Studies On Anode Catalysts For Direct Formic Acid Fuel Cell

Recently, direct formic acid fuel cells (DFAFCs) have attracted considerable attention. The research on anode catalysts for formic acid oxidation is crucial for the development of DFAFCs. In this thesis, we prepared Pd and Pd-based alloy catalysts supported on multi-walled carbon nanotubes (MWCNTs). Their structures, morphologies and electrocatalytic properties for formic acid oxidation was investigated. The main results obtained are as follows:(1) The effects of electrode supporting materials, electrode preparation methods, formic acid and sulfuric acid concentrations, and temperature on electrode properties were studied. It was found that carbon cloth was the best electrode supporting material. The electrode with 30wt% Nafion in the catalyst layer demonstrated better properties. When total catalyst loading was more than 10mg/cm~2, the electrode properties could not be improved further. The preferred concentration of sulfuric acid was 0.5mol/L, and the preferred concentration range of formic acid was lmol/L-5mol/L. The electrode properties could be enhanced by increasing the temperature of solution. We also found that Pd/C catalyst electrodes for formic acid oxidation could be reactivated by applying it to a potential of 1.2V for 60s (vs Ag/AgCl).(2) The multi-walled carbon nanotube supported Pd catalysts (10wt%Pd/MWCNTs) were prepared through liquid phase reduction method. The catalysts were characterized by XRD and TEM. It was found that Pd nanoparticles had an average size of 2-3 nm with a good dispersion. The electrocatalytic properties of the Pd/MWCNTs catalysts for formic acid oxidation were investigated by cyclic voltammetry, impedance and polarization curve. The results demonstrated that Pd/MWCNTs had the best electrocatalytic performance and stability for formic acid electro-oxidation compared with other two commercial 10wt%Pd/C.(3) Pd-Ru/MWCNTs, Pd-Au/MWCNTs, Pd /MWCNTs were prepared with the same Pd loading of 10wt%. These three catalysts were investigated and characterized by cyclic voltammetry and chronoamperometry. The results demonstrated that the addition of Ru decreased the elctrocatalytic properties probably because Ru suppressed the direct pathway of formic acid oxidation on Pd catalysts. The addition of Au increased the elctrocatalytic activity and stability of catalysts for formic acid oxidation presumably owing to the synergic effect of Pd and Au.(4)We fabricated air breathing direct formic acid fuel cells (DFAFCs) with 10wt%Pd/C as anode catalysts and investigated the influences of different Nafion membranes and formic acid concentration on the performance of air breathing DFAFCs.Compared with 10wt%Pd/MWCNTs, the electrocatalytic performance and stability for formic acid electro-oxidation of 30wt%Pd/MWCNTs catalysts were better. The air breathing DFAFC with 30wt%Pd/MWCNT as the anode catalyst showed the maximum power density of 22.0mW/cm~2 at the ambient temperature, while the one fed with oxygen gave the maximum power density of 31.4mW/cm~2.