A donor-chromophore-catalyst assembly for solar CO₂ reduction

Area of Science:

• Materials Science
• Electrochemistry
• Photocatalysis

Background:

• Efficient conversion of carbon dioxide (CO2) into valuable products like carbon monoxide (CO) is crucial for sustainable energy solutions.
• Photocathode assemblies offer a promising route for solar-driven CO2 reduction, but often face challenges with efficiency and stability.
• Layer-by-layer assembly techniques provide a versatile platform for constructing complex functional materials for electrochemical applications.

Purpose of the Study:

• To design and characterize a novel photocathode assembly for the reduction of CO2 to CO.
• To investigate the role of specific components, such as electron donors and light absorbers, in enhancing the efficiency of CO2 reduction.
• To understand the electron transfer dynamics within the assembly under visible light irradiation.

Main Methods:

• Fabrication of a photocathode assembly on mesoporous NiO films using a layer-by-layer approach with Zr(iv)-phosphonate bridging units.
• Integration of a dianiline-based electron donor (DA), a ruthenium-based light absorber (RuCP2+), and a rhenium-based CO2 reduction catalyst (Re(i)).
• Characterization using photocurrent measurements, incident photon-to-current efficiency (IPCE), and nanosecond transient absorption spectroscopy.

Main Results:

• The assembled photocathode demonstrated visible light-driven CO2 reduction to CO in acetonitrile solution.
• A steady-state photocurrent density of 65 μA cm-2 was achieved under one sun illumination, with an IPCE of 1.9% at 450 nm.
• The presence of the dianiline donor significantly enhanced photocurrent by 8 times, highlighting its critical role in electron transfer.
• Transient absorption measurements confirmed sub-nanosecond formation of the RuCP+ intermediate and microsecond-scale back electron transfer competing with catalysis.

Conclusions:

• The developed NiO|-DA-RuCP2+-Re(i) photocathode assembly is effective for visible light-driven CO2 reduction to CO.
• The dianiline donor plays a vital role in facilitating efficient electron transfer from the excited light absorber to the catalyst.
• Understanding the electron transfer kinetics is key to optimizing future photocathode designs for enhanced CO2 conversion efficiency.