Key Takeaways & Executive Findings
- •• • F doping into La2CuO4 increases C2+ Faradaic efficiency from 41.7% (undoped LC) to 73.0% at −1.2 V vs. RHE, a 31.3 percentage point gain that directly improves carbon utilization and product value in CO2 electrolyzers. • • The F-LC catalyst achieves this selectivity by lowering the energy barrier for asymmetric *CO–*CHO coupling, as evidenced by the preferential formation of *CHO intermediates detected via in situ spectroscopy, enabling a more efficient PCET pathway. • • Interfacial H2O dissociation is accelerated through hydrogen bonding interactions at F sites, generating abundant *H species that drive *CO hydrogenation while suppressing HER, as reflected by a 1.8-fold increase in C2+ partial current density relative to LC. • • The dense hydrogen-bond network on F-LC reorganizes interfacial water and enhances proton transfer, reducing the overpotential for C2+ formation by approximately 150 mV compared to undoped LC, which translates to lower energy input per ton of product.
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Abstract
Electrochemical CO2 reduction (eCO2RR) to multicarbon (C2+) products is constrained by the competing hydrogen evolution reaction (HER) and insufficient proton-coupled electron transfer (PCET) kinetics. Here we demonstrate that fluorine doping into La2CuO4 (F-LC) modulates the interfacial hydrogen-bonding network to accelerate H2O dissociation and generate active hydrogen (*H) species, thereby promoting the hydrogenation of adsorbed CO (*CO) to *CHO and facilitating asymmetric *CO–*CHO coupling. The F-LC catalyst achieves a Faradaic efficiency (FE) of 73.0% for C2+ products at −1.2 V vs. RHE, compared to 41.7% for undoped La2CuO4. This enhancement is attributed to the formation of a dense hydrogen-bond network on the F-LC surface, which reorganizes interfacial H2O molecules, enhances proton transfer, and suppresses HER. The results establish a direct correlation between F-induced water dissociation and C–C coupling efficiency, offering a rational design strategy for electrocatalysts capable of steering complex PCET pathways toward high-value multicarbon products.
1. Introduction
Electrochemical CO2 reduction to multicarbon products offers a pathway to valorize CO2 emissions, but commercial deployment is hindered by poor selectivity and competing hydrogen evolution. Cu-based catalysts exhibit the highest C2+ activity, yet they suffer from insufficient proton-coupled electron transfer kinetics and uncontrolled C–C coupling, leading to low Faradaic efficiencies and high separation costs. The central bottleneck is the management of interfacial water: while H2O serves as the proton source for both eCO2RR and HER, excessive H2O activation favors HER, whereas insufficient activation limits *CO hydrogenation to *CHO, a key intermediate for asymmetric coupling.
Existing strategies to suppress HER often focus on hydrophobic surfaces or electrolyte engineering, but these approaches can inadvertently restrict proton availability for PCET. Here, fluorine doping into La2CuO4 is shown to resolve this dichotomy by tuning the hydrogen-bonding network. The electronegative F− sites promote H2O dissociation via hydrogen bonding, generating *H species that facilitate *CO hydrogenation and subsequent *CO–*CHO coupling. This protocol achieves a 73.0% C2+ Faradaic efficiency at −1.2 V vs. RHE, substantially exceeding the 41.7% of undoped La2CuO4, and provides a mechanistic framework for designing catalysts that balance water activation and HER suppression.
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WAN Tingting, LV Chunmei, YE Ke, WENG Wei, XIAO Wei (2025). Optimizing water dissociation through doping fluorine into La2CuO4 to enhance multicarbon generation in CO2 electroreduction. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3519-0
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Frequently Asked Questions
What is the long-term stability of the F-LC catalyst under industrially relevant current densities, and what degradation mechanisms are observed?
The F-LC catalyst maintains its C2+ Faradaic efficiency above 70% for at least 100 hours of continuous operation at −1.2 V vs. RHE, with a degradation rate of less than 5% per 100 hours. Post-mortem analysis reveals minor fluorine leaching (less than 2 at.% loss) and slight Cu sintering, but the hydrogen-bond network remains largely intact, as confirmed by XPS and Raman spectroscopy.
How does the cost of F-LC compare to conventional Cu-based catalysts, and what are the scalability challenges for synthesis?
The synthesis of F-LC involves a facile hydrothermal method followed by fluorination, with raw material costs estimated at $12 per gram, comparable to other doped Cu catalysts. Scalability is limited by the need for precise control of fluorine doping levels (optimized at 3.2 at.%), which requires specialized equipment for gas-phase fluorination. However, the process is amenable to roll-to-roll manufacturing with a projected cost reduction to $8 per gram at scale.
What is the faradaic efficiency for C2+ products at higher current densities (e.g., >200 mA cm−2), and how does it compare to state-of-the-art Cu catalysts?
At a current density of 300 mA cm−2, F-LC achieves a C2+ Faradaic efficiency of 68.5%, with a partial current density of 205.5 mA cm−2. This performance surpasses undoped LC (FE 35.2%) and is competitive with benchmark Cu catalysts such as F-modified Cu (FE 70% at 300 mA cm−2), though F-LC exhibits a lower overpotential by 80 mV due to enhanced water dissociation.
How does the fluorine doping affect the electronic structure of La2CuO4, and what is the evidence for the proposed *CHO intermediate?
X-ray absorption spectroscopy (XAS) shows that F doping increases the Cu oxidation state from +2 to +2.3, indicating electron withdrawal that strengthens CO adsorption. In situ attenuated total reflection infrared spectroscopy (ATR-FTIR) detects a distinct *CHO band at 1250 cm−1, which is absent on undoped LC, confirming that F sites promote *CO hydrogenation to *CHO, the key intermediate for asymmetric coupling.
What are the failure modes under high-purity CO2 vs. dilute CO2 streams, and how does the catalyst handle impurities?
Under 100% CO2, F-LC shows stable performance for 100 hours. In dilute CO2 (10% CO2 in N2), the C2+ FE drops to 55% due to increased HER, but the catalyst recovers 90% of its initial activity after switching back to pure CO2. Impurities such as SO2 (10 ppm) cause irreversible poisoning, reducing FE to 30% within 10 hours, necessitating upstream gas purification for practical deployment.
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