Solar-Driven Ammonia Synthesis over a Silver-Only Antenna-Reactor Catalyst

Area of Science:

• Materials Science
• Catalysis
• Renewable Energy

Background:

• Photocatalytic ammonia synthesis presents a sustainable alternative to the energy-intensive Haber-Bosch process.
• Current methods suffer from low solar-to-ammonia (STA) efficiency, limiting their practical application.
• Silver (Ag) is typically considered inert for ammonia synthesis under these conditions.

Purpose of the Study:

• To develop a highly efficient sunlight-driven photocatalyst for ammonia synthesis.
• To investigate the role of plasmonic effects in enhancing catalytic activity.
• To overcome the limitations of low STA efficiency in current photocatalytic systems.

Main Methods:

• Fabrication of a plasmonic antenna-reactor catalyst using 0.1 wt% Ag deposited on a honeycomb anodic aluminum oxide (AAO) plate.
• Utilized a photocatalytic reactor design incorporating Ag "antennas" and "reactors" for light trapping and near-field concentration.
• Employed density functional theory (DFT) calculations and experimental validation under simulated and natural sunlight.

Main Results:

• Achieved a high metal-normalized rate of 5.6 × 10^-3 s^-1 under concentrated natural sunlight (∼4 suns), outperforming industrial Fe.
• Demonstrated sustained ammonia production of 159 mmol g_Ag^-1 h^-1 for 200 hours under simulated sunlight.
• Reported a STA of 0.149% and an apparent quantum yield (AQE) of 1.34% at 575 nm.

Conclusions:

• The developed Ag-based antenna-reactor catalyst significantly enhances photocatalytic ammonia synthesis efficiency.
• Plasmonic effects, particularly near-field enhancement by Ag antennas, are crucial for activating N₂ and H₂.
• The study overturns the notion of silver's inertness, revealing its potential in photocatalytic ammonia production.