Construction of Defect‐Rich Ni‐Fe‐Doped K0.23MnO2 Cubic Nanoflowers via Etching Prussian Blue Analogue for Efficient Overall Water Splitting

Abstract Designing elaborate nanostructures and engineering defects have been promising approaches to fabricate cost‐efficient electrocatalysts toward overall water splitting. In this work, a controllable Prussian‐blue‐analogue‐sacrificed strategy followed by an annealing process to harvest defect‐rich Ni‐Fe‐doped K 0.23 MnO 2 cubic nanoflowers (Ni‐Fe‐K 0.23 MnO 2 CNFs‐300) as highly active bifunctional catalysts for oxygen and hydrogen evolution reactions (OER and HER) is reported. Benefiting from many merits, including unique morphology, abundant defects, and doping effect, Ni‐Fe‐K 0.23 MnO 2 CNFs‐300 shows the best electrocatalytic performances among currently reported Mn oxide‐based electrocatalysts. This catalyst affords low overpotentials of 270 (320) mV at 10 (100) mA cm −2 for OER with a small Tafel slope of 42.3 mV dec −1 , while requiring overpotentials of 116 and 243 mV to attain 10 and 100 mA cm −2 for HER respectively. Moreover, Ni‐Fe‐K 0.23 MnO 2 CNFs‐300 applied to overall water splitting exhibits a low cell voltage of 1.62 V at 10 mA cm −2 and excellent durability, even superior to the Pt/C||IrO 2 cell at large current density. Density functional theory calculations further confirm that doping Ni and Fe into the crystal lattice of δ‐MnO 2 can not only reinforce the conductivity but also reduces the adsorption free‐energy barriers on the active sites during OER and HER.