Preparation And Characterization Of Pd-based Catalyst For Direct Ethanol Fuel Cells With High Stability

Direct ethanol fuel cells(DEFCs)have attracted enormous attention as potential power sources due to their low toxicity,environmental sustainability,high energy density,and high energy-conversion efficiency.However,their insufficient durability and high cost of catalysts hinders broad development and widespread commercialization of noble metal-based fuel cells.In recent years,the higher catalytic activity,higher CO anti-poisoning ability and lower cost of Pd metal catalysts over Pt catalysts make Pd catalysts more efficient for the ethanol oxidation reaction(EOR)in alkaline media.Besides,introducing oxophilic metals such as Ru,Sn and Ni can benefit from facilitating the formation of OHads,and in turn the OHads can transform COads poisoning species on Pd into CO2 at lower potentials,and thus the active sites on Pd can be released for further chemical reaction.Therefore,it is essential to synthesise a series of Pd-based catalysts with long-term stability and low cost towards the EOR.The research is carried out mainly from the aspects of catalyst composition and electrocatalytic EOR process of Pd-based catalysts,explore the catalytic mechanism of the catalyst.The main work are as follows:1)Self-recoverable Pd1-Rux/TiO2 nanocatalysts have been prepared by electrochemical stripping of Pd-Ru/TiO2 precursors and their electrocatalytic performance have been tested.The characterization of catalysts via chronoamperometry has been repeated 15 times.After 15 times stability tests,the residual current density of Pd1-Ru0.69/TiO2 nanocatalysts(309.42 mA mgPd-1)is 9.40 times that of commercial Pd/C catalysts(33.01 mA mgPd-1).From the 5th to 15th test,the initial and residual current density of the catalysts could recover to the original value.Herein,these Pdl-Ru,/TiO2 nanocatalysts with ultrastability towards ethanol electrooxidation are self-recoverable.Density functional theory(DFT)calculations reveal that the introduction of oxophilic metal Ru and a TiO2 support into Pd-based catalysts and the synergistic effects between Ru and TiO2 have led to the ultrastability towards the EOR.The introduction of oxophilic metal Ru and a TiO2 support into catalysts can reduce the adsorption energy of OHads on the Pd-Ru/TiO2 nanocatalysts,and it will inhibit the COads produced and adsorbed on the Pd surface.2)Pd1-Snx/SiO2 nanocatalysts with high CO anti-poisoning ability towards EOR have been prepared by chemical reduction method and their electrocatalytic performance have been tested.The residual current density of Pd,-Sn0.5/SiO2 nanocatalysts(567 mA mgPd-1)for EOR is 3.50 times that of Pd,-Sn0.5/C(163 mA mgPd-1)after a 20000 s durability test,and it also higher than that of Pd1-Ru0.69/TiO2 nanocatalysts after a 10000 s durability test.So the synthesis of Pdi-Sn0.5/SiO2 catalysts with long-term stability can reduce the use of precious metals and the cost of catalysts.DFT calculations are carried out to study the function of introducing Sn and SiO2 into Pd-based nanocatalysts,the results reveal that the introduction of oxophilic metals Sn and SiO2 support into catalysts could reduce the adsorption energy of OHads on Pd1-Snx/SiO2 nanocatalysts,which would facilitate the oxidation of the CO adsorbed on Pd surface.These catalysts are in favor of excellent electrocatalytic performance and high CO anti-poisoning ability towards EOR.