Binder-free Fe-doped NiCo₂O₄/Ni₃S₄ hollow heterostructure nanotubes for highly efficient overall water splitting

For overall water splitting, a vital challenge is to design active sites at interfaces. Heterogeneous catalysts with enhanced mass/charge transfer and accelerated adsorption of intermediates have exhibited significantly enhanced activities. Herein, a Fe-doped NiCo₂O₄/Ni₃S₄ heterogeneous electrocatalyst is synthesized for the HER and OER. On account of the synergistic effect of heterostructures, Ni-O-S presents a low overpotential of 29.1 mV (10 mA cm^-2), a relatively small Tafel slope of 53.3 mV dec^-1 for the HER, and 259 mV at a current density of 100 mA cm^-2 (33.1 mV dec^-1) for the OER. What is more, Ni-O-S acts as a binder-free bi-functional electrode in an alkaline electrolyte for overall water splitting, exhibiting a cell voltage of 1.45 V (10 mA cm^-2) with good stability. This work offers an efficient approach for designing stable and high-efficiency heterogeneous electrodes for overall water splitting.