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Nitrate (NO3−), a nitrogen-containing pollutant, is prevalent in aqueous solutions, contributing to a range of environmental and health-related issues. The electrocatalytic reduction of NO3− holds promise as a sustainable approach to both eliminating NO3− and generating valuable ammonia (NH3). Nevertheless, the reduction reaction of NO3− (NO3−RR), involving 8-electron transfer process, is intricate, necessitating highly efficient electrocatalysts to facilitate the conversion of NO3− to NH3. In this study, Fedoped Co3O4 nanowire strutted three-dimensional (3D) pinewood-derived carbon (Fe-Co3O4/PC) is proposed as a high-efficiency NO3−RR electrocatalyst for NH3 production. Operating within 0.1 M NaOH containing NO3−, Fe-Co3O4/PC demonstrates exceptional performance, obtain an impressively large NH3 yield of 0.55 mmol·h−1·cm−2 and an exceptionally high Faradaic efficiency of 96.5% at −0.5 V, superior to its Co3O4/PC counterpart (0.2 mmol·h−1·cm−2, 73.3%). Furthermore, the study delves into the reaction mechanism of Fe-Co3O4 for NO3−RR through theoretical calculations. [ABSTRACT FROM AUTHOR]

[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]

Electrocatalytic nitrate (NO3−) reduction has emerged as an attractive dual-function strategy to produce ammonia (NH3) and simultaneously mitigate environmental issues. However, efficient electrocatalysts with high selectivity for NH3 synthesis are highly desired. In this work, we report the Co–NCNT nanohybrid as a highly active electrocatalyst towards NO3−-to-NH3 conversion. In 0.1 M NaOH solution containing 0.1 M NO3−, the Co–NCNT catalyst is capable of attaining a large NH3 yield of 5996 μg h−1 cm−2 and a high faradaic efficiency of 92% at −0.6 V versus reversible hydrogen electrode. Moreover, it displays excellent electrochemical stability. [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]

[Display omitted] • Facile co-precipitation method yields efficient Co-doped graphdiyne catalysts. • Co-doped graphdiyne enhances NH 3 decomposition (100% conversion at 550 ℃). • NH x dehydrogenation (x = 3) is the rate-determining step on Co-doped graphdiyne. Manufacturing hydrogen from ammonia decomposition is an efficient and promising approach for hydrogen utilization. However, its scalable application is significantly impeded by the requirements of precious metal ruthenium (Ru) as catalysts. Herein, we report a type of Co-doped graphdiyne catalyst for catalytically decomposing ammonia (NH 3) to generate H 2. The metal-doped graphdiyne catalysts were synthesized facilely using co-precipitation approach. The resultant composite catalysts significantly enhanced the reactivity and stability of ammonia decomposition. The Co-doped graphdiyne catalyst achieved nearly complete decomposition of ammonia at 550 ℃, and the conversion rate remained stable over 18 h of continuous reaction. The adsorption and decomposition of ammonia by Co-doped graphdiyne was studied by density functional theory (DFT) calculations. Nitrogen binding strength was used as a descriptor to elucidate the catalyst's activity and reaction kinetics, further supported by the reaction energy barrier. Our study highlights the tremendous potential of metal-doped graphdiyne catalysts for facile hydrogen production via NH 3 decomposition, enabling safe and scalable hydrogen utilization. [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]

[Display omitted] • A strategy to design metal-free catalyst for nitric oxide reduction is developed. • Molecular orbital theory and band theory are combined to study catalytic mechanism. • A particular C center -CN 2 active site on hBN-graphene interface is discovered. • The high-activity C center -CN 2 configuration is applicable to other 2D materials. Electrochemical reduction reaction of nitric oxide (NORR) to ammonia has been considered as a promising alternative to capturing and utilizing NO emitted from thermal-power plants. Various metal-containing catalysts have been proved to possess efficient catalytic activities for NORR, yet the attempt on metal-free NORR catalysts is quite limited. Herein, by employing first-principle calculations, we propose a novel strategy of designing metal-free NORR catalyst by introducing C center -CN 2 configuration into hexagonal boron nitride-graphene heterostructures (hBN-graphene). The hBN-graphene heterostructures demonstrate excellent NORR activity, achieving a fairly low limiting potential of −0.22 V. The superior NORR activity is ascribed to the introduced unique configuration at the modified hBN-graphene interface. Moreover, the hBN-graphene heterostructures can efficiently suppress hydrogen evolution—the main competitive reaction. The ab-initio molecular dynamic simulations indicate that hBN-graphene heterostructures can retain considerable thermal stability. Our work opens an avenue to design metal-free catalysts for NORR by modulating the interface in two-dimensional heterostructures. [ABSTRACT FROM AUTHOR]

Ammonia is a prospective fuel for hydrogen storage and production, but its application is limited by the high cost of the catalysts (Ru, etc.) to decompose NH 3. Decomposing ammonia using non-precious Ni as catalysts can therefore improve its prospects to produce hydrogen. This work proposes several Ni/MgAl 2 O 4 with the support properties tuned and investigates the support effect on the catalytic performance. Ni/MgAl 2 O 4 -LDH shows high NH 3 conversion (∼88.7%) and H 2 production rate (∼1782.6 mmol g−1 h−1) at 30,000 L. kg−1 h−1 and 600 °C, which is 1.68 times as large as that of Ni/MgAl 2 O 4 -MM. The performance remains stable over 30 h. The characterizations manifest that the high specific surface area of Ni/MgAl 2 O 4 -LDH can introduce highly dispersed Ni on the surface. Kinetics analysis implies promoted NH 3 decomposition reaction and alleviated H 2 poisoning for Ni/MgAl 2 O 4 -LDH. A roughly linear relationship is obtained by fitting the curves of dispersed Ni on the surface vs the reaction orders regarding H 2 and NH 3. This indicates that enhanced NH 3 decomposition performance can be ascribed to the strengthened NH 3 decomposition reaction and weakened H 2 poisoning by the highly dispersed Ni on the MgAl 2 O 4 -LDH surface. This work provides an opportunity to develop highly active and cost-effective catalysts to produce hydrogen via NH 3 decomposition. [Display omitted] • NH 3 decomposition over Ni-based catalyst is support-dependent. • Support effect of Ni/MgAl 2 O 4 -LDH improves NH 3 decomposition to H 2. • A new strategy to tune the catalytic activity for NH 3 decomposition is proposed. [ABSTRACT FROM AUTHOR]

Ru-doped TiO 2 nanoribbon array supported on Ti plate acts as an efficient catalyst for NH 3 synthesis via electrochemical NO 2 − reduction, obtaining an ultra-large NH 3 yield of 1.56 mmol h−1 cm−2 and a super-high Faradaic efficiency of 98.9%. [Display omitted] • Ru doping is shown as an effective strategy to boost NO 2 −-to-NH 3 conversion over TiO 2 nanoribbon array supported on Ti plate. • Ru–TiO 2 /TP achieves an ultra-large NH 3 yield of 1.56 mmol h−1 cm−2 and a super-high Faradaic efficiency of 98.9% with long-term electrolytic durability. • DFT calculations reveal the catalytic mechanism of NO 2 –RR on Ru–TiO 2. Electrochemical reduction of nitrite (NO 2 –) not only removes NO 2 – contaminant but also produces high-added value ammonia (NH 3). This process, however, needs efficient and selective catalysts for NO 2 −-to-NH 3 conversion. In this study, Ruthenium doped titanium dioxide nanoribbon array supported on Ti plate (Ru–TiO 2 /TP) is proposed as an efficient electrocatalyst for the reduction of NO 2 − to NH 3. When operated in 0.1 M NaOH containing NO 2 –, such Ru–TiO 2 /TP achieves an ultra-large NH 3 yield of 1.56 mmol h−1 cm−2 and a super-high Faradaic efficiency of 98.9%, superior to its TiO 2 /TP counterpart (0.46 mmol h−1 cm−2, 74.1%). Furthermore, the reaction mechanism is studied by theoretical calculation. [ABSTRACT FROM AUTHOR]

To achieve carbon neutrality by 2050 is an emergent challenge facing the world in order to tackle the climate change. Ammonia, being one of the most promising media for hydrogen storage, is regarded as an ideal carbon-free energy carrier. Moreover, ammonia exhibits critical superiority in long-distance transportation and storage, which are the essential bottlenecks yet to be solved for hydrogen. Furthermore, the electrochemical synthesis of 'green ammonia' from renewable energy and its efficient utilization to generate electricity can be well integrated with reversible solid oxide cell (R-SOC), which is a promising technology that provides a potential route to decarbonize a number of applications dependent on fossil fuels. For electrochemical ammonia synthesis using both solid oxide electrolytic cell (SOEC) and proton ceramic electrolytic cell (PCEC), the state-of-the-art ammonia production rate can reach 8–9 × 10−9 mol s−1 cm−2 at temperatures as low as 400 °C. For direct ammonia conversion using solid oxide fuel cell (SOFC) and proton ceramic fuel cell (PCFC), the best power density reported is comparable to that of the hydrogen fuel cells, reaching >1.2 W/cm2. This review aims to provide a comprehensive summary of the latest advances in both aspects: electrochemical ammonia synthesis (also known as electrochemical Haber-Bosch Process) and direct ammonia fuel cells. The process mechanisms of two major types of electrochemical routes based on oxygen ion conductor and proton conductor have been reviewed, with a discussion on material development and stability issues. • Ammonia is regarded as an ideal carbon-free energy carrier. • Electrochemical ammonia synthesis and utilization can be well integrated with R-SOCs. • State-of-the-art progress in material system has been summarized. • Mechanism and progress of electrochemical ammonia synthesis have been presented. • Latest progress in direct ammonia fuel cell (both SOFC and PCFC) are described in detail. [ABSTRACT FROM AUTHOR]