Hydrogen From Simulated Seawater Using Long‐Term Stable and Cost‐Effective Plasmonic Photocatalysts

Generating hydrogen directly from seawater is an attractive feature for realizing large‐scale solar fuel production. Here, we present an effective photocatalyst design that not only considers solar light activity but also long‐term durability and optimized manufacturing costs. A series of stabilized bimetallic Au–Ag plasmonic “rainbow” nanoparticles were synthesized and grafted at low loadings onto TiO ₂ substrates, yielding strong visible‐light absorption and enhanced photocatalytic activity. To address the intrinsic instability of (plasmonic) metal nanoparticles in saline environments, two encapsulation strategies were investigated: insulating layer‐by‐layer (LbL) polyelectrolyte shells and conductive polyaniline (PANI) shells formed via in situ polymerization. In simulated seawater, a maximum H ₂ evolution rate of 348 ± 108 µmol g ⁻¹  h ⁻¹ was achieved for TiO ₂  + 2 wt% “rainbow” PANI‐stabilized nanoparticles. PANI‐stabilized plasmonic catalysts outperformed both bare and LbL‐coated samples while maintaining full activity even after 1 month of storage in the dark in simulated seawater. These results demonstrate that conductive polymer encapsulation effectively preserves plasmonic activity even in harsh media, offering a prospect toward durable and economically viable solar hydrogen production from simulated seawater.