IrOx Supported on Submicron-Sized Anatase TiO2 as a Catalystfor the Oxygen Evolution Reaction

Abstract

Ir-based catalysts are the best in terms of activity and stability for oxygen evolution reactions (OERs) in proton exchange water electrolysis. Due to their cost, efforts have been made to decrease their load without a loss of activity. In this paper, Ir nanoparticles measuring 2–3 nm were loaded on TiO2 anatase supports of submicrometric size in different amounts using the microwave polyol method to optimize their mass activity. Using anatase particles with a diameter of about 100 nm and titania nanotubes (TNTs), Ir/TiO2 catalysts with Ir contents of 5, 10, 20, and 40 wt.% were synthesized and characterized via structural and electrochemical techniques. It was shown that the amount of Ir must be regulated to obtain continuous coverage on titania with strong Ir–TiO2 interactions which, for the 100 nm diameter anatase, is limited to about 20 wt.%. A higher percentage of Ir over 40 wt.% can be dispersed over the TNTs. Exceeding one layer of coverage leads to a decrease in the catalyst’s utilization. Ir/TiO2(10:90), Ir/TiO2(20:80), and Ir/TiO2(40:60) presented the highest pseudocapacitive currents per unit of Ir mass. The electrochemical active areas and mass activities for these later catalysts were also the highest compared to Ir/TiO2(05:95), Ir/TNT(40:60), and the unsupported catalysts and increased from 40 to 10 wt.% Ir. They also presented the lowest overpotentials of about 300 mV at 10 mA cm−2 for the OER, with Ir/TiO2(10:90) presenting the best specific activities and surface turnover frequencies, thus showing that the size of the support can be regulated to decrease the Ir content of the catalyst without a loss of activity.