Topologic transition-induced abundant undercoordinated Fe active sites in NiFeOOH for superior oxygen evolution

Highly active, robust and low-cost oxygen evolution reaction (OER) electrodes are urgently required to satisfy the industrial hydrogen production via water electrolysis. However, numerous earth-abundant materials have severely suffered from the low stability over thousands of hours at large current densities. Herein, ultrathin NiFeOOH nanosheets with abundant undercoordinated Fe active sites on a Ni foam electrode for OER were obtained via an electrochemically topologic transition process. They deliver a low overpotentials of 210 mV at 10 mA cm-2 and a small Tafel slope of 32 mV dec-1 owing to the abundant Fe active sites and exhibit high stability at high current densities of 400–600 mA cm-2 over 2000 h due to their strong adhesion to Ni foam. Moreover, only a 370 mV overpotentials is required to produce a high current density of 400 mA cm-2 in a two-electrode water electrolysis system, demonstrating an energy efficiency as high as ∼77%.