Remarkable Bifunctional Oxygen and Hydrogen Evolution Electrocatalytic Activities with Trace-Level Fe Doping in Ni- and Co-Layered Double Hydroxides for Overall Water-Splitting

Large-scale H₂ production from water by electrochemical water-splitting is mainly limited by the sluggish kinetics of the nonprecious-based anode catalysts for oxygen evolution reaction (OER). Here, we report layer-by-layer in situ growth of low-level Fe-doped Ni-layered double hydroxide (Ni_1–xFe_x-LDH) and Co-layered double hydroxide (Co_1–xFe_x-LDH), respectively, with three-dimensional microflower and one-dimensional nanopaddy-like morphologies on Ni foam, by a one-step eco-friendly hydrothermal route. In this work, an interesting finding is that both Ni_1–xFe_x-LDH and Co_1–xFe_x-LDH materials are very active and efficient for OER as well as hydrogen evolution reaction (HER) catalytic activities in alkaline medium. The electrochemical studies demonstrate that Co_1–xFe_x-LDH material exhibits very low OER and HER overpotentials of 249 and 273 mV, respectively, at a high current density of 50 mA cm^–2, whereas Ni_1–xFe_x-LDH exhibits 297 and 319 mV. To study the overall water-splitting performance using these electrocatalysts as anode and cathode, three types of alkaline electrolyzers are fabricated, namely, Co_1–xFe_x-LDH­(+)∥Co_1–xFe_x-LDH­(−), Ni_1–xFe_x-LDH­(+)∥Ni_1–xFe_x-LDH­(−), and Co_1–xFe_x-LDH­(+)∥Ni_1–xFe_x-LDH­(−). These electrolyzers require only a cell potential (E_cell) of 1.60, 1.60, and 1.59 V, respectively, to drive the benchmark current density of 10 mA cm^–2. Another interesting finding is that their catalytic activities are enhanced after stability tests. Systematic analyses are carried out on both electrodes after all electrocatalytic activity studies. The developed three types of electrolyzers to produce H₂, are very efficient, cost-effective, and offer no complications in synthesis of materials and fabrication of electrolyzers, which can greatly enable the realization of clean renewable energy infrastructure.