Investigation of methods and metrics for improving benchmarking of photocatalytic carbon dioxide reduction

Solar fuel production utilizing carbon dioxide through the process of photocatalysis is an attractive method to sustainably generate energy carriers. Research into photocatalytic CO2 reduction has however been challenged by low conversion. To enable progress, this thesis works through the challenges of benchmarking, to address experimental conditions and results reporting. Starting with a literature survey to identify parameters affecting photoreduction, and assess key terms reported, crucial challenges are isolated. These challenges are limited benchmarking, experimental standardization, and the dual term challenge. Terms are proposed to address critical limitations in data interpretation, and a list is proposed for benchmark-necessary reporting. Two sets of identical experimental condition tests were conducted focusing on gas phase experiments conducted with titanium dioxide-based photocatalysts, with commercially available catalysts, including an anatase TiO2, P25, and Mirkat 211, and modified samples, including doping, structure order, and calcination. To investigate metrics comparisons Mirkat 211 and Au doped TiO2 are explored further for interaction effects and regime identification with the results analyzed three ways: through unitary product formation, photonic yield, and an extended rate normalization. Benchmarking of the Mirkat 211, through single variable experiments, and Au doped TiO2, through a design of experiments, is assessed as compared to the existing literature. In conclusion, the importance of greater context of regimes is emphasized, identification of the importance of the reaction length, irradiance, and catalyst loading experimental variables is ranked, the catalytic versus photonic quantification compared, and recommendations for improving the experimental set up and necessary experimental reporting for photocatalysis are given.Engineering and Physical Sciences [EPS] - Fees Only Scholarshi

Investigation of process parameters assessment via Design of Experiments for CO2 photoreduction in two photoreactors

CO2 photoreduction with water to obtain solar fuels is one of the most innovative and sustainable processes to harvest light energy and convert it into hydrocarbons. Although photocatalytically active materials and photoreactors have been developed for this purpose, lack of standardisation in testing conditions makes the assessment of process parameters and the comparison of material performance a challenge. Therefore, this paper is aimed at investigating the effect of CO2 photoreduction parameters irradiance and reaction time on production of methane from two photocatalytic rigs. This was pursued through a design of experiments (DOE) approach, which assessed the influence of experimental conditions between different setups. Using low irradiance (40-60 W m-2), reaction time and temperature significantly affected methane production, with a maximum production of 28.50 μmol gcat-1 (40 W m-2, 4 h). When using high irradiance (60-2400 W m-2), only irradiance was found to significantly affect methane production, with a maximum production of 1.90 ∙ 10-1 μmol gcat-1 (1240 W m-2, 2 h). Considering proposed reaction mechanism for CO2 photoreduction, this paper highlights that experimental results give different yet complementary information on the two most important steps of the process, i.e. photoexcitation and surface chemical reaction