Electron transfer dynamics and electrocatalytic oxygen evolution activities of the Co₃O₄ nanoparticles attached to...

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 × 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.