Activating Single-Atom Ni Site via First-Shell Si Modulation Boosts Oxygen Reduction Reaction.

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Atomically dispersed nitrogen-coordinated 3d transition-metal sites on carbon supports (M-NC) are promising for oxygen reduction reaction (ORR).
• Existing M-NC catalysts, like Fe-NC and Co-NC, suffer from poor durability due to Fenton reactions.
• There is a need for robust M-NC catalysts with improved stability for ORR applications.

Purpose of the Study:

• To develop a novel Si-doped Ni-NC catalyst (Ni-SiNC) with enhanced activity and stability for the oxygen reduction reaction (ORR).
• To elucidate the atomic structure and active sites of the Ni-SiNC catalyst.
• To evaluate the catalytic performance and durability of Ni-SiNC in alkaline media and Zn-air batteries.

Main Methods:

• Synthesis of Si-doped Ni-NC catalyst (Ni-SiNC).
• Characterization using X-ray absorption fine structure (XAFS) and aberration-corrected transmission electron microscopy (AC-TEM).
• Electrochemical testing for ORR activity and durability, including Zn-air battery performance.
• Density functional theory (DFT) calculations to understand the catalytic mechanism.

Main Results:

• The Ni-SiNC catalyst features single-atom Ni sites coordinated with one Si and three N atoms (Ni-Si1N3 moiety).
• Achieved a high half-wave potential (E1/2) of 0.866 V vs RHE for ORR.
• Demonstrated excellent long-term durability with only a 10 mV negative shift in E1/2 after 35,000 cycles in alkaline media.
• Validated performance in a Zn-air battery.

Conclusions:

• The Ni-Si1N3 moiety in the Si-doped Ni-NC catalyst is crucial for high ORR activity and stability.
• Ni-SiNC presents a promising alternative to Pt-based catalysts for ORR, addressing durability issues.
• The catalyst's stability and activity make it suitable for applications like Zn-air batteries.