Rational design of carbon network structure in microporous layer toward enhanced mass transport of proton exchange membrane fuel cell

Abstract

Microporous layer (MPL) is commonly applied to gas diffusion layer to improve water management performance of a proton exchange membrane fuel cell (PEMFC). In this work, we introduce a new type of MPL comprising whisker-like carbon nanotubes (WCNTs) and Ketjen Blacks (KBs) onto the macroporous substrate to optimize the pore structures. Scanning electron microscopy images show that KBs populate overlapping networks formed by WCNTs, leading to an increased proportion of mesopores (about 34.87%) of crack-free MPL. This optimal structure of MPL with a superhydrophobic surface ensures the maximum power density up to 2.046 W cm−2 at 100% relative humidity. The electrochemical impedance spectroscopy verifies that the mass transfer resistance is significantly lower, which means rapid drain of excess water and supply of reactant gas, and it is further confirmed by theoretical analysis of pore characteristics. A mechanism of gas-water transport balance promoted by the network structures of MPL constructed by WCNTs/KBs is proposed, which allows enhancing PEMFC performance at high humidity conditions.