Cation-Coordinated Inner-Sphere CO₂ Electroreduction at Au-Water Interfaces.

Area of Science:

• Electrochemistry
• Computational Chemistry
• Materials Science

Background:

• Electrochemical CO2 reduction (CO2RR) is vital for clean energy, but its mechanism, particularly the role of electrolyte ions, remains unclear.
• Alkali metal cations' influence on CO2RR at interfaces is controversial, with a complete free energy diagram lacking.
• Understanding these factors is crucial for optimizing CO2RR efficiency.

Purpose of the Study:

• To systematically investigate the mechanism of CO2RR at Au-water interfaces.
• To elucidate the specific role of potassium (K+) cations in CO2 activation and selectivity.
• To derive a comprehensive free energy diagram for CO2RR and the competing hydrogen evolution reaction (HER).

Main Methods:

• Ab initio molecular dynamics (AIMD) simulations.
• Slow-growth sampling integrated with AIMD (SG-AIMD) for accurate free energy calculations.
• Computational modeling of electrochemical interfaces.

Main Results:

• CO2RR is facile at the inner-sphere interface with K+ cations, showing a low free energy barrier of 0.66 eV for CO2 activation.
• Interfacial K+ cations inhibit the competitive HER by inducing a kinetic blockage effect, raising the Volmer step barrier to 1.27 eV.
• A comprehensive free energy diagram illustrating the thermodynamics and kinetics of CO2RR and HER was successfully derived.

Conclusions:

• Potassium cations play a critical role in enhancing CO2 electroreduction performance.
• K+ cations facilitate CO2 adsorption and activation while simultaneously suppressing the hydrogen evolution reaction.
• The findings provide crucial mechanistic insights for designing efficient CO2RR electrocatalysts.