N2 Reduction Reaction Research Articles

Atomically dispersed metal catalysts for the electrochemical nitrogen reduction reaction

The current breakthroughs in designing atomically dispersed metal catalysts for the electrochemical N2reduction reaction are summarized from both experimental and theoretical points of view. The outstanding performances of these catalysts are emphasized.

Theoretical Study on the Efficient Electrocatalytic N2 Reduction Reaction of Bimetallic Single Atom Embedded in Phthalocyanine

Theoretical Study on the Efficient Electrocatalytic N2 Reduction Reaction of Bimetallic Single Atom Embedded in Phthalocyanine

Electroreduction of N2 to NH3 catalyzed by a Mn/Re(111) single-atom alloy catalyst with high activity and selectivity: a new insight from a first-principles study

Periodic density functional theory calculations show that a Mn/Re(111) single-atom alloy may be an excellent catalyst with high activity and selectivity for the electrocatalytic N2 reduction reaction.

Application of machine-learning-based global optimization: potential-dependent co-electrosorbed structure and activity on the Pd(110) surface.

Electrodes can adsorb different reaction intermediates under electrochemical conditions, which in turn significantly affect their electrochemical performance. This complex phenomenon attracts continuous interest in both science and industry for understanding the co-electrosorbed structure and activity under electrochemical conditions. Here, we report the first theoretical attempt by combining the machine-learning-based global optimization (SSW-NN method) and modified Poisson-Boltzmann continuum solvation (CM-MPB) based on first-principles calculations to elucidate the potential-dependent co-electrosorbed species on the Pd(110) surface. We reveal the potential-dependence adsorption/absorption hydrogen phases, the phase transition of α-Hri/Pd to β-Hri/Pd, and the co-electrosorbed Hri-NHy surface structures. In particular, we found that Hri-NH2 and Hri-NH3 are favorable intermediates for the N2 reduction reaction, and the subsurface H is the key species responsible for NH2 hydrogenation on the Pd(110) electrode.

Pressurized N2 directly fed to the RuAu/CeO1.76 catalyst porous electrode in a proton exchange membrane electrolyzer favoring electrochemical NH3 production.

The limited N2 solubility in the present aqueous electrolyte critically restricts the selectivity and activity of environment-friendly electrochemical NH3 production at high current density. Here we developed a high-performance electrolyzer for the electrochemical N2 reduction reaction (eNRR) using amorphous RuAu clusters anchored on CeO1.88 nanorods with rich oxygen vacancies (OVs) as the catalyst and a proton exchange membrane (PEM) as the solid-state electrolyte, in which N2 is directly delivered to the electrode across a gas diffusion layer. The PEM electrolyzer achieved a remarkable NH3 yield rate of 185.53 μg mg-1 h-1 at -0.3 V vs. RHE under an applied N2 pressure of 4 bar, which is 5 times higher than that in aqueous electrolyte.

Reaction mechanism and kinetics for N2 reduction to ammonia on the Fe–Ru based dual-atom catalyst

To understand the reaction mechanism and kinetics of N2 reduction reaction and competing hydrogen evolution reaction on the dual-atom catalyst as a function of applied potential by applying the Grand canonical potential kinetics.

Two-dimensional graphdiyne analogue containing Mo-coordinated porphyrin covalent organic framework as a high-performance electrocatalyst for nitrogen fixation

Graphdiyne (GDY), as a burgeoning two-dimensional (2D) material, is regarded as an excellent carbon support owing to its unique polyyne structure, but lack of active sites. Meanwhile, metalloporphyrins can anchor various metals as eminent catalytic center and have been extensively applied in various electrochemical reactions, including N2 reduction reaction (NRR). Integrating metalloporphyrins connected by polyynes as GDY analogues may create facile and charming heterogeneous electrochemical catalysts by merging their complementary advantages and broad prospects. Herein, the electrocatalytic behaviors of a sequence of 2D metalloporphyrin-based GDY analogues connected by butadiyne (TM-PDYs, TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, and W, respectively) toward NRR have been investigated by employing first-principles calculations. The computations demonstrate that 2D Mo-PDY owns superior electrocatalytic property for N2 fixation with an ultralow overpotential of 0.14 V via the preferred distal pathway among the 19 candidates, together with the capability of inhibiting the competing hydrogen evolution reaction (HER). This work not only puts forward an innovative idea based on multi-active components to realize attainable functional 2D lattices for the design of high-performance catalysts, but also promotes more experimental researches in this field to achieve sustainable NH3 production.

Oxygen Vacancies of CeO2 Nanospheres by Mn-Doping: An Efficient Electrocatalyst for N2 Reduction under Ambient Conditions.

The electrochemical N2 reduction reaction (NRR) demonstrates a process of NH3 synthesis from N2 molecules under ambient conditions, which is environmentally friendly and recyclable. However, it requires an efficient electrocatalyst to activate inert N2 molecules, which is still difficult to satisfy. Recently, as an active NRR electrocatalyst and a typical metal oxide, CeO2 has featured ultrahigh thermal stability and the ability to apply heteroatom doping, which is an imperative approach importing oxygen vacancy by replacing metal ions with selective elements to greatly influence the activity of catalysts. Here, we analyze the unique properties of manganese dopants in modulating the activity of CeO2 nanospheres for NRR. It attains a larger NH3 yield of 27.79 μg h-1 mgcat-1 and a higher Faradaic efficiency of 9.1% than pure CeO2 at -0.30 V in 0.1 M HCl, with high electrochemical and structure stability. With calculations by density functional theory, the performance enhancement of Mn-doped CeO2 is also proved mathematically.

Unveiling the Synergy of O‐Vacancy and Heterostructure over MoO3‐x/MXene for N2 Electroreduction to NH3

AbstractThe electrochemical N2 reduction reaction (NRR) offers a promising approach for sustainable NH3 production, and modulating the structural/electronic configurations of the catalyst materials with optimized electrocatalytic properties is pivotal for achieving high‐efficiency NRR electrocatalysis. Herein, vacancy and heterostructure engineering are rationally integrated to explore O‐vacancy‐rich MoO3‐x anchored on Ti3C2Tx‐MXene (MoO3‐x/MXene) as a highly active and selective NRR electrocatalyst, achieving an exceptional NRR activity with an NH3 yield of 95.8 µg h−1 mg−1 (−0.4 V) and a Faradaic efficiency of 22.3% (−0.3 V). A combination of in situ spectroscopy, molecular dynamics simulations and density functional theory computations is employed to unveil the synergistic effect of O‐vacancies and heterostructures for the NRR, which demonstrates that O‐vacancies on MoO3‐x serve as the active sites for N2 chemisorption and activation, while the MXene substrate can further regulate the O‐vacancy sites to break the scaling relation to effectively stabilize *N2/*N2H while destabilizing *NH2/*NH3, resulting in more optimized binding affinity of NRR intermediates toward reduced energy barriers and an enhanced NRR activity for MoO3‐x/MXene.

Comparison between Fe2O3/C and Fe3C/Fe2O3/Fe/C Electrocatalysts for N2 Reduction in an Alkaline Electrolyte.

Cost-effective and nonprecious iron-based catalysts were synthesized, evaluated, and compared for electrocatalytic N2 reduction reaction (NRR) under alkaline conditions in the potential range from -0.4 to 0.1 V [vs reversible hydrogen electrode (RHE)] at low temperature (≤60 °C) and atmospheric pressure. The tested H-type cell was separated by an anion exchange membrane in 6 M KOH alkaline electrolyte (pH = over 14) in order to minimize hydrogen evolution reaction and to directly form NH3 gas. The amount of ammonia synthesized was quantified using an indophenol blue method and cross-checked with 1H nuclear magnetic resonance spectroscopy and ion chromatography using both 14N2 and 15N2 gases. Because of the synergistic effect between the Fe3C, Fe2O3, and Fe composites in the NRR, both the ammonia formation rate and faradaic efficiency in Fe3C/Fe2O3/Fe/C were approximately fourfold higher than those in Fe2O3/C at 60 °C and 0.1 V (vs RHE). These results can provide insights into designing Fe-based electrocatalysts for NRR at atmospheric pressure.

Engineering vacancy and hydrophobicity of two-dimensional TaTe2 for efficient and stable electrocatalytic N2 reduction

Demand for ammonia continues to increase to sustain the growing global population. The direct electrochemical N2 reduction reaction (NRR) powered by renewable electricity offers a promising carbon-neutral and sustainable strategy for manufacturing NH3, yet achieving this remains a grand challenge. Here, we report a synergistic strategy to promote ambient NRR for ammonia production by tuning the Te vacancies (VTe) and surface hydrophobicity of two-dimensional TaTe2 nanosheets. Remarkable NH3 faradic efficiency of up to 32.2% is attained at a mild overpotential, which is largely maintained even after 100 h of consecutive electrolysis. Isotopic labeling validates that the N atoms of formed NH4+ originate from N2. In situ X-ray diffraction indicates preservation of the crystalline structure of TaTe2 during NRR. Further density functional theory calculations reveal that the potential-determining step (PDS) is ∗NH2 + (H+ + e–) → NH3 on VTe-TaTe2 compared with that of ∗ + N2 + (H+ + e–) → ∗N–NH on TaTe2. We identify that the edge plane of TaTe2 and VTe serve as the main active sites for NRR. The free energy change at PDS on VTe-TaTe2 is comparable with the values at the top of the NRR volcano plots on various transition metal surfaces.

Boosting the Electrocatalytic Conversion of Nitrogen to Ammonia on Metal-Phthalocyanine-Based Two-Dimensional Conjugated Covalent Organic Frameworks.

The electrochemical N2 reduction reaction (NRR) under ambient conditions is attractive in replacing the current Haber-Bosch process toward sustainable ammonia production. Metal-heteroatom-doped carbon-rich materials have emerged as the most promising NRR electrocatalysts. However, simultaneously boosting their NRR activity and selectivity remains a grand challenge, while the principle for precisely tailoring the active sites has been elusive. Herein, we report the first case of crystalline two-dimensional conjugated covalent organic frameworks (2D c-COFs) incorporated with M-N4-C centers as novel, defined, and effective catalysts, achieving simultaneously enhanced activity and selectivity of electrocatalytic NRR to ammonia. Such 2D c-COFs are synthesized based on metal-phthalocyanine (M = Fe, Co, Ni, Mn, Zn, and Cu) and pyrene units bonded by pyrazine linkages. Significantly, the 2D c-COFs with Fe-N4-C center exhibit higher ammonia yield rate (33.6 μg h-1 mgcat-1) and Faradaic efficiency (FE, 31.9%) at -0.1 V vs reversible hydrogen electrode than those with other M-N4-C centers, making them among the best NRR electrocatalysts (yield rate >30 μg h-1 mgcat-1 and FE > 30%). In situ X-ray absorption spectroscopy, Raman spectroelectrochemistry, and theoretical calculations unveil that Fe-N4-C centers act as catalytic sites. They show a unique electronic structure with localized electronic states at Fermi level, allowing for stronger interaction with N2 and thus faster N2 activation and NRR kinetics than other M-N4-C centers. Our work opens the possibility of developing metal-nitrogen-doped carbon-rich 2D c-COFs as superior NRR electrocatalyst and provides an atomic understanding of the NRR process on M-Nx-C based electrocatalysts for designing high-performance NRR catalysts.

Ordered Vacancies on the Body-Centered Cubic PdCu Nanocatalysts.

Defect engineering has become one of the important considerations in today's electrocatalyst design. However, the vacancies in the ordered crystal structure (especially body-centered cubic (bcc) and the effect of ordered vacancies (OVs) on the electronic fabric have not been researched yet. In this work, we report the inaugural time of the generation of OVs in the bcc architecture and discuss the insight of the modulation system of the material and its part in the electrochemical N2 reduction reaction (NRR). OV-PdCu-2 achieves the highest Faradaic efficiency value of 21.5% at 0.05 V versus RHE. When the potential increases to 0 V versus RHE, the highest ammonia yield is 55.54 μg h-1 mgcat-1, which is significantly better than the unetched PdCu nanoparticles (12.83 μg h-1 mgcat-1). It is the latest reported catalyst to date in the NRR process at 0 V versus RHE (see Supporting Information).

The activity evidence of Ti defect towards electrocatalytic N2 reduction

Electrochemical N2 reduction reaction (NRR) for NH3 synthesis, which usually needs highly-efficient electrocatalysts for N2 activation, is a carbon-neutral alternation compared to the traditional Haber–Bosch process. Although Ti-based compounds is widely used as electrocatalysts, what Ti defect affects NRR activity is still illusive. In this work, our systematic density functional calculations on Ti defect-decorated titanium oxide disclose that the unsaturated-Ti with the orbital splitting of defect electron states is the necessary feature for N2 binding and activation, which can be further enhanced by increasing the splitting degree. The bonding/antibonding orbital population and projected density of states indicate that the nature of N2 binding and activation on Ti-defect site is attributed to the elimination of the bonding orbital population in the conduction bands and the formation of * π back-bonding in the valence bands. For the whole NRR process, the synergy of Ti-defect and oxygen vacancy (VO) promotes N2 reduction, and the required maximum energy input scales quite well with the adsorption strength of *NNH. Finally, the formed volcano shape successfully predicts new candidate catalysts for ammonia synthesis, such as TiO2 combined VO with Ti interstitial or H atom. This work provides disclosure of the key elements on the rational design of Ti-based nanomaterial electrocatalysts for artificial N2 fixation.

Communication—Partial Oxidation of MnS for Synergistic Electrocatalysis of N2-to-NH3 Fixation at Ambient Conditions

Compared with the traditional Haber-Bosch process, electrochemical N2 to NH3 reduction affords an eco-friendly and sustainable alternative to ambient NH3 synthesis with the aid of efficient electrocatalysts. In this work, partial oxidation of MnS to obtain the MnS-Mn3O4 is proved as a promising noble-free electrocatalysts of N2 to NH3 fixation at ambient conditions. When tested in 0.1 M Na2SO4, the electrochemical N2 reduction reaction performance of MnS-Mn3O4 is improved comparing with the MnS, which achieves large NH3 yield of 16.74 μg h–1 mgcat. –1 and a high Faradaic efficiency of 5.72%. It also exhibits excellent selectivity of N2 to NH3 and strong long-term electrochemical stability.

Carbon-Based Metal-Free Electrocatalysts: Past, Present, and Future

ConspectusDue to the overuse of fossil fuels, various detrimental effects along with the excess CO2 emissions have induced global warming and sea-level rising. To tackle climate change and provide a cleaner environment for the air we breathe and water we consume, the existing energy mix needs to be changed into fossil-free, clean, renewable energy with zero emission (e.g., fuel cells). While providing a promising and scalable strategy to the energy and environmental challenges, renewable energy processes often involve noble-metal-based catalysts (i.e., Pt, RuO2). However, the disadvantages of noble-metal-based catalysts, including their high cost and scarcity, have hampered the large-scale application of renewable energy technologies. In 2009, we discovered earth-abundant carbon materials functioning as efficient low-cost, carbon-based metal-free electrocatalysts (C-MFECs) attractive for renewable energy and environmental remediation. Since then, C-MFECs have become an emerging new research field over the world. They are demonstrated to be efficient multifunctional catalysts for various key reactions important to renewable energy and environmental technologies, including oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), oxygen evolution reaction (OER), CO2 reduction reaction (CO2RR), and N2 reduction reaction (NRR), to name a few. Charge transfer/redistribution induced by heteroatom (e.g., N) and/or defect doping was recognized as the driving force for the metal-free catalytic activities. This finding has been used as a guidance to design and develop various new and multifunctional C-MFECs for many reactions even beyond the renewable energy and environmental remediation. In this Account, we first summarize our previous work on the development and mechanistic understanding of C-MFECs for ORR, HER, and OER to promote renewable energy conversion and storage. Then, we present recent advances in C-MFECs for new important reactions for environment remediation (e.g., CO2RR, NRR), seawater splitting, and metal–CO2 batteries. However, different dopant locations for C-MFECs even with the same doping element and content can cause variable catalytic properties for heteroatom-doped carbon materials. Therefore, vast opportunities remain for further developing numerous innovative C-MFECs with defined structures to gain a better understanding of their structure-based properties. In this context, we finally conclude with the current challenges and future perspectives in this exciting field.

In Situ Electrocatalytic Infrared Spectroscopy for Dynamic Reactions

The modern society is confronted with severe problems of energy consumption, climatic variation, and environmental pollution. A series of electrocatalysis reactions, including oxygen evolution reaction (OER), hydrogen evolution reaction (HER), CO2 reduction reaction (CO2RR), N2 or nitrate reduction reaction (NRR or NOxRR), and methanol or ethanol oxidation reaction (MOR or EOR), have become promising ways to solve these serious issues and realize sustainable development. However, the limited understanding of the dynamic process of electrocatalysis still hinders the rational design of these electrocatalysts. Combining infrared spectroscopy with electrocatalysis, in situ electrochemical infrared spectroscopy (in situ EIRS) is a mighty tool to acquire deep insight of dynamic electrocatalytic reaction process at molecule level. Moreover, the surface sensitive in situ EIRS could acquire information about the adsorbates and the key intermediate, making it broad prospects in the study of electrocatalytic dynamic process. In this short review, we summarize recent progress of in situ EIRS with the focus of probing dynamic reactions. In particular, we first briefly introduce the fundamental and the methodological development of in situ EIRS. Then, the recent advances of in situ EIRS applications in electrocatalytic reaction is demonstrated, including OER, HER, CO2RR, NRR, and MOR. Finally, challenges and perspectives of future research in related fields are discussed.

Superaerophobic copper-based nanowires array for efficient nitrogen reduction

Electrocatalytic N2 reduction reaction (NRR) provides a promising route for NH3 production under ambient conditions to replace traditional Haber-Bosch process. For this purpose, efficient NRR electrocatalysts with high NH3 yield rate and high Faradaic efficiency (FE) are required. Cu-based materials have been recognized catalytic active for some multi-electron-involved reduction reactions and usually exhibit inferior catalytic activities for hydrogen evolution reaction. We report here the preparation and characterization of a series of Cu-based nanowires array (NA) catalysts in situ grown on Cu foam (CF) substrate, including Cu(OH)2 NA/CF, Cu3N NA/CF, Cu3P NA/CF, CuO NA/CF and Cu NA/CF, which are directly used as self-supported catalytic electrodes for NRR. The electrochemical results show that CuO NA/CF achieves a highest NH3 yield rate of 1.84 × 10−9 mol s−1 cm−2, whereas Cu NA/CF possesses a highest FE of 18.2% for NH3 production at −0.1 V versus reversible hydrogen electrode in 0.1 M Na2SO4. Such catalytic performances are superior to most of recently reported metal-based NRR electrocatalysts. The contact angle measurements and the simulated calculations are carried out to reveal the important role of the superaerophobic NA surface structure for efficient NRR electrocatalysis.

Electrocatalytic N2 Reduction on FeS2 Nanoparticles Embedded in Graphene Oxide in Acid and Neutral Conditions

The development of stable, low-cost, and highly efficient electrocatalysts for the N2 reduction reaction (NRR) process is challenging but crucial for ammonia production. Herein, we demonstrate the synthesis of pyrite nanoparticles wrapped by graphene oxide (FeS2@GO) acting as a highly efficient NRR catalyst in a wide pH range. The FeS2 nanoparticles are uniformly dispersed across the GO nanosheet, thus leading to the fine exposure of active sites, the promotion of charge transfer, and the increment of a contact surface area, which are all beneficial for a desired catalyst. In the meantime, the low-coordinated Fe atoms are activated as highly active sites, which is in favor of the enhanced electrochemical performance for the NRR. Furthermore, density functional theory (DFT) calculations illustrated that the high activity of N2 reduction over the FeS2@GO catalyst arises from the well-exposed Fe active sites and the increment of charge density at the valence band edge. Benefiting from the well-optimized interface, the barrier of the addition of the first hydrogen atom to N2 forming *NNH species as the potential-determining step is as low as 0.93 eV in N2 electroreduction. The electrochemical test results reveal that, as expected, FeS2@GO exhibits high Faradaic efficiencies (4.7% in 0.1 M HCl solution and 6.8% in 0.1 M Na2SO4 solution) and advanced NH3 yields (78.6 and 27.9 μg h-1 mgcat.-1 in 0.1 M HCl and 0.1 M Na2SO4 solutions, respectively) in both acid and neutral conditions. This work offers a new avenue for exploring novel electrocatalysts, which has great promise to accelerate the practical application of the NRR.

High-spin state Fe(III) doped TiO2 for electrocatalytic nitrogen fixation induced by surface F modification

It is a challenging task to overcomes the bottleneck of N2 adsorption and activation in N2 reduction reaction (NRR). Regulating the catalyst surface electronic state is treated as a potential strategy to prevail over the barrier. Here, Incorporating Fe as a dopant in the TiO2 nanoparticles can generate oxygen vacancies and dopant energy levels, promoting the adsorption and activation of N2 molecules. F surface modification induces Fe (III) in the high spin state and upshifts the dopant energy level. That facilitates Fe 3d electrons backdonation to N 1πg* orbital promotes the activation of N2 molecule and reduces the limiting potential of NRR. Therefore, F-Fe: TiO2 electrocatalyst achieved the highest Faradaic efficiency and maximum NH3 production rate of 27.67% and 27.86 µg h1 mgcat.1 at −0.5 V v.s. reversible hydrogen electrode. This work provides deep insights into the design surface electronic state of catalyst toward efficient N2 to NH3 conversion.