Engineering Bilayer Tandem Catalysts on Si-Based Photocathodes for High-performance CO₂ Reduction to Produce Methane

Area of Science:

• Electrochemistry and catalysis
• Renewable energy and sustainable fuels
• Materials science for energy conversion

Background:

• Solar-driven photoelectrochemical (PEC) reduction of carbon dioxide (CO2) to hydrocarbon fuels is a key strategy for sustainable energy.
• Current limitations include poor light absorption and slow reaction kinetics, hindering efficient methane (CH4) production.
• Enhanced selectivity and catalytic rates are crucial for practical application of CO2 reduction technologies.

Purpose of the Study:

• To develop and investigate tandem catalysts on photocathodes for improved CO2 reduction selectivity.
• To enhance the conversion of CO2 to methane (CH4) using a designed photoelectrochemical system.
• To elucidate the reaction mechanisms underlying the tandem catalytic process.

Main Methods:

• Fabrication of a p-type Si photocathode with a pyramid-structured surface.
• Immobilization of Cu/Ag-Cu bilayer tandem catalysts on the photocathode.
• Characterization using operando Raman and synchrotron-radiation Fourier transform infrared spectroscopy.
• Computational analysis via Density Functional Theory (DFT).

Main Results:

• Achieved a high CO2-to-CH4 conversion selectivity of 60.2 ± 3.4% at a current density of -32.9 ± 1.9 mA cm−2.
• Identified the roles of Ag and Cu nanoparticles in catalyzing intermediate formation (*CO and *H species).
• Demonstrated sequential reaction steps: CO2 reduction to *CO, H2O dissociation to *H, *CO protonation to *CHO, and final CH4 production.

Conclusions:

• The tandem catalyst design effectively promotes sequential reactions for selective CO2 reduction to CH4.
• The synergistic effect of the catalyst layers significantly enhances photoelectrochemical performance.
• This approach provides a viable pathway for high-performance, selective solar fuel production from CO2.