Life cycle analysis of sustainable H2 production and hydrogenation of chemicals in a large-scale coupled photoelectrochemical system

Abstract

Photoelectrochemical (PEC) water splitting is a potentially promising technology for renewable hydrogen production, addressing the growing demand for clean and sustainable energy sources. However, current PEC production of hydrogen is still not cost-competitive. A strategic approach to enhance the economic competitiveness of PEC-generated hydrogen is to couple it to selected homogeneous catalytic hydrogenation reactions to synthesize higher-value chemicals. Our previous studies have shown that combining PEC with these hydrogenation reactions effectively reduces the cost of hydrogen, but the lifecycle environmental impact of such a system is still unclear. In this study, we perform a life cycle analysis of a prospective large-scale coupled PEC hydrogenation system to evaluate its overall environmental impacts and compare them with the benchmark hydrogen production methods. Three coupled hydrogenation pathways were examined based on their previously demonstrated economic viability. Our results indicate that coupling hydrogenation reactions significantly mitigate the system's negative environmental impacts across its lifecycle, with the hydrogenation of itaconic acid to methyl succinic acid offering the highest reduction in cumulative energy demand (CED) and the addition of acetophenone to 1-phenylethanol hydrogenation demonstrating the most significant reduction of global warming potential (GWP). Notably, adding phenol-to-cyclohexanol hydrogenation, despite being economically attractive, produces higher environmental burdens, making it less favorable. Sensitivity analysis highlights the pivotal roles of solar-to-H₂ efficiency, H₂-to-chemicals conversion, and system longevity in reducing the system's environmental impact. Overall, our study emphasizes that careful selection of the coupled hydrogenation pathways can substantially enhance the sustainability of the PEC system and underscores the potential of integrated solar-driven hydrogenation processes.