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Synergistic electronic interplay between CoFe single atom and nitrogen on 2D carbon boosts bifunctional oxygen redox in metal-air batteries

Summary

The work reports a dual-metallic single-atom electrocatalyst (CoFe-2DSA) on two-dimensional nitrogen-doped carbon, made by a molten salt–assisted pyrolysis route from a ZIF-type precursor, and evaluates it as a bifunctional oxygen electrocatalyst for metal–air battery cathodes. Density functional theory is used to relate graphitic versus pyridinic nitrogen motifs near Co–Fe dual-atom sites to charge transfer, intermediate binding, and computed oxygen reduction and evolution energetics, alongside electrochemical and zinc–air cell measurements.

Methods

  • Synthesis and experiments: CoFe-2DSA is derived from a 3D ZIF framework converted to a 2D bi-metallic single-atom catalyst on N-doped carbon (details in Supporting Information). Electrocatalytic oxygen reduction (ORR) and oxygen evolution (OER) are characterized, and zinc–air battery tests report power density, specific capacity, energy density, and long-term cycling.
  • Atomistic modeling: The study uses density functional theory to probe ORR/OER mechanisms on model Co–FeN\(_6\) ensembles with different combinations of nearby graphitic and pyridinic nitrogen, including cases with hydroxyl species at the bi-metallic bridge as in prior work. Nørskov-type thermochemical analysis (free-energy profiles at 0 V vs RHE, overpotentials from rate-limiting steps) is applied to compare configurations. The main text emphasizes trends in \(\Delta G\) for key steps (e.g., water formation step \(\Delta G_4\)) and assigns rate-limiting steps for different N motifs; exchange–correlation functional, plane-wave/PAW settings, k-mesh density, and DFT–D3-style dispersion (if any) are specified in the Supporting Information rather than duplicated in this note—see SI tables/figures for exact reaction pathways and energies/barriers used in the free-energy property model.

Findings

  • CoFe-2DSA delivers strong bifunctional performance in the experiments quoted in the article: ORR half-wave potential \(E_{1/2} \approx 0.886\) V vs RHE and OER overpotential \(\eta \approx 290\) mV at 10 mA cm\(^{-2}\), with a small overall ORR/OER voltage gap \(\Delta V \approx 0.634\) V relative to a Pt–Ru benchmark discussed in the paper.
  • In zinc–air battery testing, the catalyst is reported to reach about 229.6 mW cm\(^{-2}\) power density, 811.5 mA h g\(^{-1}\) specific capacity, and 997 W h kg\(^{-1}\) energy density, with multi-week cycling stability (on the order of 74 days / thousands of cycles as stated).
  • DFT indicates that graphitic nitrogen can strengthen metal–oxygenate coupling and improve charge transfer to Co–Fe sites, lowering the thermodynamic overpotential for the water-formation step in some models, whereas pyridinic nitrogen introduces sp\(^3\)-like defects that accumulate charge and can weaken metal–oxygenate binding and raise overpotentials. The relative amounts of these motifs shift which step is rate-limiting (e.g., \(\Delta G_4\) vs \(\Delta G_1\) for *OOH-related steps).

Limitations

  • Detailed exchange–correlation functional, basis set, and electronic-structure code settings are not fully reproduced in the main text reviewed here; quantitative DFT comparisons should use the Supporting Information and original tables.
  • Experimental catalyst structures are represented by idealized cluster models; real distributions of N types and Co/Fe coordination are more heterogeneous than the few configurations shown.

Relevance to group

Adri C. T. van Duin is a co-author; the study couples experimental electrochemistry with DFT-based interpretation of N–metal synergy on carbon for oxygen electrocatalysis.

Citations and evidence anchors

Reader notes (navigation)

  • Experimental synthesis and additional computational parameters: Supporting Information referenced in the article.