Analysis of palladium based anode electrode using electrochemical impedance spectra in direct formic acid fuel cells

In this study, we used the electrochemical impedance spectra to evaluate the anode performance of direct formic acid fuel cell (DFAFC), and how its anode charge transfer resistance (R_anode,ct) and electrolyte resistance (R_ele) are affected by various cell operating parameters. These parameters that we have investigated in this study include the anode overpotentials, cell operation times, formic acid feed concentrations and cell temperatures. The anode impedance spectra demonstrated that the R_anode,ct and R_ele are low for the DFAFC using 5M formic acid feed concentration, which leads to its high power density output of 250 mW/cm² at 0.35 V and 30°C. This high performance of the DFAFC shows that it has a great potential for portable power applications. The R_anode,ct increases gradually as either the cell operation time increases or the formic acid feed concentration is raised from 10M to 15M, which leads to deactivations of the anode and the overall cell performances. However, these deactivation processes are reversible and the cell performance can be easily reactivated.