Switching off Competing Hydrogen Formation in CO₂ Electroreduction via Substrate Defect Engineering.

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Carbon nanotubes (CNTs) are common supports for molecular electrocatalysts in CO2 reduction (CO2R).
• The exact nature of catalyst-support interactions, often attributed to π-π stacking, is not fully understood.
• Nickel phthalocyanine (NiPc) is a benchmark catalyst for CO2R.

Purpose of the Study:

• To investigate the immobilization mechanism of NiPc on CNTs.
• To understand how CNT defect density influences CO2R performance.
• To optimize CNTs for enhanced CO2R catalysis.

Main Methods:

• Theoretical simulations to model catalyst-support interactions.
• Operando X-ray absorption spectroscopy to study catalyst behavior under bias.
• Thermal graphitization to control CNT defect density.
• Electrochemical testing of NiPc/CNT catalysts for CO2R.

Main Results:

• NiPc preferentially anchors at CNT defect sites, not via uniform π-π stacking.
• CNTs with fewer defects, despite non-uniform NiPc distribution, show higher CO2R activity and CO selectivity.
• High defect densities distort NiPc symmetry under bias, reducing performance.
• Optimized CNT defects yield a NiPc/CNT catalyst with >16100:1 CO:H2 selectivity and 1072 s⁻¹ turnover frequency at -0.60 V.
• The optimized catalyst in a 100 cm² electrolyzer sustains 50 A with >95% CO selectivity at ≈3.5 V.

Conclusions:

• CNT defect engineering is a viable strategy to enhance molecular CO2R catalysts.
• Controlling CNT defect density is crucial for catalyst integrity and performance.
• Optimized NiPc/CNT catalysts show superior performance compared to state-of-the-art Ag-based systems.