Fe-doped Ni- and Co-layered double hydroxides for Electrochemical overall water splitting

G. Rajeshkhanna, Thangjam Ibomcha Singh, Nam Hoon Kim,* and Joong Hee Lee*

Large-scale H2 production from water by electrochemical water splitting is mainly limited by the sluggish kinetics of the non-precious 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 (Ni1-xFex-LDH), and Co-layered double hydroxide (Co1-xFex-LDH), respectively, with 3D microflower and 1D nanopaddy-like morphologies on Ni foam, by a one-step eco-friendly hydrothermal route. In this work, an interesting finding is that both Ni1-xFex-LDH and Co1-xFex-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 Co1-xFex-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, while Ni1-xFex-LDH exhibits 297 and 319 mV. In order to study the overall water splitting performance using these electrocatalysts as anode and cathode, three types of alkaline electrolyzers are fabricated namely Co1-xFex-LDH(+)ǁCo1-xFex-LDH(-), Ni1-xFex-LDH(+)ǁNi1-xFex-LDH(-) and Co1-xFex-LDH(+)ǁNi1-xFex-LDH(-). These electrolyzers require only a cell potential (Ecell) 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 the electrodes after all electrocatalytic activity studies. The developed three types of electrolyzers are very efficient to produce H2, cost-effective, offers no complications in synthesis of materials and fabrication of electrolyzers, which can greatly enable the realization of clean renewable energy infrastructure.