Effect of Metal Foam Anode Structures on Passive Direct Formate Fuel Cell Performance

Direct formate fuel cells (DFFCs) excel in sustainable energy by utilizing formate salts derived from carbon dioxide capture to mitigate greenhouse gas emissions. Polarization curves, electrochemical impedance spectroscopy (EIS) spectra, and anode electrochemical surface area (ECSA) values of the passive DFFCs using nickel (Ni) foam with varying porosity and pore density as an anode catalyst layer are measured here to determine an optimal foam permeability predicted by a model suggested here. Results show that Ni foam with a permeability greater than 10 −7 m 2 and suitable pore density can achieve an ECSA value over 9 m 2 /g, a 15% increase compared to anodes with a permeability of 6 × 10 −9 m 2 . Low porosity (90%) and low pore density (94 pore per inch [PPI]) result in low ohmic resistance, while high permeability (>10 −7 m 2 ) reduces concentration overpotential. Passive DFFC with an anode permeability greater than 10 −7 m 2 and a pore density of 94 PPI achieves the highest maximum power density (MPD) of 39 mW/cm 2 . In contrast, an anode with the lowest permeability (6 × 10 −9 m 2 ) has the lowest MPD of 24 mW/cm 2 . However, the cathode flooding associated with the high anode permeability causes the current output at 0.4 V of the DFFC to drop from 100 mA/cm 2 to zero after 3 h.