Ultra‐Fast In Situ Reconstructed Nickel (Oxy)Hydroxide Nanoparticle Crosslinked Structure for Super‐Efficient Alkaline Water Electrolysis by Sacrificing Template Strategy

The rapid construction of water electrolysis catalysts by a sacrificing template in an electrochemical environment is rarely a concern. Herein, using a fluorine‐rich (F‐rich) nickel fluoride (NiF 2 ) grown on nickel foam (NF) as a sacrificial template, a highly effective alkaline catalyst is designed. In terms of in situ reassembling, the NiF 2 template can be transformed into nickel hydroxide (Ni(OH) 2 ) in hydrogen evolution reaction (HER) and nickel oxyhydroxide (NiOOH) in oxygen evolution reaction (OER), respectively, after only 100 CV cycles, on account of the rapid ion exchange of F − and OH − in an electrochemical environment. Due to the presence of nanocatalytic units, abundant lattice defects, and porous large specific surface structures caused by the reconstruction, it only takes low overpotentials of 57 mV for HER and 228 mV for OER (@10 mA cm −2 ), with outstanding stability up to 15 d (@100 mA cm −2 ). Consequently, only a low cell voltage of 1.53 V (@10 mA cm −2 ) is needed for overall water splitting, superior to commercial noble metal catalysts as benchmarks. Meanwhile, it can output stable current densities of 10, 100, and 500 mA cm −2 approaching 10 d under constant cell voltages of 1.55, 2.0, and 2.5 V, respectively.