Preparation Of Pt - Based Catalysts By Cyano - Gel Reduction Method And Its Application In Fuel Cells

Proton exchange membrane fuel cell (PEMFC) has been received widespread attention due to its simple structure, no pollution to the environment, high specific energy, the safety of the storage and transportation of the fuel, etc. The PEMFC can not only be used as a power source for fuel cell vehicles, but can also be used for decentralized electricity, heating source, and portable power, etc. However, their commercialization is seriously impeded by the slow kinetics of the oxygen reduction reaction (ORR) and fuel molecule oxidation reaction on the Pt catalysts and the high cost of Pt. Alloying is an effective way to solve the problem of improving the reaction activity and reducing the cost of Pt. In this thesis, we synthesize a series of Pt-based alloy electrocatalysts by the cyanogel-reduction method, and investigate their electrocatalytic performance for methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR) and oxygen reduction reaction.The main results obtained are as follows.1. In this work, we successfully synthesize dark yellow jelly-like K2PdCl4/K2Pt(CN)4 cyanogel with 3D backbone property by mixing K2PdCl4 and K2Pt(CN)4. By using K2PdCl4/K2Pt(CN)4 cyanogel as reaction precursor,3D corallite-like Pd-Pt alloy nanostructures (Pd-Pt CANs) are facilely obtained by simple NaBH4 reduction method in absence of surfactants and templates. The size, morphology and surface composition of the Pd-Pt CANs are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy dispersive spectrum (EDX), EDX mapping, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The fascinating properties of K2PdCl4/K2Pt(CN)4 cyanogel, such as 3D backbone structure and bimetallic property, are responsible for the 3D porous morphology of the Pd-Pt CANs. Compared to commercial Pt and Pd black, the Pd-Pt CANs exhibit superior electrocatalytic activity and stability for the ethanol oxidation reaction (EOR), which is ascribed to their unique interconnected 3D structure, electronic effect, and synergistic alloy effect.2. K2PtCl4/K3Co(CN)6-K2PdCl4/K3Co(CN)6 mixed-cyanogels were firstly synthesized by mixing K2PtCl4, K2PdCl4 and K3Co(CN)6. Three-dimensional (3D) Pt-Pd-Co trimetallic network nanostructures (TNNs) with a high alloying degree are synthesized through the room temperature wet-chemical synthetic method using mixed-cyanogels as reaction precursor and NaBH4 as reductant. The size, morphology and surface composition of the Pt-Pd-Co TNNs are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy dispersive spectrum (EDX), EDX mapping, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The 3D backbone structure, solid nature and triple-metallic property of mixed-cyanogels are responsible for the 3D structure and high alloying degree of as-prepared products. Compared to commercial Pt black, the Pt-Pd-Co TNNs exhibit superior electrocatalytic activity and stability towards the ORR, which is ascribed to their unique 3D structure, low hydroxyl surface coverage and alloy property.3. K2PdCl4/K2Ni(CN)4 cyanogel can be synthesized by mixing K2PdCl4 and K2Ni(CN)4. After obtaining Pd-Ni alloy networks (ANWs) prepared by reducing K2PdCl4/K2Ni(CN)4 cyanogel with NaBH4,3D porous PdNi@Pt core-shell nanostructures (CSNSs) are facilely synthesized by a following galvanic displacement reaction to generate the Pt-rich shell. The size, morphology and surface composition of the PdNi@Pt CSNSs are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy dispersive spectrum (EDX), EDX mapping, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The as-synthesized novel PdNi@Pt CSNSs exhibit a much improved catalytic activity and durability for the methanol oxidation reaction (MOR) in the acidic media in comparison with the commercial used Pt black because of their specific structural characteristics.