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

Abstract

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.

A Mini Review on Carbon Quantum Dots: Preparation, Properties, and Electrocatalytic Application

“…CQDs can provide more catalytically active sites by both surrounding edges and many functional groups in electrocatalysis (Wei et al, 2018; Cirone et al, 2019; Shin et al, 2019; Zhang et al, 2019). Lv et al (2017) prepared a bifunctional precious-metal-free electrocatalyst by in-situ formation of nitrogen-doped graphene quantum dots (NGQDs) and Ni 3 S 2 nanocomposites on nickel foam (NF).…”

Recent Advances on Graphene Quantum Dots for Bioimaging Applications

“…The obtained GQDs were 5 nm in diameter, exhibited high photostability and non-cytotoxicity. Similarly, ascorbic acid-assisted hydrothermal cutting of graphite to synthesize GQDs was also demonstrated (Cirone et al, 2019). Recently, in contrast to the GQDs, Wang et al prepared sulfurdoped GQDs (S-GQDs) by one pot hydrothermal exfoliation reaction (Wang et al, 2018a).…”

Graphene Quantum Dots – Hydrothermal Green Synthesis, Material Characterization and Prospects for Cervical Cancer Diagnosis Applications: A Review

“…Cirone et al produced GQDs by this procedure and the products thus obtained consisted of epoxy groups only at their edges and were defect-free. [118] Furthermore, these edge functional groups acted as anchoring sites for Co atoms, which on attachment replaced the oxygen groups and largely improved the PL of the material. [118] In a reaction mixture, when the concentration of supersaturated precursor solution surpasses the critical nucleation threshold, nucleation occurs.…”