| Metadata | Details |
|---|
| Publication Date | 2024-04-24 |
| Journal | Advanced Science |
| Authors | Wenxin Guo, Jinlong Li, DongâFeng Chai, Dongxuan Guo, Guozhe Sui |
| Institutions | Qingdao University of Science and Technology, Zhejiang Wanli University |
| Citations | 31 |
| Analysis | Full AI Review Included |
- Novel Strategy: A liquid nitrogen (LN2) quenching strategy was engineered to induce rapid iron (Fe) active center coordination reconstruction within iron carbide (Fe3C) supported on biomass-derived N-doped porous carbon (NC).
- Material and Precursors: The optimal catalyst, Fe3C/NC-550, utilizes low-cost, earth-abundant biomass (chrysanthemum tea, elm seeds, corn leaves) as the carbon and nitrogen source, ensuring environmental friendliness and scalability.
- Structural Transformation: LN2 quenching generates a strong resultant force, changing the thermodynamic stability and inducing a phase transformation from Cohenite (Fe3C) to Iron Carbide (Fe3C), creating rich carbon vacancies.
- Bifunctional Performance: Fe3C/NC-550 exhibits outstanding activity for both the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) in 1.0 M KOH.
- Ultra-Low Overpotentials: Achieved an overpotential of 26.3 mV for HER (@ -10 mA cm-2) and 281.4 mV for OER (@ 10 mA cm-2).
- Overall Water Splitting (OWS): The full alkaline electrolyzer requires only 1.57 V to reach 10 mA cm-2, demonstrating high stability over 110 hours.
- Mechanism Confirmation: DFT calculations confirm that the coordination reconstruction optimizes the adsorption free energy of reaction intermediates, significantly boosting intrinsic electrocatalytic activity (ÎGH* = 0.21 eV).
| Parameter | Value | Unit | Context |
|---|
| Optimal Quenching Temperature | 550 | °C | Fe3C/NC-550 Synthesis |
| HER Overpotential (η) | 26.3 | mV | @ -10 mA cm-2 in 1.0 M KOH |
| OER Overpotential (η) | 281.4 | mV | @ 10 mA cm-2 in 1.0 M KOH |
| Overall Water Splitting (OWS) Voltage | 1.57 | V | @ 10 mA cm-2 in 1.0 M KOH |
| HER Tafel Slope | 83.3 | mV dec-1 | Fe3C/NC-550 (Lowest among samples) |
| OER Tafel Slope | 127.0 | mV dec-1 | Fe3C/NC-550 |
| HER Stability (i-t) | 168 | h | @ -10 mA cm-2 |
| OWS Stability (i-t) | 110 | h | @ 10 mA cm-2 |
| Ultrahigh Cooling Rate | 246-946 | °C s-1 | LN2 Quenching Process |
| BET Specific Surface Area | 319.9 | m2 g-1 | Fe3C/NC-550 |
| ECSA (Double-Layer Capacitance) | 23.9 | ”F cm-2 | Fe3C/NC-550 (Highest Active Site Density) |
| Fe3C Content (TG Analysis) | 10.2 | % | Fe3C/NC-550 |
| H Adsorption Free Energy (ÎGH*) | 0.21 | eV | DFT calculation (Near ideal 0 eV) |
| Fe-Fe Coordination Number | 3.96 ± 0.38 | N | Fe3C/NC-550 (EXAFS fitting) |
| Fe-C Coordination Number | 2.63 ± 0.19 | N | Fe3C/NC-550 (EXAFS fitting) |
- Iron Precursor Preparation: A C6H5FeO7 solution was prepared by dissolving FeCl3, NaHCO3, and C6H8O7 in deionized water.
- Biomass Loading: Chrysanthemum tea (5 g) was immersed in the C6H5FeO7 solution and subsequently dried. Other biomass sources (elm seeds, corn leaves, shaddock peel) were also tested successfully, confirming universality.
- High-Temperature Pyrolysis: The dried precursor was thermally treated at 750 °C for 10 minutes in a horizontal tube furnace under a continuous flow of mixed hydrogen and argon gases. This step formed the initial Fe3C/NC material (Cohenite phase).
- Liquid Nitrogen Quenching (LN2-Q): Immediately following the 750 °C calcination, the material was rapidly quenched in liquid nitrogen (-196 °C).
- Quenching Temperature Control: The surface high temperature (TQ) immediately prior to quenching was varied (50 °C to 750 °C). The optimal catalyst, Fe3C/NC-550, was obtained at TQ = 550 °C, which generated the necessary resultant force for coordination reconstruction and phase transition.
- Structural Analysis: The resulting materials were characterized using HRTEM, SAED, XRD (confirming phase shift from Cohenite to Iron Carbide), XPS/XANES/EXAFS (confirming Fe coordination reconstruction), and EPR (confirming rich carbon vacancies and optimal electron spin state).
- Green Hydrogen Generation: The primary application, utilizing the highly efficient and stable bifunctional catalyst (Fe3C/NC-550) in alkaline electrolyzers for large-scale, cost-effective hydrogen production.
- Renewable Energy Integration: Serving as a key component in power-to-gas systems, converting surplus renewable electricity into storable chemical energy (H2).
- Sustainable Catalyst Manufacturing: The synthesis method relies on abundant, low-cost biomass precursors, offering a scalable and environmentally friendly alternative to noble metal catalysts (Pt/IrO2).
- Advanced Electrocatalyst Design: The LN2 quenching strategy provides a novel, non-traditional method for precisely modulating metal active center coordination and inducing beneficial phase transitions, applicable to designing next-generation catalysts for various energy conversion systems.
View Original Abstract
Abstract In this work, a novel liquid nitrogen quenching strategy is engineered to fulfill iron active center coordination reconstruction within iron carbide (Fe 3 C) modified on biomassâderived nitrogenâdoped porous carbon (NC) for initiating rapid hydrogen and oxygen evolution, where the chrysanthemum tea (elm seeds, corn leaves, and shaddock peel, etc.) is treated as biomass carbon source within Fe 3 C and NC. Moreover, the original thermodynamic stability is changed through the corresponding force generated by liquid nitrogen quenching and the phase transformation is induced with rich carbon vacancies with the increasing instantaneous temperature drop amplitude. Noteworthy, the optimizing intermediate absorption/desorption is achieved by new phases, Fe coordination, and carbon vacancies. The Fe 3 C/NCâ550 (550 refers to quenching temperature) demonstrates outstanding overpotential for hydrogen evolution reaction (26.3 mV at â10 mA cm â2 ) and oxygen evolution reaction (281.4 mV at 10 mA cm â2 ), favorable overall water splitting activity (1.57 V at 10 mA cm â2 ). Density functional theory (DFT) calculations further confirm that liquid nitrogen quenching treatment can enhance the intrinsic electrocatalytic activity efficiently by optimizing the adsorption free energy of reaction intermediates. Overall, the above results authenticate that liquid nitrogen quenching strategy open up new possibilities for obtaining highly active electrocatalysts for the new generation of green energy conversion systems.