Effect of the Ratio Carbon Nanofiber/Carbon Black in the Anodic Microporous Layer on the Performance of Passive Direct Methanol Fuel Cell

The low mass transfer at the anode and cathode, low catalyst utilization, and methanol crossover are amongst the factors affecting the performance of passive direct methanol fuel cells (pDMFC). In this work, in order to enhance the overall cell performance, we investigate the effect of different weight percentages (0, 20, ..., 100) of carbon nanofibers (CNF) added to the anodic microporous layer (MPL) of a pDMFC operating at different methanol concentrations (1, 2, ..., 5 M). Scanning electron microscopy and air permeability measurements of the anodic catalyst/MPL showed a decrease of permeability resulting from a decrease in the surface fissures and cracks with the increase of CNF content. From cyclic voltammetry, we found that the maximum values of the electrochemically active surface area (ECSA) and the catalyst utilization is with 60 wt% CNF. The polarization measurements showed that the effect of CNF on the cell performance follows the same trend as the ECSA. Furthermore, we found from the maximum power density measurements that the optimum concentration increases with the CNF content. The electric performance of the pDMFCs are discussed in connection with the effects of CNF on the ECSA and mass transfer. (C) 2016 The Electrochemical Society. All rights reserved.