Iridium dioxide (IrO₂) is well known as an electrocatalyst with good activity for the oxygen evolution reaction (OER). We demonstrated earlier that IrO₂ nanosheets, which are prepared via exfoliation of layered IrO₂, exhibited similar performance to IrO₂ nanoparticles (2-3 nm in diameter).¹⁾ In this study, we show that the OER activity of IrO₂ nanosheet can be improved by down-sizing the lateral size of IrO₂nanosheets.

IrO₂ nanosheet was derived via exfoliation of layered H_0.3Ir_0.93O₂×nH₂O through a process reported previously. The lateral size of IrO₂ nanosheet was reduced by ultrasonic treatment for 30 min with a homogenizer. The working electrode was prepared by dropping the IrO₂ nanosheet on a glassy carbon electrode. A thin layer of Nafion ionomer was cast on the electrode. All electrochemical measurements were conducted in 0.1 M HClO₄ (25^oC).

The lateral size of as-prepared IrO₂ nanosheet decreased from 258 nm to 111 nm by ultrasonic treatment. The electrochemically active surface area for both nanosheets was similar. The OER activity of IrO₂ nanosheet with small lateral size was 881 A (g-IrO₂)^‒1, 1.9 times higher than that of as-prepared IrO₂ nanosheet (451 A (g-IrO₂)^‒1). The edge sites of small lateral nanosheet size were 1.7 times higher than that of as-prepared nanosheets, corresponding well the enhancement in OER activity. The result suggests that the OER activity of IrO₂nanosheet was enhanced by down-sizing the lateral size of nanosheet, which increased the amount of edge sites.

1)      W. Shimizu, T. Ishida, S. Miyasaka, Y. Ayato, and W. Sugimoto, 227th ECS meeting, Chicago, IL (2015).