Chemically Cross-linked Conductive Network Hydrogel as Dual-Functional Layer Enabling Stable Solar Water Splitting

Photoelectrochemical (PEC) water splitting offers a promising solution for solar-to-hydrogen energy conversion. However, slow charge transfer and severe photocorrosion limit the activity and stability. To break the activity-stability trade-off, we developed a highly conductive and structurally stable three-dimensional (3D) porous network hydrogel (Gel) via cross-linking polyaniline (PANI) and poly(acrylic acid) (PAA). Functional groups within the Gel anchor metal ions, enabling the synthesis of a P(ANI-AA)-CoFe dual-functional layer, where CoFe is chemically bonded to the hydrogel network. The Gel-CoFe coupled with NiO hole transfer layer, was integrated onto semiconductor metal oxide (MO: TiO₂, Fe₂O₃, WO₃, and BiVO₄) arrays, forming Gel-CoFe/NiO/MO photoanodes. Especially, the P(ANI-AA)-CoFe/NiO/BiVO₄ photoanode achieves a high photocurrent density of 6.26 mA cm^-2 at 1.23 V vs RHE. Moreover, a large-scale P(ANI-AA)-CoFe/NiO/BiVO₄ system sustains a photocurrent of 27 mA with 500 h long-term operational stability at 1.1 V vs RHE, outperforming previously reported PEC systems. The porous 3D framework suppresses photocorrosion and facilitates the transport of reactive species, whereas the high conductivity and abundant active sites enhance interfacial charge mobility. This rationally designed hydrogel-catalyst dual-network establishes a universal and extendable paradigm overcoming durable activity-stability trade-off in PEC system.