Study On Catalytic Performace Of Nanosized Pd For Formic Acid Electrooxidation

Direct formic acid fuel cell (DFAFC) has great advantages such as, high energy density, high performance at low operation temperature and environment friendly. It has high application potential. Widely studied anode catalysts of DFAFC are Pt-based and Pd-based catalysts. Pd-based catalysts usually catalyze electrooxidation of formic acid via a direct oxidation pathway and thus show high catalytic activity. However their stability need to be enhanced. Therefore, the development of Pd-based electrocatalysts with higher activity and extended durability is very important for DFAFC application. In this work, the electrocatalytic performance of nanosized Pd for formic acid electrooxidation were investigated.Formic acid electrooxidation on Pd nanoparticles was examined by cyclic voltammetrys. The effects of electrolyte H+concentration, formic acid concentration and electrolyte anionic adsorption on formic acid electrooxidation on Pd were investigated. TEM and XRD analysis showed that the Pd nanoparticles were face-centered cubic lattice with high crystallinity, and the average particle size was around 25 nm. Electrochemical test results showed that formic acid electrooxidation on Pd was a completely irreversible reaction with diffusion control. With increasing the telectrolyte H+concentration, the peak current of formic acid electrooxidation increased first and then decreased. With increasing the formic acid concentration, the performance of formic acid electrooxidation was improved gradually. The optimum concentration of formic acid and sulfuric acid were 0.1 mol/L and 0.2 mol/L, respectively. The weaker the electrolyte anionic adsorption intensity, the higher the performance of formic acid electrooxidation. Formic acid electrooxidation on Pd nanoparticles went through direct pathway without strong adsorption intermediate products.The carbon encapsulated titanium dioxide nanowire arrays (C/TiO2) on Ti sheet substrates were prepared by pyrolysis of acetone at high temperature, and used as Pd supports. The Pd-C/TiO2 electrodes were prepared by electrodeposition of Pd on C/TiO2 using potential step method. The morphology and phase composition were characterized by XRD and SEM, respectively. The results showed that C/TiO2 were nanowire arrays structure with rutile TiO2. The effects of electrodeposition conditions on the morphology of Pd-C/TiO2 electrodes were investigated. The oxidation potential, nuclear potential, growth potential for Pd eleclrodeposition were determined to be 1.0 V,-1.6 V,-0.2 V, respectively. And the oxidation time, nuclear time, growth time were 10 s,0.1 s,2400 s, respectively. Pd can be electrodeposited on C/TiO2 in the form of film (F-Pd-C/TiO2) or wire (W-Pd-C/TiO2) by controlling the concentration of the solution for electrodeposition. ICP analysis showed that the Pd loanding on the F-Pd-C/TiO2 and W-Pd-C/TiO2 were 0.22 mg/cm2 and 1.50 mg/cm2, respectively. SEM and XRD results showed that Pd were uniform distributed on C/TiO2 with face-centered cubic lattice, and both the Pd film and Pd wire were composed of Pd nanoparticles with diameter around 20 nm. Electrochemical tests showed that, F-Pd-C/TiO2 electrode had high catalytic activity for formic acid electrooxidation, and its electrochemical activity surface area was 35.17 m2/g. The peak potential and peak current density of formic acid oxidation on F-Pd-C/TiO2 were 0.38 V and 225.41 mA/mg, respectively.