Electrochemical Ammonia Synthesis Research Articles

Synergistic N/F Dual-Doped MoC/C Catalyst Synthesized via Liquid Phase Plasma for Sustainable Ammonia Production.

NH3 is a versatile solution for the storage and distribution of sustainable energy, offering high energy density and promising applications as a renewable hydrogen carrier. However, electrochemical NH3 synthesis under ambient conditions remains challenging, such as low selectivity and efficiency, owing to the inertness of N≡N and competing reactions. In this study, a catalyst (MoC/NFC) comprising molybdenum carbide evenly dispersed on carbon doped with N and F heteroatoms was successfully synthesized using liquid-phase plasma. The MoC/NFC catalyst exhibited a maximum NH3 yield of 115 μg h-1 mg-1cat. with a faradaic efficiency of 1.15% at -0.7 V vs reversible hydrogen electrode in 0.1 M KOH electrolyte. Pyridinic- and pyrrolic-N atoms adjacent to the carbon pores served as active sites for N2 adsorption and enabled N2 triple bond cleavage. In addition, F doping contributed to N2 activation owing to the high electronegativity of 3.98, resulting in the attraction of more electrons. These findings demonstrate a significant advancement in the development of efficient catalysts for electrochemical ammonia synthesis, potentially paving the way for scalable and sustainable NH3 production methods that can support the growing demand for renewable energy storage solutions.

In situRaman investigation to electrochemical synthesis of ammonia on Pd nanocrystals.

Nitrate and nitrite are widely present in industrial wastewater and domestic sewage, so electrocatalytic reduction of both nitrate and nitrite to ammonia synthesis is considered to be a sustainable development approach. Pd nanostructures have attracted much attention because of their high activity in catalyzing the nitrate electrochemical reduction reaction. Here we prepare Pd nanocube and octahedron for the electrochemical reduction of nitrate and nitrite. It is found that Pd octahedron shows slightly higher activity toward nitrate reduction than Pd nanocube, while for nitrite reduction, Pd octahedron shows much higher activity than Pd nanocube. The ammonia yield rate is more potential-dependent.In situRaman characterization further confirms the existence of adsorbed ammonia on the surface of nanocube and octahedron, indicating similar reduction pathways on (111)-facet octahedron and (100)-facet nanocube.

Boosting electrochemical ammonia synthesis via dynamic nitrogen carriers coupled with electron-rich Lewis acidic sites on TiO2−x nanofiber

In light of the high energy consumption and substantial carbon emissions associated with traditional NH3 production based on the Haber–Bosch process, the aqueous electrochemical nitrogen reduction reaction (NRR) offers a clean and sustainable alternative production route. Nevertheless, activating the NN bonds at room temperature is challenging due to the high bond energy, severely hindering the development and commercialization of the electrochemical NRR. Herein, we report a synergistic strategy for achieving efficient N2 activation at ambient conditions that combines electrolyte engineering with catalytic site-modulated TiO2−x nanofiber electrocatalysts. The synthesized TiO2−x nanofiber electrocatalysts contained abundant intrinsic oxygen vacancies and were further modified with hydroxyl groups to create electron-rich Lewis acidic Ti sites. Additionally, BF3 was engineered into the electrolyte microenvironment, and it could form adducts with N2, serving as a dynamic carrier for N2 transport. The electron-rich Lewis acidic sites and the dynamic carriers exerted a ‘pull–pull’ effect on N2, thereby weakening the NN bonds. Through electrochemical performance evaluation, the designed electrocatalytic scheme achieved an NH3 yield of ∼57.15 μg h−1 mg−1 and a Faradaic efficiency of ∼15.14 %. We anticipate that this methodology will provide new insights into the development of electrochemical ammonia synthesis, particularly in relation to multifaceted design.

Recent research trends in the rational design strategies of carbon-based electrocatalysts for electrochemical ammonia synthesis

Ammonia electrosynthesis is the most sustainable way to produce carbon-free hydrogen carriers, which would pave the way for the foreseen hydrogen economy and carbon neutralization as it has the potential to replace the conventional Haber-Bosch process. The electrocatalytic production of ammonia, which renewable energy resources could drive, reduces the carbon footprint contribution to fossil fuel consumption. Moreover, ammonia electrosynthesis also paves the way for recycling industrial/chemical wastewater and NO emissions. Hence, the advancement of electrocatalytic ammonia synthesis techniques is highly mandated for a greener future. This review consolidates the recent research trends associated with carbon-based electrocatalysts, which could elevate this viable technology with cost-effectiveness.

Reducing the overpotential of overall water spitting by micro-pump-like electrode engineering

Electrolyzing water for hydrogen generation consumes a significant amount of electricity. Minimizing bubble accumulation on the electrodes can reduce the overpotential, thereby enhancing the efficiency of water electrolysis. In this work, Co1.8Mn1.2S4 as the catalyst for oxygen evolution reaction (OER) was optimized from 54 compounds of oxides and sulfides of Ni, Co, and Mn, then designed a three-dimensional electrode with a pump-like function to expel bubbles from the electrodes. Using laser-assisted curing 3D printing technology, a capillary array with side holes was fabricated and utilized as a support structure for the Co1.8Mn1.2S catalyst. During water electrolysis, the electrolyte enters the interior of the capillary through the side holes, and the bubbles inside the capillary are released from both ends of the capillary. The optimized electrode achieved 10 mA cm−2 at an overpotential of 345 mV during the OER, and reached 100 mA cm−2 at an overpotential of 435 mV. In-situ optical microscopy observations and fluid dynamics simulations demonstrated that bubbles were effectively released through the main outlet of the capillary. In overall water splitting, the current density reached 10 mA cm−2 at 1.646 V, without significant current decay after 60 h continuous operation. The electrode design presented holds promise for broader applications in catalytic reactions, such as CO2 reduction, electrochemical ammonia synthesis, and electrochemical treatment of water pollutants.

Scalable ammonia synthesis on the modified crystal structure of Cu3PS4 electrocatalyst

Ammonia production, which is vital for agricultural and industrial applications, typically relies on energy-intensive processes that contribute to global CO2 emissions. Electrochemical nitrogen reduction is a promising alternative, although it faces challenges such as low yield and selectivity. Transition-metal-based catalysts, particularly Cu, are promising for overcoming these limitations. Cu3PS4 catalysts were synthesized and evaluated using a 9 cm2-scale electrode, revealing enhanced performance attributed to change in the crystal and electronic structure of Cu, facilitating N2 adsorption and improving the reaction activity. Notably, the ammonia synthesis rate reached 128 μg h-1 mgcat-1 at −1.0 V vs. RHE and faradaic efficiency was 34 % at −0.8 V vs. RHE. These findings provide potential insights into the improvement of practical electrochemical synthesis of ammonia.

Toward High-Performance Electrochemical Ammonia Synthesis by Circumventing the Surface H-Mediated N2 Reduction.

The rapid performance decay with potentials is a significant obstacle to achieving an efficient electrocatalytic N2 reduction reaction (eNRR), which is typically attributed to competition from hydrogen evolution. However, the potential-dependent competitive behavior and reaction mechanism are still under debate. Herein, we theoretically defined N2 adsorption, H mediation, and H2 evolution as three crucial regions along the potentials by revisiting the potential-dependent competitive adsorption between N2 and H on FeN4 and RuN4 catalysts. We revealed that the surface H-mediated mechanism makes eNRR feasible at low potentials but introduces sluggish reaction kinetics, showing a double-edged sword nature. In view of this, we proposed a new possibility to achieve high-performance NH3 synthesis by circumventing the H-mediated mechanism, where the ideal catalyst should have a wide potential interval with N2-dominated adsorption to trigger direct eNRR. Using this mechanistic insight as a new criterion, we proposed a theoretical protocol for eNRR catalyst screening, but almost none of the theoretically reported electrocatalysts passed the assessment. This work not only illustrates the intrinsic mechanism behind the low-performance dilemma of eNRR but also points out a possible direction toward designing promising catalysts with high selectivity and high current density.

Electron Sponge Effect by Dynamic-Regulated Electron Self-Flow toward Coupled Electrochemical Ammonia Synthesis.

A dynamic-regulated Pd-Fe-N electrocatalyst was effectively constructed with electron-donating and back-donating effects, which serves as an efficient engineering strategy to optimize the electrocatalytic activity. The designed PdFe3/FeN features a comprehensive electrocatalytic performance toward the nitrogen reduction reaction (NRR, yield rate of 29.94 μg h-1 mgcat-1 and FE of 38.43% at -0.2 V vs RHE) and oxygen evolution reaction (OER, 308 mV at 100 mA cm-2). Combining in situ ATR-FTIR, XAS, and DFT results, the role of the interstitial-N-dopant-induced electron sponge effect has been significantly elucidated in strengthening the electrocatalytic NRR process. Specifically, the introduction of a N dopant, an electron acceptor, initiates the generation of robust Lewis-acidic Fe sites, facilitating free N2 capture and bonding. Simultaneously, after NH3 adsorption, the N dopant can back-donate electrons to Fe sites, strengthening the NH3 deportation through weakening the Lewis acidity of Fe centers. Besides, the electron-deficient Fe sites contribute to the reconstruction of FeOOH, the real active species during the OER, which accelerates the four-electron reaction kinetics. This research offers a perspective on electrocatalyst design, potentially facilitating the evolution of advanced material engineering for efficient electrocatalytic synthesis and energy storage.

Reversed I1Cu4 single-atom sites for superior neutral ammonia electrosynthesis with nitrate

Electrochemical ammonia (NH3) synthesis from nitrate reduction (NITRR) offers an appealing solution for addressing environmental concerns and the energy crisis. However, most of the developed electrocatalysts reduce NO3- to NH3 via a hydrogen (H*)-mediated reduction mechanism, which suffers from undesired H*-H* dimerization to H2, resulting in unsatisfactory NH3 yields. Herein, we demonstrate that reversed I1Cu4 single-atom sites, prepared by anchoring iodine single atoms on the Cu surface, realized superior NITRR with a superior ammonia yield rate of 4.36 mg h-1 cm-2 and a Faradaic efficiency of 98.5% under neutral conditions via a proton-coupled electron transfer (PCET) mechanism, far beyond those of traditional Cu sites (NH3 yield rate of 0.082 mg h-1 cm-2 and Faradaic efficiency of 36.5%) and most of H*-mediated NITRR electrocatalysts. Theoretical calculations revealed that I single atoms can regulate the local electronic structures of adjacent Cu sites in favor of stronger O-end-bidentate NO3- adsorption with dual electron transfer channels and suppress the H* formation from the H2O dissociation, thus switching the NITRR mechanism from H*-mediated reduction to PCET. By integrating the monolithic I1Cu4 single-atom electrode into a flow-through device for continuous NITRR and in situ ammonia recovery, an industrial-level current density of 1 A cm-2 was achieved along with a NH3 yield rate of 69.4 mg h-1 cm-2. This study offers reversed single-atom sites for electrochemical ammonia synthesis with nitrate wastewater and sheds light on the importance of switching catalytic mechanisms in improving the performance of electrochemical reactions.

Transition Metal-Gallium Intermetallic Compounds with Tailored Active Site Configurations for Electrochemical Ammonia Synthesis.

Gallium (Ga) with a low melting point can serve as a unique metallic solvent in the synthesis of intermetallic compounds (IMCs). The negative formation enthalpy of transition metal-Ga IMCs endows them with high catalytic stability. Meanwhile, their tunable crystal structures offer the possibility to tailor the configurations of active sites to meet the requirements for specific catalytic applications. Herein, we present a general method for preparing a range of transition metal-Ga IMCs, including Co-Ga, Ni-Ga, Pt-Ga, Pd-Ga, and Rh-Ga IMCs. The structurally ordered CoGa IMCs with body-centered cubic (bcc) structure are uniformly dispersed on the nitrogen-doped reduced graphene oxide substrate (O-CoGa/NG) and deliver outstanding nitrate reduction reaction (NO3RR) performance, making them excellent catalysts to construct highly efficient rechargeable Zn-NO3- battery. Operando studies and theoretical simulations demonstrate that the electron-rich environments around the Co atoms enhance the adsorption strength of *NO3 intermediate and simultaneously suppress the formation of hydrogen, thus improving the NO3RR activity and selectivity.

Resorcinol–Azodianiline Covalent Organic Framework Supported FeOOH Quantum Dot-Catalyzed Electrochemical Ammonia Synthesis under Ambient Conditions

Resorcinol–Azodianiline Covalent Organic Framework Supported FeOOH Quantum Dot-Catalyzed Electrochemical Ammonia Synthesis under Ambient Conditions

A bioinspired Fe/Mo bimetallic nitride catalyst for efficient electrochemical ammonia synthesis and Zn-nitrate battery

The electrocatalytic nitrate reduction reaction to ammonia (NRA) offers a promising alternative to traditional ammonia synthesis methods. In nature, enzymes containing molybdenum and iron sites catalyze the reduction of nitrate and nitrite ions. Drawing inspiration from these enzymes, we synthesized a carbon-coated nano-octahedra of FeMo-based nitride (FeMoN@C NO) by pyrolyzing phosphomolybdic acid hydrate (POM) doped Fe-NH2-MIL-101 to catalyze NRA. Experimental results demonstrate that in an alkaline environment, FeMoN@C NO exhibits a suitable hydrogen evolution reaction (HER) capacity, and the protons or hydroxyls produced effectively facilitate the hydrogenation reaction in the ammonia synthesis process. Additionally, the introduction of Mo increases the number of active sites and effectively reduces the thermodynamic barrier in NRA, thereby enhancing the rate of ammonia synthesis. As a result, FeMoN@C NO displays outstanding NH3 Faradaic efficiency (FE) of 98.2 % and an NH3 yield of 434.16 µmol/h cm−2. Building upon the excellent electrocatalytic properties of FeMoN@C NO, a new Zn-nitrate battery system is assembled in this work, which exhibits an outstanding peak power density of 3.23 mW cm−2 and an FE of 91.58 % for NH3 production. This work provides a new perspective for designing enzyme-mimicking nitrate reduction catalysts and broadens the application of Zn-based batteries.

Multiple Strategies for Producing and Utilizing Ammonia Using Electrochemical Methods Using Transition Metal Based Electrocatalysts

Ammonia is one of the most important chemicals in fertilizer and industrial chemical production, stands as the world’s second-largest synthetic chemical (> 200 million tons). Additionally, its potential as a clean energy source is gaining attentions due to its carbon neutrality, high energy density, and ease of transport. Electrochemical ammonia production emerges as a 'green' method which minimize the carbon footprint. However, the development of effective systems to produce and utilize 'green' ammonia remains a significant challenge [1,2].To enhance the efficiency of electrochemical systems, modifications in both catalyst and system design are mandatory. This presentation will introduce the electrochemical nitrogen reduction reaction (eNRR) using Cu-based catalysts [3]. For catalyst modification, we addressed copper’s challenge of its low affinity and activation potential for stable dinitrogen (N2) molecules. This was achieved through phosphorus activation, which enhance the adsorption and activation of N2 by creating electron-deficient Cu sites on the catalyst surface. System-wise, the poor solubility of nitrogen in aqueous electrolytes limits it’s the performance of the system. Addressing this, we applied a gas diffusion electrode (GDE) coated with polytetrafluoroethylene (PTFE) into the eNRR system. This setup establishes an efficient three-phase boundary among liquid water, gaseous N2, and the solid catalyst, thus facilitating nitrogen access to the catalytic sites. Our novel catalyst in a flow-type cell attains a Faradaic efficiency of 13.15% and an ammonia production rate of 7.69 μg h-1 cm-2 at -0.2 VRHE. These figures represent 3.56- and 59.2-times improvements, respectively, over a pristine Cu electrode in a conventional electrolytic cell.Additionally, the presentation will provide a brief introduction to the amorphous Ni-Cu electrocatalyst for electrochemical ammonia oxidation, which is an essential reaction for ammonia utilization [4]. We highlight its doubled ammonia removal efficiency compared to the Ni-Cu LDH electrocatalyst, underlining the potential of these developments.[1] Y. Zeng, C. Priest, G. Wang, G. Wu, Restoring the Nitrogen Cycle by Electrochemical Reduction of Nitrate: Progress and Prospects, Small Methods, 4 (2020) 2000672.[2] B. Yang, W. Ding, H. Zhang, S. Zhang, Recent Progress in Electrochemical Synthesis of Ammonia from Nitrogen: Strategies to Improve the Catalytic Activity and Selectivity, Energy Environ. Sci., 14 (2021) 672-687.[3] J. Kim, C.H. Lee, Y.H. Moon, M.H. Lee, E.H. Kim, S.H. Choi, Y.J. Jang, J.S. Lee, Enhancing Ammonia Production Rates from Electrochemical Nitrogen Reduction by Engineering Three-Phase Boundary with Phosphorus-Activated Cu Catalysts, J. Energy Chem., 84 (2023) 394-401.[4] J.H. Jang, S.Y. Park, D.H. Youn, Y.J. Jang. Recent Advances in Electrocatalysts for Ammonia Oxidation Reaction.Catalysts., 13 (2023) 803.

Thin Film Based Membrane Electrode Assemblies for Solid-State Ammonia Synthesis

Ammonia is the of the most crucial chemicals and currently primarily produced through the Haber-Bosch process causing the industrial ammonia production to emit more CO2 than any other chemical-making reaction. While the current primary function of ammonia lies within the fertilizer production, it can also be directly used as a fuel for power generation or in the maritime industry. Compared to hydrogen, ammonia has superior storage and transportation capabilities due to its greater volumetric energy density and mild conditions for liquefication. Given the need of reducing global carbon emissions, ammonia could be synthesized electrochemically using air, water and electricity by the Solid-State Ammonia Synthesis (SSAS). Protonic ceramic cells operate within an intermediate temperature regime of around 450 - 550 °C which is well suited for this process. Within our work, we present a tubular membrane electrode unit entirely made of ceramic components based on a barium zirconate thin film electrolyte. An ammonia production rate of 9.06 × 10-10 mol s-1 cm-2 and a Faradaicefficiency of 6.58% were achieved using a NiO-BaZr0.7Ce0.2Y0.1O3- δ | BaZr0.8Y0.2O3- δ | Ru@Ba0.5Sr0.5TiO3-δ cell.A key innovation lies in the production of dense BaZr0.8Y0.2O3-δ electrolyte layers, ranging from 1 to 5 µm in thickness, utilizing a Closed-Field Unbalanced Magnetron Sputtering (CFUMS) process. This technique allows precise adjustments of stoichiometric ratios within the perovskite structure, offering improved sputtering yields compared to conventional methods. Furthermore, the crystallinity, phase purity, and microstructure of sputter-deposited thin films are enhanced through selective laser annealing (SLA), resulting in high-density films composed of single-phase BaZr0.8Y0.2O3-δ with average crystallite sizes of 200 nm while avoiding substrate damage from thermal stress. Electrochemical performance was evaluated through impedance spectroscopy, half-cell tests and full cell tests providing insights into the efficacy of the developed tubular membrane reactor for the electrochemical synthesis of ammonia. The results demonstrate the feasibility of utilizing ceramic proton conductors in SSAS, particularly highlighting the potential of high-pressure operation up to 80 bars in tubular cells at relatively low temperatures around 450 °C, thereby achieving attractive NH3 production rates.This research contributes to the evolving landscape of sustainable ammonia synthesis by presenting a novel approach that integrates advanced materials and manufacturing techniques. Electrification and decentralization of the ammonia supply chain will expand the market by supporting its current use as fertilizer source and enable a new route as green energy carrier paving the way for an ammonia-based economy. Figure 1

Understanding Interfaces Using Neutron Reflectometry in Calcium-Mediated Nitrogen Reduction for Electrochemical Ammonia Synthesis

Ammonia (NH3) synthesis from N2 via the Haber-Bosch (HB) process addressed the major challenge of finite fertilizer sources in the early 20th century,and today, it continues to sustain the human population of 8 billion.1 Furthermore, NH3 has been identified as a promising, carbon-free energy vector.2 However, HB operates at elevated temperatures and pressures in centralized facilities, accounting for 1.3% of carbon emissions.1 To decentralize and decarbonize NH3 synthesis, there is a need to develop a synthetic method that operates at ambient conditions.Methods for N2 fixation to NH3 at ambient conditions include via the nitrogenase enzyme, homogenous catalysts, and an electrochemical lithium-mediated process.1,3 Of these methods, the lithium-mediated process (Li-NRR) has demonstrated impressive gains in selectivity and stability, and it has been engineered into a continuous process.3 In Li-NRR, metallic Li is plated onto an electrode from a Li-containing salt dissolved in N2-saturated, organic solution. Electroplated lithium reacts with the saturated N2 to form surface lithium nitride (Li3N), and a proton donor, such as ethanol, provides protons to form NH3. Of note, a solid-electrolyte interphase (SEI) passivating layer forms at the Li-electrolyte interface from electrolyte decomposition products. The SEI layer moderates proton, Li+, and N2 transport, and therefore, its structure and composition have become a major focus of study.4 While much remains to be understood in the Li-NRR system, a broader question has been posed as to whether a non-Li material can mediate ammonia synthesis with a similar mechanism.5 Recently, our groups have demonstrated that Ca, the fifth most abundant element in the earth’s crust, can mediate nitrogen reduction to ammonia in a process henceforth referred to as calcium-mediated nitrogen reduction to ammonia (Ca-NRR).6 Inspired by recent advancements in Ca-metal batteries for Ca plating at room temperature, we have demonstrated that calcium tetrakis(hexafluoroisopropyloxy)borate (Ca[B(hfip)4]2) in tetrahydrofuran with ethanol can be used as the electrolyte to plate Ca and produce NH3. We hypothesized that Ca-NRR likely operates similarly to Li-NRR, where the SEI passivating layer plays a crucial role in the selective transport of species such as N2, protons, and Ca2+,6 however, much remains to be determined about the structure and composition of these interfaces.A useful method for understanding interfaces is neutron reflectometry. This technique involves the measurement of neutron reflectivity as a function of scattering vector that is fit to a model to determine the compositional and structural properties of a series of interfaces, i.e., scattering length density, thickness, and roughness of each layer.4 Neutron sensitivity to light-elements, e.g., H, and scattering contrast between isotopes, including H and D, enable tracking proton dynamics and incorporation into the layers. Of particular importance is the formation of a hydride which may lead to major side reactions, including the formation of H2. Herein, we measured the Ca-NRR system in-situ at varied applied current densities, and observed changes in layer properties. This technique, paired with ex-situ characterization, elucidates properties of the Ca-NRR plated and SEI passivation layers that can inform the rational, molecular design of nitrogen reduction systems.References Nørskov, J. et al. DOE Roundtable Report (2016).Chang, F. et al. Advanced Materials 33, 2005721 (2021).Fu, X. Pederson, J.B, Zhou, Y. et al. Science 379, 6633 707-712 (2023).Blair, S.J., Doucet, M. et al. Energy Environ. Sci., 16, 3391 (2023).Tort, R. et al. ACS Catalysis, 13, 22, 14513-14522 (2023).Fu, X., Niemann, V.A., Zhou, Y. et al. Nat. Mater. (2023).

Physically-Based Descriptors of the Nitrogen Reduction Reaction on Transition Metal Nitrides

Due to the high energy intensity and consequent carbon footprint of the Haber-Bosch process for ammonia production, researchers have been intensely studying the electrochemical nitrogen reduction reaction (NRR) as a means to directly produce ammonia using clean energy with lower emissions of carbon by-products. One exciting class of materials for NRR catalysis are transition metal nitrides (TMNs), as they have been shown to have good stability, flexible electronic structures, and decent electrochemical activity [1]. Previous studies using density functional theory (DFT) have explored the energetics of known NRR pathways (associative, dissociative, and Mars-van Krevelen) on the mononitrides of all naturally occurring d-block metals in rock salt and zincblende structures [2]. The most favorable NRR mechanism (determined to be the pathway that contains the smallest maximum potential change across all steps of the reaction) on these materials was shown to be the Mars-van Krevelen mechanism. Uncovering electronic, structural, and dynamic descriptors that correlate well with the energetics of this favorable NRR mechanism on TMNs will be useful in mitigating the need to run full DFT calculations when expanding the search space of potential catalyst candidates, such as ternary transition metal nitrides (TTMNs) and perovskite transition metal oxynitrides (TMONs). Previous literature has shown that the proton adsorption energy is a good descriptor for catalytic NRR activity on TMNs [3], oxygen vacancy content [4] and the oxygen p-band center of bulk perovskites [5] are good descriptors for catalytic oxygen evolution reaction performance, and the metal d-band center of pure transition metal catalysts is a good descriptor for reactivity and adsorption energies [6]. Inspired by these results, this work uses DFT on a set of TMNs to calculate a variety of potential physics-based descriptors, including: metal d and nitrogen p-band centers, hybridization between nitrogen p and metal d orbitals, nitrogen vacancy content, surface Bader charges, and phonon band centers. Since the energetics of the NRR can be modulated by the properties of either the atoms in the bulk or in the top surface layers, we calculate all of our descriptors from atoms in the TMN bulk form as well as from surface and subsurface atoms in the TMN slab form.Our results reveal several correlations between the descriptors and material attributes (such as adsorption energies and vacancy formation energies), which in turn govern the energetics of the NRR on the TMNs. We find that the N2 adsorption energy is negatively correlated with the metal d-band center, the N adsorption energy is positively correlated with the nitrogen p-band center, and both the proton adsorption energy and nitrogen vacancy formation energy are negatively correlated with nitrogen p and metal d orbital hybridization. Interestingly, we also find that for some attributes, the subsurface layer atoms dictate the attribute values and not the surface layer atoms. This suggests that heterogeneous catalysis reactivity may be modulated by atomic properties not purely from the bulk or purely from the surface, but rather from multiple subsurface layers as well.Overall, the insights gained from our descriptor analysis can be used to constrain the search and design space of future potential NRR catalysts, such as TTMNs and TMONs. In doing so, the descriptors can be used in future works in either a high-throughput screening or machine learning framework to allow for the inverse material design of optimal NRR catalysts. These optimal catalysts can in turn lead to the emergence of electrochemical ammonia synthesis in industrial production.References Qiao Z, Johnson D and Djire A. Cell Rep Phys Sci 2021; 2.Abghoui Y and Skúlason E. Catal Today 2017; 286: 69-77.Abghoui Y, Garden AL, Hlynsson VF, Björgvinsdóttir S, Ólafsdóttir H and Skúlason E. Physical Chemistry Chemical Physics 2015; 17: 4909-4918.Marelli E, Gazquez J, Poghosyan E, Müller E, Gawryluk DJ, Pomjakushina E, Sheptyakov D, Piamonteze C, Aegerter D, Schmidt TJ, Medarde M and Fabbri E. Angewandte Chemie - International Edition 2021; 60: 14609-14619.Jacobs R, Hwang J, Shao-Horn Y and Morgan D. Chemistry of Materials 2019; 31: 785-797.Nørskov JK, Abild-Pedersen F, Studt F and Bligaard T. Proc Natl Acad Sci U S A 2011; 108: 937-943.

(Invited) Activating Nitrogen for Electrochemical Ammonia Synthesis: Modeling the Effects of Electrified Interfaces on π-Backbonding Molecules

Electrocatalysts are expected to play a pivotal role in shaping our future sustainable energy landscape by enabling storage of renewable energy and its conversion into globally important chemicals. Computational simulations yield mechanistic insights that have supported catalyst discovery and optimization. However, the complexity of electrocatalyst interfaces has necessitated the development of quantum chemical methods that can accurately model these effects at reasonable computational cost.In this work, we employ grand canonical density functional theory (GC-DFT) to capture the nuanced effects of applied potential on a solvated catalyst interface, specifically focusing on the nitrogen reduction reaction (NRR) at sulfur vacancies in 1T'-phase MoS2. In the canonical method, the widely used the computational hydrogen electrode (CHE) predicts that adsorbed N2 structure properties are potential independent. In contrast, GC-DFT calculations reveal that reductive potentials activate N2 towards electroreduction by modulating backbonding strength, lengthening the N–N triple bond, and reducing its bond order. Similar trends are identified for CO, a classic backbonding ligand, suggesting broader relevance of this mechanism to diverse electrochemistries involving backbonded adsorbates. Furthermore, reductive potentials are required to make the subsequent N2 hydrogenation steps favorable, but concurrently destabilize both N2 and hydrogen adsorption.Our findings demonstrate that GC-DFT facilitates the comprehensive modeling of these phenomena, underscoring their collective implications in predicting electrocatalyst selectivity for the nitrogen reduction reaction and potentially other reactions. This research contributes valuable insights into the design and optimization of electrocatalysts for sustainable energy conversion. Figure 1

A Durable Vanadium Disulfide-Based Catalyst for Nitrate Reduction and Insights on in-Line Ammonia Detection By Mass Spectrometry

Ammonia is critical to agriculture worldwide and is a renewable fuel. The dominant process for ammonia synthesis, Haber-Bosch, is fossil-fuel dependent, energy intensive and highly centralized. Electrochemical N2 or NO3 - reduction promises to provide a decentralized and environmentally friendly route to ammonia synthesis. Electrochemical ammonia synthesis research is challenging due to typically low amounts of ammonia produced relative to environmental levels. In this two-part presentation, a VS2-based nitrate reduction catalyst, which has shown exceptional activity, selectivity, and durability, will be discussed. The proposed mechanism of nitrate reduction on VS2 will be discussed along with thorough characterization of the catalyst material, and we will present density functional theory mechanistic insight of nitrate reduction on VS2. Various experimental controls used in the VS2 nitrate reduction experiments, including Ar purge and NMR characterization experiments will also be detailed. Additionally, a test platform for nitrogen or nitrate reduction catalysts in a gas-diffusion electrode architecture with in-line NH3 and 15NH3 monitoring by multi-turn TOF-MS will be discussed. This part of the presentation will detail some advantages of our analytical approach that stem from the low limit of detection and high mass resolution. Finally, we will address areas of opportunity in electrochemical ammonia generation.

Trio strategy of harmonizing electronic structure, interface, and microenvironment on amorphous indium oxide nanofiber for selective electrochemical ammonia synthesis

Suppressing parasitic hydrogen evolution reaction (HER) remains a dilemma in developing aqueous electrochemical nitrogen reduction reaction (NRR). Nevertheless, previous studies have revealed the significant challenge of relying solely on electrocatalyst design to pursue selective NRR. Herein, we present a ‘Trio’ strategy to harmonize electronic structures of electrocatalysts, properties of interfaces, and configurations of microenvironments, thereby governing the intricate proton behaviors throughout the reaction, to suppress HER while boosting NRR. As proof-of-concept demonstration, the first designed amorphous In2O3-based nanofiber electrocatalyst, with optimized electronic state by oxygen vacancy and anchoring Mo species, is in conjunction with low-surface-energy monolayer interface and molecular-crowding microenvironment. Such rational synergy creates an advantageous catalytic configuration with decelerated proton diffusion and restricted proton transfer to active sites, thus achieving NH3 yield of 59.72 μg h−1 mg−1 and a FE of 30.60 %. We expect these findings will inspire “collaborative combat” strategies and desirable systems of NRR in the future.

Nitrogen-doped carbon confined Cr2S3 hybrid as an efficient low-cost catalyst for electrochemical ammonia synthesis under ambient condition

A chromium sulfide-based nanohybrid (NC/Cr2S3) has been fabricated by a facile strategy of pyrolysis and vulcanization of metal complex. In this nanocomposite, the in situ formed Cr2S3 nanoparticles with a mean size about ∼ 100 nm are confined by the nitrogen-doped carbon plates-derived from the metal complex. The composite is endowed with some structural advantages involving extended surface areas, increased catalytically active centers and enhanced conductivity. As an earth-abundant low-cost electrocatalyst for nitrogen reduction reaction (NRR), compared with bare Cr2S3, NC/Cr2S3 hybrid delivers a boosted and stable catalytic activity for NRR at a low potential under mild conditions. NC/Cr2S3 is able to exhibit a high ammonia yield rate of 30.33 μg mg-1cat h−1 at −0.4 V vs RHE in sodium sulfate solution with a Faradic efficiency up to 7.66 %. Moreover, no hydrazine byproduct can be detected, showcasing a satisfactory selectivity.