Green Synthesis and Electrochemical Study of Cobalt/Graphene Quantum Dots for Efficient Water Splitting

Hydrogen production via electrochemical water splitting is limited thermodynamically by the sluggish oxygen evolution reaction (OER) at the anode. The use of noble metal-based catalysts leads to an economic bottleneck because of the high cost associated with such materials. This article is an electrochemical investigation of an economically viable and advanced OER catalyst made of cobalt/graphene nanocomposite quantum dots (QDs). A series of characterization techniques, such as high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and fluorescence measurements, were performed, and they confirmed the formation of graphene QDs as well as the formation of cobalt-based QDs. A very high current density of 43.16 mA cm(-2) was observed for the QD nanocomposite, whereas smaller current densities were seen for Co nanoparticles (21.1 mA cm(-2)) and a benchmark Pt/C commercial catalyst (5.99 mA cm(-2)). Furthermore, an overpotential of only 0.49 V is required for the composite material at 10 mA cm(-2), which is lower than the other two catalysts studied. Electrochemical impedance studies show that the composite material has the highest affinity toward OER of all of the materials investigated at several potentials. Chronoamperometric and chronopotentiometric investigations reveal short-term stability for the composite, where instability was observed for the comparison materials. This research is the first observation of transition-metal/graphene QD nanocomposites for electrocatalysis. These observations, along with high stability, serve as an exciting starting point for the foray into earth abundant transition-metal QD-based electrocatalysts for clean energy and environmental applications.