A Highly Active, Long-Lived Oxygen Evolution Electrocatalyst Derived from Open-Framework Iridates.

Abstract

The acidic oxygen evolution reaction underpins several important electrical-to-chemical energy conversions, and this energy-intensive process relies industrially on iridium-based electrocatalysts. Here, phase-selective synthesis of metastable strontium iridates with open-framework structure and their unexpected transformation into a highly active, ultrastable oxygen evolution nano-electrocatalyst are presented. This transformation involves two major steps: Sr²⁺ /H⁺ ion exchange in acid and in situ structural rearrangement under electrocatalysis conditions. Unlike its dense perovskite-structured polymorphs, the open-framework iridates have the ability to undergo rapid proton exchange in acid without framework amorphization. The resulting protonated iridates further reconstruct into ultrasmall, surface-hydroxylated, (200) crystal plane-oriented rutile nanocatalyst, instead of the common amorphous IrO_x H_y phase, during acidic oxygen evolution. Such microstructural characteristics are found to benefit both the oxidation of hydroxyls and the formation of OO bonds in electrocatalytic cycle. As a result, the open-framework iridate derived nanocatalyst gives a comparable catalytic activity to the most active iridium-based oxygen evolution electrocatalysts in acid, and retains its catalytic activity for more than 1000 h.