Effects of Nafion loading in anode catalyst inks on the miniature direct formic acid fuel cell

Nation, within the anode and cathode catalyst layers, plays a large role in the performance of fuel cells, especially during the operation of the direct formic acid fuel cell (DFAFC). Nation affects the proton transfer in the catalyst layers of the fuel cell, and studies presented here show the effects of three different Nation loadings, 10 wt.%, 30 wt.% and 50 wt.%. Short term voltage-current measurements using the three different loadings show that 30 wt.% Nation loading in the anode shows the best performance in the miniature, passive DFAFC. Nation also serves as a binder to help hold the catalyst nanoparticles onto the proton exchange membrane (PEM). The DFAFC anode temporarily needs to be regenerated by raising the anode potential to around 0.8V vs. RHE to oxidize CO bound to the surface, but the Pourbaix diagram predicts that Pd will corrode at these potentials. We found that an anode loading of 30 wt.% Nation showed the best stability, of the three Nation loadings chosen, for reducing the amount of loss of electrochemically active area due to high regeneration potentials. Only 58% of the area was lost after 600 potential cycles in formic acid compared to 96 and 99% for 10 wt.% and 50 wt.% loadings, respectively. Lastly we present cyclic voltammetry data that suggest that the Nation adds to the production of CO during oxidation of formic acid for 12h at 0.3V vs. RHE. The resulting data showed that an increase in CO coverage was observed with increasing Nation content in the anode catalyst layer. (C) 2010 Elsevier B.V. All rights reserved.