Organic-Inorganic Halide Perovskites for Photocatalytic and Photoelectrochemical Hydrogen Production

有機─無機雜化鈣鈦礦材料在光催化及光電催化產氫領域的應用

Student thesis: Doctoral Thesis

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Award date29 Jul 2021

Abstract

To decrease the significant volume consumption of traditional fossil fuels and construct renewable energy depending systems, tremendous studies about the solar energy transfer systems predominated by photocatalytic and photoelectrochemical reactions, such as water-splitting, and artificial photosynthesis, have been put into practice in the last few decades. For these advanced technologies, the photocatalytic and photoelectrochemical hydrogen production processes have been intensively investigated. To enhance the poor performance due to low visible light harvest and the short lifetime of the charge carriers, the design and utilization of effective catalysts are of vital significance. In this thesis, the lead-free organic-inorganic halide perovskite materials have been explored as promising catalysts in photocatalytic or photoelectrochemical hydrogen production.

Account of the solar-to-fuel conversion with organic-inorganic hybrid halide perovskites has attracted growing attention as a result of conspicuous optoelectronic properties as well as the low-temperature solution process. However, the most comprehensively developed hybrid perovskite materials comprise the toxic metal lead, raising concerns about their environmental health threats. Herein, in the first study, we successfully develop environmentally friendly bismuth (Bi)-based hybrid perovskite with the in-situ growth of a heterojunction at the interface of methylammonium bismuth iodide (MA3Bi2I9) and tri(dimethylammonium) hexa-iodobismuthate (DMA3BiI6) by a facile solvent engineering technique. The air-stable MA3Bi2I9/DMA3BiI6 perovskite heterostructure with enhanced photoinduced charge separation exhibits outstanding visible-light-induced photocatalytic activity for H2 evolution in an aqueous HI solution. Powdered MA3Bi2I9/DMA3BiI6 heterostructured composite (BBP-5) shows an H2 evolution rate of 198.2 µmol h−1g-1 without the addition of Pt cocatalysts under 100 mW cm−2 visible-light (λ ≥ 420 nm) illumination.

Secondly, it is well known, the development of a photocatalytic system using hydrohalic acid (HX) to produce hydrogen is a promising way to generate clean and renewable energy with value-added chemicals (such as X2 / X3-). However, it is still a challenge to fabricate a photocatalyst that is effective over a wide range of visible light and stable under strong acid conditions. Thus, we report a series of novel bismuth-based mixed halide perovskites synthesized by anion exchange strategy. It was found that, after the anion exchange process, the remained chloride advances the band position and extends the lifetime of the charge carriers. Besides, the nonuniform distribution of iodide ions in the particles contributes to an appropriate bandgap funnel structure, which is conducive to transfer photoinduced charge carriers from the interior to the surface for a photocatalytic redox reaction. Consequently, the hydrogen generation rate is enhanced up to 300 µmol/h with Pt as a co-catalyst under irradiation of 430 nm. Accordingly, this is a promising way to design photocatalysts with boost activity for photocatalytic hydrogen production.

Finally, to gain an insightful study of the photophysical properties of the MBCl-I and MBI, we utilized temperature-dependent transient photoluminescence (TRPL) and CV in different scan rate techniques to illustrate their exciton transport and electrochemical dynamics. Stronger electronic coupling of MBCl-I arises from the overlap of electronic wavefunctions, indicating that the increased possibility for the generation of excitons. Through the determination of diffusion coefficient and electron-transfer rate by using an electrochemical method, we confirm that effective heterogeneous charge transfer at the interface of electrode and electrolyte results in a better PEC performance for hydrogen production. The exploration of the electron transfer dynamics of these perovskites helps us to gain insight for the reason for the better PEC performance. These photophysical combined electrochemical methods provide us a new avenue to investigate the mechanism of the PEC process.

In summary, this thesis provides facile preparation methods for organic-inorganic halide perovskite for catalyzing hydrogen production reactions in HI splitting. The structure, photophysical properties, and charge carrier dynamics of the participate samples have explicitly been discussed. After that, we conclude the reason for their better performance in the applications of photocatalysis and photoelectrochemistry. The ultimate target of these studies is to provide a promising strategy to develop renewable energy conversion to improve the environment.