In situ anchoring of Co9S8 nanoparticles on N and S co-doped porous carbon tube as bifunctional oxygen electrocatalysts

Abstract

The development of cost-effective yet highly active and robust bifunctional electrocatalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) has been at the forefront of research into regenerative fuel cells and metal–air batteries. Here we report Co9S8 nanoparticles grown in situ on nitrogen- and sulfur-doped porous carbon (Co9S8/NSPC) as a bifunctional catalyst for OER and ORR using poly(2-aminothiazole) as a novel all-in-one multifunctional precursor. Unexpectedly, Co9S8/NSPC exhibits a low OER overpotential, positive ORR half-wave potential, small potential gap and high durability, thus making it one of the best bifunctional OER and ORR catalysts. This may be attributed to the heteroatom doping, porous structure and synergistic effects of Co9S8 and NSPC, as confirmed by density functional theory calculations. More importantly, as a proof-of-concept application, the air electrode with Co9S8/NSPC9–45 endows the Zn–air battery with a low discharge/charge overpotential and good cycling stability. An improved way to anchor nanoparticles onto carbon substrates can halve catalyst usage in rechargeable zinc–air batteries. Lightweight metal–air batteries normally employ separate catalysts to move electrons back and forth from atmospheric oxygen. To improve design efficiency, Xin-bo Zhang from Changchun Institute of Applied Chemistry and co-workers turned to cobalt–sulfur electrocatalysts that are active towards both oxygen reduction and evolution — especially when combined with high-surface-area, conductive carbon materials. The team used poly(2-aminothiazole) nanowires produced by template-directed synthesis as an ‘all in one’ precursor to achieve this. Heating these nanowires and cobalt salts to 900 degrees Celsius spontaneously generated cobalt–sulfur nanoparticles linked directly to a porous carbon framework doped with sulfur and nitrogen. A proof-of-concept battery containing the bifunctional catalyst had similar charging properties and cyclic stability as devices containing single-purpose catalysts. Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are still kinetic barriers of regenerative fuel cell and metal–air batteries, requiring efficient and inexpensive bifunctional electrocatalysts to accelerate the reaction and improve energy efficiency. Herein, we develop Co9S8 particles in situ grown on nitrogen and sulfur co-doped porous carbon (Co9S8/NSPC) to replace the benchmark noble metal catalysts, which shows high catalytic activities including small potential gap, long-term durability and high selectivity. Importantly, the Zn–air battery with Co9S8/NSPC as air electrode displays low discharge/charge overpotential and good cyclic stability, making it the promising bifunctional catalyst for the practical applications.