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[Display omitted] • Novel strategy of bimetallic MOFs for enhanced PAAS is designed. • The enhanced PAAS is ascribed to the improved mass transfer in MOFs. • Sustainable NH 3 production rate achieves 77.5 μmol g−1·min−1 in 36 h or ∼ 30 cycles. • Hypothetical zero-carbon ammonia plant exhibits notable competitiveness. Plasma-assisted ammonia synthesis (PAAS) can produce ammonia using highly energetic, electronically excited nitrogen and Hydrogen radicals at low temperatures and atmospheric pressure, which has been regarded as a prospective alternative to the Haber − Bosch process. PAAS can exclusively use renewable power (solar, wind, etc.) to achieve green, decentralized and efficient ammonia synthesis. However, current catalysts for PAAS are suffering from low efficiency, poor stability and cyclability. Herein, we demonstrate a one-step hydrothermal synthesis of Ni-Co bimetallic metal–organic frameworks (MOFs) for PAAS. Attributed to the amplified gas transport capability and bimetallic coupling, the Ni-Co-MOF exhibits significantly improved PAAS performance: 88.21 μmol g−1·min−1, above 30 % increase over 5 wt% Ni/Al 2 O 3. The high stability of Ni-Co-MOF under the harsh electric field enables its durable performance (36 h) and excellent cyclability (24 cycles). Finally, to determine the viability of PAAS for industrial applications, we construct a hypothetical zero-carbon ammonia plant using only renewable energy sources, and the outcomes indicate that PAAS has significant competitiveness for future ammonia production. [ABSTRACT FROM AUTHOR]

• A novel stepwise Li-mediated electrochemical nitrogen reduction (Li-NRR) was developed. • The decomposition of solid-electrolyte interphase was revealed by decoupling the continuous Li-NRR. • Zn exhibited fastest electron transfer and Li+ diffusion, demonstrating best Li-NRR performance. • The proportion of active lithium was demonstrated to influence the Faraday efficiency. • LiCl generated in protonation process was found to enhance the system stability and facilitate the recycling of lithium. The lithium-mediated electrochemical nitrogen reduction reaction (Li-NRR) is a sustainable route for green NH 3 synthesis. It accelerates the N 2 reduction by reacting the inert N ≡ N with active Li metal. However, the study on the mechanism of the Li-NRR process remains limited. Herein, a novel stepwise Li-NRR system is established to separately optimize the major steps of Li-NRR: lithium-ion reduction, lithium nitridation, and Li 3 N protonation. It is revealed that during the Solid Electrolyte Interface (SEI) decomposition, the carbon chains in organic species become shorter, and Li x BF y is converted to LiF, which is similar to the continuous Li-NRR. Contrary to the continuous Li-NRR, the O/C ratio decreases as the SEI decomposes due to the absence of ethanol. Commercial Cu, Ni, and Zn are employed as cathodes in the experiments at various currents. The highest Faraday efficiency of 33.2 % and ammonia yield rate of 1404.5 μg h−1 cm−2 are achieved on Zn electrode owing to its superior electron transfer and enhanced Li+ diffusion than those of Cu and Ni. The current has also been found to affect Faraday efficiency through the portion of active lithium in coulomb efficiency experiments. Moreover, the LiCl generated in protonation process is found to facilitate lithium cycling. [ABSTRACT FROM AUTHOR]

Chemical looping ammonia synthesis (CLAS) is promising to achieve decentralized ammonia synthesis under ambient pressure. Here, we develop a highly selective composite nitrogen carrier for efficient CLAS based on transition metals (TMs=Co, Ni, Fe) decorated chromium nitride (CrN). Systematic studies indicate that the pristine CrN is extremely inert: only 4.5% lattice nitrogen can be consumed in reacting with H 2 (700 °C, 1 bar). Upon loading cobalt, the composite nitrogen carrier achieves lattice nitrogen conversion of 50.7% and ammonia selectivity up to 98.1%. Furthermore, Co-CrN exhibits excellent CLAS performance, attaining an average ammonia production rate of 466.1 μmol g−1 h−1 in 12 chemical loopings, which is ∼10 times that of the pristine CrN. Theoretical calculations reveal that the nitrogen vacancies generated in hydrogenation play a crucial role as activation centers for N 2 fixation through a Mars–van Krevelen mechanism. This work provides a novel strategy to optimize nitrogen carriers for enhanced CLAS. [Display omitted] • CLAS mediated by Cr-based nitrogen carriers was reported for the first time. • Novel strategy in designing synergistic nitrogen carriers with dual active sites. • Controlled conversion rate of lattice-N by 50.7% and high NH 3 selectivity at 98.1%. • Sustainable NH 3 production rate achieved 466.1 μmol g−1 h−1 in more than 12 cycles. • Reduced reaction energy barrier was verified in DFT calculations. [ABSTRACT FROM AUTHOR]

Chemical looping ammonia production (CLAP) technology provides additional freedom for the optimization of operating conditions via the strategy of stepwise reactions, which is promising to achieve green ammonia synthesis under mild conditions. Mn-based nitrogen carriers are ideal redox materials by virtue of their moderate thermodynamic properties and abundant crystalline phases, but their performance of hydrogenation in CLAP is still limited by the low reactivity. Herein, a series of Ni-Mn-N composite nitrogen carriers with different Ni/Mn ratios were prepared, and the effect of Ni doping on the performance of NH 3 production was investigated at atmospheric pressure. The nitrogen carriers modified with low level of Ni (<20 wt%) showed high activity and selectivity of hydrogenation, and the effective conversion of lattice nitrogen in 80Mn20Ni-N reached 36.1% at 750 °C, which was 15.7% higher than the undoped 100Mn-N. The introduction of low level of Ni can simultaneously enhance the bulk migration and interfacial reaction of lattice nitrogen and achieve the optimal kinetic matching between the both processes, thus promoting the activity and selectivity of lattice nitrogen converted to NH 3. This study presents new insights into the design of composite nitrogen carriers to enhance ammonia production in CLAP. • Ni-Mn-N composite nitrogen carriers were developed for chemical looping ammonia production. • The activity and selectivity of hydrogenation can be promoted by low level of Ni doping. • Ni dopants enhanced the bulk migration and interfacial reaction of lattice N. • Low level of Ni can achieve the optimal kinetic matching between the both processes. [ABSTRACT FROM AUTHOR]