Elemental selenium enables enhanced water oxidation electrocatalysis of NiFe layered double hydroxides

The oxygen evolution reaction (OER) is involved in various renewable energy systems, such as water-splitting, metal-air batteries and CO₂ electroreduction. Ni-Fe layered double hydroxides (LDHs) have been reported as promising OER electrocatalysts in alkaline electrolytes. Herein, we demonstrate that the introduction of elemental selenium (Se) with an optimized phase composition, i.e., monoclinic (m-) or trigonal (t-) Se, could effectively tailor the OER activity of NiFe-LDH. Compared to t-Se doped NiFe-LDH, the presence of hybrid m/t-Se could effectively tune the electronic states of Ni-O and Fe-O sites, promote the generation of OER-active γ-NiOOH, and inhibit Fe-migration during the OER process, thus enhancing the OER performance. The optimized Ni_0.8Fe_0.2-m/t-Se_0.02-LDH catalyst exhibits extraordinarily high OER activity, with an overpotential of 200 mV at 10 mA cm^-2, which is superior to those of IrO₂ and most of the reported Se-based OER catalysts. The Ni_0.8Fe_0.2-m/t-Se_0.02-LDH catalyst is further implemented as an anode for overall water splitting and demonstrates a low cell voltage of 1.50 V to achieve 10 mA cm^-2.