Electron transfer dynamics and electrocatalytic oxygen evolution activities of the Co3O4 nanoparticles attached to indium tin oxide by self-assembled monolayers

The Co3O4 nanoparticle-modified indium tin oxide-coated glass slide (ITO) electrodes are successfully prepared using dicarboxylic acid as the self-assembled monolayer through a surface esterification reaction. The ITO-SAM-Co3O4 (SAM = dicarboxylic acid) are active to electrochemically catalyze oxygen evolution reaction (OER) in acid. The most active assembly, with Co loading at 3.31 x 10(-8) mol cm(-2), exhibits 374 mV onset overpotential and 497 mV overpotential to reach 1 mA cm(-2) OER current in 0.1 M HClO4. The electron transfer rate constant (k) is acquired using Laviron's approach, and the results show that k is not affected by the carbon chain lengths of the SAM (up to 18 -CH2 groups) and that an increase in the average diameter of Co3O4 nanoparticles enhances the k. In addition, shorter carbon chains and smaller Co3O4 nanoparticles can increase the turn-over frequency (TOF) of Co sites toward OER. The Co3O4 nanoparticles tethered to the ITO surface show both a higher number of electrochemically active Co sites and a higher TOF of OER than the Co3O4 nanoparticles bound to ITO using Nafion.

Automated summary

The Co3O4 nanoparticle-modified ITO electrodes were successfully prepared using dicarboxylic acid as a self-assembled monolayer. These electrodes showed high electrochemical catalytic activity for oxygen evolution reaction (OER) in acid. The most active assembly exhibited low overpotential and high OER current density, and the electron transfer rate constant was not affected by the carbon chain lengths but enhanced by the larger diameter of Co3O4 nanoparticles. Furthermore, shorter carbon chains and smaller Co3O4 nanoparticles increased the turnover frequency (TOF) of Co sites for OER.