Artificial Leaf for Solar-Driven Ammonia Conversion at Milligram-Scale Using Triple Junction III-V Photoelectrode.

Area of Science:

• Materials Science
• Electrochemistry
• Renewable Energy

Background:

• The Haber-Bosch process, while crucial for ammonia production, is energy-intensive and relies on fossil fuels.
• There is a critical need for sustainable and energy-efficient methods for ammonia synthesis.
• Biological nitrogen fixation and photosynthesis offer natural models for efficient chemical conversion.

Purpose of the Study:

• To develop a monolithic artificial leaf for solar-driven ammonia production at ambient conditions.
• To create a photoelectrochemical (PEC) device that mimics natural processes for nitrogen fixation.
• To achieve high ammonia production rates and energy conversion efficiencies using renewable energy.

Main Methods:

• Fabrication of a monolithic artificial leaf device using a triple junction (3J) InGaP/GaAs/Ge cell.
• Integration of a gold (Au) layer as the catalytic site for nitrogen fixation using photogenerated electrons.
• Assembly of a two-electrode photoelectrochemical system, later enhanced with a nickel (Ni) foil anode for oxygen evolution reaction (OER).

Main Results:

• The Au/Ti/3J InGaP/GaAs/Ge photoelectrochemical device demonstrated efficient ammonia production without external potential.
• At 0.2 sunlight intensity, a solar-to-ammonia (STA) conversion efficiency of 1.11% and a Faradaic efficiency of 28.9% were achieved.
• The integrated device achieved an ammonia production rate of 8.5 µg cm⁻² h at 1.5 sunlight intensity, with a 3x3 cm device producing 1.0039 mg ammonia over 36 hours.

Conclusions:

• The developed artificial leaf successfully converts solar energy directly into chemical energy for ammonia generation.
• This approach provides an environmentally friendly and energy-saving alternative to conventional ammonia synthesis methods.
• The device demonstrates potential for scalable and sustainable ammonia production using sunlight.