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 TiO₂ 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 H₂ evolution rate of 348 ± 108 µmol g^-1 h^-1 was achieved for TiO₂ + 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.