Fe-Doping induced divergent growth of Ni–Fe alloy nanoparticles for enhancing the electrocatalytic oxygen reduction

Non-noble metal Ni and its alloy based catalysts are promising alternatives to Pt catalysts for the oxygen reduction reaction (ORR). Control of the exposed crystallographic facets of catalysts is an efficient way of tailoring their activity, but the practicability and the investigation of the underlying mechanisms of this protocol still present challenges for Ni and its alloys. Herein, we succeeded in preparing Ni–Fe alloy nanoparticles (NPs) with different exposed facets via pyrolysis of Fe-substituted Ni-bispyrazolate metal–organic frameworks. Fe-doping induces divergent growth in the two kinds of NPs to afford separate (111)- and (200)-faceted NPs with distinguishable diameters. Density functional theory (DFT) calculations were used to simulate the ORR process on the two facets of the Ni–Fe NPs, revealing that the (200)-faceted NPs show the highest activity due to their large compressive strain effect. The experimental results confirm the enhanced ORR activity of the derived catalysts and superior performance of assembled Zn–air batteries.