Defect-Enhanced CO₂ Reduction Catalytic Performance in O-Terminated MXenes

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrochemical carbon dioxide reduction reaction (CO2 RR) offers a sustainable route for fuel and chemical production.
• Two-dimensional metal carbides and nitrides (MXenes) show promise as CO2 RR electrocatalysts due to unique intermediate coordination.
• Tuning MXene electronic and surface structures is crucial for improving CO2 RR turnover and selectivity.

Purpose of the Study:

• To investigate the impact of defect engineering, specifically transition metal and carbon/nitrogen vacancies, on CO2 RR over M2XO2-type MXenes.
• To explore the relationship between vacancy presence, intermediate binding, and catalytic performance.
• To identify a descriptor for predicting the catalytic activity of defective MXenes.

Main Methods:

• First-principles modeling simulations were employed to systematically study CO2 RR on various M2XO2-type MXenes with vacancies.
• Analysis of intermediate binding energies for fragment-type (*COOH, *CHO) and molecule-type (*HCOOH, *H2CO) intermediates.
• Electronic structure analysis, focusing on Fermi level shifts in the presence of vacancies.

Main Results:

• Defect engineering, particularly transition metal vacancies, strongly influences the binding of fragment-type intermediates, enabling overpotential tuning.
• Hf vacancies in Hf2NO2 MXene resulted in a low overpotential of 0.45 V for CO2 RR.
• Significant shifts in the MXene Fermi level correlate with vacancy presence and catalytic performance, suggesting it as a predictive descriptor.

Conclusions:

• Defect engineering is a viable strategy to enhance MXene electrocatalysts for CO2 RR.
• The Fermi level shift serves as an effective descriptor for rapidly predicting the catalytic performance of defective MXenes.
• This approach can accelerate catalyst discovery for CO2 conversion and other catalytic applications.