Plasmonic photocatalysis applied to solar fuels

Area of Science:

• Materials Science
• Photocatalysis
• Renewable Energy

Background:

• Plasmonic systems offer strategic applications, including solar energy conversion to chemical fuels using metal nanoparticles (M NPs) and semiconductors (SC).
• A key limitation is inefficient hot electron transfer from M NPs to SCs when their localized surface plasmon resonance (LSPR) and absorption spectra do not match, due to the Schottky barrier.
• Understanding and overcoming this interfacial limitation is crucial for enhancing photocatalytic efficiency.

Purpose of the Study:

• To investigate the catalytic efficiency of gold nanoparticles (Au NP) supported on titanium dioxide (TiO2) for the photoreduction of carbon dioxide (CO2) with water (H2O) into methane (CH4).
• To explore the influence of Au NP size, TiO2 surface area, and thermal treatments on photocatalytic activity and selectivity.
• To elucidate the role of gold as a co-catalyst and recombination sites, and to quantify the contribution of plasmon-induced processes.

Main Methods:

• Preparation of 1 wt% Au/TiO2-UV100 using a NaBH4-protected 3 nm gold sol.
• Photocatalytic reduction of CO2 with H2O under solar and visible-only irradiation.
• Systematic tuning of Au NP size and TiO2 surface area through thermal treatments.
• Analysis of metal dispersion, accessible Au-TiO2 interface, NP density, and SC crystallinity.
• Investigation of surface hydroxylation and its impact on performance.

Main Results:

• The optimized 1 wt% Au/TiO2-UV100 system achieved efficient photoreduction of CO2 and H2O into CH4 with a CH4 vs. H2 selectivity of 63% under solar irradiation.
• Tuning Au NP size and TiO2 surface area highlighted the critical role of metal dispersion and the Au-TiO2 perimeter interface.
• Gold was shown to act as both a co-catalyst and a recombination site for charge carriers, with plasmon-induced processes contributing up to 20% of solar activity.
• Enhanced plasmon-based contribution was observed with larger Au NP size and higher SC support crystallinity.
• Pre-calcining TiO2-UV100 at 450 °C minimized surface hydroxylation, yielding an optimal system with 100% methane selectivity in the hot electron process.

Conclusions:

• Optimized gold nanoparticle size, dispersion, and interface with the semiconductor support are critical for efficient solar fuel production.
• The study demonstrates a high methane selectivity (100%) in the hot electron process, showcasing the potential of plasmonic systems for CO2 photoreduction.
• Minimizing surface hydroxylation while maintaining high surface area in the semiconductor support is key to achieving superior photocatalytic performance.