In Situ Adsorption of a Lewis Base Triggers Selective Seawater Oxidation Based on the Lattice Oxygen-Mediated Mechanism.

Abstract

During seawater electrolysis, the anodic oxygen evolution reaction (OER) is invariably confronted with an inescapable challenge: side reactions instigated by chloride ions and the poisoning of catalytically active sites. To address this, we put forward a strategy of doping high-valence metal Mo into Ni(OH)₂ to achieve high selectivity and activity of the OER in alkaline seawater. In situ characterization, along with theoretical calculations, demonstrates that Lewis bases (MoO₄^2-) are generated through Mo dissolution within the catalyst and subsequently adsorbed in situ on the catalyst surface. Additionally, the Ni(OH)₂ with Mo doping realizes a more rapid phase transformation of Ni(OH)₂ and the redistribution of local charge and triggers the lattice oxygen-mediated mechanism. This process elevates the active site to a higher oxidation state (Ni^3+<i>x</i>) and endows the active site with a high selectivity toward OH^-. In an alkaline seawater anion-exchange membrane electrolyzer, NiOOH-MoO₄^2- as anode achieves good durability, with the system remaining operational for over 180 h at a current density of 500 mA cm^-2. This research presents an efficient approach for the straightforward and expeditious fabrication of high-oxidation-state Ni-based electrocatalysts featuring an adsorbed Lewis base (MoO₄^2-), which holds good promise in steering the advancement of seawater electrolysis technology.