Synergistic Engineering of NiCoFe Layered Hydroxides for Enhanced Energy Storage and Electrocatalytic Water Splitting

The rational design of electrode materials with outstanding energy and power density for supercapacitors (SCc) and high-performance electrocatalysts in alkaline media plays an indispensable role in the application of energy storage and overall water splitting. In this paper, we prepared NiCoFe layered ternary hydroxides (LTH) using a hydrothermal synthesis method. The sample with a Ni/Co/Fe ratio of 1:2:0.5 (Co) exhibited the best performance, achieving a specific capacitance of 860 C g^-1 at a current density of 1 A·g^-1. When assembled into a supercapacitor, it achieved an energy density of 72.3 Wh·kg^-1 at a power density of 4050 W·kg^-1, and after 7200 charge-discharge cycles, the capacity retention rate was 69.2%. For the hydrogen evolution reaction (HER), the overpotential was 100.4 mV at 10 mA·cm^-2; in oxygen evolution, the sample with a Ni/Co/Fe ratio of 2:1:1.5 (Ni,Co) showed better performance, presenting an overpotential of 235.3 mV at 50 mA·cm^-2. Moreover, when constructing a symmetrical two-electrode system using both ratios of NiCoFe layered hydroxides, the water splitting voltage was only 1.861 V at 100 mA·cm^-2. It is hoped that NiCoFe-LDH prepared under appropriate conditions can optimise its applicability as fundamental components for SCc and water-splitting systems.