Solid-phase microwave synthesis of high-entropy graphene quantum dots as metal-free electrochemical catalysts

Abstract

In this study, high-entropy graphene quantum dots (GQDs) are synthesized and utilized as metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline electrolyte. An efficient solid-state microwave route was used to synthesize the GQD catalysts. This synthesis method involves the pyrolysis of two carbon precursors and four dopant precursors under a pulse microwave irradiation at 180 °C. The synthesized efficient catalyst possesses an average particle size of about 5 nm. The synthesized GQDs catalyst contains six elements in the graphite-like lattices with numerous surface functionalities and dopants. Synthesized high-entropy GQD catalytic electrodes displayed ultra-high electrochemically active surface area and endurance for the ORR measurements. The GQD electrode shows a well-defined reduction peak at ca. −0.5 V and an onset potential at ca. −0.1 V vs. saturated calomel electrode in the diluted potassium hydroxide solution. The heteroatom doping into the GQD nanostructure greatly increased the ORR catalytic activity. The above synthesized non-metallic and inexpensive catalyst showed remarkable properties such as enhanced catalytic activity, selectivity, and superior durability. Therefore, synthesized GQD electrodes have great potential for energy applications, especially for fuel cells.