Spent tea leaves templated synthesis of highly active and durable cobalt-based trifunctional versatile electrocatalysts for hydrogen and oxygen evolution and oxygen reduction reactions

The rational design of high-performance trifunctional catalysts for oxygen reduction and oxygen and hydrogen evolution reactions is of vital importance for the implementation of green energy conversion technologies. Herein, trifunctional electrocatalysts comprising cobalt nanoparticles uniformly embedded in porous carbon networks were fabricated using a spent tea leaves (STL) template via a one-step carbothermal-reduction strategy at different temperatures. STL played a synthetic dual role in constructing nanocatalysts by acting as efficient scavengers to trap cobalt cations via electrostatic interactions and as carbon sources to generate a porous carbon matrix. Full characterization of the as-synthesized materials revealed the crucial effect of temperature on the crystallinity, surface area, number of surface defects and interfacial charge distribution properties. Furthermore, the trifunctional catalytic activity of the nanoparticles can be finely tuned by varying the carbonization temperature. Co@PC-7 displayed a superior trifunctional catalytic activity exhibiting an excellent performance for hydrogen production with an overpotential of 153 mV (vs. RHE) to achieve 10 mA cm-2, and an impressive bifunctional oxygen electrocatalytic activity with an ultralow potential difference between OER and ORR (ΔE = η10 - E1/2) of 0.69 V, which is one of the lowest values reported in the literature for transition metal nanocatalysts. The remarkable performance of Co@PC-7 is mainly ascribed to its unique structural properties, which give rise to highly desirable charge distributions at the metal/carbon electrochemical interfaces to perform efficient trifunctional water splitting electrocatalysis. This journal is © 2020 The Royal Society of Chemistry.