New Functional 2D Structure-Based Materials for Energy Conversion

Carbon dioxide (CO2) is considered one of the major greenhouse gases (GHGs) causing climate change rapidly, and such change is more complex and complicated, having adverse effects on our species and planet. Possible strategies and policies have been formulated by the scientific community to manage and mitigate atmospheric CO2 emissions. Yet the search for an active, reliable, and scalable energy technology that limits global warming is highly warranted. In this perspective, we have developed various two-dimensional (2D) based catalytic materials for photocatalytic pure methanol (CH3OH) dehydrogenation (PC-PMD) to H2 and CO2 conversion into varied chemical fuels and energy using solar light at ambient conditions, which has been discussed comprehensively in chapter 1, and then experimentally observed results are summarised in chapters 2 to 5 within this thesis. In chapter 1, the development of 2D-based catalytic materials and their application for photocatalytic energy conversion are given. Greater emphasis has been provided for PC-PMD to H2 and industrial grade products formation, which can be a promising solution to achieve carbon neutrality. In chapter 2, we presented a series of single-layer 2D materials applications in pure CH3OH dehydrogenation to H2 formation. A colloidal chemical synthetic method was employed to prepare sandwiched single-layer transition metal dichalcogenides (TMDs) photoredox activities. The hydrogen fuel production from CH3OH over single-layer MoS2 is observed to be COx-free and reliably workable at ambient conditions with a generation rate reaching 617 mole/g/h and excellent photoredox endurability. In chapter 3, we fabricated a 2D SnS/g-C3N4 heterojunction by a hydrothermal method and extended its application to solar-driven promoter-free multivalorization of light alcohols into self-separable H2 gas/fuel and liquid chemicals without CO2 emission. The hydrogen production efficiency reaches 1.27 mmol/g/h with 95% recoverability. Mechanistic study revealed that the photocatalytic light alcohol conversion to H2 underwent a series of redox reactions, combinations, and disproportionation steps. In chapter 4, we developed a plasmonic Cu-WC/W nanohybrid structure, where the W particle is covered by a layer of WC shell with Cu particles grown on the outer surface, for pure CH3OH decomposition to H2 under solar light illumination. Collectively, the plasmonic photocatalytic activities were sustained for more than 41 days from six successive tests, avoiding the formation of CO2 compounds in the reaction. We demonstrated that the lattice strain effect and electric field (E-field) mediated the catalytic activity of WC NPs and that activities can be promotional when nanoplasmonic Cu interacts and dictates the reaction dynamics. In chapter 5, we showed the application of plasmonic Bi-BiOCl core-shells, which are attached to the assembled TiO2 nanosheets (NSs), for multi-electrons demanding photocatalytic CO2 transformation into selective CH3OH production. The optically excited plasmonic Bi NPs, which translate their electromagnetic decay energy to shell BiOCl with generating local electric-field to tailor CO2 photoreactions at the BiOCl-TiO2 heterojunctions, were responsible for the high photoactivity (235.26 mole/g/h), selectivity (~90%), and stability for CH3OH production from CO2. Predictive simulation and DFT were performed to exploit the mechanistic behaviour of photoejected charge carriers at the heterostructure interface. At the end of this thesis, we conclude by highlighting key challenges and prospects in photocatalytic CH3OH transformation to H2 and CO2 conversion processes over 2D-based nanostructure systems, whereas further development of advanced engineering catalytic materials will accelerate the sustainable (active, reliable, and scalable) production of valuable chemicals and energy as well as facilitate the reduction of CO2 emissions.