Ir-Induced Local Charge and Electron-Spin Regulation on CoNi LDH Electrocatalyst for Efficient Oxygen Evolution Reaction.

Nonprecious metal CoNi layered double hydroxides (LDHs) have received extensive attention as binary LDH-type catalysts with the lowest overpotential in the oxygen evolution reaction (OER). However, its relatively low electrical conductivity and strong adsorption on oxygen-containing intermediates limit the OER reaction rate. Therefore, we doped the iridium element containing 5d orbitals into CoNi LDH and obtained the ternary CoNiIr ZLDH (ZIF-67 derived LDH) electrocatalyst with an efficient OER performance. This strategy reduces the initial overpotential of the OER reaction. Only low overpotentials of 202 mV and 280 mV are needed to achieve current densities of 10 mA cm-2 and 100 mA cm-2, respectively. Furthermore, this electrode exhibits strong electrochemical stability and maintains the minimum degradation for nearly 24 h under the harsh OER conditions with a high current density of 60 mA cm-2. These characteristics make CoNiIr ZLDH one of the most efficient CoNi-based LDH catalysts reported to date. Density functional theory calculations indicate that the high catalytic activity of CoNiIr ZLDH mainly results from the spin-orbit coupling effect of the wide 5d-orbital containing element Ir, which alters the electron charge and electron spin distribution near the Fermi energy of the catalyst. This modification enhances the electrical conductivity, reduces the adsorption energy of oxygen species, and promotes the transfer of electrons and substances, thereby lowering the reaction overpotential and improving the reaction efficiency. This research is expected to provide new ideas for the practical design of OER electrodes in electrochemical water splitting.