Preparation And Research On Novel, Pt-free Micronano Materials As Electrocatalysts In New Energy Devices

Currently, developing efficient and clean energyhas become increasingly urgent as a result of energy crisis and environmental contamination. Due to high photoelectricconversion efficiency (PCE), fabrication with ease, low cost, environmental friendliness, etc, dye-sensitized solar cells (DSCs) have attracted intensive interests. To date, high PCEs up to 14% have been achived. Fuel cell (FCs), one kind of novel power generation device capable of converting fuel's chemical energy into electricitydirectly, have demonstrated some impressive advantages such as high energy conversion efficiency, litter pollution to environmental, broad source, etc, which is regarded as one fourth generation technology after the hydropower, thermal power, and nuclear power. The research and development of these two new energy devises will be helpful to solve the issues of energy crisis and environmental pollution. Cathodic reduction reaction is involved within both of these two newenergy devises, and it is significant to develop novel, efficient, low-cost, and stable cathodic catalytic materials so as to promote the industrialization of DSCs and FCs. At present, precious metal platinum (Pt) is the most common cathodic material in these two cells, but which is expensive and leads to increase in cell cost. Furthermoe, Pt has other disadventages such as the inferior long-term stability, the sluggish kinetics, and the decrease of Pt catalyticactivity caused by the fuel crossover, which seriously affects the cells performance. Therefore, to promote the industrialization development of DSCs and FCs, the development of non-precious metals catalytic cathodic material with high efficiency, low-cost, high stability is an urgent task. Meanwhile, further research on the catalytic mechanism of the cathode material and the effect on conversion efficiency are needed, which in turn can provide necessary theoretical guidance for further research and development of new materials.To solve the above issues, this thesis designed and synthetized high-efficience, low-cost, and stable non-precious metalscathodic catalytic materials. The structure-activity relationship between the morphology, composition, structure of the catalytic materials, and the devices' performance were investigated systematically, together with researches in-depth on catalytic performance of the non-precious metals catalyst for IRR and ORR.Firstly, NbSe2 was prepared by using solvothermal method. By adjusting the cooling rate of the solvothermal process, we successfully realized controllable synthesis of NbSe2 nanostructures, including nanosheets, nanorods, as well the composite with graphite, and finally achieved a PCE of 7.80% for DSCs, approaching that based on sputtering Pt counter electrode (CE). By controlling the composition of transition-metal selenides (TMSes), we synthesized five selenides, Cr5.6Se8, MoSe2, WSe2, TaSe2, and HfSe3 through a reductant-free solvothermal route. The relationship between the material composition and their catalytic activitiesfor I3-/I- was studied by electrochemical methods. Theoretical investigations on the electrocatalytic activity of MoSe2 and WSe2 with similar morphologies and structures were performed based on the density functional theory (DFT). The different performance of MoSe2 and WSe2 mainly originated from the processes of I3- adsorption and electron transfer. To further extanded the application of TMSes, we designed and constructedthe thin two-dimensional layered nanocomposite catalysts based on graphene and inorganic graphene analogues (IGAs) and used as catalysts for oxygen reduction reaction (ORR) of FCs. The composites possessed higher specific surface area and superior pore-structure that could facilitate oxygen adsorption and mass transport during ORR, which showed excellent electrocatalytic performance.Secondly, tellurides were developed into highly efficient Pt-free CE materials in DSCs for the first time. By an improved composite-hydroxide-mediated (CHM) approach, CoTe and NiTe2 micronano structures were synthesized successfully used as Pt-free CE materials in DSCs. DSCs based on CoTe and NiTe2 CEs achieved PCEs of 6.92% and 7.21%, respectively, comparable to that of 7.04% when using sputtered Pt-based CE. By controlling the composition of iron chalcogenides, FeS2, FeSe2, and FeTe2 were synthesized and exhibited excellent catalytic activities when serving as CEs in DSCs and the PCEs were 8.00%for FeS2, 7.92% for FeSe2, and 7.21% for FeTe2, respectively. The micron particle size of FeTe2 resulted in a decrease in the number of catalytic active sites and a slightly inferior catalytic activity. Theoretical calculation results showed that FeS2 had higher adsorption energy of ?, and FeTe2 exhibiteda lower work function, which was favorable to the charge transfer.Thirdly, W18O49 nanorods were synthesized on the surface of graphene by solvothermal method and used as cathodic catalyst in FCs. In the composite catalyst, strong interaction existed between W18O49 nanorods and reducted graphene oxide (rGO). Combining the one-dimensonal structure, abundant oxygen surface vacancies of W18O49 nanorods. and the better conductivity of rGO, the composite catalyst finally demonstrated better catalytic activity in ORR. Results showed that the electron transfer number of ORR was ca.3.88, comparable with that of commercial Pt/C. Meanwhile, the W18O49-rGO composite catalyst also exhibited outstanding fuelcrossover resistance and long-term durability in alkaline medium, which had great potentials as excellent non-Pt cathode catalyst.