Perspectives for a sustainable implementation of super-green hydrogen production by photoelectrochemical technology in hard-to-abate sectors

The energy transition's success hinges on the effectiveness to curbing carbon emissions from hard-to-abate sectors. Hydrogen (H₂) has been proposed as the candidate vector that could be used to replace fossils in such energy-intensive industries. Despite green H₂ via solar-powered water electrolysis being a reality today, the overall defossilization of the hard-to-abate sectors by electrolytic H₂ would be unfeasible as it relies on the availability of renewable electricity. In this sense, the unbiassed photoelectrochemical water splitting (PEC), as inspired by natural photosynthesis, may be a promising alternative expected in the long term. PEC could be partly or even completely decoupled from renewable electricity and then, could produce H₂ autonomously. However, some remaining challenges still limit PEC water splitting to operate sustainably. These limitations need to be evaluated before the scaling up and implementation. A prospective life cycle assessment (LCA) has been used to elucidate a positive performance scenario in which the so-called super-green H₂, or photo-H₂, could be a sustainable alternative to electro-H₂. The study has defined future scenarios by conducting a set of sensitivity assessments, determining the figures of operating parameters such as i) the energy to produce the cell; ii) solar-to-hydrogen efficiency (STH); and iii) lifetime. These parameters have been evaluated based on two impact categories: i) Global Warming Potential (GWP); and ii) fossil Abiotic Depletion Potentials (f-ADP). The mature water electrolysis was used for benchmarking in order to elucidate the target performance in which PEC technology could be positively implemented at large-scale. Efficiencies over 10% (STH) and 7 years of lifetime are compulsory in the coming developments to achieve a positive scaling-up.