Electrochemical reduction for modulating spin state of nickel: A pathway to improved water and seawater oxidation

Abstract

Understanding the electronic structure of catalysts is crucial for analyzing electrocatalyst behavior. Here, we present a straightforward method to modify the electronic configuration of active sites in nickel-iron-niobium layered double hydroxides (NiFeNb-LDHs) via electrochemical reduction (ER), uncovering key factors that enhance oxygen evolution reaction (OER) activity. The results indicate that ER-NiFeNb-LDHs display excellent OER performance and long-term stability over 60 h in various electrolytes (271.99 mV@50 mA cm−2 in 1M KOH and 280.56 mV@50 mA cm−2 in 1M KOH +0.5M NaCl). Furthermore, the cell voltage of the two-electrode electrolyzer ER-NiFeNb-LDHs ǁ Pt/C achieves a current density of 50 mA cm−2 at an ultra-low voltage of 1.58 V, significantly outperforming the commercial RuO2ǁPt/C. X-ray absorption spectroscopy, magnetic characterization, and density functional theory calculations reveal that the unsaturated coordination environment created by ER modifies the electronic state distribution between eg and t2g orbitals, effectively lowering the spin state of nickel and enhancing its OER activity.