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An artificial leaf mimicking the function of a natural leaf has recently attracted significant attention due to its minimal space requirement and low cost compared to wired photoelectrochemical and photovoltaic-electrochemical systems for solar hydrogen production. However, it remains a challenge to achieve a practical-size solar water-splitting device that can fulfill the criteria of a solar-to-hydrogen conversion efficiency above 10%, long-term durability, and scalability. Here, we develop 1 cm 2 perovskite-based photoelectrodes using a defect-less, chlorine-doped formamidinium lead triiodide as photo-absorber and ultraviolet-insensitive tin oxide as an electron transport layers. This device is encapsulated using electrocatalyst-deposited nickel foils, which demonstrates high photocurrent density and high stability for 140 h. Ultimately, we fabricate a scalable mini-module-sized artificial leaf (16 cm 2 ) consisting of a side-by-side/parallel configuration of photoanode and photocathode architecture integrated with a 4 × 4 array of 1 cm 2 photoelectrodes, which maintains a stable ‘module-level’ solar-to-hydrogen efficiency of 11.2% in an unbiased solar water-splitting under 1-sun illumination. Here the authors demonstrate a scalable and durable minimodule size artificial leaf with a solar-to-hydrogen efficiency of >10% using a metal-halide perovskite-based photoelectrodes encapsulated with metal foil deposited co-catalysts.

For practical photoelectrochemical water splitting to become a reality, highly efficient, stable and scalable photoelectrodes are essential. However, meeting these requirements simultaneously is a difficult task, as improvements in one area can often lead to deteriotation in others. Here, addressing this challenge, we report a formamidinium lead triiodide (FAPbI 3 ) perovskite-based photoanode that is encapsulated by an Ni foil/NiFeOOH electrocatalyst, which demonstrates promising efficiency, stability and scalability. This metal-encapsulated FAPbI 3 photoanode records a photocurrent density of 22.8 mA cm −2 at 1.23 V RHE (where V RHE is voltage with respect to the reversible hydrogen electrode) and shows excellent stability for 3 days under simulated 1-sun illumination. We also construct an all-perovskite-based unassisted photoelectrochemical water splitting system by connecting the photoanode with a same-size FAPbI 3 solar cell in parallel, which records a solar-to-hydrogen efficiency of 9.8%. Finally, we demonstrate the scale-up of these Ni-encapsulated FAPbI 3 photoanodes into mini-modules up to 123 cm 2 in size, recording a solar-to-hydrogen efficiency of 8.5%. Ideal photoelectrochemical systems for hydrogen production should be highly efficient, stable and scalable. Here the authors report that a perovskite-based system with promising efficiency and stability can be scaled to cells of several square centimetres in area as well as formed into mini-modules with overall area >100 cm 2 .

The intent of this chapter is to provide a basic overview of recent advances in graphene based hybrid nanostructures including their preparation, properties and potential applications in various field. The development of graphene based functional materials, has shown their tremendous interest in areas of science, engineering and technology. These materials include graphene supported inorganic nanomaterials and films, graphene-metal decorated nanostructures, Core/shell structures of nanocarbon-graphene and graphene doped polymer hybrid nanocomposites etc. They have been prepared by various methods like chemical vapor deposition of hydrocarbon on metal surface, liquid phase exfoliation of graphite, chemical reduction of GO, silver mirror reaction, catalysis, in-situ hydroxylation and sono sol-gel route, respectively. The attractive properties of graphene and their derivatives filled with metal nanoparticles (e.g. Au, Ag, Pd, Pt, Ni, and Cu) have made them ideal templates. Graphene and their derivatives have also been decorated with various semiconductor nanomaterials (e.g. metal oxides and dioxides, metal sulfides). These metal decorated graphene nanostructures can be useful as functional hybrid nanomaterials in electronics, optics, and energy based products like solar cells, fuel cells, Li-ion batteries and supercapacitors, ion exchange and molecular adsorption.