PH-Controlled Growth of Ni-Fe Layered Double Hydroxide Electro-Catalyst for Water Oxidation with Exceptional Operational Stability

Abstract

Ni-Fe layered double hydroxide (LDH) is a potential OER electro-catalyst in water electrolysis due to its layered open structure, rapid diffusion of reactant, good anion exchange and excellent hydroxyl adsorption. Its OER activity has been well reported at constant applied voltage. However, the water electrolyser utilizes renewable energy due to which it suffers irregular power supply that consequently affects its electrode activity. Therefore, the development of a stable Ni-Fe LDH under dynamic operation conditions is required. Herein, we performed pH-controlled growth of NiFe LDH (1:1) on Fe substrate in nickel sulfate solution by oxygen sparging. The prepared LDH requires a low OER overpotential of ~270 mV vs. Hg/HgO at 200 mA/cm2 in 1M KOH solution. Considering the potentiodynamic polarization curve of Ni-Fe LDH, its OER region is above 0.5 V (vs. Hg/HgO) and shutdown region is below 0.3 V (vs. Hg/HgO). The voltage fluctuation between both regions may result in phase change and structural distortion. Therefore, three stability regimes are important to consider for an actual operational stability test; upper OER regime I (constant 0.75 V (vs. Hg/HgO)), one-minute lower to upper OER regime II (0.5 to 0.75 V (vs. Hg/HgO)) and one-minute on-off regime III (0.3 to 0.75 V (vs. Hg/HgO)). The electrochemical characterization before and after each 12 hours regime showed no degradation and steady kinetics (38 mV/dec). The morphological and surface analysis using SEM, XRD, TEM and XPS confirmed that the LDH structure remained preserve after each regime.Fig. 1: Operational stability test of Ni-Fe LDH prepared by pH-controlled growth under three regimes and embedded IR-corrected polarization curve after each regime. Figure 1