Fabrication of composite nanomaterials for photo-/electro-chemical energy conversion

Abstract

Energy conversion plays an essential role in current human society. In this thesis, systematic studies have been done on the development of nanomaterial as active catalysts to achieve efficient energy conversion towards several important reaction processes. The reported works herein mainly focus on two research parts. In the first part, a great number of efforts have been paid on the fabrication of the metal-based and carbon-based composite nanomaterial, various strategies have been employed to modify these material properties in nanoscale to realize an enhanced catalytic performance. In the second part, we have exploited the potential of applying the obtained composite nanomaterials in several important energy conversion reactions, a series of the experiments have been carried out to evaluate their catalytic performance and investigate the mechanism of their high catalytic activity. In the material development part, we have tried lots of material synthesize methods, such as electrochemical approach, hydrothermal method, anodization, and chemical method, to achieve the flexible adjustment of material properties. A group of metal- and carbon-based nanomaterial have been successfully fabricated based on these approaches. In the first chapter, an electrochemical technique called cyclic electrodeposition method was utilized to fabricate an Ag-based nanostructure with high reactive area. Flower-like Ag nanostructure, porous Ag nanostructure, bimetallic Ag-Cu nanostructure have been synthesized and their formation machinimas were also studied carefully. In chapter 2, we focus on the semiconductor nanomaterials for photoreactions and fabricate TiO2 nanotube and graphitic carbon nitride. In chapter 3, carbon-based material was investigated and graphitic carbon nitride was combined with carbon nanotube to make it suitable for some electrochemical applications.

In the material application part, several representative energy conversion reactions have been set as the targets. Firstly, the bimetallic Ag-Cu nanostructure was demonstrated to possess a high oxygen reduction reaction catalytic ability, which is comparable with commercial catalysts. Secondly, the CO2 conversion to useful products has been explored through photoreduction and electroreduction ways. The metal decorated graphitic carbon nitride showed a pretty good performance in the conversion of CO2 to CO in photoreduction approach. In addition, by increasing the conductivity of graphitic carbon nitride and employing the flow cell, the modified carbon nitride and carbon nanotube composite presented a great CO selectivity under the largest current density among the reported carbon nitride based nanomaterial in the electrochemical CO2 reduction reaction. Apart from the above measurements, systematic studies including DFT calculations and a series of characterizations have been conducted to reveal the catalytic mechanism in a more fundamental aspect, and these studies could deliver helpful insights in understanding the reaction principles and the designing of catalytic materials.