Optimizing Edge Active Sites via Intrinsic In-Plane Iridium Deficiency in Layered Iridium Oxides for Oxygen Evolution Electrocatalysis.

Improving catalytic activity of surface iridium sites without compromising their catalytic stability is the core task of designing more efficient oxygen evolution electrocatalysts under acidic conditions. In this work, we present the phase transition of a bulk layered iridate Na 2 IrO 3 in acid solution at room temperature, and the subsequent exfoliation to produce two dimentional iridium oxide nanosheets with an around 4 nm thickness. The nanosheets consist of OH-terminated, honeycomb-type layers of edge-sharing IrO 6 octahedral framework with intrinsic in-plane iridium deficiency. The nanosheet material is among the most active Ir-based catalysts reported for OER in acid, and gives an iridium mass activity improvement up to a factor of 16.5 over rutile IrO 2 nanoparticles. The nanosheet material also exhibits good catalytic and structural stability, and retains the catalytic activity for more than 1,300 hours. The collective results from experimental and theoretical studies demonstrate that edge Ir sites of the layer are the active centres for OER, with structural hydroxyl groups participating in the catalytic cycle of OER via a non-traditional adsorbate evolution mechanism. The existence of intrinsic in-plane iridium deficiency is found to the key to building a unique local environment of edge active sites that have optimal surface oxygen adsorption properties and thereby high catalytic activity. This article is protected by copyright. All rights reserved.