N-doped porous carbon nanosheets as pH-universal ORR electrocatalyst in various fuel cell devices

Exploring high-activity electrocatalyst for oxygen reduction reaction (ORR) is of great significance for a variety of renewable energy conversion and storage technologies. Herein, we report a template-free, economic and environment-friendly strategy for scalable synthesis of N-doped hierarchical porous carbon nanosheets (N-HPCNSs) with biomass water lettuces as carbon precursor. The N-HPCNSs were demonstrated to possess three dimensional (3D) hierarchical porous structures with a high surface area and uniform N-doping. Systematic electrochemical study revealed that the N-HPCNSs not only hold numerous active sites but also manifest high intrinsic activity for each of the active sites toward ORR in pH-universal electrolyte of alkali, acid and neutral. With the N-HPCNSs as cathode electrocatalyst, three types of home-made fuel cells were set up that run in alkaline, acidic and neutral medium, i.e., Zn-air alkaline fuel cell, direct methanol fuel cell, and microbial fuel cell, respectively, further demonstrating its potential to replace the high-cost Pt-based electrocatalysts for practical applications. Owning to the multiple attracting features, including high catalytic activity, good durability, low cost, and scalable production, the as-developed pH-universal N-HPCNS electrocatalysts may open a promising avenue for developing the next-generation cathode electrocatalysts for fuel cells of practical significance.