Porous NiFe-Oxide Nanocubes as Bifunctional Electrocatalysts\nfor Efficient Water-Splitting

Abstract

Electrocatalytic\nwater-splitting, a combination of oxygen and hydrogen evolution reactions\n(OER and HER), is highly attractive in clean energy technologies,\nespecially for high-purity hydrogen production, whereas developing\nstable, earth-abundant, bifunctional catalysts has continued to pose\nmajor challenges. Herein, a mesoporous NiFe-oxide nanocube (NiFe-NC)\nsystem is developed from a NiFe Prussian blue analog metal–organic\nframework as an efficient bifunctional catalyst for overall water-splitting.\nThe NiFe-NCs with ∼200 nm side length have a Ni/Fe molar ratio\nof 3:2 and is a composite of NiO and α/γ-Fe₂O₃. The NCs demonstrate overpotentials of 271 and 197\nmV for OER and HER, respectively, in 1 M KOH at 10 mA cm^–2, which outperform those of 339 and 347 mV for the spherical NiFe-oxide\nnanoparticles having a similar composition. The electrolyzer constructed\nusing NiFe-NCs requires an impressive cell voltage of 1.67 V to deliver\na current density of 10 mA cm^–2. Along with a mesoporous\nstructure with a broad pore size distribution, the NiFe-NCs demonstrate\nthe qualities of a desired corrosion-resistant water-splitting catalyst\nwith long-term stability. The exposure of active sites at the edges\nand vertices of the NCs was validated to play a crucial role in their\noverall catalytic performance.