Harnessing Pyridinic N Vacancy Defect in Microporous Structures to Induce the Pre‐Adsorption of Oxygen and Boost Oxygen Reduction Reaction Kinetics
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-07-30 |
| Journal | Angewandte Chemie International Edition |
| Authors | Binbin Jia, Xuan Xie, Jie Lin, Huiqing Wang, Pengfei Hu |
| Institutions | Northwest Normal University, Beihang University |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research details the synthesis and mechanistic validation of a highly efficient Iron single-atom catalyst (Fe-Nv-C SAC) for the Oxygen Reduction Reaction (ORR), leveraging engineered pyridinic N vacancy defects.
- Core Innovation: A Fe single-atom catalyst was developed using a template-assisted strategy combined with NH3 etching, resulting in abundant pyridinic N vacancy defects (Fe-Nv-C SAC) within a high surface area microporous carbon structure.
- Performance Benchmark: The Fe-Nv-C SAC achieved an exceptional half-wave potential (E1/2) of 0.902 V (vs. RHE), significantly surpassing commercial 20% Pt/C (0.863 V).
- Kinetic Enhancement: The catalyst demonstrated superior kinetics, achieving a kinetic current density (Jk) of 45.95 mA cm-2 at 0.85 V, which is approximately eight times greater than commercial Pt/C.
- Mechanistic Discovery (Pre-Adsorption): The pyridinic N vacancies facilitate the pre-adsorption of O2 molecules, a phenomenon previously only speculated theoretically, and validated here using in situ FTIR spectroscopy.
- Electronic Tuning: DFT calculations confirmed that O2 pre-adsorption shifts the d-band center of the central Fe atom away from the Fermi level, which effectively weakens the adsorption strength of the *OH intermediate.
- Device Reliability: When used as an air cathode in a Zinc-Air Battery (ZAB), the catalyst delivered a high maximum power density (248.8 mW cm-2) and exhibited remarkable long-term stability, maintaining performance for over 500 hours.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Half-Wave Potential (E1/2) | 0.902 | V (vs. RHE) | Fe-Nv-C SAC ORR activity |
| Onset Potential (Eonset) | 1.01 | V (vs. RHE) | Fe-Nv-C SAC ORR activity |
| Kinetic Current Density (Jk) | 45.95 | mA cm-2 | Fe-Nv-C SAC (at 0.85 V) |
| Tafel Slope | 72.1 | mV dec-1 | Fe-Nv-C SAC (indicates fast kinetics) |
| Maximum Power Density (ZAB) | 248.8 | mW cm-2 | Fe-Nv-C SAC based ZAB |
| Specific Capacity (ZAB) | 799.2 | mAh g-1 | Fe-Nv-C SAC based ZAB (at 10 mA cm-2) |
| ZAB Stability Duration | >500 | h | Continuous charge-discharge at 5 mA cm-2 |
| ORR Electron Transfer Number (n) | ~4 | - | Indicates highly selective 4-electron pathway |
| H2O2 Production | <10 | % | Excellent selectivity (at 0.2-0.8 V) |
| Specific Surface Area (BET) | 1073.6 | m2 g-1 | Fe-Nv-C SAC (Microporous structure) |
| O2 Adsorption Capacity | 11.29 | cm3 g-1 | Fe-Nv-C SAC |
| Electrochemical Surface Area (ECSA) | 28.7 | mF cm-2 | Fe-Nv-C SAC (Double-layer capacitance) |
| Rate-Determining Step Barrier | 0.51 | eV | DFT calculated barrier for *OH desorption (FeN4(O2)-VN model) |
| Fe Loading (ICP-OES) | 0.92 | wt% | Fe-Nv-C SAC sample |
| N Content (XPS) | 2.01 | % | Fe-Nv-C SAC sample |
| Pyridinic N Content (XPS) | 0.46 | % | Fe-Nv-C SAC sample |
| Fe Coordination Number (EXAFS) | 3.8 | - | Fe single atom coordination in Fe-Nv-C SAC |
Key Methodologies
Section titled “Key Methodologies”The Fe-Nv-C SAC was synthesized using a combined template-assisted and ammonia etching approach to maximize defect density and microporosity.
- Precursor Synthesis: Polyaniline (PANI), Iron(III) acetylacetonate (Fe(acac)3), and NaCl (as a hard template) were combined and ball-milled to ensure intimate mixing and encapsulation (Fe-PAIN/NaCl).
- Pyrolysis: The mixture underwent high-temperature pyrolysis under an inert atmosphere (Ar/NH3). The NH3 gas flow was critical, reacting preferentially with pyridinic N atoms at the carbon edge to create abundant pyridinic N vacancy defects (VN).
- Purification: The resulting material was subjected to template removal (washing) and acid treatment to remove the NaCl template and any non-single-atom Fe species, ensuring atomic dispersion.
- Structural and Chemical Analysis:
- Fe Single Atom Confirmation: Aberration-corrected HAADF-STEM, EXAFS, and XRD confirmed the atomic dispersion of Fe and the absence of metallic Fe or Fe compound clusters.
- Defect Characterization: XPS N 1s spectra quantified the lower pyridinic N content in Fe-Nv-C SAC compared to the control (Fe-N-C SAC), confirming successful vacancy induction.
- Microporosity: N2 adsorption-desorption isotherms confirmed the significantly increased specific surface area (1073.6 m2 g-1) and microporosity of the Fe-Nv-C SAC.
- Mechanistic Validation:
- In situ FTIR Spectroscopy: Used to monitor the adsorption of O2 (*O2 peak at 1449 cm-1) and H2O (*OH peak at 1637 cm-1) during the ORR process, providing experimental evidence for enhanced O2 pre-adsorption and hydrophilicity.
- DFT Calculations: Employed to model the FeN4(O2)-VN active site, calculate the Gibbs free energy diagrams, and determine the d-band center position relative to the Fermi level, confirming that O2 pre-adsorption weakens *OH binding.
- Device Testing: The catalyst was integrated into a rechargeable aqueous Zinc-Air Battery (ZAB) and tested for OCV, polarization, specific capacity, and long-term galvanostatic charge-discharge stability.
Commercial Applications
Section titled “Commercial Applications”The development of highly active, non-precious metal ORR catalysts is critical for advancing several clean energy technologies.
- Zinc-Air Batteries (ZABs): The primary application, leveraging the catalyst’s high power density (248.8 mW cm-2) and exceptional stability (>500 h) to create high-performance, low-cost energy storage devices.
- Fuel Cells (Alkaline): The superior ORR kinetics and high methanol tolerance make this material highly suitable for use as a cathode catalyst in alkaline fuel cells.
- Portable Power Sources: The robust ZAB performance is ideal for powering small electronic devices, including light-emitting diode screens and mini electric fans, as demonstrated in the study.
- Electrocatalysis: General applications requiring efficient, non-Pt group metal catalysts for oxygen reduction, such as in various electrochemical synthesis processes.
- Defect Engineering: The methodology provides a proven strategy for engineering specific vacancy defects (pyridinic N vacancies) in carbon matrices to tune the electronic structure of single-atom active sites, applicable across various heterogeneous catalysis fields.
View Original Abstract
Abstract Defect structures within the carbon matrix play a crucial role in enhancing the oxygen reduction reaction (ORR) activity of Fe single atom and nitrogen‐doped catalysts (Fe‐N‐C SACs). However, overlooking the O 2 pre‐adsorption process induced by defective structures hampers the precise identification of active sites and the investigation of the reaction mechanism in Fe‐N‐C SACs. Hence, we report a Fe SAC with abundant pyridinic N vacancy defects in microporous structures (Fe‐N v ‐C SAC) and propose a synergistic effect between pyridinic N vacancy defects and O 2 molecules that promotes the kinetics of ORR. The developed Fe‐N v ‐C SAC demonstrates exceptional ORR performance, exhibiting superior mass activity and turnover frequency compared to conventional Fe‐N‐C SACs. The in situ Fourier transform infrared spectroscopy (FTIR) and theoretical calculations indicate that pyridinic N vacancy defects in microporous structures facilitate pre‐adsorption of O 2 molecules results in the d‐band centers of central Fe atoms shifting away from the fermi level. This shift weakens the adsorption strength of *OH species, thereby facilitating the kinetic process of ORR. This work addresses a critical gap in the field of electrocatalysis by providing the experimental validation of pre‐adsorption of O 2 molecules on Fe single‐atom catalysts, a phenomenon previously only speculated through theoretical calculations.