Composite Thin Film Iridium- Niobium Oxide Electrocatalysts for the Oxygen Evolution Electrode

Abstract

A series of (IrO 2 ) 1-x (Nb 2 O 5 ) x catalyst with Nb 2 O 5 loading from 0.1-0.7 mol% was prepared by hydrolysis method and annealed at 500 ºC. Electrodes of the catalyst powder was characterized in 0.5 mol dm − 3 H 2 SO 4 by cyclic voltammetry (CV) and quasi steady-state polarisation measurements (LSV). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) indicated a phase separation into iridium oxide and niobium pentoxide in the catalyst for all compositions and forms composite oxide rather than a solid solution. In line with this, at room temperature the catalytic activity decreased with increasing niobium content in the catalyst. However, raising the temperature to 80 o C inverted this sequence so that the catalytic activity increased in the order IrO 2 < (IrO 2 ) 0.7 (Nb 2 O 5 ) 0.3 < (IrO 2 ) 0.9 (Nb 2 O 5 ) 0.1 .