p-band regulation guides the free-standing porous carbon electrode for efficient Na-CO2 batteries

The Na-CO2 batteries with low-cost resources and high energy density have attracted huge attention in Mars and deep ocean exploration, but the slow CO2 reduction reaction (CO2RR) and CO2 evolution reaction (CO2ER) kinetics severely limit their practical application. Developing free-standing cathodes and understanding the relationship between the catalyst's active center and activity are essential to address long-standing challenges. This manuscript explores the promising metal-free porous carbon as a catalyst. The porous carbon network vertically grows on the surface of free-standing carbon paper to maximum exposure to the active site and optimization of electron/electrolyte transfer. Moreover, the active center of the carbon catalyst is optimized by introducing nitrogen or sulfur hetero-atom to regulate the p-band center, which steers the orbital hybridization and accelerates CO2RR and CO2ER kinetics The p-band optimized free-standing porous carbon electrode shows outstanding cycling of 1000 h with a small voltage gap of 1.04 V and a large energy efficiency of 71.2 % at 10 uA cm- 2. This study provides a new strategy for designing and fabricating p-band guided free-standing electrodes aiming at high-performance and wearable Na-CO2 batteries.