Floating perovskite-BiVO₄ devices for scalable solar fuel production

Photoelectrochemical (PEC) artificial leaves hold the potential to lower the costs of sustainable solar fuel production by integrating light harvesting and catalysis within one compact device. However, current deposition techniques limit their scalability¹, whereas fragile and heavy bulk materials can affect their transport and deployment. Here we demonstrate the fabrication of lightweight artificial leaves by employing thin, flexible substrates and carbonaceous protection layers. Lead halide perovskite photocathodes deposited onto indium tin oxide-coated polyethylene terephthalate achieved an activity of 4,266 µmol H₂ g^-1 h^-1 using a platinum catalyst, whereas photocathodes with a molecular Co catalyst for CO₂ reduction attained a high CO:H₂ selectivity of 7.2 under lower (0.1 sun) irradiation. The corresponding lightweight perovskite-BiVO₄ PEC devices showed unassisted solar-to-fuel efficiencies of 0.58% (H₂) and 0.053% (CO), respectively. Their potential for scalability is demonstrated by 100 cm² stand-alone artificial leaves, which sustained a comparable performance and stability (of approximately 24 h) to their 1.7 cm² counterparts. Bubbles formed under operation further enabled 30-100 mg cm^-2 devices to float, while lightweight reactors facilitated gas collection during outdoor testing on a river. This leaf-like PEC device bridges the gulf in weight between traditional solar fuel approaches, showcasing activities per gram comparable to those of photocatalytic suspensions and plant leaves. The presented lightweight, floating systems may enable open-water applications, thus avoiding competition with land use.