Preparation And Electrocatalytic Performance Of Three - Dimensional Porous Pd - Based Catalysts

Due to the unique structural characteristics (great quantity of nano-holes, big specific surface area, interconnect structure of three-dimension nanomaterial, etc.), palladium nanoparticle assemblies composed by primary structural unit such as nanospheres, nanowires, nanorods exhibit enhanced electrocatalytic performance towards hydrogen, formic acid, ethanol oxidation, etc. In the thesis, we synthesize K2PdCl4/K3Co(CN)6cyanogel, which is a kind of polynuclear metal compounds with the three-dimensional network structure and the solid gel property. The metal atoms in cyanogels can be uniformly mixed on the atomic level. Moreover, its own special inherent properties can effectively inhibit the Brownian motion of atoms during the reduction. Using the K2PdCl4/K3Co(CN)6cyanogel as reaction precursor, we prepare the Pd-based nanoassemblies with different structure and then further study their electrocatalytic properties towards formic acid and hydrazine hydrate.The main researches are as follows.1. The K2PdCl4/K.3Co(CN)6cyanogel with three-dimensional (3D) network structure is facilely synthesized using K2PdCl4and K3Co(CN)6as precursor via ligand substitution reaction. The composition and structure of the K2PdCl4/K3Co(CN)6cyanogel are characterized by infrared spectrometry (FT-IR), ultraviolet and visible spectroscopy (UV-vis), thermogravimetric analysis (TG), transmission electron microscopy (TEM), etc. Under certain temperature, K2PdCl4/K3Co(CN)6cyanogel can finally convert into palladium hexacyanocobaltate (PdHCC). Preliminary studies have shown that PdHCC has a certain ion selectivity towards alkali metal cations (Na-, K+, Cs+, etc.). Meanwhile, PdHCC also has potential applications in the field of H2O2reduction.2. Three-dimensionally (3D) networks-like palladium-cobalt alloy nanoassemblies (Pd-Co ANAs) were conveniently synthesized through a simple simultaneous reduction reaction with sodium borohydride (NaBH4) using inorganic K2PdCl4/K3Co(CN)6cyanogel as reaction precursors. The morphology, structure, size and composition of the Pd-Co ANAs are characterized by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Due to the unique3D networks structure, the abundant defects in nanoassemblies and the change of the Pd electronic structure, the Pd-Co ANAs exhibit higher electrocatalytic activity, better electrochemical stability, and higher resistance to CO poisoning over single-component Pd nanoparticles for the formic acid oxidation reaction (FAOR).3. Well-defined Pd nanodendrite assemblies (Pd-NDAs) with high surface area are successfully fabricated using the K2PdCl4/K3Co(CN)6cyanogel as a reaction precursor through simple chemical reduction with N2H4·H2O. The detailed morphology, composition and structure of the Pd-NDAs are thoroughly investigated by various characterization methods (TEM、XPS、XRD、EDS、Nitrogen adsorption-desorption isotherm (SADI), etc.), demonstrating that the Pd-NDAs are highly porous and self-supported structures. Due to their small grain size and particular interconnected structure, the as-prepared Pd-NDAs exhibit excellent electrocatalytic activity and durability for formic acid oxidation, which make them promising anodic electrocatalysts for the future.4. Porous ternary Pd-Co-P alloy network nanostructures (Pd-Co-P TANNs) were synthesized by reducing K2PdCl4/K3Co(CN)6cyanogel with mixture of NaH2PO2and NaBH4at room temperature. The detailed morphology, composition and structure of the Pd-Co-P TANNs are thoroughly investigated by SEM, TEM, XPS, XRD, EDS, Zeta petential analysis. The tests have indicated that the introduction of P can effectively tune geometric, electronic and superficial structures of Pd-Co-P TANNs. As a result, Pd-Co-P TANNs exhibit higher electrocatalytic activity (mass activity and specific activity) and durability towards hydrazine oxidation compared to Pd-Co alloy, which demonstrates that Pd-Co-P TANNs are indeed promising electrocatalysts towards hydrazine oxidation.