Enhanced water management via the optimization of cathode microporous layer using 3D graphene frameworks for direct methanol fuel cell

Abstract

Water management is one of the key roles in determining the output performance of a passive direct methanol fuel cell (DMFC). By decreasing the size of hydrophobic pores inside the cathode microporous layer (MPL), a high hydraulic pressure can be built up inside the cathode catalyst layer, which enhances the water recovery from cathode to anode and thus improves the cathode mass transfer. To achieve this, three-dimensional graphene frameworks are adopted to construct cathode MPL for the first time, whose intrinsic pore structure and characteristics contribute to an enhanced water management. Experimental results show that the performance and stability of the as-prepared DMFC are significantly improved. To illustrate the mechanism of the improvement, the in-situ measurements of polarization and methanol crossover are conducted, which reveals a greatly lowered water transport coefficient, along with a reduced in-situ methanol crossover rate. Since the role of polytetrafluoroethylene (PTFE) is weakened in the novel design of MPL, a further optimization via reducing PTFE content is realized, leading to a total increase of 43% of the output performance. The significant elevation of both the performance and stability of DMFC can expand its potential as a green energy source in practical applications.