Hierarchically Porous and Defective Carbon Fiber Cathode for Efficient Zn-Air Batteries and Microbial Fuel Cells

Developing low-cost, efficient oxygen reduction reaction (ORR) catalysts to replace Pt-based materials is urgently required for the application of Zn-air batteries (ZABs) and microbial fuel cells (MFCs). In this work, meso-microporous carbon fibers with tunable defect density were synthesized by carrageenan fibers. A highly defective carbon fiber (HDCFs) was produced which exhibited an outstanding ORR catalytic activity, reaching to the half-wave potential of 0.841 and 0.44 V in alkaline and neutral electrolytes, respectively. These HDCFs can also act as highly efficient air cathodes for ZABs (delivered potential of 0.69 V and power density of 220 mW cm –2 at 300 mA cm –2 ) and MFCs (high power density of 69.7 mW cm –2 ). Simulation by the density functional theory indicated that a high density of defections in a carbon based framework can remarkably modulate the electrical properties. For instance the charge entrapments in the carbon active sites may reduce the energy barrier of ORR. Graphical abstract