Iridium nanohollows with porous walls for acidic water splitting

Abstract

Engineering iridium (Ir)-based electrocatalysts towards high activity and satisfactory durability for the oxygen evolution reaction (OER) in acidic media has been long pursued to commercialize proton exchange membrane-based electrolyzers. Here we report a novel class of Ir porous nanohollows (p-NHs) with tunable wall thickness, which electrocatalyze acidic OER with much enhanced performance relative to conventional Ir nanoparticles. The p-NH structure is deliberately-tailored via a facile hydrothermal approach, in which the initially-formed solid Ir spheres were in situ etched via the Kirkendall effect. At an overpotential of 300 mV, the Ir p-NH catalyst delivers a mass activity of 1.75 A mg_Ir⁻¹, which is 6.25 and 3.20 times higher than those of commercial Ir/C and control Ir solid nanosphere catalysts, respectively. Ir p-NHs as an anode enable voltages of 1.50 V and 1.59 V at 10 and 100 mA cm⁻², respectively, for acidic water splitting. We explore how porosity energetically promotes OER activity of Ir-based catalysts using density functional theory (DFT) calculations, which reveal that the adsorption of *OOH and thus OER activity can be described by the generalized coordination number of surface Ir sites. Our findings offer new insights into the rational design of highly-open Ir-based nanostructures for efficient OER electrocatalysis.