No abstract

Carbon papers (CPs), as the substrate materials for gas diffusion layers in proton exchange membrane fuel cells, require high electrical conductivity, efficient gas permeability, and robust mechanical properties, which are unable to be completely satisfied by graphitization at a high temperature. Herein, the boroncatalytic graphitization of CPs is reported. The boron-doped CP matrix starts to graphitize at 1800 C, and evolves into well-oriented graphitic carbon at 2100 C. In contrast, the graphitization temperature for undoped CPs increases by several 100 degrees. The boron-doped CPs achieve the in-plane electrical conductivity of around 4.8 Â 10 4 S m À1 after graphitization at 2100 C, which is %2 times as high as that of undoped CPs graphitized at 2700 C. In addition, the tensile strength of the former one is 1.7 times of that of the latter one. The through-plane gas permeability of boron-doped CPs is comparable to that of a commercial Toray CP. Boron-catalytic graphitization at a moderate temperature provides a more sustainable pathway of producing high-performance CPs.

Lithium−sulfur (Li−S) batteries have high theoretical energy density but low sulfur utilization due to the inherent insulating nature of sulfur and the shuttle effect of polysulfides. Herein, the CO 2 -activation carbon paper was prepared by poly(pphenylenebenzobisoxazole) (PBO) nanofiber and was first applied as an interlayer for efficiently alleviating the shuttle effect of polysulfides in Li−S batteries. This interlayer exhibits good flexibility and strength with rich −C�O and −COOH functional groups on the three-dimensional porous structure, which improves chemical adsorption on Li 2 S x species and ion rapid diffusion via interconnected diffusion channels and thus enhances the electrochemical kinetics. The initial specific capacity is 1367.4 mAh g −1 and remains 999.8 mAh g −1 after 200 cycles at 0.2C and 780.1 mAh g −1 at 5C, and the Coulombic efficiency is high, up to 99.8%, which is much better than that for the carbon paper without CO 2 activation. The highly conductive flexible PBO carbon paper may bring breakthroughs in performance and thus lead to more practical applications of Li−S batteries.

No abstract