High NH3 Yield Rate Research Articles

Salt‐Templated Construction of Ultrathin Cobalt Doped Iron Thiophosphite Nanosheets toward Electrochemical Ammonia Synthesis

Exploiting efficient electrocatalysts for electrochemical nitrogen reduction (NRR) is highly desired and deeply meaningful for realizing sustainable ammonia (NH3 ) production under ambient conditions. The Fe protein contains one [Fe4 S4 ] cluster and P cluster, which play an important role for transfer electron during the nitrogen fixing of nitrogenases. Based on the understanding of nitrogenase, the rising-star 2D iron thiophosphite (FePS3 ) nanomaterials may be highly active electrocatalysts toward NRR due to the ideal elemental composition. In this work, 2D FePS3 nanosheets are successfully synthesized by a facile salt-templated method. The FePS3 nanosheets show better electrocatalytic NH3 yield and faradaic efficiency (FE) than Fe2 S3 , which demonstrates that the P element indeed improves the NRR activity of Fe-S. Theoretically, Co incorporation not only effectively prompts the conductivity of FePS3 , but also enhances the catalytic activities of Fe-edge sites. Experimentally, Co-doped FePS3 (Co-FePS3 ) nanosheets exhibit a remarkable electrocatalytic performance toward NRR, such as high NH3 yield rate of 90.6 µg h-1 mgcat -1 , high FE of 3.38%, and an excellent long-term stability. Being the first theoretical and experimental report regarding FePS3 -based electrocatalyst toward NRR, this work represents an important beginning to the family of metal thiophosphite as advanced electrocatalysts toward NRR.

Tuning the Electron Localization of Gold Enables the Control of Nitrogen-to-Ammonia Fixation.

The (photo)electrochemical N2 reduction reaction (NRR) provides a favorable avenue for the production of NH3 using renewable energy in mild operating conditions. Understanding and building an efficient catalyst with high NH3 selectivity represents an area of intense interest for the early stages of development for NRR. Herein, we introduce a CoOx layer to tune the local electronic structure of Au nanoparticles with positive valence sites for boosting conversion of N2 to NH3 . The catalysts, possessing high average oxidation states (ca. 40 %), achieve a high NH3 yield rate of 15.1 μg cm-2 h-1 and a good faradic efficiency of 19 % at -0.5 V versus reversible hydrogen electrode. Experimental results and simulations reveal that the ability to tune the oxidation state of Au enables the control of N2 adsorption and the concomitant energy barrier of NRR. Altering the Au oxidation state provides a unique strategy for control of NRR in the production of valuable NH3 .

Tuning the Electron Localization of Gold Enables the Control of Nitrogen‐to‐Ammonia Fixation

AbstractThe (photo)electrochemical N2 reduction reaction (NRR) provides a favorable avenue for the production of NH3 using renewable energy in mild operating conditions. Understanding and building an efficient catalyst with high NH3 selectivity represents an area of intense interest for the early stages of development for NRR. Herein, we introduce a CoOx layer to tune the local electronic structure of Au nanoparticles with positive valence sites for boosting conversion of N2 to NH3. The catalysts, possessing high average oxidation states (ca. 40 %), achieve a high NH3 yield rate of 15.1 μg cm−2 h−1 and a good faradic efficiency of 19 % at −0.5 V versus reversible hydrogen electrode. Experimental results and simulations reveal that the ability to tune the oxidation state of Au enables the control of N2 adsorption and the concomitant energy barrier of NRR. Altering the Au oxidation state provides a unique strategy for control of NRR in the production of valuable NH3.

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.

Efficient Photoelectrochemical Route for the Ambient Reduction of N2 to NH3 Based on Nanojunctions Assembled from MoS2 Nanosheets and TiO2.

Efficient nitrogen fixation under ambient conditions is an exigent task in both basic research and industrial applications. Recently, reduction of N2 to NH3 based on photocatalysis and/or electrocatalysis offers a possible route to the typical Haber-Bosch process. However, achieving a high yield of N2 reduction reaction (NRR) is still a challenging goal because of the limitations of efficient catalysts. Herein, we propose a photoelectrochemical NRR route based on the rational design of MoS2@TiO2 semiconductor nanojunction catalysts through a facile hydrothermal synthetic method. The developed MoS2@TiO2 photocathode attains a high NH3 yield rate (1.42 × 10-6 mol h-1 cm-2) and a superhigh faradaic efficiency (65.52%), which is the highest record to the best of our knowledge. Moreover, MoS2@TiO2 exhibits high stability over 10 consecutive reaction cycles. Therefore, this work demonstrates an effective NRR photoelectrocatalyst and results in a breakthrough in the low faradaic efficiency because of the interfacial electronic coupling and synergistic effects between the MoS2 and TiO2 components.

Nitrogen-coordinated single Fe sites for efficient electrocatalytic N2 fixation in neutral media

Electrocatalytic nitrogen reduction reaction (NRR) for NH3 generation under ambient conditions presents a promising alternative to the conventional Haber–Bosch process. Here, we report a Fe single-atom catalyst for ambient electrochemical NH3 synthesis. This catalyst achieves high Faradaic efficiency (18.6 ± 0.8%) and NH3 yield rate (62.9 ± 2.7 μg h−1 mgcat.−1) in neutral aqueous electrolyte at room temperature and −0.4 V versus reversible hydrogen electrode. Furthermore, this catalyst exhibits a negligible activity decay during electrolysis for 24 h. X-ray absorption fine structure analyses and theoretical calculations reveal that atomically dispersed single Fe species are stabilized by N in Fe–N4 configuration, which is favorable for N2 activation. This work opens new opportunities for developing advanced single atomic site catalysts for NH3 synthesis via NRR.

(Invited) Atomically Dispersed Eletrocatalysts for High-Efficiency Ambient N2 Fixation

NH3 synthesis by the electrocatalytic N2 reduction reaction (NRR) under ambient conditions is regarded as an appealing alternative to the industrial method that requires high temperature and pressure. Finding a material that can efficiently catalyze electrochemical N2 fixation at ambient condition is a subject of considerable current interest. Atomically dispersed catalysts with mononuclear metal complexes or single metal atoms anchored on supports would be a promising candidate, because of their maximum atom efficiency, unique catalytic performances, and the similarity of the metal coordination environment to the ligand fields in molecular catalysts. A series of cost-effective and optimized atomically-dispersed eletrocatalysts for NRR will be reported. Our results show that the catalysts are featured with high density of single metal atoms supported on hierarchically porous carbon frameworks. They exhibited remarkable selectivity of NH3 formation and high NH3 yield rate at low applied potentials at room temperature. Moreover, the catalysts show negligible activity decay in an NRR electrolysis as long as 50,000 s. On the basis of our results and the previously reported work, a possible mechanism for NRR on the catalyst will be proposed to provide a fundamental insight into the high-efficiency NRR.

Bimodal nanoporous Pd3Cu1 alloy with restrained hydrogen evolution for stable and high yield electrochemical nitrogen reduction

Electrocatalytic nitrogen reduction reaction (NRR) under ambient temperature and pressure holds a great promise for NH3 production while it is still impeded by the low active site density and sluggish kinetics, leading to a low product yield rate. In this work, bimodal nanoporous PdCu alloys that have three-dimensional hierarchical interconnected porous network and tailored Pd/Cu atomic ratios are designed and used for electrocatalytic NRR with high NH3 yield rate at room temperature and atmosphere pressure. The Pd3Cu1 alloy that has large surface area for high active site density, bimodal porous structure for efficient reactant accessibility as well as desired electronic structure for restrained hydrogen evolution reaction exhibits a high NH3 yield rate of 39.9 μg h−1 mgcat−1, which is among the highest values for recently reported NRR electrocatalysts with high loading amount. Even at a low overpotential of − 0.15 V versus reversible hydrogen electrode (vs RHE), the alloy can still deliver a NRR yield rate of more than 10 μg h−1 mgcat−1. Moreover, structural integrity of the Pd3Cu1 alloy makes it a highly stable NRR electrocatalyst that keeps 100% of its original activity after 18 h operation, retaining its great potential for promising NRR electrocatalysis. The synergistic combination of bimodal nanoporous structure and alloy strategy could be used to design efficient catalysts for a wide range of reactions.

Atomically Dispersed Molybdenum Catalysts for Efficient Ambient Nitrogen Fixation

AbstractNH3 synthesis by the electrocatalytic N2 reduction reaction (NRR) under ambient conditions is an appealing alternative to the currently employed industrial method—the Haber–Bosch process—that requires high temperature and pressure. We report single Mo atoms anchored to nitrogen‐doped porous carbon as a cost‐effective catalyst for the NRR. Benefiting from the optimally high density of active sites and hierarchically porous carbon frameworks, this catalyst achieves a high NH3 yield rate (34.0±3.6 μg h−1 mgcat.−1) and a high Faradaic efficiency (14.6±1.6 %) in 0.1 m KOH at room temperature. These values are considerably higher compared to previously reported non‐precious‐metal electrocatalysts. Moreover, this catalyst displays no obvious current drop during a 50 000 s NRR, and high activity and durability are achieved in 0.1 m HCl. The findings provide a promising lead for the design of efficient and robust single‐atom non‐precious‐metal catalysts for the electrocatalytic NRR.

Electrochemical Fabrication of Porous Au Film on Ni Foam for Nitrogen Reduction to Ammonia.

Electrochemical reduction of N2 to NH3 provides an alternative strategy to replace the industrial Haber-Bosch process for facile and sustainable production of NH3 . The development of efficient electrocatalysts for the nitrogen reduction reaction (NRR) is highly desired. Herein, a micelle-assisted electrodeposition method is presented for the direct fabrication of porous Au film on Ni foam (pAu/NF). Benefiting from its interconnected porous architectonics, the pAu/NF exhibits superior NRR performance with a high NH3 yield rate of 9.42 µg h-1 cm-2 and a superior Faradaic efficiency of 13.36% at -0.2 V versus reversible hydrogen electrode under the neutral electrolyte (0.1 m Na2 SO4 ). The proposed micelle-assisted electrodeposition strategy is highly valuable for future design of active NRR catalysts with desired compositions toward various electrocatalysis fields.

A perovskite La2Ti2O7 nanosheet as an efficient electrocatalyst for artificial N2 fixation to NH3 in acidic media.

The synthesis of NH3 heavily relies on the Haber-Bosch process suffering from a large amount of CO2 emission and energy consumption. Possessing eco-friendly and sustainable characteristics, electrochemical reduction is considered as a promising candidate for artificial N2 fixation under ambient conditions, but efficient electrocatalysts are crucial for the N2 reduction reaction (NRR). In this communication, we report that perovskite La2Ti2O7 nanosheets behave as an efficient NRR electrocatalyst with excellent selectivity under ambient conditions. In 0.1 M HCl, this catalyst achieves a high NH3 yield rate of 25.15 μg h-1 mgcat.-1 with a faradaic efficiency of 4.55% at -0.55 V vs. a reversible hydrogen electrode. Notably, it also shows high electrochemical stability.

Tailoring Oxygen Vacancies of BiVO4 toward Highly Efficient Noble‐Metal‐Free Electrocatalyst for Artificial N2 Fixation under Ambient Conditions

AbstractAmmonia (NH3) is vital to human beings as an important energy carrier, fertilizer precursor, and fuel, while breakage of the NN bond in nitrogen (N2) is a kinetically complex and energetically challenging multistep reaction. Development of electrocatalysts for efficient NH3 electrosynthesis via the N2 reduction reaction (NRR) is highly desirable but remains a key challenge. In this work, based on the density functional theory calculations, a novel and effective strategy to boost the nitrogen electroreduction performance of BiVO4 by tailoring its oxygen vacancies (OVs) is first proposed and demonstrated. Unexpectedly, the noble‐metal‐free BiVO4 with the highest OVs concentration shows excellent NRR performances, including high NH3 yield rate (up to 8.60 µg h−1 mg−1cat.), high faradaic efficiency (10.04% at −0.5 V vs reversible hydrogen electrode), and good stability (up to 24 h) at ambient conditions, outperforming most reported NRR electrocatalysts under ambient conditions and even some under harsh conditions, which can be attributed to enhanced N2 adsorption energy and a more favorable active reaction site at the V atom with lower coordination and higher spin‐polarization with a localized magnetic moment due to the introduction of OVs.

Molybdenum Carbide Nanodots Enable Efficient Electrocatalytic Nitrogen Fixation under Ambient Conditions.

Electrocatalytic nitrogen fixation is considered a promising approach to achieve NH3 production. However, due to the chemical inertness of nitrogen, it is necessary to develop efficient catalysts to facilitate the process of nitrogen reduction. Here, molybdenum carbide nanodots embedded in ultrathin carbon nanosheets (Mo2 C/C) are developed to serve as a catalyst candidate for highly efficient and robust N2 fixation through an electrocatalytic nitrogen reduction reaction (NRR). The as-synthesized Mo2 C/C nanosheets show excellent catalytic performance with a high NH3 yield rate (11.3 µg h-1 mg-1 Mo2C ) and Faradic efficiency (7.8%) for NRR under ambient conditions. More importantly, the isotopic experiments using 15 N2 as a nitrogen source confirm that the synthesized ammonia is derived from the direct supply of nitrogen. This result also demonstrates the possibility of high-efficiency nitrogen reduction even though accompanied with vigorous hydrogen evolution.