The Research Of Palladium-based Catalytic Materials For Electro-catalytic Oxidation Of Formic Acid And Hydrazine

In recent years, direct formic acid fuel cell (DFAFC) has received more and more attention because it has many advantages. Many efforts are on the improve in the electrocatalytic performance of the catalysts of DFAFC.The electrocatalytic performance of the catalysts is mainly related to the component, structure and supportting materials of the catalyst. This thesis mainly investigated two aspects to increase the electrocatalytic performance of the catalysts in DFAFC. The first one is find the suitable palladium-based binary alloy catalyst, the second one is improve the supporting materials for the catalyst. We synthesized several kinds catalysts and studied their electrocatalytic properties for the oxidation of formic acid, including carbon-supported Pd-Cr catalyst (PdCr/C), graphene supported Pd catalyst (Pd/Graphene) and the structure of Pd deposited on UME and glassy carbon substrate. The X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and scanning electron microscope (SEM) were used to characterize the catalysts. The cyelic voltammetry (CV), linear sweeping curves (LSV) and chronoamperometric curves (CA) were used to measure the electrocatalytic activity and stability of the catalysts for the oxidation of formic acid. The main results obtained are as follows:1. We synthesized Pd-Cr alloy catalyst and used it as a catalyst for the anodic oxidation of formic acid (FAO). A series of carbon supported Pd-Cr alloy (Pd-Cr/C) catalysts with different Pd-Cr atom ratios were prepared with chemical reduction method. The PdxCr1-x/C catalysts (0.6< x<1) showed better performance toward the anodic oxidation of formic acid than Pd/C and Pt/C. Among them, Pd0.8Cr0.2/C (Pd/Cr=8:2, atomic ratio) exhibits the highest catalytic activity. Compared with Pd/C catalyst, the potential of anodic peak of formic acid at the Pd0.8Cr0.2/C catalyst electrode shifted towards negative value by 50 mV. The potential shift is similar to Pd2Co/C. Pd0.8Cr0.2/C also exhibit high stability, suggesting that Pd0.8Cr0.2/C is a good candidate for the formic acid fuel cell.2. We discovered an improved one-pot method to synthesized Pd nanoparticles support on single and few-layer (1-2 layer) graphene containing hydrophilic groups (C-O, C=O). The as prepared Pd/Graphene catalyst shows better performance toward the anodic oxidation of formic acid than Pd/C catalyst. The potential of anodic peak of formic acid at the Pd/Graphene electrode is negative shift ～150 mV than Pd/C catalyst. XPS spectra shows that the binding energy of the Pd 3d5/2 in Pd/Graphene is positive shift by 1.6 eV, compared to Pd/C, the positive shift indicates the decrease of Pd 3d electron density and Pd with low 3d electron density can decrease the adsorption affinity of CO and COOHads on Pd, thus would promote the formic acid oxidation through the direct pathway. Besides, Pd/Graphene showed higher stability and durability than Pd/C, suggesting that it is a good candidate for the formic acid fuel cell.3. We studied the electrooxidation behavior of the hybrid structure of Pd deposited on UME and glassy carbon substrate. We used electro-deposition method to deposit Pd nanoparticles on glassy carbon electrode and ultramicro electrode, and studied their effect on the electrooxidation of formic acid and hydrazine hydrate.