Controlling the physical and electrochemical properties of block copolymer-based porous carbon fibers by pyrolysis temperature

Abstract

Block copolymer-based porous carbon fibers are emerging materials for electrochemical energy conversion and storage. Pyrolysis temperature governs the properties of carbons. To design porous carbon fibers with tunable pore size, surface area, heteroatom content, electrical conductivity, and electrochemical performance, block copolymer poly(acrylonitrile-block-methyl methacrylate) (PAN-b-PMMA) was converted to porous carbon fibers via self-assembly, stabilization, and pyrolysis at temperatures ranging from 600 to 1200 °C. An increase in the pyrolysis temperature increases the total pore volume, specific surface area, and graphitic level, but decreases the amounts of nitrogen and oxygen heteroatoms, as well as the electrical resistance. As electrochemical supercapacitor electrodes, the porous carbon fibers pyrolyzed at 800 °C exhibit the highest gravimetric capacitance, owing to the balanced structural, chemical, and physical properties. The porous carbon fibers pyrolyzed at 600 °C have the highest heteroatom content to induce pseudocapacitance, but their capacitance and rate capability are the lowest due to the poorest electrical conductivity. In contrast, the porous carbon fibers pyrolyzed at 1200 °C show the best rate capability because of the highest electrical conductivity, the largest pore volume, the lowest diffusion resistance, and the best electron/ion transport. This work systematically reveals the thermal processing principles of porous carbon fibers with controlled structural, physical and electrochemical properties. The findings provide a guideline for designing block copolymer-based porous carbon fibers for electrochemical energy conversion and storage.