In situ hydrogen production in all-level-humidity air: integrating atmospheric water harvesting with photocatalysis†

H₂ production from air holds great promise as a sustainable method for green energy harvesting. However, its widespread adoption faces challenges in realizing mobile, distributed, community-managed, off-grid in situ H₂ production systems. Here, we report a bilayer nanofibrillated cellulose composite gel incorporating lithium chloride hygroscopic salt and a supported SrTiO₃:Al photocatalyst (denoted as NLS), designed specifically for in situ photocatalytic splitting of atmospheric water to produce H₂, using only naturally occurring moisture and sunlight. The NLS gel features a self-supply of atmospheric water, spectral splitting for efficient solar energy delivery and complementary utilization, instantaneous H₂ evolution, and stable catalyst immobilization. As a result, the NLS bilayer gel successfully achieves in situ H₂ production in full-range-humidity environments, demonstrating a hygroscopicity of 4.26 g_H2O g_sorbent⁻¹ and an H₂ production activity of 65.45 μmol h⁻¹ in a 90% relative humidity environment, achieving a solar-to-hydrogen efficiency of up to 0.3%. This work represents a promising step towards realizing in situ H₂ production from air across varying humidity levels, independent of geographical constraints.