Abstract:

The existing energy and environmental issues are the primary issues that restrict the continual development of the mankind. Cost-effective energy storage and conversion devices have attracted significant attention. Rechargeable zinc-air batteries (ZABs) are widely studied because they are portable, possess high power density, and are environmentally friendly. However, the slow kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) limit their practical application. It is crucial to develop dual-functional electrocatalysts with excellent electrocatalytic performance, low price, simple operation, and outstanding stability. Therefore, transition metals and carbon-based materials should be combined. Although Co₂P has been widely reported as an efficient OER catalyst, there are few studies based on the ORR activity. Herein, a facile pyrolysis of cobalt salt, phytic acid, and k-carrageenan aerogel was carried out on Co₂P nanoparticles within P-doped porous carbon (Co₂P-PCA-800), showing enhanced ORR activity. The resulting composite (Co₂P-PCA-800) with a three-dimensional (3D) hierarchical porous architecture exhibited outstanding ORR activity with a high half-wave potential (E_1/2) of approximately 0.84 V, which is comparable to that of Pt/C. Simultaneously, we fabricated phosphorus-doped porous carbon (PCA) and cobalt-doped porous carbon (Co-CA) to compare the effect of structural morphology on the catalytic performance. Studies have found that a regular interconnected porous structure can be beneficial for mass transfer and can ensure uniform distribution of ion current, thereby resulting in increased number of effective active sites. The outstanding ORR activity mainly results from the synergistic effect of the 3D honeycomb hierarchical porous structure and positively charged Co₂P nanoparticles encapsulated in P-doped carbon. In addition, the 3D honeycomb porous carbon structure not only facilitates mass transfer and accelerates electron transfer but also protects the cobalt phosphide. Finally, we assembled a rechargeable ZAB with Co₂P-PCA-800 as the air cathode catalyst. Compared with precious metal catalysts, the catalyst has considerable charge-discharge performance and energy density as well as higher specific capacity and better cycle stability. We believe that this study will provide a significant direction for solving energy and environmental issues.

Key words: Co₂P nanoparticles, 3D porous carbon, Electrocatalysis, Oxygen reduction reaction, Zn-air battery