Integrated Photoelectrochemical Systems for Scalable Water Splitting and CO₂ Reduction

Photoelectrochemical (PEC) systems hold the potential to lower the costs of sustainable solar fuel production by integrating light harvesting and catalysis within one compact device.^[1] However, current deposition techniques limit their scalability, while fragile and heavy bulk materials can affect their transport and deployment. Here, we first demonstrate the fabrication of lightweight artificial leaves by employing thin, flexible substrates and carbonaceous protection layers.^[2] Lead halide perovskite photocathodes deposited onto indium tin oxide coated polyethylene terephthalate achieve an activity of 4266 μmol H₂ g^-1 h^-1 using a platinum catalyst, whereas photocathodes with a molecular Co catalyst for CO₂ reduction attain a high CO:H₂ selectivity of 7.2 under a lower 0.1 sun irradiation. The corresponding lightweight perovskite-BiVO₄ PEC devices display unassisted solar-to-fuel efficiencies of 0.58% (H₂) and 0.053% (CO),respectively. Their potential for scalability is demonstrated by 100 cm² standalone artificial leaves, which sustain a comparable performance and stability of ≈24 h to their 1.7 cm² counterparts. Bubbles formed under operation further enable the 30-100 mg cm^-2 devices to float, while lightweight reactors facilitate gas collection during outdoor testing on a river. The leaf-like PEC device bridges the gulf in weight between traditional solar fuel approaches, showcasing activities per gram comparable to photocatalytic suspensions and plant leaves.^[2] The presented lightweight, floating systems are compatible with modern fabrication techniques,^[3] and may enable open water applications, while avoiding competition with land use. The carbonaceous protection layers and rational design principles are successfully applied to an underexplored BiOI light absorber, increasing the photocathode stability towards hydrogen evolution from minutes to months.^[4] Similar PEC systems approaching a m² size can take advantage of the modularity of artificial leaves,^[5] whereas thermoelectric generators can further bolster water splitting by utilizing waste heat to provide an additional Seebeck voltage.^[6,7]<br/> <br/>[1] Andrei, V.; Roh, I.; Yang, P. <i>Sci. Adv.</i> 2023, 9, eade9044.<br/>[2] Andrei, V.; Ucoski, G. M.; Pornrungroj, C.; Uswachoke, C.; Wang, Q.; Achilleos, D. S.; Kasap, H.; Sokol, K. P.; Jagt, R. A.; Lu, H.; Lawson, T.; Wagner, A.; Pike, S. D.; Wright, D. S.; Hoye, R. L. Z.; MacManus-Driscoll, J. L.; Joyce, H. J.; Friend, R. H.; Reisner, E., Nature 2022, 608, 518–522.<br/>[3] Sokol, K. P.; Andrei, V. Nat. Rev. Mater. 2022, 7, 251–253.<br/>[4] Andrei, V.; Jagt, R. A. et al. Nat. Mater. 2022, 21, 864–868.<br/>[5] European Commission; Directorate-General for Research; Innovation. Artificial photosynthesis : fuel from the sun : EIC Horizon Prize; Publications Office of the European Union, 2022. DOI: 10.2777/682437.<br/>[6] Andrei, V.; Bethke, K.; Rademann, K. Energy Environ. Sci. 2016, 9, 1528–1532.<br/>[7] Pornrungroj, C.; Andrei, V.; Reisner, E. J. Am. Chem. Soc. 2023, 145, 13709–13714.