Developing exceedingly efficient, cost-effective, and environmentally friendly bifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) especially at high current density is crucial for realizing the industrial application of electrocatalytic overall water splitting. In this work, non-noble-metal bifunctional catalysts with single Ni atoms, single Fe atoms, and NiFe nanoalloys supported on carbon nanotubes (Ni SA Fe SA -Ni x Fe/CNT) are rationally designed and fabricated. In 1 M KOH, the optimized Ni SA Fe SA -Ni 50 Fe/CNT catalyst affords low overpotentials of 64 and 227 mV at 10 mA cm −2 for catalyzing the HER and OER, respectively. Moreover, the catalyst enables the overall water splitting at a low cell voltage of 1.49 V to achieve 10 mA cm −2 in 1 M KOH. At a cell voltage of 1.80 V, the current density is as high as 382 mA cm −2 , which surpasses those of most materials reported so far. After a simple two-step oxidation and rereduction procedure, the catalytic performances of the OER, HER, and overall water splitting recover completely to their original levels. This work not only provides a potential catalyst candidate for economically realizing water splitting but also shows a method for reactivatable catalyst design.

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