Hierarchical Heterostructure of Nife2o4 Nanoflakes Grown on the Tip of Nico2o4 Nanoneedles with Enhanced Interfacial Polarization Effect to Achieve Highly Efficient Electrocatalytic Oxygen Evolution

Abstract

In this work, a heterostructure OER electrocatalyst consisting of NiFe 2 O4 nanoflakes grown on the tip of NiCo 2 O 4 nanoneedles arrays supported on nickel foam (NCO-NNs@NFO-NFs/NF) was obtained via simultaneous cation (Co 3+ by Fe 3+ ) and ligand exchange (OH - by 1,4-benzenedicarboxylic acid) and further annealing of the hydroxide/MOF precursor in air. HRTEM and Raman characterizations confirmed the formation of NCO/NFO heterostructure. XPS characterization and charge density difference calculations clarified the electron transfer from Fe to Ni and Co at the NCO/NFO heterointerface. Electrochemical tests showed that NCO-NNs@NFO-NFs/NF possesses excellent OER electrocatalytic activity (overpotential of 265 mV@50 mA cm -2 ) and durability (stable for 100 h@1A cm -2 ). The NCO-NNs@NFO-NFs/NF‖20% Pt/C two-electrode system can achieve a current density of 200 mA cm -2 under 1.52 V for water splitting at 85 °C in 6.0 M KOH, surpassing the performance of commercial RuO 2 (1.63 V). XPS, and HRTEM characterizations after the V-t test, along with in-situ Raman characterizations, confirmed that Co and Fe sites underwent synergistic surface reconstruction to form specific CoOOH/FeOOH active interfaces, as to exert the synergistic electrocatalytic effect of the dual active sites during the OER process. DOS calculations revealed that the density of state at the Fermi level increased after the introduction of Fe, thereby improving the conductivity and facilitating the activation of the adsorbed oxygen-containing intermediate species. This study showed a significant methodology for simultaneous improvement of the electrocatalytic stability and activity of spinel oxides-based heterostructures, which is critical for them to be used in real applications.

Keywords: Spinel oxides, oxygen evolution reaction, Heterostructure, interfacial electron transfer, surface reconstruction