Efficient and durable multifunctional nickel-doped cobalt phosphate hydrate electrocatalysts for hybrid supercapacitors and zinc-air batteries

Abstract

High-performance and long-life cycle supercapacitor (SC) electrodes and air cathodes are es-sential for the development of efficient hybrid SCs (HSCs) and rechargeable zinc-air batteries (ZABs). In this report, we developed a novel nickel (Ni)-doped cobalt phosphate hydrate ((Ni/Co)3(PO4)2·8H2O)) material via a single-step hydrothermal process, which was employed in SC electrodes and bifunctional electrocatalysts. The doping of Ni metal into the material ef-fectively enhanced its SC performance and electrocatalytic properties. The (Ni/Co)3(PO4)2·8H2O SC electrode exhibited excellent specific capacity/capacitance of 220/1760 (mAh g-1/F g-1) with superior rate capability of 74.5%. More importantly, the (Ni/Co)3(PO4)2·8H2O SC electrode demonstrated outstanding capacity retention of 92% after 100,000 cycles. The assembled (Ni/Co)3(PO4)2·8H2O//activated carbon HSC device revealed high energy and power densities (Ed and Pd) of 47.28 Wh kg-1 and 5588.48 W kg-1, respectively. Moreover, the prepared HSC exhibited excellent capacitance retention of 95% after the comple-tion of 100,000 cycles. The oxygen evolution reaction overpotential of the (Ni/Co)3(PO4)2·8H2O was 157 mV, which is lower than the Co3(PO4)2·8H2O (178 mV), RuO2 (276 mV), and IrO2 (377 mV) in 1 M KOH. The (Ni/Co)3(PO4)2·8H2O represented decent onset (Eonset) and half-wave (E1/2) potentials of 0.90 and 0.81 V, respectively. Specifically, the (Ni/Co)3(PO4)2·8H2O-based ZAB exhibited excellent open circuit voltage (1.425 V), specific capacity (733 mAh (gZn)-1), and power density (225.5 mW cm-2) values compared to the Pt-C + RuO2-based ZAB. The (Ni/Co)3(PO4)2·8H2O-based ZAB revealed superior cycling stability of 70 h at 2 mA cm-2. Following the above advantages, the SC and ZAB performances of the (Ni/Co)3(PO4)2·8H2O material create a novel path for energy storage applications efficiently.