The Theoretical Design Of Efficient Anode Catalysts In Direct Formic Acid Fuel Cells

Fuel cell is a kind of new energy which is highly efficient and clean. The demandsfor efficient energy systems for transportation, alleviating environmental pollutions, andhigh energy density power sources for portable electronic applications have created aworld-wide effort to develop fuel cell materials and fuel cell systems. Direct formic acidfuel cells（DFAFCs） have attracted much attention because of their good electrochemicalproperties. However, the anode catalysts are often poisoned by CO generated by theoxidation of the formic acid. Therefore, the design of efficient and high anti-drugcapability anode catalysts is important for the development of DFAFC. In this work, thegeometrical and electronic structures of Pd and its binary alloy （PdPt） clusters wererevealed using density functional theory, which was used as simulation models toexplore their possible reaction path and possibility as candidate of anode catalysts ofDFAFC.Before the investigation of catalytic properties of Pd clusters, we adopted thedensity functional theory based method to explore the physical properties of binary alloyclusters of Pd-X（X=Ni, Ru, Pt）, hoping to find the relationship between theircompositions and the natures. The computed results show that the stability and thechemical reactivity of Pd-X clusters are higher than that of the Pd₇clusters, and thechemical reactivity of Pd-Pt clusters are the best. By comparing and analyzing themolecular orbitals of Pd6Pt and Pd₅Pt₂cluster, it indicates that, the more X atoms are, thebetter the chemical activity of alloy cluster is. As a result, the binary alloy Pd₄Pt₃clusteris selected as the theoretical model of the anode catalyst of DFAFC in the calculation.In view of the good catalytic properties showed by Pd clusters in many catalyticreactions, this article utilize the density functional theory to calculate the reactionmechanisms of the catalytic oxidation of formic acid on Pd₇cluster under conditions ofvacuum and water solvent, in order to verify the feasibility and catalytic property of Pdcluster as the anode catalyst of DFAFC. Found by calculating, regardless of the medium,the main oxidation pathway of HCOOH on Pd₇cluster is direct CO₂-based. In a vacuum,HCOOH can not generate the CO intermediate. Though in solution, there may be COproduction.The reaction mechanisms of the catalytic oxidation of formic acid on the Pd₄Pt₃cluster in solution were calculated in this work, either. It shows that, when catalyzed byPd₄Pt₃cluster, CO may be the intermediate product, consistent with the experimental phenomenon, which manifest that the catalytic property of Pd₄Pt₃cluster for formic acidis not as good as pure Pd₇clusters. The above theoretical studies have shown that thetransition metal Pd clusters can be used as the anode catalyst material in DFAFCs. SmallPd cluster containing seven atoms has nice catalytic property and anti-drug capability.Moreover, the cluster modes can replace the metal surface models for the theoreticalstudies on the oxidation mechanisms of the formic acid, which not only save thecomputational cost, but also can be applied to the prediction of the catalytic property ofvarious alloy combinations.