Iridium oxide-based nanocrystalline particles as oxygen evolution electrocatalysts

Abstract

Iridium-based oxides are highly active as oxygen evolving electrocatalysts in PEM water electrolyzers. In this work XRD reveals that Ir-Sn oxides contain a single rutile phase with lattice parameters between those of pure IrO₂ and SnO₂. Addition of Ru leads to the synthesis of a core-shell type material due to the strong agglomeration of Ru colloids during the preparation procedure. The shell of this material consists of an Ir-Sn-Ru oxide deficient in Ru relative to the bulk. This leads to a decrease in the surface noble metal concentration (as found by XPS), which in turn results in a significant reduction in electrochemically active surface area. Polarization analysis indicates that the addition of Ru can influence the rate-determining step or mechanism by which oxygen is evolved. In a PEM water electrolysis cell, small additions of Sn do not significantly reduce the operating performance, however larger additions cause a performance loss due to a reduction in active surface area and increased ohmic resistance. When a pure IrO₂ anode is used, a cell voltage is 1.61 V at 1 A cm⁻² and 90°C.