Proton Donors Induce a Differential Transport Effect for Selectivity toward Ammonia in Lithium-Mediated Nitrogen Reduction

In Situ Neutron Reflectometry Reveals the Interfacial Microenvironment Driving Electrochemical Ammonia Synthesis

Electrified interfaces are critical to the performance of energy systems and often demonstrate substantial complexity under operating conditions. A nanoscale understanding of the interfacial microenvironment, i.e., the solid-electrolyte interphase (SEI), in lithium-mediated nitrogen reduction (Li-N2R) is key for realizing efficient ammonia (NH3) production. Herein, we used time-resolved neutron reflectometry (NR) to observe SEI formation under Li-N2R conditions. We found that the LiBF4-based electrolyte provided a substantially more well-defined SEI layer than previous SEI NR interrogations that used LiClO4, highlighting the underlying chemistry that dictates electrolyte design and enabling new NR-based studies. Using in situ NR, we found that the LiBF4-derived SEI under Li-N2R conditions comprises a thick, diffuse outer layer and a thin, compact inner layer at low current cycling (<2 mA/cm2), revealing a structure which ex situ studies have not been able to probe. Increased current cycling and sustained current cycling led to the merging of the layers into a single-layer SEI. We used isotope contrast methods with d6-EtOH and d8-THF to drive time-resolved tracking of SEI growth at low current cycling, revealing that the proton donor modifies the inner layer, and the solvent modifies the outer layer. Li dendritic growth was observed in the absence of a proton donor. Neutron absorption also indicated the presence of boron in the SEI, underscoring the value of neutron-based interrogation. Our results inform Li-based systems and reaction microenvironments, and these methods can be applied broadly to interfacial energy technologies.

Revealing Mechanisms of Lithium-Mediated Nitrogen Reduction Reaction from First-Principles Simulations

Recently, lithium-mediated nitrogen reduction reaction (Li-NRR) in nonaqueous electrolytes has proven to be an environmentally friendly and feasible route for ammonia electrosynthesis, revealing tremendous economic and social advantages over the industrial Haber-Bosch process which consumes enormous fossil fuels and generates massive carbon dioxide emissions, and direct electrocatalytic nitrogen reduction reaction (NRR) which suffers from sluggish kinetics and poor faradaic efficiencies. However, reaction mechanisms of Li-NRR and the role of solid electrolyte interface (SEI) layer in activating N2 remain unclear, impeding its further development. Here, using electronic structure theory, we discover a nitridation-coupled reduction mechanism and a nitrogen cycling reduction mechanism on lithium and lithium nitride surfaces, respectively, which are major components of SEI in experimental characterization. Our work reveals divergent pathways in Li-NRR from conventional direct electrocatalytic NRR, highlights the role of surface reconstruction in improving reactivity, and sheds light on further enhancing efficiency of ammonia electrosynthesis.

Multivariate Approaches Boosting Lithium-Mediated Ammonia Electrosynthesis in Different Electrolytes

Ammonia electrosynthesis through the lithium-mediated approach has recently reached promising results towards high activity and selectivity in aprotic media, reaching high Faradaic efficiency (FE) values and NH3 production rates. To fasten the comprehension and optimization of the complex lithium-mediated nitrogen reduction system, for the first time a multivariate approach is proposed as a powerful tool to reduce the number of experiments in comparison with the classical one-factor-at-a-time approach. Doehlert design and surface response methodology are employed to optimize the electrolyte composition for a batch autoclaved cell. The method is validated with the common LiBF4 salt, and the correlations between the FE and the amount of lithium salt and ethanol as proton donor are elucidated, also discussing their impact on the solid electrolyte interphase (SEI) layer. Moreover, a new fluorinated salt is proposed (i.e., lithium difluoro(oxalate) borate (LiFOB)), taking inspiration from lithium batteries. This salt is chosen to tailor the SEI layer, with the aim of obtaining a bifunctional interfacial layer, both stable and permeable to N2, the latter being an essential characteristic for batch systems. The SEI layer composition is confirmed strategic and its tailoring with LiFOB boosts FE values.

The Development, Essence and Perspective of Nitrogen Reduction to Ammonia

Ammonia plays a pivotal role in agriculture and meanwhile holds promising potential as an energy vector for the hydrogen economy, where the nitrogen reduction to ammonia is a critical pathway for achieving sustainable development. Over the past hundred years, ammonia synthesis has undergone several breakthrough developments from Haber-Bosch process to photo/electro-catalysis and Li-mediated strategy, but still faces the challenges of low yield rate, selectivity and efficiency. Therefore, there is a pressing demand to develop efficient and green ammonia synthesis from nitrogen. This review summarizes the development of the nitrogen reduction to ammonia, highlighting six milestones during the whole journey. From the development direction, this work finds and extracts the essence of ammonia synthesis, that is the reaction pathways are affected by the energy barrier of reaction intermediates, which can be altered by proton sources, auxiliaries and catalysts. Then this work discusses the detailed overview of the significant development of proton source, auxiliaries and catalysts. Finally, based on the essence, the possible opportunities of ammonia synthesis from nitrogen reduction are presented, including the design of new ammonia synthesis pathways and efficient catalysts. The deep insight of nitrogen reduction to ammonia will provide a design guidance for efficient ammonia synthesis.

Localized High-Concentration Electrolyte in Li-Mediated Nitrogen Reduction for Ammonia Synthesis

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising green alternative to the Haber-Bosch process for ammonia synthesis. The solid electrolyte interphase (SEI) is crucial for high efficiency and stability, as it regulates reactant diffusion and suppresses side reactions. The SEI properties are greatly influenced by the Li+ ion solvation structure, which is controllable through electrolyte engineering. Although anion-derived SEI enhances selectivity and stability, it has typically been engineered using high-concentration electrolytes (HCEs), which face mass transfer, viscosity, and cost issues. In this study, a localized high-concentration electrolyte (LHCE) in the Li-NRR is first introduced, enabling the formation of anion-derived SEI in a low-concentration electrolyte (LCE) by enhancing the Li-anion coordination using an antisolvent. Among various antisolvents, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) achieves the highest ammonia Faradaic efficiency (73.6 ± 2.5%), more than double that of the LCE (34.3 ± 2.8%) and exceeding the HCE (56.0 ± 2.8%). Systematic calculations and experimental analyses show that the LHCE exhibits anion-rich solvation structures and forms thin, inorganic SEI. Moreover, the LHCE has advantages of low viscosity and high N2 solubility, which facilitate mass transport. This study suggests the application of LHCE as an effective electrolyte engineering strategy to enhance the Li-NRR efficiency.

Insight into Fluoride Additives to Enhance Ammonia Production from Lithium-Mediated Electrochemical Nitrogen Reduction Reaction

Demands for green ammonia production increase due to its application as a proton carrier, and recent achievements in electrochemical Li-mediated nitrogen reduction reactions (Li-NRRs) show promising reliability. Here, it is demonstrated that F-containing additives in the electrolyte improve ammonia production by modulating the solid electrolyte interphase (SEI). It is suggested that the anionic additives with low lowest unoccupied molecular orbital levels enhance efficiency by contributing to the formation of a conductive SEI incorporated with LiF. Specifically, as little as 0.3 wt.% of BF4 - additive to the electrolyte, the Faradaic efficiency (FE) for ammonia production is enhanced by over 15% compared to an additive-free electrolyte, achieving a high yield of 161 ± 3 nmol s-1 cm-2. The BF4 - additive exhibits advantages, with decreased overpotential and improved FE, compared to its use as the bulk electrolyte. The observation of the Li3N upper layer implies that active Li-NRR catalytic cycles are occurring on the outermost SEI, and density functional theory simulations propose that an SEI incorporated with LiF facilitates energy profiles for the protonation by adjusting the binding energies of the intermediates compared to bare copper. This study unlocks the potential of additives and offers insights into the SEIs for efficient Li-NRRs.

Regulating Interfacial Microenvironment in Aqueous Electrolyte via a N2 Filtering Membrane for Efficient Electrochemical Ammonia Synthesis

Electrochemical synthesis of ammonia (NH3) in aqueous electrolyte has long been suffered from poor nitrogen (N2) supply owing to its low solubility and sluggish diffusion kinetics. Therefore, creating a N2 rich microenvironment around catalyst surface may potentially improve the efficiency of nitrogen reduction reaction (NRR). Herein, a delicately designed N2 filtering membrane consisted of polydimethylsiloxane is covered on catalyst surface via superspreading. Because this membrane let the dissolved N2 molecules be accessible to the catalyst but block excess water, the designed N2 rich microenvironment over catalyst leads to an optimized Faradaic efficiency of 39.4% and an NH3 yield rate of 109.2 µg h-1 mg-1, which is superior to those of the most report metal-based catalysts for electrochemical NRR. This study offers alternative strategy for enhancing NRR performance.

Pathway toward Scalable Energy-Efficient Li-Mediated Ammonia Synthesis

Lithium-mediated ammonia synthesis (LiMAS) is an emerging electrochemical method for NH3 production, featuring a meticulous three-step process involving Li+ electrodeposition, Li nitridation, and Li3N protolysis. The essence lies in the electrodeposition of Li+, a critical phase demanding current oscillations to fortify the solid-electrolyte interface (SEI) and ensure voltage stability. This distinctive operational cadence orchestrates Li nitridation and Li3N protolysis, profoundly influencing the NH3 selectivity. Increasing N2 pressure enhances the NH3 faradaic efficiency (FE) up to 20 bar, beyond which proton availability controls selectivity between Li nitridation and Li3N protolysis. The proton donor, typically alcohols, is a key factor, with 1-butanol observed to yield the highest NH3 FE. Counterion in the Li salt is also observed to be significant, with larger anions (e.g., exemplified by BF4-) improving SEI stability, directly impacting LiMAS efficacy. Notably, we report a peak NH3 FE of ∼70% and an NH3 current density of ∼-100 mA/cm2 via a delicate balance of process conditions, encompassing N2 pressure, proton donor, Li salt, and their respective concentrations. In contrast to the recent literature, we find that the theoretical maximum energy efficiency of LiMAS hinges significantly on the proton source, with LiMAS utilizing H2O calculated to have a maximum achievable energy efficiency of 27.8%. Despite inherent challenges, a technoeconomic analysis suggests high-pressure LiMAS to be more feasible than both ambient LiMAS and a modified green Haber-Bosch process. Our analysis finds that, at a 100 mA/cm2 NH3 current density and a 6 V cell voltage, LiMAS delivers green NH3 at an all-inclusive cost of $456 per ton, significantly lower than conventional cost barriers. Our economic analysis underscores high-pressure LiMAS as a potentially transformative technology that may revolutionize large-scale NH3 production, paving the way for a sustainable future.

Phenol as proton shuttle and buffer for lithium-mediated ammonia electrosynthesis

Ammonia is a crucial component in the production of fertilizers and various nitrogen-based compounds. Now, the lithium-mediated nitrogen reduction reaction (Li-NRR) has emerged as a promising approach for ammonia synthesis at ambient conditions. The proton shuttle plays a critical role in the proton transfer process during Li-NRR. However, the structure-activity relationship and design principles for effective proton shuttles have not yet been established in practical Li-NRR systems. Here, we propose a general procedure for verifying a true proton shuttle and established design principles for effective proton shuttles. We systematically evaluate several classes of proton shuttles in a continuous-flow reactor with hydrogen oxidation at the anode. Among the tested proton shuttles, phenol exhibits the highest Faradaic efficiency of 72 ± 3% towards ammonia, surpassing that of ethanol, which has been commonly used so far. Experimental investigations including operando isotope-labelled mass spectrometry proved the proton-shuttling capability of phenol. Further mass transport modeling sheds light on the mechanism.

NH3 Electrosynthesis from N2 Molecules: Progresses, Challenges, and Future Perspectives

Green ammonia (NH3), made by using renewable electricity to split nearly limitless nitrogen (N2) molecules, is a vital platform molecule and an ideal fuel to drive the sustainable development of human society without carbon dioxide emission. The NH3 electrosynthesis field currently faces the dilemma of low yield rate and efficiency; however, decoupling the overlapping issues of this area and providing guidelines for its development directions are not trivial because it involves complex reaction process and multidisciplinary entries (for example, electrochemistry, catalysis, interfaces, processes, etc.). In this Perspective, we introduce a classification scheme for NH3 electrosynthesis based on the reaction process, namely, direct (N2 reduction reaction) and indirect electrosynthesis (Li-mediated/plasma-enabled NH3 electrosynthesis). This categorization allows us to finely decouple the complicated reaction pathways and identify the specific rate-determining steps/bottleneck issues for each synthesis approach such as N2 activation, H2 evolution side reaction, solid-electrolyte interphase engineering, plasma process, etc. We then present a detailed overview of the latest progresses on solving these core issues in terms of the whole electrochemical system covering the electrocatalysts, electrodes, electrolytes, electrolyzers, etc. Finally, we discuss the research focuses and the promising strategies for the development of NH3 electrosynthesis in the future with a multiscale perspective of atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes/interfaces, and macroscale electrolyzers/processes. It is expected that this Perspective will provide the readers with an in-depth understanding of the bottleneck issues and insightful guidance on designing the efficient NH3 electrosynthesis systems.

Extending Ring-Chain Coupling Empirical Law to Lithium-Mediated Electrochemical Ammonia Synthesis

With its efficient nitrogen fixation kinetics, electrochemical lithium-mediated nitrogen reduction reaction (LMNRR) holds promise for replacing Haber-Bosch process and realizing sustainable and green ammonia production. However, the general interface problem in lithium electrochemistry seriously impedes the further enhancement of LMNRR performance. Inspired by the development history of lithium battery electrolytes, here, we extend the ring-chain solvents coupling law to LMNRR system to rationally optimize the interface during the reaction process, achieving nearly a two-fold Faradaic efficiency up to 54.78±1.60 %. Systematic theoretical simulations and experimental analysis jointly decipher that the anion-rich Li+ solvation structure derived from ring tetrahydrofuran coupling with chain ether successfully suppresses the excessive passivation of electrolyte decomposition at the reaction interface, thus promoting the mass transfer of active species and enhancing the nitrogen fixation kinetics. This work offers a progressive insight into the electrolyte design of LMNRR system.

Lithium-Mediated Ammonia Electrosynthesis with Ether-Based Electrolytes

Ammonia is of great importance in fertilizer production and chemical synthesis. It can also potentially serve as a carbon-free energy carrier for a future hydrogen economy. Motivated by a worldwide effort to lower carbon emissions, ammonia synthesis by lithium-mediated electrochemical nitrogen reduction (LiNR) has been considered as a promising alternative to the Haber-Bosch process. A significant performance improvement in LiNR has been achieved in recent years by exploration of favorable lithium salt and proton donor for the electrolyte recipe, but the solvent study is still in its infancy. In this work, a systematic investigation on ether-based solvents toward LiNR is conducted. The assessments of solvent candidates are built on their conductivity, parasitic reactions, product distribution, and faradaic efficiency. Notably, dimethoxyethane gives the lowest potential loss among the investigated systems, while tetrahydrofuran achieves an outstanding faradaic efficiency of 58.5 ± 6.1% at an ambient pressure. We found that solvent molecules impact the above characteristics by dictating the solvation configurations of conductive ions and inducing the formation of solid electrolyte interphase with different compositions. This study highlights the importance of solvents in the LiNR process and advances the electrolyte optimization for better performance.

Is Ethanol Essential for the Lithium-Mediated Nitrogen Reduction Reaction?

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising method for decentralized ammonia synthesis using renewable energy. An organic electrolyte is utilized to combat the competing hydrogen evolution reaction, and lithium is plated to activate the inert N2 molecule. Ethanol is commonly used as a proton shuttle to provide hydrogen to the activated nitrogen. In this study, we investigate the role of ethanol as a proton shuttle in an electrolyte containing tetrahydrofuran and 0.2 M lithium perchlorate. Particularly designed electrochemical experiments show that ethanol is necessary for a good solid-electrolyte interphase but not for the synthesis of ammonia. In addition, electrochemical quartz crystal microbalance (EQCM) demonstrates that the SEI formation at the onset of lithium plating is of specific importance. Chemical batch synthesis of ammonia combined with real-time mass spectrometry confirms that protons can be shuttled from the anode to the cathode by other species even without ethanol. Moreover, it raises questions regarding the electrochemical nature of Li-NRR. Finally, we discuss electrolyte stability and electrochemical electrode potentials, highlighting the role of ethanol on electrolyte degradation.

Efficient Electroreduction of Nitrate to Ammonia with CuPd Nanoalloy Catalysts

The electroreduction of nitrate (NO3 - ) to valuable ammonia (NH3 ) is a green and appealing alternative to the Haber-Bosch process. Nevertheless, this process suffers from low performance for NH3 due to the sluggish multi-electron/proton-involved steps. In this work, a CuPd nanoalloy catalyst was developed toward NO3 - electroreduction at ambient conditions. By modulating the atomic ratio of Cu to Pd, the hydrogenation steps of NH3 synthesis during NO3 - electroreduction can be effectively controlled. At -0.7 V versus reversible hydrogen electrode (vs. RHE), the optimized CuPd electrocatalysts achieved a Faradaic efficiency for NH3 of 95.5 %, which was 1.3 and 1.8 times higher than that of Cu and Pd, respectively. Notably, at -0.9 V vs. RHE, the CuPd electrocatalysts showed a high yield rate of 36.2 mg h-1  cm-2 for NH3 with a corresponding partial current density of -430.6 mA cm-2 . Mechanism investigation revealed the enhanced performance originated from the synergistic catalytic cooperation between Cu and Pd sites. The H-atoms adsorbed on the Pd sites prefer to transfer to adjacent nitrogen intermediates adsorbed on the Cu sites, thereby promoting the hydrogenation of intermediates and the formation of NH3 .

Nitrogen Electrocatalysis: Electrolyte Engineering Strategies to Boost Faradaic Efficiency

The electrochemical activation of dinitrogen at ambient temperature and pressure for the synthesis of ammonia has drawn increasing attention. The faradaic efficiency (FE) as well as ammonia yield in the electrochemical synthesis is far from reaching the requirement of industrial-scale production. In aqueous electrolytes, the competing electron-consuming hydrogen evolution reaction (HER) and poor solubility of nitrogen are the two major bottlenecks. As the electrochemical reduction of nitrogen involves proton-coupled electron transfer reaction, rationally engineered electrolytes are required to boost FE and ammonia yield. In this Review, we comprehensively summarize various electrolyte engineering strategies to boost the FE in aqueous and non-aqueous medium and suggest possible approaches to further improve the performance. In aqueous medium, the performance can be improved by altering the electrolyte pH, transport velocity of protons, and water activity. Other strategies involve the use of hybrid and water-in-salt electrolytes, ionic liquids, and non-aqueous electrolytes. Existing aqueous electrolytes are not ideal for industrial-scale production. Suppression of HER and enhanced nitrogen solubility have been observed with hybrid and non-aqueous electrolytes. The engineered electrolytes are very promising though the electrochemical activation has several challenges. The outcome of lithium-mediated nitrogen reduction reaction with engineered non-aqueous electrolyte is highly encouraging.

Electrocatalytic Reduction of Dinitrogen to Ammonia with Water as Proton and Electron Donor Catalyzed by a Combination of a Tri-ironoxotungstate and an Alkali Metal Cation

The electrification of ammonia synthesis is a key target for its decentralization and lowering impact on atmospheric CO2 concentrations. The lithium metal electrochemical reduction of nitrogen to ammonia using alcohols as proton/electron donors is an important advance, but requires rather negative potentials, and anhydrous conditions. Organometallic electrocatalysts using redox mediators have also been reported. Water as a proton and electron donor has not been demonstrated in these reactions. Here a N2 to NH3 electrocatalytic reduction using an inorganic molecular catalyst, a tri-iron substituted polyoxotungstate, {SiFe3W9}, is presented. The catalyst requires the presence of Li+ or Na+ cations as promoters through their binding to {SiFe3W9}. Experimental NMR, CV and UV-vis measurements, and MD simulations and DFT calculations show that the alkali metal cation enables the decrease of the redox potential of {SiFe3W9} allowing the activation of N2. Controlled potential electrolysis with highly purified 14N2 and 15N2 ruled out formation of NH3 from contaminants. Importantly, using Na+ cations and polyethylene glycol as solvent, the anodic oxidation of water can be used as a proton and electron donor for the formation of NH3. In an undivided cell electrolyzer under 1 bar N2, rates of NH3 formation of 1.15 nmol sec-1 cm-2, faradaic efficiencies of ∼25%, 5.1 equiv of NH3 per equivalent of {SiFe3W9} in 10 h, and a TOF of 64 s-1 were obtained. The future development of suitable high surface area cathodes and well solubilized N2 and the use of H2O as the reducing agent are important keys to the future deployment of an electrocatalytic ammonia synthesis.

Recent Advances in Metal-Organic Framework-Based Nanomaterials for Electrocatalytic Nitrogen Reduction

The production of ammonia under moderate conditions is of environmental and sustainable importance. The electrochemical nitrogen reduction reaction (E-NRR) method has been intensively investigated in the recent decades. Nowadays, the further development of E-NRR is largely hindered by the lack of competent electrocatalysts. Metal-organic frameworks (MOFs) are considered as the next-generation catalysts for E-NRR, featuring their tailorable structures, abundant active sites and favorable porosity. To present a comprehensive review on both the fundamental and advanced development in MOFs catalyst-based E-NRR field, this paper first introduces the basic principles of E-NRR, including the reaction mechanism, major apparatus components, performance criteria, and ammonia detection protocols. Next, the synthesis and characterization methods for MOFs and their derivatives are discussed. In addition, a reaction mechanism study via density functional theory calculations is also presented. After that, the recent advancement of MOF-based catalysts in the E-NRR field as well as the modification approaches on MOFs for E-NRR optimization is elaborated. Finally, the current challenges and outlook of MOF catalyst-based E-NRR field are emphasized.

Electrochemical Nitrogen Fixation for Green Ammonia: Recent Progress and Challenges

Ammonia, a key feedstock used in various industries, has been considered a sustainable fuel and energy storage option. However, NH3 production via the conventional Haber-Bosch process is costly, energy-intensive, and significantly contributing to a massive carbon footprint. An electrochemical synthetic pathway for nitrogen fixation has recently gained considerable attention as NH3 can be produced through a green process without generating harmful pollutants. This review discusses the recent progress and challenges associated with the two relevant electrochemical pathways: direct and indirect nitrogen reduction reactions. The detailed mechanisms of these reactions and highlight the recent efforts to improve the catalytic performances are discussed. Finally, various promising research strategies and remaining tasks are presented to highlight future opportunities in the electrochemical nitrogen reduction reaction.

The role of ion solvation in lithium mediated nitrogen reduction

Since its verification in 2019, there have been numerous high-profile papers reporting improved efficiency of lithium-mediated electrochemical nitrogen reduction to make ammonia. However, the literature lacks any coherent investigation systematically linking bulk electrolyte properties to electrochemical performance and Solid Electrolyte Interphase (SEI) properties. In this study, we discover that the salt concentration has a remarkable effect on electrolyte stability: at concentrations of 0.6 M LiClO4 and above the electrode potential is stable for at least 12 hours at an applied current density of -2 mA cm-2 at ambient temperature and pressure. Conversely, at the lower concentrations explored in prior studies, the potential required to maintain a given N2 reduction current increased by 8 V within a period of 1 hour under the same conditions. The behaviour is linked more coordination of the salt anion and cation with increasing salt concentration in the electrolyte observed via Raman spectroscopy. Time of flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy reveal a more inorganic, and therefore more stable, SEI layer is formed with increasing salt concentration. A drop in faradaic efficiency for nitrogen reduction is seen at concentrations higher than 0.6 M LiClO4, which is attributed to a combination of a decrease in nitrogen solubility and diffusivity as well as increased SEI conductivity as measured by electrochemical impedance spectroscopy.

P-Block Metal-Based Electrocatalysts for Nitrogen Reduction to Ammonia: A Minireview

Electrochemical nitrogen reduction reaction (NRR) to ammonia (NH₃ ) using renewable electricity provides a promising approach towards carbon neutral. What's more, it has been regarded as the most promising alternative to the traditional Haber-Bosch route in current context of developing sustainable technologies. The development of a class of highly efficient electrocatalysts with high selectivity and stability is the key to electrochemical NRR. Among them, P-block metal-based electrocatalysts have significant application potential in NRR for which possessing a strong interaction with the N 2p orbitals. Thus, it offers a good selectivity for NRR to NH₃ . The density of state (DOS) near the Fermi level is concentrated for the P-block metal-based catalysts, indicating the ability of P-block metal as active sites for N₂ adsorption and activation by donating p electrons. In this work, we systematically review the recent progress of P-block metal-based electrocatalysts for electrochemical NRR. The effect of P-block metal-based electrocatalysts on the NRR activity, selectivity and stability are discussed. Specifically, the catalyst design, the nature of the active sites of electrocatalysts and some strategies for boosting NRR performance, the reaction mechanism, and the impact of operating conditions are unveiled. Finally, some challenges and outlooks using P-block metal-based electrocatalysts are proposed.

Analysis of the Scale of Global Human Needs and Opportunities for Sustainable Catalytic Technologies

We analyzed the enormous scale of global human needs, their carbon footprint, and how they are connected to energy availability. We established that most challenges related to resource security and sustainability can be solved by providing distributed, affordable, and clean energy. Catalyzed chemical transformations powered by renewable electricity are emerging successor technologies that have the potential to replace fossil fuels without sacrificing the wellbeing of humans. We highlighted the technical, economic, and societal advantages and drawbacks of short- to medium-term decarbonization solutions to gauge their practicability, economic feasibility, and likelihood for widespread acceptance on a global scale. We detailed catalysis solutions that enhance sustainability, along with strategies for catalyst and process development, frontiers, challenges, and limitations, and emphasized the need for planetary stewardship. Electrocatalytic processes enable the production of solar fuels and commodity chemicals that address universal issues of the water, energy and food security nexus, clothing, the building sector, heating and cooling, transportation, information and communication technology, chemicals, consumer goods and services, and healthcare, toward providing global resource security and sustainability and enhancing environmental and social justice.

Water Increases the Faradaic Selectivity of Li-Mediated Nitrogen Reduction

The lithium-mediated system catalyzes nitrogen to ammonia under ambient conditions. Herein we discover that trace amount of water as an electrolyte additive-in contrast to prior reports from the literature-can effect a dramatic improvement in the Faradaic selectivity of N2 reduction to NH3. We report that an optimal water concentration of 35.9 mM and LiClO4 salt concentration of 0.8 M allows a Faradaic efficiency up to 27.9 ± 2.5% at ambient pressure. We attribute the increase in Faradaic efficiency to the incorporation of Li2O in the solid electrolyte interphase, as suggested by our X-ray photoelectron spectroscopy measurements. Our results highlight the extreme sensitivity of lithium-mediated N2 reduction to small changes in the experimental conditions.

Nonaqueous Li-Mediated Nitrogen Reduction: Taking Control of Potentials

The performance of the Li-mediated ammonia synthesis has progressed dramatically since its recent reintroduction. However, fundamental understanding of this reaction is slower paced, due to the many uncontrolled variables influencing it. To address this, we developed a true nonaqueous LiFePO4 reference electrode, providing both a redox anchor from which to measure potentials against and estimates of sources of energy efficiency loss. We demonstrate its stable electrochemical potential in operation using different N2- and H2-saturated electrolytes. Using this reference, we uncover the relation between partial current density and potentials. While the counter electrode potential increases linearly with current, the working electrode remains stable at lithium plating, suggesting it to be the only electrochemical step involved in this process. We also use the LiFePO4/Li+ equilibrium as a tool to probe Li-ion activity changes in situ. We hope to drive the field toward more defined systems to allow a holistic understanding of this reaction.

Near ambient N2 fixation on solid electrodes versus enzymes and homogeneous catalysts

The Mo/Fe nitrogenase enzyme is unique in its ability to efficiently reduce dinitrogen to ammonia at atmospheric pressures and room temperature. Should an artificial electrolytic device achieve the same feat, it would revolutionize fertilizer production and even provide an energy-dense, truly carbon-free fuel. This Review provides a coherent comparison of recent progress made in dinitrogen fixation on solid electrodes, homogeneous catalysts and nitrogenases. Specific emphasis is placed on systems for which there is unequivocal evidence that dinitrogen reduction has taken place. By establishing the cross-cutting themes and synergies between these systems, we identify viable avenues for future research.

Oxygen Functionalization-Induced Charging Effect on Boron Active Sites for High-Yield Electrocatalytic NH3 Production

Ammonia has been recognized as the future renewable energy fuel because of its wide-ranging applications in H₂ storage and transportation sector. In order to avoid the environmentally hazardous Haber-Bosch process, recently, the third-generation ambient ammonia synthesis has drawn phenomenal attention and thus tremendous efforts are devoted to developing efficient electrocatalysts that would circumvent the bottlenecks of the electrochemical nitrogen reduction reaction (NRR) like competitive hydrogen evolution reaction, poor selectivity of N₂ on catalyst surface. Herein, we report the synthesis of an oxygen-functionalized boron carbonitride matrix via a two-step pyrolysis technique. The conductive BNCO₍₁₀₀₀₎ architecture, the compatibility of B-2p_z orbital with the N-2p_z orbital and the charging effect over B due to the C and O edge-atoms in a pentagon altogether facilitate N₂ adsorption on the B edge-active sites. The optimum electrolyte acidity with 0.1 M HCl and the lowered anion crowding effect aid the protonation steps of NRR via an associative alternating pathway, which gives a sufficiently high yield of ammonia (211.5 μg h^-1 mg_cat^-1) on the optimized BNCO₍₁₀₀₀₎ catalyst with a Faradaic efficiency of 34.7% at - 0.1 V vs RHE. This work thus offers a cost-effective electrode material and provides a contemporary idea about reinforcing the charging effect over the secured active sites for NRR by selectively choosing the electrolyte anions and functionalizing the active edges of the BNCO₍₁₀₀₀₎ catalyst.