Ultrasmall Nickel Nanoclusters Accelerating Protonation for Efficient CO₂ Electroreduction towards CO

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Proton-coupled electron transfer (PCET) is crucial for electrochemical CO2 reduction (CO2RR).
• The protonation step in PCET is often the kinetic bottleneck, limiting CO2RR efficiency.
• Modulating catalyst microstructures to accelerate protonation is a key strategy to improve CO2 to CO selectivity.

Purpose of the Study:

• To develop ultrasmall Ni nanocluster catalysts (Ni3─N─C) for enhanced CO2RR.
• To investigate the role of unique Ni coordination environments in sub-nanoclusters on catalytic performance.
• To elucidate the mechanism by which Ni3─N─C catalysts improve the rate-limiting protonation step.

Main Methods:

• One-step pyrolysis of Ni-containing precursors under H2 atmosphere to synthesize Ni3─N─C catalysts.
• Electrochemical characterization to evaluate CO2RR performance, including Faradaic efficiency (FECO) and overpotentials.
• Density functional theory (DFT) calculations to understand the reaction mechanism and energy barriers.
• In situ FTIR spectroscopy to confirm intermediate formation and reaction pathways.

Main Results:

• Ni3─N─C catalysts delivered >90% CO Faradaic efficiency across a wide potential range (-0.6 to -1.0 V vs RHE), with a peak of ~95% at -0.8 V.
• DFT calculations revealed that Ni3─N─C lowers the energy barrier for *COOH formation due to altered adsorption configurations.
• In situ FTIR confirmed accelerated *COOH formation on Ni3─N─C surfaces, validating the enhanced protonation step.

Conclusions:

• Ultrasmall Ni sub-nanoclusters (Ni3─N─C) effectively modulate PCET, accelerating the rate-limiting protonation step in CO2RR.
• The distinct local Ni coordination environments in Ni3─N─C are critical for enhancing CO2 to CO selectivity.
• This work establishes a rational design principle for nanocluster-based catalysts for efficient electrochemical CO2 reduction.