Maximizing active site utilization in carbocatalysts for high-performance oxygen reduction reactions and zinc–air battery-powered capacitive deionization

Abstract

The underutilization of active sites limits the performance enhancement of functional carbon nanomaterials in electrocatalytic oxygen reduction reactions (ORR). Here, we propose a molten salt-regulated synthesis of indole-based hypercrosslinked polymers to create a series of nitrogen-doped porous carbon materials (NPC) with controllable quantities of active sites and specific surface areas (SSA). A deep investigation of the structure–property relationship indicates that the environment of the active sites, particularly the electrochemical active surface area (ECSA), plays a pivotal supporting role. Furthermore, the ECSA per active site (EPA) correlates directly with ORR performance. The NPC–Zn catalyst, which possesses the highest EPA, demonstrates the highest half-wave potential (0.859 V) and kinetic current density (102.64 mA cm⁻²), and excellent performance in the rechargeable zinc–air battery (ZAB). Furthermore, the NPC–Zn-based capacitive deionization (CDI) device, powered by NPC–Zn-based ZAB, exhibits a stable adsorption capacity of 27.8 mg g⁻¹ for 6 hours, which is consistent with that driven by a direct-current supply. This work provides new insights into the utilization efficiency of active sites in carbocatalysts for ORR, serving as a prime example for designing high-performance ORR electrocatalysts with broad application prospects in the field of environmental energy.