Passive direct methanol fuel cell using woven carbon fiber fabric as mass transfer control medium

The passive liquid-feed direct methanol fuel cell (DMFC) has great potential for portable applications. This study focuses on the anode structural optimization by developing a composed diffusion medium (CDM) with a gradient porosity. The CDM typically includes three carbon-based layers such as the woven carbon-fiber fabric (WCFF), carbon paper and carbon-powder micro-porous layer. The WCFF contains ordered micro- and macro-pores, which not only provides additional resistance to reduce methanol crossover (MCO), but also helps form a self-driving and self-releasing mechanism to facilitate removal of the produced gas. The feasibility of using the WCFF to control the mass transfer process is experimentally validated. Results show that the use of WCFF enables the fuel cell to work satisfactorily at a higher methanol concentration. Especially when the double-layer structure of the WCFF is used, the fuel cell obtains the highest performance at a methanol concentration of 12 M. Based on the visualization method, it is proven that the WCFF promotes uniform distribution and fast removal of the gas bubbles. The dynamic characteristics suggest that the cell performance is affected by a combined effect from both operational and structural factors. The impact of the perforated anode current collector is also evaluated in this work.