Hydrothermal Synthesis And Electrocatalytic Performance Of Tungsten(Molybdenum) Disulfide/Reduced Graphene Oxide Composite

Transition metal dichalcogenides?TMDs? tungsten disulfide?WS₂? and molybdenum desulfide?MoS₂? are typically layered materials. Due to the weak interactions of Van der Waals' force between the layers, they can be exfoliated to few-layer or monolayer structure by physical or chemical methods. WS₂ and MoS₂ layers can be easily stacked each other and its electronic conductivity is relatively low, and this leads to limited electrochemical properties. Therefore, in this thesis We synthesized WS₂/RGO and MoS₂/RGO composites through one-pot hydrothermal method. The flakes of WS₂ and MoS₂ are uniformly dispersed on the graphene carrier, and their combination rely on the adsorption between each other. We attempted to employ the composites as non-noble metal oxygen reduction catalyst for fuel cells, and explore the effect of hydrothermal method on the oxygen reduction reaction?ORR? performance of the catalysts. The main achievements are listed as below:1. We present a facile process to synthesize WS₂ and studied the influence of different precursors on the structure and electrochemical properties of WS₂. When using sodium tungstate and thiourea as precursors, WS₂-1 layers were easily stacked together. Electrochemical tests showed that the oxygen reduction activity of WS₂-1 was relatively low, and ORR process was mainly carried out through two electron pathway. We tried to employ tungsten?VI? chloride and thioacetamide as precursors, then we got uniformly distributed few-layer WS₂-2. Electrochemical test results showed that ORR activity of WS₂-2 was higher than WS₂-1, and the number of electron transferred increased during ORR process. In the stability test, the retention rate of ORR current density was 76%, but its catalytic activity was still far lower than commercial Pt/C.2. We prepared graphene oxide by modified Hummers method, and obtained RGO by adding hydrazine hydrate under hydrothermal conditions. RGO structure were transparent and curled each other. Because of its large specific surface area and electronic conductivity, it showed strong electric double-layer capacitance in the CV test. During the ORR process, the peak potential was rather negative and the limiting current density was low either, hence demonstrating weak oxygen reduction activity.3. We prepared WS₂/RGO composite through one-pot hydrothermal route using tungsten?VI? chloride, thioacetamide and graphene oxide as raw materials, and found that the few layers of WS₂ was uniformly distributed on the surface of transparent and thin graphene layer. Electrochemical tests indicated that the ORR performance of WS₂/RGO catalyst significantly increased, and it was better than that of pure WS₂ and RGO. The number of electron transferred in ORR process is near 4, which is very close to the corresponding value of Pt/C. The stability test showed that it had good stability and even surpassed Pt/C in the long-term catalytic process, so the oxygen reduction performance of the catalyst greatly improved.4. We further investigated the electrocatalytic properties of MoS₂/RGO prepared by one-pot hydrothermal method using ammonium molybdate and thiourea as precursors. Electrochemical test results show that the hydrothermal synthesis of pure MoS₂ in alkaline medium China showed a weaker catalytic oxygen reduction activity, and the ORR process was mainly in two electron pathway. In contrast, MoS₂/RGO with few layer petal-like structure was uniformly dispersed on the transparent thin layer of RGO. The electrochemical tests showed that the onset potential and current density had a remarkable increase, indicating more excellent electrocatalytic performance. In addition, its cycle stability was even higher than Pt/C catalyst. Compared to RGO and MoS₂, the catalytic activity of MoS₂/RGO significantly improved. Therefore, we can conclude that MoS₂ and RGO carrier play a synergistic catalytic effect in the ORR process, and it can be a potential alternative of Pt/C as a non-noble metal catalyst.