Author: You, Huilin
Title: Piezo-catalysis and pyro-catalysis for hydrogen production and pollutant treatment
Advisors: Lam, Chi-hang (AP)
Huang, Haitao (AP)
Degree: Ph.D.
Year: 2022
Subject: Piezoelectric materials
Hydrogen as fuel
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Physics
Pages: xix, 128 pages : color illustrations
Language: English
Abstract: Due to the limited fossil-fuels and their serious environmental impact, clean energy generation and pollutant treatment has attracted enormous attention. Photo-catalysis has demonstrated wide range of potential applications including pollutant treatment, clean energy generation and biological applications. Apart from the catalytic reaction excited by photons, catalytic reactions can also be triggered by mechanical vibration and thermal fluctuation energies, which can be easily harvested from our living environment. Piezo-catalysis and pyro-catalysis thus refer to the catalysis by piezoelectric materials under the mechanical vibration and the catalysis by pyroelectric materials under the thermal cycling, respectively. The piezo-catalytic and pyro-catalytic reactions can be self-powered by harvesting waste energy from the environment. Although the research of piezo-catalysis and pyro-catalysis has attracted increasing attention, there are some drawbacks which hinder their practical application.
Comparing with well explored photocatalysis, the intrinsic mechanism of piezo-catalysis is still unclear, which is indispensable for piezo-catalyst selection and achieving higher piezo-catalytic efficiency. In my first work, a strong piezo-catalytic hydrogen production via hydrothermally synthesized BiFeO3 square nanosheets is realized at a rate of 124.1 µmol·g-1 under a 100 W vibration excitation at the resonant frequency for 1 h. The piezo-catalytic property of the BiFeO3 square nanosheets is attributed to the tilting of the conduction band under the strong piezoelectric field induced by mechanical vibration, which make the conduction band of BiFeO3 more negative than the H2/H2O redox potential, enabling the hydrogen evolution. Our work experimentally demonstrated the band tilting induced by internal electric effect produced by piezo-catalysis.
Hydrogen evolution is only a half-reaction in water splitting, while the other half, oxygen evolution, is of little or no value. It would be ideal if this half-reaction can be used for value-added purposes, such as organic pollutant treatment. In second work, we achieve simultaneous piezo-catalytic hydrogen production and Rhodamine B (RhB) dye decomposition by using piezoelectric g-C3N4 nanosheets. The addition of RhB helps promote the hydrogen production up to 69.19 µmol·g-1 after 90-minute vibration, with a simultaneous dye decomposition ratio of 45.81%. Theoretical study shows that H+ adsorption and H2 desorption processes of g-C3N4 are facilitated under compression and elongation, respectively, during mechanical vibration, beneficial to hydrogen production. Our work demonstrates a win-win strategy to utilize the oxidative half-reaction for organic pollutant treatment and at the same time promote the reductive half-reaction for more hydrogen production via harvesting vibration energy using piezo-catalysis.
Finally, on the base of studies of pyro-catalysis, the introduction of localized plasmonic heat sources to increase temperature change rate for high clean energy production is investigated. Pyro-catalytic materials that utilize repeated and rapid temperature changes for catalysis have received enormous attention recently. However, the greatest challenge that limits the application of pyro-catalytic materials is the lack of sufficiently large temperature change and, more importantly, highly frequent thermal cycling due to the enormous heat capacity of the ambient environment. In third work, we introduce localized plasmonic heat sources to rapidly heat up the pyro-catalytic material itself without wasting energy to raise the surrounding temperature, triggering a significantly expedited pyro-catalytic reaction and enabling multiple pyro-catalytic cycling per unit time. A plasmonic metal/pyro-catalyst composite is fabricated by in-situ grown gold nanoparticles on three-dimensional hierarchically structured coral-like BaTiO3 nanoparticles, which achieves a high hydrogen production rate of ~181.2 μmol·g-1 h-1 under pulsed laser irradiation. The synergy between plasmonic local heating and pyro-catalysis will bring new opportunities in significantly accelerated pyro-catalysis for pollutant treatment, clean energy production and biological applications.
Rights: All rights reserved
Access: open access

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