Abstract:

Electrocatalytic reduction of oxygen is a growing synthetic technique for the sustainable production of hydrogen peroxide (H₂O₂). The current challenges concern seeking low-cost, highly active, and selective electrocatalysts. Cobalt-nitrogen-doped carbon containing catalytically active cobalt-nitrogen (Co-N_x) sites is an emerging class of materials that can promote the electrochemical generation of H₂O₂. Here, we report a straightforward method for the preparation of cobalt-nitrogen-doped carbon composed of a number of Co-N_x moieties using low-energy dry-state ball milling, followed by controlled pyrolysis. This scalable method uses inexpensive materials containing cobalt acetate, 2-methylimidazole, and Ketjenblack EC-600JD as the metal, nitrogen, and carbon precursors, respectively. Electrochemical measurements in an acidic medium show the present material exhibits a significant increase in the oxygen reduction reaction current density, accompanied by shifting the onset potential into the positive direction. The current catalyst has also demonstrated an approximate 90 % selectivity towards H₂O₂ across a wide range of potential. The H₂O₂ production rate, as measured by H₂O₂ bulk electrolysis, has reached 100 mmol g_cat.^-1 h^-1 with high H₂O₂ faradaic efficiency close to 85% (for 2 h at 0.3 V vs. RHE). Lastly, the catalyst durability has been tested (for 6 h at 0.3 V vs. RHE). The catalyst has shown relatively consistent performance, while the overall faradic efficiency reaches approximate 85% throughout the test cycle indicating the promising catalyst durability for practical applications. The formed Co-N_x moieties, along with other parameters, including the acidic environment and the applied potential, likely are the primary reasons for such high activity and selectivity to H₂O₂ production.

Key words: Hydrogen peroxide, Two-electron oxygen reduction, Carbon catalyst, Electrocatalysis