Enhancing Solar-Driven CO₂ Reduction Reactions Using Broadband Plasmonic Absorbers

Photosynthesis is an eco-friendly process that converts sunlight energy into chemical energy, creating fuels and essential intermediates. Drawing inspiration from nature, nanostructured photocatalysis has become a prominent method for photochemical CO₂reduction reaction (CO₂RR), utilizing chemically modified nanoparticles and nanolithography techniques. Despite its potential, challenges such as reproducibility, high costs, and complexity hinder its broader application. In this work, we introduce a lithography-free plasmonic perfect absorber. This innovative approach features a sandwich structure with a variable-thickness TiO₂ gap layer (ranging from 0 to 15 nm) placed between gold nanoparticles (AuNPs) and Titanium Nitride (TiN). This structure is fabricated using mask-assisted e-beam evaporation, presenting a simpler, more cost-efficient alternative suitable for large-scale production. It exhibits dual-peak absorption, achieving 90% at wavelengths centered between 497-529 nm for the short wavelength peak and 628-644 nm for the long wavelength peak. The total absorption band spans an impressive 80% across 400-750 nm. FDTD calculations reveal a strong electromagnetic field within the TiO₂ layer, which enhances exciton generation. The gap plasmon resonance significantly boosts the photocatalytic efficiency for solar-driven CO₂RR,<br/>reaching rates as high as ~2000 μmol/g*h—six times higher than previous benchmarks. This structure not only facilitates scalable and reproducible photocatalysis but also paves the way for innovative fabrication techniques. We will also discuss the detailed working mechanism of this approach.