Back-illuminated photoelectrochemical flow cell for efficient CO₂ reduction

Area of Science:

• Electrochemistry
• Materials Science
• Renewable Energy

Background:

• Photoelectrochemical (PEC) CO2 reduction flow cells offer a promising route for solar fuel production.
• Challenges exist in integrating narrow bandgap photoelectrodes and achieving high current densities for efficient CO2 reduction.
• Wide bandgap photoelectrodes limit efficient CO2 reduction, while opaque narrow bandgap photoelectrodes pose integration challenges in flow cells.

Purpose of the Study:

• To design and fabricate a back-illuminated silicon (Si) photoanode-promoted PEC flow cell for efficient CO2 reduction.
• To decouple illumination area and catalytic sites on the Si photoelectrode for enhanced performance.
• To achieve high solar-to-fuel conversion efficiencies for CO and C2+ products.

Main Methods:

• Fabrication of a back-illuminated Si photoanode.
• Effective passivation of defect states to achieve long minority carrier diffusion length.
• Integration into a PEC flow cell configuration for CO2 reduction reaction.

Main Results:

• Achieved a solar-to-fuel conversion efficiency of 2.42% for CO production with 90% Faradaic efficiency using Ag catalysts.
• Demonstrated CO2 to C2+ product conversion with 53% Faradaic efficiency and 0.29% solar-to-fuel efficiency using Cu catalysts.
• The developed Si photoelectrode design effectively decouples illumination and catalytic sites, surpassing substrate thickness limitations.

Conclusions:

• The back-illuminated Si photoanode design is effective for promoting PEC CO2 reduction in flow cells.
• This approach overcomes limitations of traditional photoelectrode configurations, enabling efficient solar fuel production.
• The study demonstrates a viable pathway for industrial-scale solar fuel generation through optimized PEC CO2 reduction.