Effect of Electronic Conductivities of Iridium Oxide/Doped SnO₂ Oxygen-Evolving Catalysts on the Polarization Properties in Proton Exchange Membrane Water Electrolysis

Abstract

We have developed IrOx/M-SnO2 (M = Nb, Ta, and Sb) anode catalysts, IrOx nanoparticles uniformly dispersed on M-SnO2 supports with fused-aggregate structures, which make it possible to evolve oxygen efficiently, even with a reduced amount of noble metal (Ir) in proton exchange membrane water electrolysis. Polarization properties of IrOx/M-SnO2 catalysts for the oxygen evolution reaction (OER) were examined at 80 °C in both 0.1 M HClO4 solution (half cell) and a single cell with a Nafion® membrane (thickness = 50 μm). While all catalysts exhibited similar OER activities in the half cell, the cell potential (Ecell) of the single cell was found to decrease with the increasing apparent conductivities (σapp, catalyst) of these catalysts: an Ecell of 1.61 V (voltage efficiency of 92%) at 1 A cm-2 was achieved in a single cell by the use of an IrOx/Sb-SnO2 anode (highest σapp, catalyst) with a low Ir-metal loading of 0.11 mgIr cm-2 and Pt supported on graphitized carbon black (Pt/GCB) as the cathode, with 0.35 mgPt cm−2. In addition to the reduction of the ohmic loss in the anode catalyst layer, the increased electronic conductivity contributed to decreasing the OER overpotential due to the effective utilization of the IrOx nanocatalysts on the M-SnO2 supports, which is an essential factor in improving the performance with low noble metal loadings.

Towards stable and highly active IrO2 catalysts supported on doped tin oxides for the oxygen evolution reaction in acidic media

“…Non-noble metal oxides, specifically doped tin oxides (M-SnO 2 ) with hypovalent or hypervalent ions such as Sb, Nb, F, In, or Ta have been gaining momentum as they show great stability in strong acidic media and delivering noteworthy electronic conductivities, surpassing 0.2 S•cm -1 [8][9][10]. As most metal oxides are semiconductors, doping them with such types of ions present the ultimate pre-requisite to allow an increase of electrical conductivities without compromising a path-free interconnected structure compatible with facile mass transport rates (water and oxygen).…”