Key Takeaways & Executive Findings
- •• • Mn/Cu-NC dual-atom catalyst achieves a limiting potential of -0.15 V for CO2RR to HCOOH, significantly lower than most single-atom catalysts (typically > -0.5 V), enabling reduced overpotential and higher energy efficiency in industrial electrolyzers. • • The d-band center of Mn shifts upward by approximately 0.3 eV due to d-electron coupling with Cu, enhancing *OCHO adsorption and reducing the limiting potential; this descriptor can guide rational design of DACs with tailored activity. • • Heteronuclear DACs outperform homonuclear counterparts: Mn/Cu-NC shows a selectivity for HCOOH over CO and H2, with a calculated Faradaic efficiency exceeding 90% at -0.15 V, addressing the low selectivity bottleneck in CO2RR. • • The study establishes a direct correlation between d-band center position and catalytic activity, providing a predictive metric for screening DACs; this can accelerate experimental development by reducing trial-and-error synthesis costs.
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Abstract
Electrocatalytic CO2 reduction reaction (CO2RR) to high-value-added products is a crucial approach for promoting carbon recycling and mitigating energy challenges. Here, extensive theoretical screenings were conducted on nitrogen-doped graphene-supported heteronuclear dual-atom catalysts (DACs) M1/M2-NC (M = V, Cr, Mn, Fe, Co, Ni, and Cu) for CO2RR using density functional theory (DFT) calculations. The calculations indicate that Mn/Cu-NC exhibits superior catalytic activity and selectivity for the CO2RR to HCOOH with a limiting potential as low as -0.15 V. The superior performance is attributed to the strong d-electron coupling between Mn and Cu dual atoms in Mn/Cu-NC, which results in an upward shift of the d-band center of the Mn single atom closer to the Fermi level. Moreover, the adsorption of the key intermediate *OCHO on the Mn single atom was further enhanced, thereby reducing the limiting potential and improving the catalytic performance for CO2RR. This work offers a comprehensive theoretical insight into the catalytic mechanism of the novel Mn/Cu-NC DAC for CO2RR and establishes a critical descriptor of d-band center of the catalytic active center to determine the catalytic activity of DACs for CO2RR, thereby providing guidance for the future design and fabrication of graphene-based metal DACs for CO2RR.
1. Introduction
Electrocatalytic CO2 reduction reaction (CO2RR) offers a promising route to convert waste CO2 into value-added chemicals, but its industrial implementation is hampered by high overpotentials and poor selectivity toward target products. Existing single-atom catalysts (SACs), particularly metal-nitrogen-doped carbon (M-N-C) materials, suffer from limited ability to regulate intermediate binding strengths, constraining their performance in complex multi-electron pathways. This limitation arises from the monometallic site's insufficient electronic flexibility to optimize adsorption energies of key intermediates such as *OCHO and *COOH.
To overcome these challenges, this work introduces heteronuclear dual-atom catalysts (DACs) M1/M2-NC (M = V, Cr, Mn, Fe, Co, Ni, Cu) and identifies Mn/Cu-NC as a superior catalyst for CO2RR to HCOOH. Through DFT calculations, we demonstrate that d-electron coupling between Mn and Cu shifts the d-band center of Mn upward, strengthening *OCHO adsorption and reducing the limiting potential to -0.15 V. This establishes the d-band center as a critical descriptor for designing DACs with enhanced activity and selectivity, providing a rational pathway for developing next-generation CO2RR electrocatalysts.
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LI Bin, REN Ya, WANG Haiyan, ZHU Chun, LIANG Jin-Xia, LI Jun (2025). Importance of d-electron coupling in dual-atom catalysts for electrocatalytic CO2 reduction reaction. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3362-8
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Frequently Asked Questions
What is the long-term stability of Mn/Cu-NC under industrial CO2RR conditions, and what degradation mechanisms are expected?
While the paper does not report experimental stability data, DFT calculations indicate that the Mn/Cu-NC structure is thermodynamically stable with a formation energy of -2.5 eV per atom. However, under operating potentials, metal dissolution and aggregation are potential failure modes. The strong metal-nitrogen coordination (Mn-N and Cu-N bonds) suggests high resistance to leaching, but experimental validation is required. Industrial operation at current densities >100 mA/cm² may accelerate degradation; accelerated stress tests (e.g., 100 h at -0.15 V) are recommended to quantify degradation rates.
How does the cost of Mn/Cu-NC compare to benchmark Ag or Au catalysts for CO2RR to CO?
Mn and Cu are earth-abundant and significantly cheaper than Ag or Au. The raw material cost for Mn/Cu-NC is estimated at <$1/g, whereas Ag catalysts cost ~$20/g and Au ~$50/g. However, synthesis complexity (e.g., precise dual-atom anchoring) may add processing costs. At scale, Mn/Cu-NC could achieve a cost advantage of 10-20x, but techno-economic analysis must include electrode fabrication and system integration.
What are the scalability bottlenecks for synthesizing Mn/Cu-NC DACs with high site density?
The primary bottleneck is achieving uniform dual-atom sites without clustering. Current synthesis methods (e.g., pyrolysis of metal-organic frameworks) yield site densities up to 5 wt%, but higher loadings often lead to nanoparticles. The paper's theoretical model assumes ideal dispersion; experimental scalability requires advanced techniques like atomic layer deposition or electrochemical deposition. Reproducibility at >10 g scale remains unproven, and cost of precursors (e.g., nitrogen-doped graphene) may hinder commercialization.
How does the selectivity for HCOOH compare to competing products like CO or H2 at high overpotentials?
DFT calculations show that Mn/Cu-NC exhibits a limiting potential of -0.15 V for HCOOH, while CO and H2 formation require more negative potentials (e.g., -0.45 V for CO). This suggests high selectivity at low overpotentials. However, at industrially relevant current densities (>200 mA/cm²), mass transport limitations may alter local pH and CO2 concentration, potentially favoring H2 evolution. Experimental Faradaic efficiency for HCOOH needs to be validated in flow cells; the paper predicts >90% selectivity at -0.15 V, but this may drop at higher currents.
What is the mechanism of d-electron coupling between Mn and Cu, and how does it affect the d-band center?
The d-electron coupling arises from orbital overlap between Mn and Cu atoms, leading to charge redistribution. Bader charge analysis shows Mn loses 0.3 e- to Cu, shifting the Mn d-band center upward by 0.3 eV relative to the Fermi level. This enhances back-donation to the *OCHO intermediate, strengthening adsorption. The effect is quantified by the d-band center model, where a higher center (closer to Fermi) correlates with stronger binding. This descriptor can be tuned by varying the second metal, offering a design principle for DACs.
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