Performance of direct formic acid fuel cell using transition metal‐nitrogen‐doped carbon nanotubes as cathode catalysts

Summary The application of nonprecious metal catalysts, such as iron (Fe) and cobalt (Co) catalyst, to direct liquid fuel cells (DLFCs), especially in direct methanol fuel cells, has been widely investigated. However, the application of such non‐Pt catalysts as cathode catalysts in direct formic acid fuel cell (DFAFC) operations has not yet been investigated. This study intends to evaluate the formic acid tolerance of such catalysts in case of oxygen reduction reaction. In addition, we investigate their performances in DFAFC using the Fe‐ and Co‐nitrogen‐doped carbon nanotubes (Fe‐NCNT and Co‐NCNT) as the cathode catalysts and compare these performances with the commercial Pt/C catalyst. Herein, Fe‐NCNT and Co‐NCNT were synthesized using the conventional method by the pyrolysis of the multiwalled carbon nanotubes, dicyandiamide, and metal salt under the flow of N2 at 800°C. Both the Fe‐NCNT and Co‐NCNT catalysts exhibit higher formic acid tolerance when compared with that exhibited by the Pt/C catalyst. Further, single‐cell tests with hydrogen‐fed polymer electrolyte fuel cell (PEFC) and DFAFC operations were conducted under various operating conditions to compare the performances of the cells while using the prepared catalysts and the conventional Pt/C catalyst. The PEFC performances in both the Fe‐NCNT and Co‐NCNT catalysts were significantly low (94.9mW cm−2 for Fe‐NCNT and 164.0 mW cm−2 for Co‐NCNT at 60°C). Regardless, the Co‐NCNT catalyst exhibited a maximum power density of 160.7 mW cm−2 in DFAFC operated at 60°C and7‐M formic acid. This value is comparable with that for DFAFC with a Pt/C catalyst (128.9mW cm−2) and is considerably higher than that obtained for other DLFCs while using a non‐Pt catalyst. Therefore, the usage of a non‐Pt metal catalyst as the cathode catalyst is preferable in case of DFAFC. Fe‐ and Co‐nitrogen‐doped carbon nanotube catalysts prepared exhibit higher formic acid tolerance than conventional Pt/C catalyst. The highest maximum power density achieved by single DFAFC with Co‐NCNT cathode catalyst, which is 142.4 mW cm−2 at 60°C and 5‐M formic acid concentration. This value is higher than that achieved by DFAFC with Pt/C cathode catalyst under similar operating condition.