A density-functional-theory investigation of Cu5 atomic quantum clusters deposited on TiO2 and Cu substrates as catalysts for green energy

Alhawiti, Fatimah Rafi and Lambert, Colin (2024) A density-functional-theory investigation of Cu5 atomic quantum clusters deposited on TiO2 and Cu substrates as catalysts for green energy. PhD thesis, Lancaster University.

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Abstract

Environmental concerns are exacerbated by the fact that conventional fossil fuel combustion is still a significant source of atmospheric CO2. Several strategies are being investigated to counter this. The first promising avenue is an environmentally friendly way to produce hydrogen by splitting water with solar energy. Hydrogen (H2) has emerged as a clean, renewable, and energy-efficient energy vector. However, the majority of hydrogen gas comes from fossil fuels through processes like steam reforming or coal gasification. There is a pressing need for environmentally friendly methods, particularly novel inorganic photocatalysts, to produce green hydrogen through renewable means by splitting water using sunlight. Another important way to reduce emissions and produce useful materials is to reduce CO2 levels in order to produce valuable carbon-based chemicals. Based on density-functional theory (DFT), using the Vienna ab initio simulation package (VASP), I employed the generalized gradient approximation (GGA) and a hybrid functional combined with Hartree Fock (HF) theory to systematically study their geometric and electronic structures. The first focus of this thesis is to enhance the photocatalytic properties of perfect and defective rutile TiO2 by doping with Cu5 atomic quantum clusters (AQCs). Furthermore, the influence of silicate (SiO32−), which is added experimentally during the purification of the AQCs, on the electronic structures of titania is examined. I found that the creation of a single polaron at either a five-fold coordinated (Ti5c) or a six-fold coordinated (Ti6c) atoms, indicating increased surface activity, is caused by the Cu AQCs donating electrons to both perfect and decreased TiO2 surfaces. I also discovered that the gap states of Cu5/TiO2 are unaffected by the presence of SiO32−. In the second part, I investigate the CO2 reduction reaction (CO2RR) using electrocatalysts based on (Cu) electrodes. According to a suggested energy diagram, adding Cu5 dramatically reduces the energy barriers needed to form important intermediates, improving the selectivity of the process for producing carbon monoxide (CO) and formic acid (HCOOH). For this reason, Cu5 is recommended as a surface modification that can be used to optimize catalytic performance in CO2 reduction on Cu surfaces. This provides a workable approach to defect engineering, which can optimize catalyst efficiency.