Effect of anode diffusion media on direct formic acid fuel cells

The effect of the anode diffusion media on the cell performance and mass transport in a direct formic acid fuel cell (DFAFC) has been characterized. Based on electrochemical impedance spectroscopy along with the cell performance tests of the fuel cell, it was found that, depending on the properties of the diffusion media, different molar concentrations of formic acid were required to avoid mass transfer limitation, i.e. maintain a sustained performance. By measuring the external contact angle, the wettability of the diffusion media was investigated in order to estimate the transport properties of formic acid through the diffusion media. Unlike the direct methanol fuel cell, the DFAFC suffers from severe mass transport limitations in more hydrophobic anode diffusion media. As an alternative to higher concentration operations, mixed fuel systems have been suggested to alleviate the IR drops and promote the performance without any voltage loss due to fuel crossover and membrane dehydration at relatively low-current density. Accordingly, not only favorable combinations of the hydrophobicity for gas product transport and the hydrophilicity for formic acid transport within the porous layer are necessary but also the proper choice of fuel concentration and type is needed to obtain the required performance for a simplified system or for higher fuel efficiency.