Direct formic acid fuel cells on Pd catalysts supported on hybrid TiO2-C materials

Abstract

The electrooxidation of formic acid was performed on Pd-based catalysts supported on hybrid TiO2-C materials prepared from different carbon origins by solvothermal and slurry synthesis. It has been found that carbonized hybrid TiO2-C supports with mesopore texture and high anatase:rutile ratio in the TiO2 framework led to about three times higher activity per Pd mass unit than the catalyst prepared on a commercial Vulcan XC-72 carbon black, which will allow to reduce considerably the amount of expensive noble metal at the anode of DFAFC. The conductivities of raw TiO2/C supports are several orders of magnitude lower than that for carbon Vulcan XC-72. However, the hybrid TiO2-C supports acquire high conductivity during palladium deposition. The rate of electrooxidation of formic acid on Pd/TiO2-C catalysts, calculated per one surface Pd atom (TOF), is for TOF<1s−1 independent of Pd particle size and morphology of the supports. Higher activity of the Pd/TiO2-C catalysts, compared to Pd/C catalyst, results from their higher hydrophilicity which ensures good access of formic acid to the Pd crystallites in the catalyst layer, and sufficiently high conductivity providing easy electron flow from the Pd active sites to current collector. Present results indicate that hybrid inorganic/organic materials are promising supports for the direct formic acid fuel cells with Pd-based catalysts.