Electrocatalytic Synthesis Of Ammonia Research Articles

Cation Substitution Strategy for Developing Perovskite Oxide with Rich Oxygen Vacancy-Mediated Charge Redistribution Enables Highly Efficient Nitrate Electroreduction to Ammonia.

The electrocatalytic nitrate (NO3-) reduction reaction (eNITRR) is a promising method for ammonia synthesis. However, its efficacy is currently limited due to poor selectivity, largely caused by the inherent complexity of the multiple-electron processes involved. To address these issues, oxygen-vacancy-rich LaFe0.9M0.1O3-δ (M = Co, Ni, and Cu) perovskite submicrofibers have been designed from the starting material LaFeO3-δ (LF) by a B-site substitution strategy and used as the eNITRR electrocatalyst. Consequently, the LaFe0.9Cu0.1O3-δ (LF0.9Cu0.1) submicrofibers with a stronger Fe-O hybridization, more oxygen vacancies, and more positive surface potential exhibit a higher ammonia yield rate of 349 ± 15 μg h-1 mg-1cat. and a Faradaic efficiency of 48 ± 2% than LF submicrofibers. The COMSOL Multiphysics simulations demonstrate that the more positive surface of LF0.9Cu0.1 submicrofibers can induce NO3- enrichment and suppress the competing hydrogen evolution reaction. By combining a variety of in situ characterizations and density functional theory calculations, the eNITRR mechanism is revealed, where the first proton-electron coupling step (*NO3 + H+ + e- → *HNO3) is the rate-determining step with a reduced energy barrier of 1.83 eV. This work highlights the positive effect of cation substitution in promoting eNITRR properties of perovskites and provides new insights into the studies of perovskite-type electrocatalytic ammonia synthesis catalysts.

Nitric oxide assists nitrogen reduction reaction on 2D MBene: A theoretical study

Electrocatalytic synthesis of ammonia as an environment-friendly and sustainable development method has received widespread attention in recent years. Two-dimensional (2D) materials are a promising catalyst for ammonia synthesis due to their large surface area. In this work, we have constructed a series of 2D metal borides (MBenes) with transition metal (TM) defects (TMd-MBenes) and comprehensively calculated the reactivity of electrocatalytic synthesis of ammonia-based on density functional theory. The results have demonstrated that the TMd-MBenes can effectively activate nitrogen oxide (NO) and nitrogen (N2) molecules thermodynamically. Particularly interesting, the co-chemisorption of O atoms, dissociated from NO, can facilitate the spilled of the inert N2 molecules into single N atoms, which can further hydrogenate into ammonia easily with an ultralow limiting potential of 0.59 V on TMd-MnB. Our research has not only provided clues for catalyst design for experimental study but also paved the way for the industrial application of electrocatalytic ammonia synthesis.

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.

(Invited) Electrocatalytic Synthesis of Ammonia and Urea

Many industrial chemical processes involve a high-energy demand (often still derived from fossil fuels), toxic reactants, and the production of high amounts of waste. A good example is the production of ammonia and urea via the Haber-Bosh and Bosch-Meiser processes, respectively. These two nitrogen-containing compounds are mostly used in the fertilizer industry and with the increase in the world population, their production is expected to increase. Additionally, NH3 itself is responsible for 2% of the annual world energy consumption and has a carbon footprint of 1.5 tons of CO2 per ton of NH3 [1]. Therefore, the development of more efficient, less hazardous technologies that are based on renewable energies to produce valuable N- containing compounds, has become one of the most challenging topics for chemical synthesis. By using electrochemical methods for the synthesis of ammonia and urea, toxic and dangerous chemicals can be replaced with clean electrons. Furthermore, the efficiency and selectivity of the reactions can be tuned by the applied potential, and more importantly, the energy used can come from renewable sources like wind or solar [2].In this talk, I will show the recent advances from our group in the development of catalysts for the electrocatalytic synthesis of ammonia and urea (as for example Cu2O and CuRh) and the reaction mechanism when using nitrate as a substrate [3].

Benchmarking Heterogeneous Photocatalysts for the Nitrogen Reduction Reaction

Ammonia is the key ingredient for living organisms, and artificial catalytic synthesis of ammonia (known as the Haber-Bosch process) is undoubtedly a milestone in scientific research in the 20th century and the cornerstone of today's society.[1] However, the Haber-Bosch process is energy-intensive (2% of the global energy consumption) and is accompanied by large CO2 emissions (1% of global CO2 emission).[2] To catch up with the goal of “Net Zero CO2 Emissions” by 2050, it is imperative to develop a carbon-free and sustainable ammonia production process. The photocatalytic ammonia synthesis method relies only on renewable feedstocks (water and air) and sustainable energy input (light) and can be operated under ambient conditions. The current progress in photocatalytic ammonia synthesis suggests, however, there exists a large gap in performance before commercial use is viable. To replace the Haber-Bosch process and produce commercial fertilizer, the solar-to-ammonia (STA) efficiency needs to be at least 0.1% and the highest reported efficiency carried out in a lab setting is approaching 0.04%[2][3] With advances in measurement techniques, recent studies in the field of electrocatalytic ammonia synthesis have shown that many reported highly active catalysts have later been shown to be inactive toward nitrogen reduction.[4] This false positive result is mainly due to the adventitious ammonia in the environment. A series of discussions were triggered, including identifying and eliminating contaminations, developing robust measurements for low-concentration ammonia detection, and establishing rigorous testing protocols.[4-7] At present, the ammonia yield of electrocatalysis is at least an order of magnitude higher than that of photocatalysis, so the problem of nitrogen contamination will only be more serious in the field of photocatalysis.[7] Unfortunately, such discussions have not received equal attention in this field, and few if any rigorous testing protocols have been employed in existing reports.It is imperative to benchmark and develop a robust testing protocol for the growing field of photocatalytic ammonia synthesis. Here, we developed a rigorous setup to suppress all known ammonia contaminations (e.g., ammonia and NOx), systematically discussed the effect of various gas pretreatment methods, and established the background contamination level in the system. We synthesized three highly active photocatalytic materials (Fe-BiOBr, OVs-TiO2, and Fe2O3/g-C3N4) from the literature and measured their ammonia yield using the setup with strict controls.[8-10] To avoid potential interference effects during the measurements, we cross-compared different ammonia-detecting methods (Indophenol blue method and ion chromatography).[6] In addition, we applied isotope labeling with quantitative NMR to confirm the genuine production of photo-fixed ammonia. Going a step further, we methodically compare the effects of two experimental parameters (temperature and gas flow rate) on the performance of photocatalytic ammonia synthesis. These parameters vary greatly across reports, making it difficult to objectively analyze their impacts on the production of photo-fixed ammonia. Based on our findings, we aim to provide a solid benchmark for this burgeoning field and draw more attention to the importance of rigorous testing. Reference: Smil, Vaclav. Enriching the earth: Fritz Haber, Carl Bosch, and the transformation of world food production. MIT press, 2004.Medford, Andrew J., and Marta C. Hatzell. "Photon-driven nitrogen fixation: current progress, thermodynamic considerations, and future outlook." Acs Catalysis4 (2017): 2624-2643.Yuan, Jili, et al. "Efficient Photocatalytic Nitrogen Fixation: Enhanced Polarization, Activation, and Cleavage by Asymmetrical Electron Donation to N N Bond." Advanced Functional Materials4 (2020): 1906983.Andersen, Suzanne Z., et al. "A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements." Nature7762 (2019): 504-508.Choi, Jaecheol, et al. "Identification and elimination of false positives in electrochemical nitrogen reduction studies." Nature communications1 (2020): 1-10.Zhao, Yunxuan, et al. "Ammonia detection methods in photocatalytic and electrocatalytic experiments: how to improve the reliability of NH3 production rates?." Advanced Science8 (2019): 1802109.Iriawan, Haldrian, et al. "Methods for nitrogen activation by reduction and oxidation." Nature Reviews Methods Primers1 (2021): 1-26.Liu, Yang, Zhuofeng Hu, and Jimmy C. Yu. "Fe enhanced visible-light-driven nitrogen fixation on BiOBr nanosheets." Chemistry of Materials4 (2020): 1488-1494.Zhang, Guoqiang, et al. "Constructing a tunable defect structure in TiO 2 for photocatalytic nitrogen fixation." Journal of Materials Chemistry A1 (2020): 334-341.Mou, Hongyu, et al. "A one-step deep eutectic solvent assisted synthesis of carbon nitride/metal oxide composites for photocatalytic nitrogen fixation." Journal of materials chemistry A10 (2019): 5719-5725.

Mechanistic origin and scale-up science in an electrochemical ammonia synthesis process

The electrocatalytic synthesis of ammonia via electrochemical nitrogen reduction reaction (eNRR) has the potential as an efficient decarbonizing method for ammonia production in decentralized production facilities. Due to the elusive design of the standard catalysts for eNRR, research efforts have been generally focused on the selectivity issues on the various catalyst proposed until today. Herein, we suggest the development strategies for eNRR, not only from the point of view of the catalyst design to overcome the selectivity issues, but also from the electrolyte and reactor types. We believe that this perspective article provides new insights into the scale-up science for the eNRR and the future commercialization ofelectrocatalytic ammonia synthesis process.

La single atoms promoted electrocatalytic ammonia synthesis on few-layer MoS2 via maximum orbital overlap

Electrocatalytic nitrogen reduction reaction (ENRR) provides a promising method for synthetic NH3 under ambient condition. However, this method is faced with the bottleneck of low Faraday efficiency. In this work, maximum orbital overlapping strategy was proposed to select suitable transition metal catalysts for activation of N2 to facilitate ENRR. By the aid of theoretic calculation, it was found that lanthanum (La) had high degree of orbital overlapping with N2 molecular orbital in side-on configuration. La single-atom catalysts were then loaded onto few-layer MoS2 surface (La SACs/FL-MoS2) and used as cathodic catalyst for ENRR. Results showed that introduction of La single-atom greatly improved the Faradaic efficiency of NH3 to 18.2 % with a considerable NH3 yield rate (3.68 μg h−1cm−2) at − 0.25 V (vs. RHE). Further in-situ IR analysis and theoretical calculation revealed the influence of La single-atom on the adsorption and activation of N2. Moreover, the maximum orbital overlap strategy was also applicable to the activation and reduction of N2 on other La transition metals with larger d-orbital size. This study provides a potential solution for the development of high efficiency catalyst for NH3 synthesis by ENRR.

Electrodeposited Ni‐Mo‐P nanoparticles on TiO2 nanoribbon array for electrocatalytic ammonia synthesis by reducing nitrite

Electrocatalytic reduction of six-electron nitrite (NO2−) to NH3 is a very promising avenue for the effective removal of widespread nitrite from groundwater and the generation of high-value-added products. Herein, we investigated Ni–Mo–P nanoparticles decorated TiO2 nanoribbon arrays as an efficient NO2−RR catalyst. Tested in 0.1 M NaOH with 0.1 M NO2−, a high NH3 yield of 16124.8 μg h−1 cm−2 and an ultrahigh faradaic efficiency of 95.6% at −0.6V can be achieved. The excellent catalytic performance of Ni–Mo–P/TiO2 can be attributed to the synergistic effect of Ni–Mo–P and TiO2 heterojunction, together with abundant active sites. In addition, the Zn–NO2− battery with Ni–Mo–P/TiO2 as the anode exhibits excellent battery performance, its power density can reach 6.0 mW cm−2, and a large amount of NH3 can be produced while generating electricity.

The novel π–d conjugated TM2B3N3S6 (TM = Mo, Ti and W) monolayers as highly active single-atom catalysts for electrocatalytic synthesis of ammonia

Recently, single-atom catalysts (SACs) are receiving significant attention in electrocatalysis fields due to their excellent specific activities and extremely high atomic utilization ratio. Effective loading of metal atoms and high stability of SACs increase the number of exposed active sites, thus significantly improving their catalytic efficiency. Herein, we proposed a series (29 in total) of two-dimensional (2D) conjugated structures of TM2B3N3S6 (TM means those 3d to 5d transition metals) and studied the performance as single-atom catalysts for nitrogen reduction reaction (NRR) using density functional theory (DFT). Results show that TM2B3N3S6 (TM = Mo, Ti and W) monolayers have superior performance for ammonia synthesis with low limiting potentials of −0.38, −0.53 and −0.68 V, respectively. Among them, the Mo2B3N3S6 monolayer shows the best catalytic performance of NRR. Meanwhile, the π conjugated B3N3S6 rings undergo coordinated electron transfer with the d orbitals of TM to exhibit good chargeability, and these TM2B3N3S6 monolayers activate isolated N2 according to the “acceptance–donation” mechanism. We have also verified the good stability (i.e., Ef < 0, and Udiss > 0) and high selectivity (Ud = –0.03, 0.01 and 0.10 V, respectively) of the above four types of monolayers for NRR over hydrogen evolution reaction (HER). The NRR activities have been clarified by multiple-level descriptors (ΔG*N2H, ICOHP, and Ɛd) in the terms of basic characteristics, electronic property, and energy. Moreover, the aqueous solution can promote the NRR process, leading to the reduction of ΔGPDS from 0.38 eV to 0.27 eV for the Mo2B3N3S6 monolayer. However, the TM2B3N3S6 (TM = Mo, Ti and W) also showed excellent stability in aqueous phase. This study proves that the π-d conjugated monolayers of TM2B3N3S6 (TM = Mo, Ti and W) as electrocatalysts show great potentials for the nitrogen reduction.

Crystal structures of molybdenum borides dictate electrocatalytic ammonia synthesis efficiency

Rather than multivalence molybdenum (Mo), the low valence Mo has rarely been reported as active site for nitrogen reduction. Herein, molybdenum borides with various Mo-B stoichiometry ratios (Mo2B, α-MoB, and Mo2B4) in which Mo shows low valence (<1) are synthesized as electrochemical nitrogen reduction reaction (eNRR) catalysts. Mo2B4 demonstrates the highest NH3 yield of 7.65 µg h− 1/mg at − 0.15 V with Faradaic efficiency (FE) of 12.47 %, while α-MoB exhibits the fastest intrinsic eNRR reaction rate with a higher FE of 17.17 % after considering electrochemically active surface area. DFT calculations reveal that both enzymatic and consecutive mechanisms via side-on configuration can proceed on α-MoB. Additionally, α-MoB exhibits suppressed HER activity due to an optimal surface B occupancy. The eNRR of molybdenum borides were verified qualitatively and quantitatively by 15N2 isotope experiments. This study demonstrated a synergistic design of eNRR and HER activity to achieve efficient electrocatalytic ammonia production with high eNRR selectivity.

Unveiling “Sabatier principle” for electrocatalytic nitric oxide reduction on single cluster catalysts: A DFT and machine learning guideline

As a revolutionary chemical engineering, the electrocatalytic synthesis of ammonia (NH3) has become one alternative option for green hydrogen storage. However, under the guidance of Sabatier principle, favored single atom catalyst (SAC) hardly gets rid of the perplexity of element selection. Here, a span-new structure-activity correlation for nitric oxide reduction reaction (NORR) was well-proposed on single cluster catalyst (SCC), which not only contributes to improve the activity with the cluster growth, but also breaks the consistent pattern of catalytic performance toward designed SAC. By performing DFT calculations, Co4@GaS was selected out because of its unexceptionable activity, only −0.06 V for working potential rarely reported yet. More eye-catching, as the displacement of activity descriptors obtained from elusory electronic characteristics only, a universal expression that handles free energy change was put forward with the assistance of machine learning (ML). This work may open a fresh avenue for the rational and straightforward design of desirable catalysts and even the development of interdisciplinary in chemistry.

Computational insights on potential dependence of electrocatalytic synthesis of ammonia from nitrate

Electrochemical nitrate reduction reaction (eNO3RR) has been considered as an alternative route for decentralized ammonia (NH3) synthesis. However, a major challenge is products selectivity at low overpotentials, namely, the competition between nitrite (HNO2) and ammonia. Herein, we employed a single-atom catalyst (FeN4) as model to study the competitive mechanism of NH3 and HNO2 by density functional theory calculations. It was found the optimal paths for ammonia and nitrite productions share a key intermediate (NO2*), whose adsorption structures and preference in the following conversion determines the selectivity. We have incorporated potential-dependent barriers and microkinetic modeling to understand the Faradaic efficiency at different potentials. Our results are in good agreement with the experimental trend of Faradaic efficiencies of NH3 and HNO2, which can be rationalized well by the charge transfer coefficient (β) for NO2* protonation to cisHNO2* with respect to that to HNO2. A low selectivity of ammonia production at small overpotentials can be ascribed to a kinetic issue. The electron localization function and crystal orbital Hamilton population were analyzed on the initial and transition states for NO2* protonation to cisHNO2* and HNO2. The computational mechanistic insights can help to design new catalyst for eNO3RR highly active and selective to NH3.

P‐d Orbital Hybridization Engineered Single‐Atom Catalyst for Electrocatalytic Ammonia Synthesis

The rational design of metal single‐atom catalysts (SACs) for electrochemical nitrogen reduction reaction (NRR) is challenging. Two‐dimensional metal–organic frameworks (2DMOFs) is a unique class of promising SACs. Up to now, the roles of individual metals, coordination atoms, and their synergy effect on the electroanalytic performance remain unclear. Therefore, in this work, a series of 2DMOFs with different metals and coordinating atoms are systematically investigated as electrocatalysts for ammonia synthesis using density functional theory calculations. For a specific metal, a proper metal‐intermediate atoms p‐d orbital hybridization interaction strength is found to be a key indicator for their NRR catalytic activities. The hybridization interaction strength can be quantitatively described with the p−/d‐ band center energy difference (∆d‐p), which is found to be a sufficient descriptor for both the p‐d hybridization strength and the NRR performance. The maximum free energy change (ΔGmax) and ∆d‐p have a volcanic relationship with OsC4(Se)4 located at the apex of the volcanic curve, showing the best NRR performance. The asymmetrical coordination environment could regulate the band structure subtly in terms of band overlap and positions. This work may shed new light on the application of orbital engineering in electrocatalytic NRR activity and especially promotes the rational design for SACs.

Interfacial hydrogen bonding-involved electrocatalytic ammonia synthesis on OH-terminated MXene

MXene basal planes are generally considered catalytically inert, due to the passivation by inactive surface groups. However, theoretical calculation predicates that MXene basal planes can become active by tuning its terminal groups. The above understandings are ambiguous on whether the MXene basal planes are indeed electrocatalytically active, and in turn what are the true active sites on MXene. Herein, we functionalized Ti3C2 MXene by introducing terminal oxygen groups to reveal the active sites and probe the reaction mechanism for electrocatalytic nitrate reduction reaction (eNO3-RR). On the basis of the data presented, the in situ transformed surface hydroxyl groups were identified as a new active site for nitrate reduction. A novel reaction mechanism involving hydrogen-bonding (H-bonding) between nitrate and the -OH groups on the Ti3C2 MXene basal plane was proposed, which adequately explained the high applied potentials and low selectivity for HER on the OH-terminated Ti3C2 MXene during eNO3-RR. This hydrogen-bonding-mediated process is likely applicable to a wide range of other materials and reactions.

Defective 1Tˊ-MoX2 (X = S, Se, Te) monolayers for electrocatalytic ammonia synthesis: Steric and electronic effects on the catalytic activity

Point defects, including both vacancy (Vd) and antisite defects (Ad) are common in transition metal dichalcogenides (TMDs). Both types of defects are produced due to the deviation from stoichiometric ratio of precursor materials and both point defects can serve as active sites in catalytic reactions. In this study, by means of first-principles calculations, the activities of single-point defective 1T′–MoX2 (X = S, Se, Te) monolayers for the electrocatalytic nitrogen reduction reaction (eNRR) and nitric oxide reduction reaction (eNORR) are investigated. Our results show that these catalysts have great potential toward eNRR and eNORR by exhibiting low limiting potentials (UL). For eNRR, the antisite defects (UL’s are −0.45, −0.31 and −0.27 V for 1T′–MoS2@SAd, 1T′–MoSe2@SeAd and 1T′–MoTe2@TeAd) have better catalytic activity than the vacancy defects (UL’s are −0.94, −0.53 and −0.36 V for 1T′–MoS2@SVd, 1T′–MoSe2@SeVd and 1T′–MoTe2@TeVd). All the calculated UL’s are much smaller than that of the Ru (0001) surface (UL = −0.98 V), the benchmark catalyst for eNRR. For eNORR, except for the 1T′–MoS2@SVd catalyst, antisite defects still perform better (UL’s are correspondingly −0.45, 0 and 0 V for 1T′–MoS2@SVd, 1T′–MoSe2@SeVd and 1T′–MoTe2@TeVd; for vacancy defects, they are 0, −0.13 and −0.36 V). In addition, for eNRR, the hydrogen evolution reaction (HER) is effectively inhibited over the 1T′–MoTe2@TeVd, 1T′–MoS2@SAd, 1T′–MoSe2@SeAd and 1T′–MoTe2@TeAd catalysts. Meanwhile, for eNORR, HER is inhibited over all six catalysts. During the eNORR process at at high NO concentration, except for the 1T′–MoSe2@SeVd and 1T′–MoTe2@TeVd catalysts, the other four show better selectivity toward NH3 than the byproducts of N2O/N2. The activity superiority of the antisite defects is mainly steric, i.e., the steric hindrance is larger at the bowl-shaped vacancy defect. In contrast, the activity difference among the catalysts with the same type of defects is largely electronic, which can be represented by work function. For example, the capability of N2/NO activation and electron transfer increases with the decreasing value of work function:1T′–MoS2@SAd (5.62 eV) < 1T′–MoSe2@SeAd (5.10 eV) < 1T′–MoTe2@TeAd (4.53 eV). Overall, these catalysts are promising for electrochemical ammonia synthesis from N2 and NO. This work may also be useful to the rational design of TMD-based catalysts.

Electrocatalytic Reduction of Nitrate to Ammonia via a Au/Cu Single Atom Alloy Catalyst.

Electrocatalytic ammonia (NH3) synthesis from the reduction of nitrate (NO3-) is one of the effective and mild methods to treat nitrogen-containing wastewater from stationary sources and to obtain NH3 readily compared with the Haber-Bosch process. However, the low efficiency of electrocatalytic NO3- reduction to NH3 on traditional Cu-based catalysts hinders their practical application. Here, we prepare a Au/Cu single atom (SA) alloy (Au/Cu SAA) that shows a high performance of NH3 synthesis with 99.69% Faradaic efficiency at -0.80 V vs RHE. The structures of Au SAs and alloyed Au/Cu are confirmed by the detailed characterizations. Online differential electrochemical mass spectrometry confirms the occurrence of key reaction intermediates (*NO2, *NO, and *NH3). Density functional theory calculations demonstrate that Au SAs efficiently reduce the adsorption energy of *NO3-, and the newly formed Au-Cu bonds boost the reduction process of *NO2 to *NO. Meanwhile, Au/Cu SAAs produce significantly less N2 and N2O byproducts due to the prohibition of N-N coupling on single atoms, which finally leads to excellent Faradaic efficiency and NH3 selectivity.

Electrocatalytic ammonia synthesis on Fe@MXene catalyst as cathode of intermediate-temperature proton-conducting solid oxide cell

As the only carbon-free energy carrier without CO2 emission upon decomposition, ammonia is an ideal storage medium for H2. However, the current low efficiency of ammonia synthesis is a main challenge on intermediate-temperature proton-conducting electrochemical cells. Herein, we develop a novel non-precious cathode catalyst consisting of Fe nanoparticles loaded on two-dimensional MXene nanosheets (Fe@MXene) that can achieve a high Faradaic efficiency of 8.4% and an NH3 yield of 8.24 × 10−9 mol. s−1·cm−2 on an anode-supported Ba0·95Ce0·6Tb0·1Y0·2Zr0·1O3-δ-based electrolyte. The resultant catalyst with high specific surface area and catalytic active sites is beneficial to N2 reduction, resulting from the effective activation of N2 molecules imposed by the transported protons. The mechanism of catalytic NRR reveals that Fe@MXene catalyst can increase the electrocatalytic efficiency because of the improvement in the reaction rate constant. These show a promising catalyst of Fe@MXene for N2 reduction reaction using intermediate-temperature proton-conducting solid oxide cell.

Engineering hydrophobic-aerophilic interfaces to boost N2 diffusion and reduction through functionalization of fluorine in second coordination spheres.

Ammonia is a crucial biochemical raw material for nitrogen containing fertilizers and a hydrogen energy carrier obtained from renewable energy sources. Electrocatalytic ammonia synthesis is a renewable and less-energy intensive way as compared to the conventional Haber-Bosch process. The electrochemical nitrogen reduction reaction (eNRR) is sluggish, primarily due to the deceleration by slow N2 diffusion, giving rise to competitive hydrogen evolution reaction (HER). Herein, we have engineered a catalyst to have hydrophobic and aerophilic nature via fluorinated copper phthalocyanine (F-CuPc) grafted with graphene to form a hybrid electrocatalyst, F-CuPc-G. The chemically functionalized fluorine moieties are present in the second coordination sphere, where it forms a three-phase interface. The hydrophobic layer of the catalyst fosters the diffusion of N2 molecules and the aerophilic characteristic helps N2 adsorption, which can effectively suppress the HER. The active metal center is present in the primary sphere available for the NRR with a viable amount of H+ to achieve a substantially high faradaic efficiency (FE) of 49.3% at -0.3 V vs. RHE. DFT calculations were performed to find out the rate determining step and to explore the full energy pathway. A DFT study indicates that the NRR process follows an alternating pathway, which was further supported by an in situ FTIR study by isolating the intermediates. This work provides insights into designing a catalyst with hydrophobic moieties in the second coordination sphere together with the aerophilic nature of the catalyst that helps to improve the overall FE of the NRR by eliminating the HER.

Coupling electrocatalytic cathodic nitrate reduction with anodic formaldehyde oxidation at ultra-low potential over Cu2O

An HCHO oxidation reaction for electrocatalytic ammonia synthesis was developed to replace the sluggish anodic oxygen evolution reaction involving electrocatalytic oxidative dehydrogenation and tandem reaction pathways.

Environmental and economic potential of decentralised electrocatalytic ammonia synthesis powered by solar energy.

Intense efforts have been devoted to developing green and blue centralised Haber-Bosch processes (gHB and bHB, respectively), but the feasibility of a decentralised and more sustainable scheme has yet to be assessed. Here we reveal the conditions under which small-scale systems (NH3-leaves) based on the electrocatalytic reduction of nitrogen (eN2R) powered by photovoltaic energy could realise a decentralised scheme competitive in terms of environmental and economic criteria. For this purpose, we calculated energy efficiency targets worldwide, providing clear values that may guide research in the incipient eN2R field. Even at this germinal stage, the NH3-leaf technology would compete favourably in sunny locations for CO2-related Earth-system processes and human health relative to the business-as-usual production scenario. Moreover, a modest 8% gain in energy efficiency would already make them outperform the gHB in terms of climate change-related impacts in the sunniest locations. If no CO2 taxation is enforced, the lowest estimated ammonia production cost would be 3 times the industrial standard, with the potential to match it provided a substantial decrease of investment costs and very high selectivity toward ammonia in eN2R are achieved. The disclosed sustainability potential of NH3-leaf makes it a strong ally of gHB toward defossilised ammonia production.