Is photocatalytic hydrogen production sustainable? – Assessing the potential environmental enhancement of photocatalytic technology against steam methane reforming and electrocatalysis

In the face of the burgeoning interests toward the utilization of nanomaterials in catalyzing solar-aided chemical processes, the doubts upon the capability of these emerging low-TRL technologies in offsetting the potential environmental impacts of conventional approaches have endured for years. Despite the scarcity of commercial-level data for low-TRL process route, an extensive life cycle study is necessitated to spotlight the demerit and potential enhancement of these systems, which would be beneficial for the future process upscaling. Therein, this study conducted a cradle-to-gate life cycle assessment (LCA) on electrocatalysis and photocatalysis, with steam methane reforming (SMR) simulated as the base case. With a functional unit of 1 kg hydrogen, the results demonstrated that electrocatalysis led to the greatest climate change (GWP 100 ), exceeding that of photocatalysis and SMR by 7.04 and 56.63 kg CO 2 -Eq, respectively. In contrast to photocatalysis, which has its main impact released from the catalyst synthesis stage (95.87%), the reaction phase in the electrolyzer was revealed as the major contributor (96.10%) to the resulting GWP 100 in electrocatalysis, attributed to the huge consumption of aqueous electrolyte. Solid polymer electrolyte has latterly been recognized as a potential candidate to replace liquid electrolyte. In view of the existing uncertainty in inventory data of both the emerging technologies, a significant fluctuation was observed in their resulting human toxicity (HTPinf), where the large reagent input for large-scale catalyst synthesis was raised as a contributing factor. In line with the promoted employment of renewables, power supply of the simulated system was varied from electricity mix to hydro and wind power, resulting in an improvement of 14% and 10% to the GWP 100 level of photocatalysis, and 5.33% and 3.73% to that of electrocatalysis. Hence, this spotlights the potential of incorporating renewables-sourced electricity in the production plant, which lays a promising foundation for future carbon neutrality.