free-binder conimn ldh/nickel foam electrodes for supercapacitor and water splitting applications

Ternary layered double hydroxides (ldhs) have garnered significant attention due to their unique properties and potential applications in energy storage and conversion devices. the ldhs are composed of positively charged metal hydroxide layers with intercalated anions and water molecules. the tunable chemistry of ldhs allows for the incorporation of different metal cations, resulting in ternary ldh materials with enhanced electrochemical properties. the co, ni, and mn cations are chosen due to their favorable redox behavior and potential for synergistic effects. in this study, a simple one-step hydrothermal method was employed to prepare the free-binder needle-like conimn ldh/nickel foam (nf) by using the metal nitrates, urea, and ammonium fluoride (nh4f). the urea plays as a precipitant by its thermally hydrolyzation at 130 °c to increase the ph of precursor solution. the single phase conimn ldh electrode has the needle-like morphology with an average diameter of 170 nm and length of 5 nm as observed by scanning electron microscopy (sem). the microneedles are regularly assembled as sea urchin. the microneedles ldhs with a high aspect ratio promote the charge transfer kinetics and ion diffusion during electrochemical processes. the electrochemical performance of the conimn ldh/nf electrode was evaluated in a three-electrode system by using ag/agcl as reference electrode, pt wire as count electrode, and 3 m koh solution as electrolyte. the galvanostatic charge/discharge tests show that the specific capacitance of the conimn ldh/nf electrode was 2210 f g-1 at a current density of 1 a g-1, confirming its excellent capacitive behavior and high energy storage capacity. the specific capacitance is 2070, 1785, 1650, 1512, and 1280 f g-1 at current densities of 2, 3, 4, 5, and 8 a g-1, respectively, corresponding to the capability rate of 58 %. the high specific capacitance can be attributed to the needle-like morphology of ldhs, which provides the large electrochemically active surface area for efficient charge storage. the main storage mechanism analyzed from the cyclic voltammetry curves is battery-type with diffusion-controlled process. the conimn ldh/nf electrode is also applied as an electrocatalyst for the oxygen evolution reaction (oer). the overpotential of oer is 259 mv which is better than 360 mv for the bare nickel foam at a current density of 10 mv cm-2. furthermore, the tafel slope of conimn ldh/nf is 52 mv dec-1, showing much better performance than bare nickel foam (173 mv dec-1). the low overpotential exhibits the excellent catalytic activity of the conimn ldh towards the oer, which is a crucial step in water splitting. the efficient oer performance can be attributed to the synergistic effects of co, ni, and mn cations, which facilitate the electrochemical reaction and minimize energy losses.