Interfacial oxidation using potassium ferrate to fabricate self-supported hydrophilic NiFe-LDH nanoarrays for overall water splitting at high current density

The preparation of NiFe layered double hydroxide (NiFe-LDH)-based efficient bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through eco-friendly and convenient methods remains challenging. To overcome this, herein, we employed a novel one-step hydrothermal synthesis strategy by exploiting the strong oxidisability of potassium ferrate, which allows the oxidisation of the Ni foam (NF) surface, to obtain self-supporting, oversized, and hydrophilic NiFe-LDH nanosheet arrays. Because of the advantageous self-supporting structure, satisfactory hydrophilicity, excellent conductivity of the NF substrate as well as the strong interaction and synergistic optimisation of Ni and Fe bimetallic active centres, the catalytic performance of the NiFe-LDH was significantly enhanced. The optimised NiFe layered double hydroxide nanosheet array catalyst grown on nickel foam with 3.5 mmol K2FeO4 added [NiFe-LDH/NF-3.5] required overpotentials of only 75 and 223 mV (for the HER) and 249 and 303 mV (for the OER) to achieve 10 and 100 mA cm−2, respectively. An alkaline electrolyser based on NiFe-LDH/NF-3.5 achieved these current densities at battery voltages as low as 1.57 and 1.75 V. At a high current density (500 mA cm−2), the catalyst was also successfully operable for 230 h, demonstrating its remarkable stability. Furthermore, DFT calculation results verified that the adsorption energy of NiFe-LDH/NF-3.5 was suitable for H and OH. Thus, this study not only proposes an efficient strategy for NiFe-LDH synthesis but also promotes the development of non-precious-metal catalysts for practical applications.