Design, Synthesis And Application Of One-Dimensional Electrocatalysts

Access to clean and reliable energy has become the main strategy and cornerstone of dealing with the global energy and pollution problems. Fuel cells are regarded as the most potential choice and ideal solution for transportation, portable mobile power supply and power generation devices applications, due to their non-polluting, high efficiency and various fuels. However, the poor stability and high cost remain severe challenges to the ultimate commercialization of fuel cells. Till now, advanced stratigies have been developed and investigated to lower the cost, heighten platinum (Pt) utilization and improve the catalytic performence through composition and structure control. Understanding of the synthesis reaction mechanism is advantageous to synthesize the catalysts with specific structure, size and composition.The present dissertation will foucus on large-scale synthesis and catalytic application of one-dimensional (1D) electrocatalysts. We developed a modified template-scrificial method with low cost. The templates not only used to maintain1D morphology of the final products and the reducing agents, but also the not-reacted template atoms would be further form alloy with noble metal. The formation of the alloy and the addition of non-noble metal will improve the electronic structure of Pt and reduce the adsorption energy of the reaction intermediates to enhance the catalytic activity and stability. It is a broad applicable synthetic method with unique superiority owing to the high reactivity, well dispersity and controllability of the templates. It is efficient to prepare a series of ID material with high active surface area and structure stability. In addition, dealloying process is useful to expose more active sites, increase surface roughness and improve catalytic performance. The main results can be summarized as follows:1. A partial sacrificial template route was developed for preparing1D electrocatalysts with different composition by using cheap Cu nanowires (NWs) as templates. Although pure Cu NWs do not have high catalytic activity, alloying Cu with Pt, Pd or Ru metals would improve the activity of the alloy electrocatalysts owing the ligand effect and strain effect. The keys for successful synthesis of nanoparticle-on-nanotube structure catalysts are to use high active Cu NWs as templates and high reaction temperature coupling with Kirkendall effect. We also investigated the composition and structure effect on the activity of oxygen reduction reaction (ORR) and methonal oxidation reaction (MOR).2. One-dimensional ultrathin electrocatalysts with various compositions were prepared by partial sacrificial template route. Ultrathin tellurium (Te) NWs with high aspect ratio (>104), high reactivity, good flexibility and easy dispersion in different solvent (eg. water, ethanol, ethylene glycol, n-hexane etal.) were selected as templates for preparing ultrathin and porous PtPdTe and PtTe NWs catalysts. More importantly, the existence of single-crystalline segments (SCSs) of the PtPdTe NWs allowed for the preferential exposure of long segments with high crystallinity and low energy crystal facets, which is highly advantageous for the electrocatalytic reactions. In addition, these Te NWs can be synthesized in large scale by our group and provide the possibility for large-scale preparation of catalysts.3. We design and successfully synthesize ultrathin, ultralong and porous1D dotted line structure catalysts with NPs on the surface. The ultrathin Te NWs are used as template to confine the size in the range of5-7nm, to generate complex but tunable nanostructures from homogeneous PtTe to heteronanostructured and Pt decorated Pt/PtTe electrocatalysts. We revealed the formation of weaker oxidant PtmCln complexes from m×PtCl42-ions through the Pt-Pt bond during aging of K2PtCl4in ethylene glycol (EG) solution by using time-resolved in-situ UV-vis and X-ray absorption fine structure (XAFS) spectroscopies. The coexistence of PtCl42-ions and PtmCln complexes is the key of successful synthesis of ultrathin NWs with holes in the interior and Pt NPs on the surface of the NWs (increased structural complexity) coupling with the Kirkendall effect and improving upon Pt utilization and stability for electrocatalysis. The reaction kinetics is refined by tuning the coordination state of Pt precursors further enriched and expanded the template sacrificial method.4. The sacrificial template method was further developed for fabricating core-shell structure catalysts, including Pt monolayer catalysts. We examined the effects of the thickness of the Pt shell, lattice mismatch, and composition of the core on catalytic activities for ORR. Firstly, we prepared ultrathin PdTe and PdAuTe NWs using Te NWs as templates. Then, Pt-shell could be deposited on the PdTe and PdAuTe NWs combing the under potential deposition method with galvanic replacement reaction. The thickness of Pt shell could be tuned by repeat such processes. The synthesis of core-shell structure catalysts is useful to optimize the Pt utilization and loading.