Life Cycle and Techno-Economic Assessments of Photocatalytic Hydrogen Production
Creators: Maurya, Jayranjan Omranjan
Publisher: name: University of Alberta Library
Year: 2022

<p>Hydrogen (H2) can play a critical role in global greenhouse gas (GHG) mitigation. Photoelectrochemical water splitting using solar radiation is a promising H2 technology. Titanium dioxide (TiO2)- and carbon nitride (g-C3N4)-based photocatalysts are the most widely used photocatalytic materials because of their activity and abundance. Several attempts have been made to improve the photocatalytic performance of these materials in terms of their activity level, life span, response to visible radiation, and stability. However, the environmental impacts of these modifications are often not included in existing studies. This research, therefore, develops a bottom-up cradle-to-grave life cycle assessment (LCA) framework to evaluate environmental performance by comparing GHGs and energy payback time (EPBT). A framework was also developed to conduct a techno-economic assessment (TEA) to estimate the economic feasibility by calculating the Levelized cost of hydrogen (LCOH) of four alternative pathways: TiO2 nanorods (TNR), fluorine-doped carbon nitride quantum dots embedded with TiO2 (CNF: TNR/TiO2), g-C3N4, and a g-C3N4/BiOI composite. Unlike most studies that focus only on certain stages, such as laboratory-scale photocatalytic fabrication, this study includes utility-scale cell production, assembly, operation, and end-of-life to give a more precise environmental performance estimate. The results show that g-C3N4/BiOI has the lowest GHG footprint (0.43 kg CO2 eq per kg of H2) and CNF: TNR/TiO2 has the lowest energy payback time (0.4 years). In every pathway, energy use in material extraction processes makes up the largest GHG contribution, between 83% and 89%. Photoelectrochemical water splitting is highly feasible for adaptation as a mainstream H2 production pathway in the future.<br>
The TEA results show that TNR has the lowest cost, 4.9 $/kg of H2. The H2 cost ranges from 4.9 to 7.8 $/kg of H2. In all four pathways, the largest contribution is from capital investment and labour costs; together they make up around 75% of the total cost. Material costs account for 13% to 29% of the overall cost. Photoelectrochemical water splitting has significant feasibility for adaptation as a mainstream H2 production pathway in the future.<br>
Sensitivity and uncertainty analyses were performed to identify the key input parameters that have significant impacts on the GHG emissions and the LCOH, as well as to obtain a range of results (through Monte Carlo simulation). Sensitivity analysis showed that cell life span, solar insolation, and silver extraction are key inputs impacting the GHG emissions, whereas panel manufacturing cost and solar insolation have a significant impact on the LCOH. The GHG emissions values are 〖1.4〗<em>(-0.55)^(+0.4), 〖0.89〗</em>(-0.24)^(+0.16), 〖1.96〗<em>(-0.26)^(+0.24) , and  〖0.49〗</em>(-0.11)^(+0.21) kg of CO2 eq per kg of H2 produced for TNR, CNF: TNR, g-C3N4-S, and BiOI/g-C3N4-S, respectively. The LCOH values are 〖4.9〗<em>(-0.70)^(+0.75),〖5.7〗</em>(-0.65)^(+0.45),〖5.8〗<em>(-1.15)^(+0.55),and  〖7.8〗</em>(-0.95)^(+0.45) $ per kg of H2 produced for TNR, CNF: TNR, g-C3N4-S, and BiOI/g-C3N4-S, respectively.<br>
Photoelectrochemical water splitting is still in the initial stage of development and hence materials are still being developed. In addition, the technology is not yet economically feasible at a mass production level. Technological limitations such as uncertainty in the life span of the cell and low solar insolation in some locations limit the applicability of the technology. However, with current research on the development of earth-abundant, stable, and active photocatalyst materials, it is expected that the technology will be adopted in the near future for H2 production. In summary, photocatalytic H2 production has immense potential to be adopted for large-scale commercialization shortly.</p>