Cobalt selenide electrocatalyst supported by nitrogen-doped carbon and its stable activity toward oxygen reduction reaction

• CoSe2/N-carbon of stable ORR activity in acidic medium has been synthesized.
• N-carbon is an optimized nitrogen-doped carbon with durable activity.
• Cubic phase CoSe2 is responsible for enhanced activity, but not durable.

We have prepared durable catalysts of CoSe2/N-carbon using low-cost raw materials, measured their activities, peroxide yields, stabilities in reducing molecular oxygen, and characterized their crystalline phases and morphology. CoSe2/N-carbon is featured with an active support, N-carbon, which by itself shows high stability as evidenced in its small activity decay. After 1000 CV cycles, the half-wave potential (E1/2) of N-carbon decreases from 0.667 V to 0.636 V in 0.5 M H2SO4. Loading of CoSe2 enhances the activity of N-carbon, when the samples were synthesized above 385 °C and formulated with the Se/Co ratio higher than 10. The higher activity is attributed to the pyrite phase of CoSe2. But the stability of pyrite CoSe2 is less than that of N-carbon. Corrosion during the stability test exposes the active sites of underlying N-carbon, which sustains the catalyst activity. Consequently the E1/2 value of the active CoSe2/N-carbon decreases moderately, from 0.711 V to 0.644 V after 1000 CV cycles. In contrast, the E1/2 value of CoSe2/C descends much more, from 0.681 V to 0.475 V.