Stabilizing calcium nitride for efficient, long- term electrochemical ammonia synthesis

• 成果类型: Article
• 署名作者: Goyal, Ishita; Isa, Hasiya Najmin; Gande, Vamsi Vikram; Chauhan, Rohit; Singh, Meenesh R.
• 署名单位: University of Illinois System; University of Illinois Chicago; University of Illinois Chicago Hospital
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2513960122
• 发表日期: 2025-12-23
• 页码: e2513960122
• 关键词: electrochemical N-2 reduction; electrochemical NH3 synthesis; Li mediated NH3 synthesis; Ca-mediated NH3 synthesis; ADSORBATE-ADSORBATE INTERACTIONS; nitrogen reduction; AMBIENT CONDITIONS; electrosynthesis

摘要

Electrochemical ammonia synthesis at ambient conditions via calcium-mediated nitrogen fixation holds considerable promise but is impeded by fundamental gaps such as poor gas-liquid interface stability, sluggish hydrogen oxidation reaction (HOR) kinetics, and instability of the critical intermediate calcium nitride. To systematically address these barriers, we i) introduced a high surface-area Ni-based anode specifically selected for enhancing HOR kinetics and minimizing solvent oxidation; ii) substituted the conventionally used tetrahydrofuran solvent with dimethoxyethane (DME) to significantly improve chemical stability; and iii) developed a tailored flow cell configuration to enhance gas-liquid mass transport and stabilize reaction intermediates. Employing in-situ Raman spectroscopy and X-ray photoelectron spectroscopy, we provided direct evidence of stabilized calcium nitride formation, elucidating the crucial roles of solvent stability and electrode composition in sustaining reactive intermediates. As a result of these combined innovations, our system demonstrates substantial performance improvements, achieving a Faradaic efficiency (FE) of 34.35 +/- 1.76% in short-term tests and sustaining similar to 20% FE over extended continuous operation (similar to 56 h). At elevated current densities, the improved gas-liquid interface stability enables robust ammonia production, reaching partial current densities of approximately 219 mA cm(-2) at similar to 29% FE. Isotope-labeling studies with N-15(2) confirmed the direct electroreduction of N-2, while kinetic analyses underscored the impact of anode material selection on HOR efficiency and overall electrochemical stability. These insights establish critical mechanistic understanding and clear design principles for future calcium-mediated electrochemical nitrogen fixation systems, enabling stable, efficient, and selective ammonia synthesis.