Construction of iridium oxide nanoparticle modified indium tin oxide electrodes with polycarboxylic acids and pyrophosphoric acid and their application to water oxidation reactions

Abstract

Nanoparticle-modified electrode surfaces are of fundamental interests for electrochemical and photoelectrochemical applications. By adopting polycarboxylic acids and pyrophosphoric acid as the bridging molecules, iridium oxide nanoparticle modified indium tin oxide (ITO) electrodes are formed. X-ray photoelectron spectroscopy, inductively coupled plasma-mass spectroscopy, and cyclic voltammetry (CV) all confirm the successful modification of the ITO surface. When used to catalyze the water oxidation reaction, the most active electrode (ITO-Ben-IrOx) with the surface coverage of Ir at 3.96 × 10−9 mol cm−2 (estimated by CV) exhibits 194 mV onset overpotentials and 249 mV overpotentials to reach 1 mA cm−2 in 0.1 M HClO4. The turn-over frequency (TOF) for oxygen evolution at 280 mV overpotentials is 1.33 s−1. The electron transfer kinetics of a series of electrodes are investigated, and the results suggest that the electron transfer rate from the electrode substrate to the catalyst does not limit the rate of the water oxidation reaction at low overpotentials, and that the bridging molecules with resonant structures are desirable to enhance the TOF of the water oxidation reaction.