for either acidic or alkaline water electrolysis. Herein, the hierarchical Fe–Ni phosphide shelled with ultrathin carbon networks on Ni foam (FeNiP@C) is reported and shows exceptional OER activity and enhanced chemical stability in 1 M KOH. This unique electrode provides large active sites, facile electron transport pathways, and rapid gas release, resulting in a remarkable OER activity that delivers a current density of 100 mA/cm² at an overpotential of 182 mV with a Tafel slope of 56 mV/dec. Combining the hydrogen evolution reaction with organic pollutant (methylene blue) oxidation, a multifunctional electrolyzer for simultaneous cost-effective hydrogen generation and organic pollutant decomposition in acid wastewater is proposed. Our strategies in this work provide attractive opportunities in energy- and environment-related fields

Hierarchical FeNiP@Ultrathin Carbon Nanoflakes as Alkaline Oxygen Evolution and Acidic Hydrogen Evolution Catalyst for Efficient Water Electrolysis and Organic Decomposition

Efficiency of hydrogen evolution via water electrolysis is mainly impeded by the kinetically sluggish oxygen evolution reaction (OER). Thus, it is of great significance to develop highly active and stable OER catalyst for alkaline water electrolysis or to substitute the more kinetically demanding acidic OER with a facile electron-donating reaction such that OER is no longer the bottleneck half-reaction for either acidic or alkaline water electrolysis. Herein, the hierarchical Fe–Ni phosphide shelled with ultrathin carbon networks on Ni foam (FeNiP@C) is reported and shows exceptional OER activity and enhanced chemical stability in 1 M KOH. This unique electrode provides large active sites, facile electron transport pathways, and rapid gas release, resulting in a remarkable OER activity that delivers a current density of 100 mA/cm² at an overpotential of 182 mV with a Tafel slope of 56 mV/dec. Combining the hydrogen evolution reaction with organic pollutant (methylene blue) oxidation, a multifunctional electrolyzer for simultaneous cost-effective hydrogen generation and organic pollutant decomposition in acid wastewater is proposed. Our strategies in this work provide attractive opportunities in energy- and environment-related fields