Study On The Performance Of Pd - Based Catalysts For Direct Formic Acid Fuel Cells

Formic acid has gained a lot of concern due to its advantages, such as non-toxic, non-flammable, good oxidation resistance and low Nafion membrane permeability in recent years. Researches on direct formic acid fuel cell (DFAFCs) anode palladium catalysts were mainly focused on the preparation method and the catalyst carrier. However, it is found that Pd-based anode catalysts in DFAFCs have some drawbacks: Firstly, the stability of Pd electrocatalyst is still poor. Secondly, Pd could be soluble in acid medium. Therefore, it is of great importance to improve the electro-oxidation activity of formic acid of anode Pd catalyst for the development of DFAFCs. In this paper, we innovatively employed the following three methods to improve the electrocatalytic properties of palladium-catalyzed direct formic acid fuel cells:1. Electrocatalytic properties for formic acid oxidation of 3D Pd-Sn nano networkThe Pd-Sn intermetallic compound with 3D network structure (Pd-Sn-INNs) was prepared by a simple polyol synthesis method under basic conditions. The morphology, structure, size and composition of the as-obtained nanostructures were investigated by transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Electrochemical test results showed that the 3D network-like Pd-Sn-INNs nanostructure catalysts exhibit greater electrocatalytic activity for formic acid oxidation reaction than commercial Pd black owing to their unique electronic effect and more catalytic active sites of the nano network structure.2. Surface functionalization of Pd-Co nanoparticles and their electrocatalytic activity for formic acid oxidationThe surface-functionalized Pd-Co nanoparticles were conveniently synthesized through the direct thermal decomposition method of metallic acetate salt. On the one hand, probably due to the electrostatic adherence between OAm and O2 molecules and the influence of OAm barrier networks on Pd-Co-OAm surface, Pd-Co-OAm showed excellent electrocatalytic activity for electro-oxidation of formic acid and better tolerance of CO in acidic media. On the other hand, Pd-Co-OA inhibited electrocatalytic activity for the ORR because of the electrostatic repulsion between Pd-Co-OA and O2 molecules. The present experimental result demonstrated that the surface modification of the Pd-Co nanoparticles is also a promising strategy to improve their electrocatalytic activity for formic acid oxidation.3. Porous Pd nanorods and their electrocatalytic properties for formic acid oxidationWe synthesized a kind of porous Pd nanorods (Pd-PNs) by using formic acid solution as reducing agent in the presence of polyvinyl pyrrolidone (PVP). The morphology, structure, particle size and composition of the Pd PNs were characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy-dispersive X-ray (EDX). Electrochemical test showed that Pd-PNs exhibited much higher electrocatalytic activity and better stability than the commercial palladium catalyst. CO-stripping voltammetry tests also indicated that it had excellent ability to resist CO poisoning, owing to their unique porous structure.