Preparation And Catalytic Properties Of Metal/Graphene Composites

The noble metal nanocatalyst plays a key role in the field of fuel cells, biosensor, car tail gastreatment, etc. Fuel cells are identified as promising energy converters for a variety of portableapplications due to the high energy-conversion efficiency, system simplicity, low pollution andenvironmental friendliness. Non-enzyme glucose sensors with stable performance and lowrequirement to the external environment become a research focus of workers in the scientificresearch. However, the activity of catalysts used in fuel cells and non-enzyme glucose sensors islow and the cost is high, which hinder the commercial application of catalysts in the twotechniques. Therefore, the key of the current study is to increase the activity and utilization ofcatalysts and noble metals and reduce the dosage of noble metals. In this thesis, the reducedgraphene (rGO) was chosen as the support material to fabricate the PdPt/rGO, PdCu/rGO andPtPdCu/rGO catalysts by the electrochemical method and chemical synthetic method, and thecatalytic performances of these catalysts are studied. The main research contents and results areas follows:(1) Reduced graphene oxide-supported PtPd bimetallic nanoparticles (PtPd/rGO) weresynthesized by the simple electrochemical method and used as efficient catalysts for theelectro-oxidation of methanol, ethanol and formic acid. The graphitization degree andelectrochemical activity of rGO sheets were adjusted by the reduction degree of rGO whenchanging the reduction time of GO. Our results indicated that the moderately reduced rGO sheetson ITO substrates presented adequate oxygen functionalities as reactive sites for the nucleationand growth of bimet allic nanoparticles. Therefore, the graphitization and oxygenated groups ofrGO played a bifunctional effect on the catalytic activity and stabilization of PtPd bimetallicnanoparticles on rGO. The PtPd/rGO hybrids showed higher peak currents and electron transferrates for the oxidation of methanol, ethanol and formic acid than the PtPd bimetallic catalysts inthe neutral media. The rGO sheets favored the improvement of tolerance to carbonaceousintermediate poisoning and electron transfer due to the graphitization structure.(2) A bimetallic PdCu nanoparticle (NP) decorated three-dimensional graphene hydrogel (PdCu/rGO) was developed by a simple one-step hydrothermal method. The PdCu/rGO hybridsexhibited an interconnected microporous framework with PdCu NPs dispersed andencapsulated within the rGO layers. The PdCu/rGO hybrids showed significant electrocatalyticactivity toward glucose oxidation due to the synergistic effect of PdCu NPs and rGO sheets inthe alkaline solution containing chloride ions, presenting a substantial increase in the oxidationcurrent and decrease in the onset potential of oxidation compared to the monomet allic modifiedrGO hybrids. At an applied potential of0.4V, the PdCu/rGO modified electrode withoptimized bimet allic ratio presented quick respond to glucose oxidation with a wide linear rangeup to18mM and a reproducible sensitivity of48μA (mg/mM)1in the presence of chloride ions.Furthermore, the PdCu/rGO modified electrode exhibited high selectivity to glucose andresistance against poisoning by commonly interfering species such as dopamine, ascorbic acid,uric acid, acetami-dophenol and some monosaccharides.The PdCu/rGO hybrid hydrogels with3D micropores were therefore promising for the future development of non-enzymaticamperometric glucose sensors with improved electrochemical performances.(3) The PtPdCu/rGO nanocomposite catalysts were fabricated by a two-step hydrothermalmethod and the catalytic performances for catalytic oxidation of methanol and ethanol werestudied. Compared to the Pt/rGO catalyst, the PtPdCu/rGO catalysts possessed higher peakcurrent density and better poison tolerance for the catalytic oxidation of methanol and ethanolwith a lower onset potential to the oxidation of methanol, indicated that the PtPdCu/rGOcatalysts needed to cross a lower barrier. Catalyst stability test also proved that the PtPdCu/rGOcatalysts had better stability PtPd/rGO and Pt/rGO catalysts.