Performance of Direct Formate Fuel Cell Using Non-Precious Metal Cathode Catalyst

This study reports on direct formate fuel cell (DFFC) operation using non-precious metal (NPM) as the cathode catalyst. Iron- and cobalt-nitrogen- doped carbon nanotube (Fe-NCNT and Co-NCNT) were synthesized by pyrolysis of multiwalled carbon nanotubes, metal precursor and nitrogen precursor. These NPM catalysts showed high fuel tolerance in acidic medium, but the fuel tolerance in alkaline medium remains unclear. Herein, we determine the formate tolerance on the NPM catalysts and commercial Pt/C catalyst in alkaline medium. The DFFC performance test was conducted and the results compared with the direct formic acid fuel cell (DFAFC) reported in our previous work. The oxygen reduction reaction (ORR) activity and the formate tolerance on the NPM catalysts were evaluated by rotating disk electrode (RDE) in alkaline medium. Both NPM catalysts showed lower ORR activity than the Pt/C catalyst, but they exhibited higher formate tolerance than the Pt/C catalyst. Comparing the single-cell performance under various HCOONa concentrations, DFFC with Co-NCNT catalyst showed higher maximum power density than with Pt/C catalyst with 2 M KOH containing 4 M and 6 M HCOONa due to its higher formate tolerance. Therefore, it is considered that the NPM cathode is available for high concentration operation of DFFC. However, DFFC with Fe-NCNT and Co-NCNT cathode catalyst exhibited the highest maximum power density of 39.7 mW cm(-2) and 89.8 mW cm(-2), respectively, at 60 degrees C with optimal fuel concentration, i.e. 2 M KOH containing 4 M HCOONa. These performances were lower than that of DFFC with Pt/C cathode catalyst at optimal fuel concentration, i.e. 2 M KOH containing 2M HCOONa. Considering the fact that the power density of DFAFC (acidic condition) using NPM catalyst was higher than that with Pt/C catalyst at optimum fuel concentration, the NPM catalysts are more preferable for the acidic condition than the alkaline condition.