Single-Step Electrochemical Synthesis of Cobalt Nanoclusters Embedded on Dense Graphite Sheets for Electrocatalysis of the Oxygen Evolution Reaction

Abstract

Thin nanoparticle clusters have been proven to be excellent electrocatalysts as the number of active centers present in these films is several folds higher than their thicker counterparts. However, reports to date suggest that it is highly challenging to fabricate such nanoparticle-modified electrodes and usually involves multistep routes of chemical synthesis, purification, and finally, embedment onto the electrode surface, often at very high temperature. To the best of our knowledge, this is the first time that a single-step electrochemical preparation and in situ deposition of thin clusters of cobalt nanoparticle onto the electrode surface are being reported. The thickness of the nanoparticle clusters was not uniform and varied between 20 and 90 nm. The cobalt nanoparticles on the dense graphite sheet reported could attain an oxygen evolution reaction (OER) current of 10 mA/cm2 at a very low overpotential of 350 mV despite a very low catalyst loading. The turnover frequency (0.78 s−1) and activation energies (21 kJ/mol) for OER indicate that these are potential anode catalysts in the alkaline media-based oxygen evolution reaction. The fabrication methodology of these ready-to-use cobalt-based graphite substrates has several advantages like the use of an environment-friendly medium such as an aqueous deep eutectic solvent mixture, inexpensive graphite sheet, and rapid single-step preparation under ambient room-temperature conditions.