Tailored Graphitic Carbon Nitride Films for Photoelectrochemical Applications

用於光電化學應用的改性氮化碳薄膜

Student thesis: Doctoral Thesis

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Award date30 Aug 2019

Abstract

In response to the surprisingly growing energy demands, it is advisable to harness inexhaustible and intermittent solar energy conversion into stable chemical fuels, such as hydrogen, which is an attractive pathway for slowing down the consumption of fossil fuels. In a powder water splitting photocatalysis system, hydrogen and oxygen are generated in a mixed atmosphere, which has potentially explosive possibility. Therefore, a photoelectrochemical cell (PEC) is considered as one effective and safe method to produce hydrogen and oxygen and collect them into separate compartments. PECs have been studied for nearly half a century and different types of semiconductor photoelectrodes (for instance TiO2, MoS2, and BiVO4) have been developed. However, it is still far from widely commercial applications owing to some inherent deficiencies, such as the high cost of photoelectrode materials, complex preparation processes, and fast recombination of photogenerated charge carriers. Therefore, cost-competitive photoelectrodes with high performance are desired. In this thesis, the studies about tailored graphitic carbon nitride are presented in five chapters.

In the first chapter, the general background of graphitic carbon nitride (g-CN) is introduced. It contains the varieties of methods to fabricate graphitic carbon nitride films, modifications about tailoring the properties of graphitic carbon nitride and the PEC efficiency comparisons.

In the second chapter, we introduce an unprecedented and effective strategy for tuning the (100) and (001) crystal facets of g-CN. A synergistic protocol is adopted to combine the monomer modification and element doping methods to tune the light absorption and electronic properties of g-CN films with exceptional advantages over the individual strategy. We first utilize poly melamine formaldehyde resin as a new monomer to fabricate monomer tailored and element doped g-CN films. The current density of as-prepared photoelectrode is as high as 228.2 μA cm-2.

In the third chapter, we introduce the fabrication of g-CN films with a wide range of different colors. We provide an alternative route to fabricate the colorful carbon nitride films, which are prepared by adopting multiple-steps thermal vapor condensation (MSTVC) method owing to the design simplicity, without utilizing time-consuming and expensive lithography methods, vacuum evaporation or pulsed laser deposition equipment.

In the fourth chapter, a pseudo-metal-free strategy is creatively adopted to fabricate the g-CN/SnS2 heterogenous photoelectrode with high photoelectrochemical performance.

The fifth chapter provides a summary of the thesis work and prospect of g-CN based photoelectrodes.