Tailoring a Poly(acrylic acid)-Based Hydrogel Protective Layer for Durable Photoelectrochemical Water Splitting in Acidic Media

Photoelectrochemical (PEC) water splitting offers a sustainable route for solar-to-hydrogen conversion, yet the limited durability of photoelectrodes due to photocorrosion and catalyst degradation remains a challenge. Herein, we present a novel strategy to design a poly(acrylic acid) (PAAC)-based hydrogel protective layer with tunable physical and mechanical properties achieved by incorporating NaCl and polyethylene glycol (PEG). Na+ reorganizes the hydrogen-bonding network of water, leading to compact chain packing and enlarged pores, while PEG forms hydrogen bonds with PAAC, maintaining network flexibility and elasticity. This cooperative effect yields robust pore architecture, featuring enlarged pores and thickened pore walls with elasticity and fatigue resistance retained. When integrated with Sb2(S,Se)3 photocathodes, the hydrogel enables stable operation for 220 h in an acidic electrolyte (0.1 M H2SO4), facilitating gas bubble release and mitigating device degradation. This study highlights the potential of hydrogel engineering to extend the operating lifetime of PEC systems, advancing durable green hydrogen production.