Electrochemical N2 Reduction Reaction Research Articles

Enhanced Electrochemical N2 Reduction to NH3 on Reduced Graphene Oxide by Tannic Acid Modification

Developing high-efficiency nonmetal electrocatalysts for the electrochemical N2 reduction reaction (NRR) is of great significance for the sustainable development of human society. Here, we demonstr...

Surface-defective FeS2 for electrochemical NH3 production under ambient conditions

Abstract In the viewpoint of ammonia economy, electrochemical N2 reduction reaction (NRR) under mild condition is a very promising approach for sustainable development. By virtue of robust activity and low cost, transition-metal-based materials become one kind of the most attractive electrocatalysts in realizing ammonia synthesis to the industrial level. However, the investigation related to NRR electrocatalysts still mainly rely on costly substance or fabrication process, which greatly restrict their large-scale applications. In this work, a simple fabricated FeS2 electrode is adopted as NRR catalysts. The abundant surface defects due to the existence of Cr element, as well as the synergistic effect between FeS2 crystal planes provided excellent electrocatalytic performance with a high NH3 yield rate (11.5 μg h−1mg -1 Fe) and Faradaic efficiency (14.6%) at -0.2 V vs. reversible hydrogen electrode (RHE) toward NRR under ambient conditions. The superior catalytic performance of such non-precious metal catalysts would strongly promote the application of NRR process industrially.

Enhanced Electrocatalytic N2 Reduction via Partial Anion Substitution in Titanium Oxide–Carbon Composites

AbstractThe electrochemical conversion of N2 at ambient conditions using renewably generated electricity is an attractive approach for sustainable ammonia (NH3) production. Considering the chemical inertness of N2, rational design of efficient and stable catalysts is required. Therefore, in this work, it is demonstrated that a C‐doped TiO2/C (C‐TixOy/C) material derived from the metal–organic framework (MOF) MIL‐125(Ti) can achieve a high Faradaic efficiency (FE) of 17.8 %, which even surpasses most of the established noble metal‐based catalysts. On the basis of the experimental results and theoretical calculations, the remarkable properties of the catalysts can be attributed to the doping of carbon atoms into oxygen vacancies (OVs) and the formation of Ti−C bonds in C‐TixOy. This binding motive is found to be energetically more favorable for N2 activation compared to the non‐substituted OVs in TiO2. This work elucidates that electrochemical N2 reduction reaction (NRR) performance can be largely improved by creating catalytically active centers through rational substitution of anions into metal oxides.

Enhanced Electrocatalytic N2 Reduction via Partial Anion Substitution in Titanium Oxide-Carbon Composites.

The electrochemical conversion of N2 at ambient conditions using renewably generated electricity is an attractive approach for sustainable ammonia (NH3 ) production. Considering the chemical inertness of N2 , rational design of efficient and stable catalysts is required. Therefore, in this work, it is demonstrated that a C-doped TiO2 /C (C-Tix Oy /C) material derived from the metal-organic framework (MOF) MIL-125(Ti) can achieve a high Faradaic efficiency (FE) of 17.8 %, which even surpasses most of the established noble metal-based catalysts. On the basis of the experimental results and theoretical calculations, the remarkable properties of the catalysts can be attributed to the doping of carbon atoms into oxygen vacancies (OVs) and the formation of Ti-C bonds in C-Tix Oy . This binding motive is found to be energetically more favorable for N2 activation compared to the non-substituted OVs in TiO2 . This work elucidates that electrochemical N2 reduction reaction (NRR) performance can be largely improved by creating catalytically active centers through rational substitution of anions into metal oxides.

Spinel LiMn2O4 Nanofiber: An Efficient Electrocatalyst for N2 Reduction to NH3 under Ambient Conditions.

The production of ammonia (NH3) in the industrial scale basically relies on the traditional technology of Haber-Bosch, which is operated under harsh conditions with high energy consumption and a huge number of greenhouse gas emissions. Electrochemical N2 reduction reaction (NRR) is a promising route for artificial N2-to-NH3 fixation with less energy consumption. However, an effective electrocatalyst, as a prerequisite of the NRR, is of significance. Here, we report that a spinel LiMn2O4 nanofiber acts as a noble-metal-free electrocatalyst for NH3 synthesis with excellent performance under ambient conditions. The electrocatalyst, which was tested in 0.1 M HCl, has an excellent Faradaic efficiency of 7.44% and a NH3 yield of 15.83 μg h-1 mgcat.-1 at -0.50 V versus reversible hydrogen electrode. Moreover, it also possesses excellent electrochemical and structure stability.

Activated TiO2 with tuned vacancy for efficient electrochemical nitrogen reduction

Renewable energy-driven electrochemical N2 reduction reaction (NRR) provides a green and sustainable route for NH3 synthesis under ambient conditions but is plagued by a high reaction barrier and low selectivity. To promote NRR, modification of the catalyst surface to increase N2 adsorption and activation is key. Here, we show that engineering surface oxygen vacancies of TiO2 permits significantly enhanced NRR activity with an NH3 yield rate of about 3.0 μgNH3 h−1 mgcat.−1 and a faradaic efficiency (FE) of 6.5% at -0.12 V (vs. the reversible hydrogen electrode, RHE). Efficient conversion of N2 to NH3 is achieved in a wide applied potential range from -0.07 to -0.22 V (vs. RHE) with NH3 production rates ≥ 2.0 μgNH3 h−1 mgcat.-1 and NH3 FEs ≥ 4.9%, respectively. An NH3 FE as high as 9.8% is obtained at a low overpotential of 80 mV. Density functional theory calculations reveal that the surface oxygen vacancies in TiO2 play a vital role in facilitating electrochemical N2 reduction by activating the first protonation step and also increasing N2 chemisorption (relative to *H).

Electrochemical Nitrogen Reduction Reaction on Ruthenium

Ruthenium is a good catalyst for ammonia synthesis in the Haber–Bosch process and a promising electrocatalyst for electrochemical N2 reduction reaction (NRR). However, the NRR pathway on Ru is uncl...

In Situ Hydrothermal Growth of TiO2 Nanoparticles on a Conductive Ti3C2T x MXene Nanosheet: A Synergistically Active Ti-Based Nanohybrid Electrocatalyst for Enhanced N2 Reduction to NH3 at Ambient Conditions.

The traditional power-wasting Haber-Bosch process still dominates industrial NH3 production. Recent years witnessed the rapid development of an electrochemical N2 reduction reaction (NRR) because of its environmentally benign and sustainable feature. Here, we demonstrate the first utilization of a Ti3C2T x MXene nanosheet as both the precursor and conductive substrate toward the in situ hydrothermal growth of TiO2 nanoparticles. The marriage of TiO2 and Ti3C2T x leads to a synergistically active Ti-based nanohybrid catalyst that can strengthen N2 reduction electrocatalysis. When tested in 0.1 M HCl, such a TiO2/Ti3C2T x hybrid is superior in catalytic performance, capable of affording a NH3 yield of 26.32 μg h-1 mg-1cat. with a 8.42% Faradaic efficiency (FE) at -0.60 V versus reversible hydrogen electrode (RHE), larger than those for TiO2 and Ti3C2T x. Notably, this nanohybrid also shows good NH3 selectivity with high electrochemical durability.

NiO Nanodots on Graphene for Efficient Electrochemical N2 Reduction to NH3

Current artificial NH3 synthesis relies heavily on the Haber–Bosch process that involves enormous energy consumption and huge CO2 emission. The electrochemical N2 reduction reaction (NRR) offers an...

High‐Performance Electrocatalytic Conversion of N2 to NH3 Using Oxygen‐Vacancy‐Rich TiO2 In Situ Grown on Ti3C2Tx MXene

AbstractTo achieve the energy‐effective ammonia (NH3) production via the ambient‐condition electrochemical N2 reduction reaction (NRR), it is vital to ingeniously design an efficient electrocatalyst assembling the features of abundant surface deficiency, good dispersibility, high conductivity, and large surface specific area (SSA) via a simple way. Inspired by the fact that the MXene contains thermodynamically metastable marginal transition metal atoms, the oxygen‐vacancy‐rich TiO2 nanoparticles (NPs) in situ grown on the Ti3C2Tx nanosheets (TiO2/Ti3C2Tx) are prepared via a one‐step ethanol‐thermal treatment of the Ti3C2Tx MXene. The oxygen vacancies act as the main active sites for the NH3 synthesis. The highly conductive interior untreated Ti3C2Tx nanosheets could not only facilitate the electron transport but also avoid the self‐aggregation of the TiO2 NPs. Meanwhile, the TiO2 NPs generation could enhance the SSA of the Ti3C2Tx in return. Accordingly, the as‐prepared electrocatalyst exhibits an NH3 yield of 32.17 µg h−1 mg−1cat. at −0.55 V versus reversible hydrogen electrode (RHE) and a remarkable Faradaic efficiency of 16.07% at −0.45 V versus RHE in 0.1 m HCl, placing it as one of the most promising NRR electrocatalysts. Moreover, the density functional theory calculations confirm the lowest NRR energy barrier (0.40 eV) of TiO2 (101)/Ti3C2Tx compared with Ti3C2Tx or TiO2 (101) alone.

Defect-rich fluorographene nanosheets for artificial N2 fixation under ambient conditions.

NH3, synthesized by the Haber-Bosch process, is essential for fertilisers in order to feed the world's growing population, however, it causes massive energy consumption and generates large amounts of greenhouse gases. Electrochemical N2 reduction reaction (NRR) at ambient conditions is highly desirable for energy-efficient and sustainable NH3 production but this requires an efficient catalyst. In this work, we report a defect-rich fluorographene nanosheet synthesised via fluorination of graphene for NRR electrocatalysis. Such an electrocatalyst shows an NH3 formation rate of 9.3 μg h-1 mgcat.-1 and a faradaic efficiency of 4.2% at -0.7 V vs. reversible hydrogen electrode in 0.1 M Na2SO4. Density functional theory calculations reveal that the fluorination of graphene induces defects, which not only provide reaction sites for NRR but effectively activate N2 molecules.

Ceria-reduced graphene oxide nanocomposite as an efficient electrocatalyst towards artificial N2 conversion to NH3 under ambient conditions.

For over a century, NH3 synthesis via the Haber-Bosch process has brought huge energy costs and high CO2 emission. The electrochemical N2 reduction reaction is an environmentally-benign alternative, which can be driven by renewable energy. In this work, CeO2 nanoparticle-reduced graphene oxide nanocomposites (CeO2-rGO) behave as an efficient non-noble-metal N2 reduction reaction electrocatalyst with excellent selectivity. In 0.1 M Na2SO4, CeO2-rGO achieves a high faradaic efficiency of 4.78% and a large NH3 yield of 16.98 μg h-1 mgcat.-1 at -0.7 V vs. reversible hydrogen electrode. The catalytic mechanism was explored using density functional theory calculations.

MoS2 Polymorphic Engineering Enhances Selectivity in the Electrochemical Reduction of Nitrogen to Ammonia

The electrochemical N2 reduction reaction (NRR) offers a direct pathway to produce NH3 from renewable energy. However, aqueous NRR suffers from both low Faradaic efficiency (FE) and low yield rate. The main reason is the more favored H+ reduction to H2 in aqueous electrolytes. Here we demonstrate a highly selective Ru/MoS2 NRR catalyst on which the MoS2 polymorphs can be controlled to suppress H+ reduction. A NRR FE as high as 17.6% and NH3 yield rate of 1.14 × 10–10 mol cm–2 s–1 are demonstrated at 50 °C. Theoretical evidence supports a hypothesis that the high NRR activity originates from the synergistic interplay between the Ru clusters as N2 binding sites and nearby isolated S-vacancies on the 2H-MoS2 as centers for hydrogenation; this supports formation of NH3 at the Ru/2H-MoS2 interface.

High-Performance N2-to-NH3 Conversion Electrocatalyzed by Mo2C Nanorod.

The synthesis of NH3 is mainly dominated by the traditional energy-consuming Haber–Bosch process with a mass of CO2 emission. Electrochemical conversion of N2 to NH3 emerges as a carbon-free process for the sustainable artificial N2 reduction reaction (NRR), but requires an efficient and stable electrocatalyst. Here, we report that the Mo2C nanorod serves as an excellent NRR electrocatalyst for artificial N2 fixation to NH3 with strong durability and acceptable selectivity under ambient conditions. Such a catalyst shows a high Faradaic efficiency of 8.13% and NH3 yield of 95.1 μg h–1 mg–1cat at −0.3 V in 0.1 M HCl, surpassing the majority of reported electrochemical conversion NRR catalysts. Density functional theory calculation was carried out to gain further insight into the catalytic mechanism involved.

Rational Design of Fe–N/C Hybrid for Enhanced Nitrogen Reduction Electrocatalysis under Ambient Conditions in Aqueous Solution

Developing efficient noble-metal-free catalysts for the electrochemical N2 reduction reaction (NRR) under ambient conditions shows promise in fertilizer production and hydrogen storage. Here, as a proof-of-concept prototype, we design and implement an Fe–N/C–carbon nanotube (CNT) catalyst derived from a metal–organic framework and carbon-nanotube-based composite with built-in Fe–N3 active sites. This catalyst exhibits enhanced NRR activity with NH3 production (34.83 μg·h–1·mg–1cat.), faradaic efficiency (9.28% at −0.2 V vs RHE), selectivity, and stability in 0.1 M KOH aqueous media under mild conditions. Experimental and theoretical results both reveal that Fe–N3 species are the primary catalytically active centers for the NRR. This work provides insight into precise construction of more efficient and stable NRR electrocatalysts and further expands the possibilities of transition metal–nitrogen–carbon (M–N–C)-based nanomaterials in NRR fields.

Efficient Electrochemical N2 Reduction to NH3 on MoN Nanosheets Array under Ambient Conditions

Electrochemical N2 reduction reaction (NRR) under ambient conditions offers us an environmentally friendly route for artificial synthesis of NH3. However, up to now, few noble-metal-free electrocatalysts with satisfactory catalytic activities have been explored. In this Letter, we demonstrate that MoN nanosheets array on carbon cloth (MoN NA/CC) acts as a high-performance NRR electrocatalyst toward NH3 electrosynthesis in 0.1 M HCl under ambient conditions. This catalyst achieves a large NH3 yield of 3.01 × 10–10 mo1 s–1 cm–2 and a Faradaic efficiency of 1.15% at −0.3 V vs reversible hydrogen electrode with strong electrochemical durability and selectivity. Density functional theory calculations reveal that MoN NA/CC catalyzes NRR via the Mars–van Krevelen mechanism.

Aqueous electrocatalytic N2 reduction under ambient conditions

Recently, the electrochemical N2 reduction reaction (NRR) in aqueous electrolytes at ambient temperature and pressure has demonstrated its unique advantages and potentials. The reactants are directly derived from gaseous N2 and water, which are naturally abundant, and NH3 production is important for fertilizers and other industrial applications. To improve the conversion yield and selectivity (mainly competing with water reduction), electrocatalysts must be rationally designed to optimize the mass transport, chemisorption, and transduction pathways of protons and electrons. In this review, we summarize recent progress in the electrochemical NRR. Studies of electrocatalyst designs are summarized for different categories, including metal-based catalysts, metal oxide-derived catalysts, and hybrid catalysts. Strategies for enhancing the NRR performance based on the facet orientation, metal oxide interface, crystallinity, and nitrogen vacancies are presented. Additional system designs, such as lithium-nitrogen batteries, and the solvent effect are introduced. Finally, existing challenges and prospects are discussed.

Highly Efficient Ammonia Synthesis Electrocatalyst: Single Ru Atom on Naturally Nanoporous Carbon Materials

AbstractStabilizing single‐atom metal catalysts with carbon materials and utilizing their synergistic effect remains challenging due to weak interactions between carbon‐based supports and metals. Density functional theory (DFT) calculations indicate that a single Ru atom was supported on a wide range of natural nanoporous carbon materials, including C2N, triazine‐C3N4 (T‐C3N4), and γ‐graphene. These carbon materials belong to a new generation of highly efficient electrocatalysts for the N2 reduction reaction (NRR) and are named Ru1@C2N, Ru1@T‐C3N4, and Ru1@γ‐graphyne, respectively. Ab initio molecular dynamic (AIMD) simulations show that a single Ru atom can be stably anchored in the nanopores of these carbon materials with strong cohesive energy. Compared with parallel adsorption configuration, the vertical adsorption configuration of N2 exhibits higher adsorption energy. The calculated Gibbs free energy reveals N2 reduction on the three catalysts via associative mechanisms. Despite the similar limiting potentials (−0.96, −0.94, and −0.98 V on Ru1@C2N, Ru1@T‐C3N4, and Ru1@γ‐graphynes, respectively), the limiting step differs, indicating the significant effects of carbon material substrates on electrochemical NRR. However, the competitive and efficient hydrogen evolution reaction (HER) changes the potential determining step and increases the overpotential for the electrochemical nitrogen reduction (NRR). This study provides insights for experimental synthesis of electrocatalysts for N2 reduction.