Palladium-based Catalysts Supported On Carbon-based Materials For Electro-catalytic Oxidation Of Formic Acid

Direct formic acid fuel cells?DFAFC?have been attracting widespread attention as power sources to convert chemical energy into electricity by electrochemical reactions.Formic acid is non-toxic environment friendly material which can be used as food and drug additives,and with the advantages of low crossover,non flammable,storage and transportation safety.In recent years,people have paid great attention to the research of direct formic acid fuel cells.It is great significant to research and prepare anode catalyst with high performance and low cost of direct formic acid fuel cell to accelerate the development of fuel cells,but there still is a bigger challenge.Recently Pd-based catalysts are widely used as anode catalyst of formic acid fuel cells.The study found that metal Pd and Pt have similar crystal structure and electronic properties,but Pd has lower cost and better catalytic activity and poison resistance than Pt catalyst,so the Pd catalyst become the preferred catalyst for direct formic acid fuel cells.In recent years,many efforts is focused on the improvement of Pd electrocatalytic performance of DFAFC.The electrocatalytic performance of the catalysts is mainly related to the component,structure and support of the catalyst.It not only can increase the catalytic efficiency,but also the high specific surface area and porous structure of support can promote the homogeneous dispersion of the catalyst to load catalyst nanoparticles on support,which can also restrain the agglomeration of Pd nanoparticles to improve the utilization and stability of the catalyst.So the main work of this paper include the improvement of catalyst support and the prepareration of oxide-containing binary Pd-based alloy catalyst.This paper use the transmission electron microscope?TEM?,Scanning electron microscopy?SEM?,X-ray diffraction spectrum?XRD?,X-ray photoelectron spectroscopy?XPS?,Raman spectroscopy,Inductively coupled plasma-atom emission spectrometry?ICP-AES?and other research methods to characterize the structure and composition of catalyst.The electrochemical properties of the catalyst was studied by electrochemical test technology such as cyclic voltammetry?CV?and linear sweep method?LSV?,chronoamperometry?CA?and AC impedance?EIS?.The main work of this paper is as follows:1.We prepared graphene-Vulcan XC-72R carbon black with different mass ratios as binary carbon supports to load Pd?Pd/Gr-C?nano-composite catalysts.The relationship between the different ratios of graphene to Vulcan XC-72R carbon black and the catalytic performance of formic acid oxidation was discussed.The Pd/Gr_0.3C_0.7 catalyst exhibited excellent catalytic activity for formic acid electro-oxidation when the mass ratio of graphene to Vulcan XC-72R carbon black is3:7.The anodic peak potential at the Pd/Gr_0.3C_0.7 was 112 mV negative than that of Pd/C catalyst.The current density at the Pd/Gr_0.3C_0.7 catalyst was as high as up to102.14 mA.mg_Pd^-1,which was about 3 times of that for Pd/C catalyst(34.40mA.mg_Pd^-1).2.We prepared carbon nanospheres with relatively uniform particle size by hydrothermal method taking glucose as raw material,and further synthesized palladium/carbon nanospheres(Pd/C_-NS)catalyst by one-pot NaBH₄ method used in formic acid fuel cells.The particle size,morphology and electrochemical properties of Pd/C_-NS catalyst were characterized by X-ray diffraction?XRD?,transmission electron microscopy?TEM?and cyclic voltammograms tests.The prepared Pd/C_-NS exhibits good electrocatalytic activity and stability for formic acid oxidation.It suggests that the Pd/C_-NS nanocomposite has a wide application prospect in the fields of formic acid fuel cells.3.We prepared carbon loaded oxide-containing Pd-Pb alloy electrocatalysts(Pd_xPb_1-x/C)with different atom ratios by sodium borohydride reduction methods.The crystal structure and particle morphology of the samples were characterized by X-ray diffraction?XRD?and transmission electron microscopy?TEM?.The results show that these samples are corresponding to Pd face-centered cubic structure with homogeneous particle size about 4 nm and uniform dispersion.Electrochemical test results show that Pb/C catalyst for formic acid oxidation has no catalytic activity.Compared to Pd/C catalyst,oxide-containing Pd_0.9Pb_0.1/C catalyst exhibits excellent catalytic activity for formic acid oxidation when the atom ratio of Pd to Pb is 9:1.With the increase of the content of Pb,carbon loaded Pd-Pb alloy catalysts can promote the indirect oxidation of formic acid,which will inhibit the catalytic activity of Pd.