【Frontiers in HaiChuan Chemical Technology】Recent discovery by a team from Shanghai Jiao Tong University offers a revolutionary technical approach for the large-scale production of green ammonia

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The latest research results from Li Jun’s team at the Transformative Molecular Frontiers Science Center at Shanghai Jiao Tong University have been published online in the top-tier journal Science. The research team reported for the first time a new system for the steady-state electrochemical synthesis of ammonia under normal temperature and pressure in continuous flow conditions, featuring a high current density of 100 mA cm-2 and a high energy efficiency of 21%. This achievement provides a revolutionary technical pathway for the large-scale production of green ammonia. The traditional Haber-Bosch process for ammonia synthesis relies on high temperatures and pressures (400–500°C, 10–30 MPa) as well as fossil fuels, accounting for approximately 1% of global CO2 emissions. Against the backdrop of the \"dual carbon\" goals, lithium-mediated electrochemical reduction of nitrogen to produce ammonia offers a new approach for efficient ammonia synthesis, with the key challenges being to improve reaction selectivity and accelerate mass transfer rates. This process relies on the solid electrolyte interphase (SEI) layer at the electrode surface to regulate lithium ion transport, but existing SEI layers suffer from drawbacks such as low ionic conductivity and high desolvation barriers, which lead to shrinkage of the reaction interface and intensified hydrogen evolution side reactions at high current densities. Despite progress made through optimizing electrode design and electrolyte formulations, the ammonia current density remains limited to 8 mA cm-2. Although high-pressure intermittent electrolysis can improve ion migration, it results in a significant increase in system energy consumption, with an energy efficiency of only 3%, making continuous production difficult to achieve. The lack of lithium ion conductivity in the SEI layer and the absence of a dynamic equilibrium mechanism have become key bottlenecks restricting the development of continuous-flow lithium-mediated ammonia synthesis technology. An original breakthrough has led to the creation of an ion-gradient transmission interface. The core challenge in the technology for synthesizing ammonia through lithium-mediated nitrogen reduction is the low ionic conductivity of the SEI layer, which hinders the transport of lithium ions at high current densities. To overcome this bottleneck, the research team innovatively designed a functionally layered hybrid SEI structure: an outer layer with low ion binding energy was created to facilitate the desolvation of lithium ions, while efficient lithium ion transport was achieved in the inner layer rich in ion-conducting domains. This design successfully increased the lithium ion flux by two orders of magnitude, enabling stable operation at a high current density of 100 mA cm-2 in a continuous flow reaction system. It is worth noting that in traditional electrolysis systems, the reaction interface shrinks sharply above 8 mA cm-2 due to the depletion of lithium ions in the SEI layer, whereas the new hybrid SEI structure effectively maintains the stability of the reaction interface, resulting in a significant improvement in the current-ammonia conversion efficiency. This breakthrough provides a key material design strategy for the development of efficient lithium-mediated ammonia synthesis technology. Figure 1. Analysis of the ion transport model in the lithium-mediated electroreduction of nitrogen system and its various solid electrolyte interphase (SEI) films. By analyzing the three-layered structure of precise ion channels, a new regulatory mechanism based on a \"desolvation-transport-catalysis\" cascade was established for the first time. After successfully constructing a SEI with a desolvation-diffusion layered architecture (DDLA), the research team used cryo-transmission electron microscopy combined with synchrotron radiation characterization techniques to determine that this DDLA consists of three precisely arranged inorganic phases: the outermost layer is a LiF layer, the middle layer is an Li2CO3 ion-conducting channel, and the innermost layer is a Li3N interface layer in contact with the cathode (with crystal plane spacings of 2.00 Å, 2.85 Å, and 3.13 Å respectively). Structural depth analysis reveals that in DDLA, the LiF surface layer accelerates the desolvation of lithium ions due to its low binding energy, while the Li2CO3 intermediate layer forms a three-dimensional ion penetration network. Synchrotron X-ray spectroscopy confirmed that this hierarchical structure establishes a continuous ion transport gradient on the 10–20 nanometer scale. It is particularly noteworthy that the symmetrically distributed Li3N domains identified within DDLA form molecular-level contact with the electrolyte interface, providing specific active sites for nitrogen reduction. These structural features explain the principle by which the DDLA electrode enables efficient lithium-mediated nitrogen reduction for ammonia synthesis at high current densities – the Li2CO3 channels increase the lithium ion flux by 100 times that of conventional homogeneous SEI systems, while the LiF/Li3N heterojunction significantly suppresses the hydrogen evolution side reaction. These findings not only reveal the cascade regulation mechanism of ion transport at the electrode-electrolyte interface, but the hierarchical ion transport mechanism also provides clear interface engineering principles for designing next-generation electrodes for efficient ammonia synthesis. It enables the efficient synthesis of ammonia at room temperature and pressure, opening up a new pathway for distributed ammonia production driven by renewable energy. Additionally, theoretical calculations reveal that DDLA possesses unique advantages in terms of ion transport kinetics: its surface LiF layer facilitates the release of lithium ions due to a low desolvation energy of 0.67 eV, while the Li2CO3 intermediate layer only needs to overcome a migration energy barrier of 0.60 eV, offering significant kinetic advantages over conventional homogeneous SEI systems (with a desolvation energy barrier of 0.73 eV and a migration energy barrier of 1.07 eV). This discovery not only explains the underlying reason for the high ionic conductivity of DDLA electrodes, but also establishes the central role of the \"desolvation-transmission-catalysis\" ternary mechanism in the efficient ammonia synthesis reaction. This synergistic stabilization effect provides a new paradigm for designing highly stable electrolytic interfaces. This study verified the theoretical predictions using a flow electrolytic cell system, achieving 98% Faradaic efficiency and 21% energy efficiency for the first time at room temperature and pressure under a current density of 100 mA cm-2, along with stability for 50 hours of continuous operation. It provides a theoretical and experimental foundation for the development of distributed ammonia synthesis technologies powered by renewable energy. These findings are applicable not only to the field of electrochemical nitrogen fixation; the ion transport regulation mechanisms they reveal also hold guiding significance for the development of new energy devices such as metal-air batteries and solid electrolyte batteries. Associate Professor Li Jun from the Center for Transformative Molecular Frontier Sciences at Shanghai Jiao Tong University and Professor Cheng Tao from Soochow University serve as corresponding authors of the paper. Zhang Qiang, a postdoctoral researcher at the Center for Frontier Science on Transformative Molecules, Li Huamin, a visiting doctoral student at the same center, Yu Peiping, a doctoral student at Soochow University, and Liu Pengyu, a doctoral student at the Center for Frontier Science on Transformative Molecules, are the first authors of the paper. This work is supported by projects such as the **Key Research and Development Program**, the National Natural Science Foundation, the National Key Laboratory for the Creation of Chemical-Biological Synergistic Materials, the Special Fund for Basic Scientific Research in Central Universities funded by the Ministry of Education, and the Shanghai Basic Research Special Zone Program.