Iridium Nanoparticles Supported on Magneli Phase Ti4O7 for PEM Water Electrolyzers

Abstract

PEM water electrolysis is one of the promising technologies for hydrogen production from renewable energy sources. Iridium and their oxides are recognized as the most suitable catalyst showing high activity and stability for oxygen evolution reaction (OER) in acidic media [1], however, overpotential is still high and its scarcity and price are also drawbacks. To overcome these problems, a number of studies concerning particle size reduction, catalyst compositions, and utilization of catalyst support have been reported [2]. Among them, use of corrosion-resistant and highly electro-conductive oxides, especially Magneli phase Ti4O7 as catalyst support would be beneficial for reducing Ir loading and increasing durability. We have developed Ti4O7-supported Ir catalyst and examined activity and durability as an anode catalyst of PEM electrolyzer. Titanium oxide support was prepared by UV laser technique [3]. Ir/Ti4O7 catalysts obtained by using H2IrCl6 precursor showed conductivity comparable with that of commercial Pt/C. MEAs with the Ir/Ti4O7 anode can be operated up to 4 A cm-2 at low cell voltage < 2.0 V (with DuPont NR212 membrane) with very low Ir loadings (0.25 mg-Ir cm-2). Considering fluctuating nature of the renewable energy inputs, catalyst stability against voltage change should be another important issue. To simulate and accelerate such degradation modes, potential sweep between 1.0 V and 2.0 V at a sweep rate of 500 mV s-1 was applied up to 10,000 cycles. The Ir/Ti4O7 MEA shows limited degradation even after 10,000 cycles. Stability of the cell performance and the catalyst structure will be discussed at the Meeting.