Enhancements in catalytic activity and duration of PdFe bimetallic catalysts and their use in direct formic acid fuel cells

The palladium–iron based bimetallic catalysts (Pd_xFe_y/Cs) and facile synthetic method are introduced to enhance the catalytic activity and operational duration for direct formic acid fuel cells. To improve the properties of Pd_xFe_y/C catalysts, such as degree of PdFe alloy and its crystallinity, heat treatment is conducted at 600 °C. According to results, the Pd–Fe bond and Fe metal particle are formed after the heat treatment, while iron oxides and Pd particles are observed in the untreated samples. Electrochemical evaluations for measuring the formic acid oxidation reaction rate demonstrates heat treated Pd₃Fe₁/C (HT-Pd₃Fe₁/C) is the best catalysts of six samples which are synthesized by using different Pd to Fe ratios (3:1, 1:1, 1:3) before and after heat treatment. This is because the HT-Pd₃Fe₁/C has high Pd–Fe alloying and Pd contents. Through the heat treatment, the indirect formic acid oxidation reaction way is activated and the resistance to CO poisoning is significantly improved. The maximum power density of direct formic acid fuel cells using HT-Pd₃Fe₁/C whose open circuit voltage is 0.83 V is 137 mW cm⁻², which is 1.6 and 1.9 times higher than that of direct formic acid fuel cells using untreated catalyst and Pd/C.