Structure-Activity Relationship of Porous Materials for Energy Conversion and Storage

The design and synthesis of porous materials are of key importance in energy conversion and storage, due to their structure-related properties in the isolation of active materials and exploration of large active site. In this thesis, the recent process in synthesis and energy-related applications of porous carbon and noble metal materials have been carefully reviewed. And three porous materials have been used as catalyst support, host materials and active sites for biomass conversion, electrolytic hydrogen evolution, lithium-sulfur battery and oxygen reduction reaction. I found that the nanostructures of porous materials can significantly affect their activity and stability by either confining active sites, boosting mass transfer, stabilizing active materials or exploring high active surface area (Figure II-1). The structure-activity relationship is used across the entire thesis, which could give an insightful understanding of the activity and stability of designed catalysts. A liquid-free synthesis of porous carbon is developed to uses gases instead of liquid to disperse carbon precursor, leach templates and remove impurities, minimizing synthetic procedures and the use of chemicals. Therefore, the effects of pore geometries in catalysis can be isolated and investigated. Two of the resulted materials with different pore geometries are studied as supports for Ru clusters in the hydrogenolysis of 5-hydroxymethylfurfural (HMF) and electrochemical hydrogen evolution reaction (HER). The results showed catalysts supported by porous carbon with bottle-beck showed benchmark activity for hydrogenolysis of HMF due to the confinement of active Ru species, while tubular pores boost charge transfer and achieve high performance in HER. In order to further investigate the effect of hollow structure on sulfur stabilization and lithium polysulfides immobilization in cathode of lithium-sulfur battery, X-ray computed tomography (X-ray CT) was applied to provide direct visualization of microstructural evolution in cathode. The results show that the combination of hollow structure and nanosized adsorbent could significantly inhibit volume expansion and reduce the polysulfides shuttle effect, thereby enhance the electrochemical performance. In addition to catalyst support and host of active materials, use of porous materials as active sites for oxygen reduction reaction (ORR) is also investigated in this thesis. A novel catalyst design of large and porous PdPt particles that are tightly attached to the carbon support and exhibit excellent catalytic performance during the oxygen reduction reaction. From catalyst characterization and theory investigation, the origin of high activity and stability of this catalyst stem from its porous morphology, the strong interaction between the particle with the carbon support and the stabilization effect of Pd to Pt.