We demonstrate a simple and effective chemical equilibrium regulation strategy to improve the efficiency of electrochemical ammonia synthesis by constructing electrochemical reaction system that ...works at significantly lower pressure than the Haber–Bosch process. Transferring the nitrogen reduction reaction from ambient conditions to a lightly pressurized environment not only accelerates the activation of the N≡N triple bond but also inhibits the competing reaction of hydrogen evolution while promoting the dissolution and diffusion of nitrogen. The verification experiment of using well‐designed Fe3Mo3C/C composite nanosheets as the nitrogen reduction catalyst shows that the lower pressure reaction system can improve the Faradaic current efficiency by one order of magnitude. Moreover, the comparatively low‐pressure reaction system can greatly reduce the cell voltage of the ammonia synthesis reaction (up to 33 %) even at the relatively low pressure of 0.7 MPa, which is of significance for decreasing the energy consumption of electrochemical ammonia synthesis under mild conditions.
Pressure drop: A simple and effective strategy for regulating chemical equilibrium improves the efficiency of electrochemical ammonia synthesis by using an only lightly pressurized reaction system. The strategy not only can improve the efficiency of the nitrogen reduction reaction, but also can greatly reduce the cell voltage of the ammonia synthesis reaction under mild 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 (Mo2C/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 Mo2C/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 15N2 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.
An effective size‐control synthesis strategy is proposed to endow the nitrogen reduction reaction (NRR) performance of Mo2C nanodots by boosting nitrogen adsorption and activation. The Mo2C nanodots show excellent NRR catalytic performance with a high NH3 yield rate (11.3 µg h−1 mg−1
Mo2C) under ambient conditions. This result demonstrates the possibility of high‐efficiency nitrogen reduction even though accompanied with vigorous hydrogen evolution.
Molecular sieving membranes with sufficient and uniform nanochannels that break the permeability-selectivity trade-off are desirable for energy-efficient gas separation, and the arising ...two-dimensional (2D) materials provide new routes for membrane development. However, for 2D lamellar membranes, disordered interlayer nanochannels for mass transport are usually formed between randomly stacked neighboring nanosheets, which is obstructive for highly efficient separation. Therefore, manufacturing lamellar membranes with highly ordered nanochannel structures for fast and precise molecular sieving is still challenging. Here, we report on lamellar stacked MXene membranes with aligned and regular subnanometer channels, taking advantage of the abundant surface-terminating groups on the MXene nanosheets, which exhibit excellent gas separation performance with H
permeability >2200 Barrer and H
/CO
selectivity >160, superior to the state-of-the-art membranes. The results of molecular dynamics simulations quantitatively support the experiments, confirming the subnanometer interlayer spacing between the neighboring MXene nanosheets as molecular sieving channels for gas separation.
Constructing efficient catalysts for the N2 reduction reaction (NRR) is a major challenge for artificial nitrogen fixation under ambient conditions. Herein, inspired by the principle of “like ...dissolves like”, it is demonstrated that a member of the nitrogen family, well‐exfoliated few‐layer black phosphorus nanosheets (FL‐BP NSs), can be used as an efficient nonmetallic catalyst for electrochemical nitrogen reduction. The catalyst can achieve a high ammonia yield of 31.37 μg h−1 mg−1cat. under ambient conditions. Density functional theory calculations reveal that the active orbital and electrons of zigzag and diff‐zigzag type edges of FL‐BP NSs enable selective electrocatalysis of N2 to NH3 via an alternating hydrogenation pathway. This work proves the feasibility of using a nonmetallic simple substance as a nitrogen‐fixing catalyst and thus opening a new avenue towards the development of more efficient metal‐free catalysts.
Well‐exfoliated few‐layer black phosphorus nanosheets (FL‐BP NSs) were developed as an efficient nonmetallic catalyst for electrochemical nitrogen reduction. The catalyst can achieve a high ammonia yield of 31.37 μg h−1 mg−1cat. under ambient conditions. DFT calculations show that the zigzag and diff‐zigzag edges of the FL‐BP NSs are the active centers, which enable selective electroreduction of N2 to NH3 via an alternating hydrogenation pathway.
The electrocatalytic nitrogen reduction reaction (NRR) to ammonia (NH3) is a highly desirable yet challenging objective because of the competing hydrogen evolution reaction (HER). Herein, a novel ...electrocatalyst of Sn‐doped black phosphorene (Sn‐BPene) is demonstrated with dramatically improved selectivity for the NRR. The Sn that is added acts as a sacrificial species for the HER to protect the NRR active sites on black phosphorene (BPene). The Sn‐BPene achieves a Faraday efficiency of up to 36.51% and a prominent NH3 yield rate of 26.98 µg h–1 mgcat–1 at a relatively low overpotential. Density functional theory calculations prove that the adsorption sites of H2O and N2 are separated after doping with Sn, with H2O adsorbing preferentially onto the Sn sites and N2 onto the NRR active sites of BPene, leading to high selectivity.
Sn‐doped black phosphorene is developed as an efficient nitrogen reduction reaction (NRR) catalyst that achieves a Faraday efficiency of up to 36.51%, which is an order of magnitude improvement over undoped black phosphorene. Density functional theory calculations prove that the adsorption sites of H2O and N2 are separated after doping with Sn, which provide more opportunities for N2 to adsorb on the NRR‐active sites of black phosphorene, thus leading to high selectivity.
The aqueous electrocatalytic reduction of NO3− into NH3 (NitrRR) presents a sustainable route applicable to NH3 production and potentially energy storage. However, the NitrRR involves a directly ...eight‐electron transfer process generally required a large overpotential (<−0.2 V versus reversible hydrogen electrode (vs. RHE)) to reach optimal efficiency. Here, inspired by biological nitrate respiration, the NitrRR was separated into two stages along a 2+6‐electron pathway to alleviate the kinetic barrier. The system employed a Cu nanowire catalyst produces NO2− and NH3 with current efficiencies of 91.5 % and 100 %, respectively at lower overpotentials (>+0.1 vs. RHE). The high efficiency for such a reduction process was further explored in a zinc‐nitrate battery. This battery could be specified by a high output voltage of 0.70 V, an average energy density of 566.7 Wh L−1 at 10 mA cm−2 and a power density of 14.1 mW cm−2, which is well beyond all previously reported similar concepts.
For the efficient electrocatalytic conversion of NO3− to NH3, a two‐stage process following the 2+6‐electron pathway is proposed inspired by biological nitrate respiration. This system produces NO2− and NH3 at low overpotentials (>+0.1 vs. RHE), resulting in a low energy consumption of 17.7 kWh kg−1 for NH3 production and high energy density of 566.7 Wh L−1 at 10 mA cm−2 for Zn−NO3− battery.
As the US healthcare system transitions from volume to value, various value‐based programs tie medical reimbursements to hospital performance relative to national top performers (i.e., benchmarks). ...However, prior studies report very limited results on how such benchmarks affect care delivery and patient outcomes across multiple performance fronts. This study examines how general acute care hospitals progress toward benchmarks measured by performance frontiers in technical efficiency, clinical quality, and patient experience over time, subjecting to external market conditions and internal focuses. Based on a panel dataset comprising hospitals in California from 2012 and 2019, our results find support for competitive‐distance‐driven progression rates, suggesting that hospitals' competitive positions measured by their distances to benchmarks drive performance improvements. Yet, the effect diminishes as they move closer to performance frontiers. In addition, we find that market competition reduces the progression rate of technical efficiency. Finally, our results also suggest that focus improves performance progression rates, yet its effects are curvilinear.
The electrochemical reduction of nitrogen into ammonia under ambient conditions is a potential strategy for sustainable ammonia production. At present, one of the main research directions in the ...field of electrochemical nitrogen fixation is to improve the current efficiency and ammonia yield by developing efficient nitrogen reduction catalysts. To optimise the selectivity and catalytic activity of nitrogen reduction catalysts more efficiently, herein, we systematically summarise the progress of research on nitrogen reduction catalysts in recent years and present some general catalyst design strategies. Considering that it is difficult for metal‐based catalysts to balance the competitive reactions of nitrogen activation and hydrogen evolution, we discuss in detail the advantages and application prospects of non‐metallic catalysts in electrochemical nitrogen fixation. Moreover, both the design strategy of surface or interface defects, and how this atomic‐level control of functionalisation helps to promote selectivity and catalytic activity are also discussed by theoretical and experimental electrochemistry. On this basis, we also discussed the future development direction, opportunities and challenges of nitrogen reduction electrocatalysts.
Herding cats: This review provides a comprehensive and critical summary of the progress of research on nitrogen reduction catalysts and some general catalyst design strategies. Considering that it is difficult for metal‐based catalysts to balance the competitive reactions of nitrogen activation and hydrogen evolution, the advantages and application prospects of non‐metallic catalysts in electrochemical nitrogen fixation are summarized and discussed.
Electrocatalytic N2 reduction reaction (NRR) is recognized as a zero‐carbon emission method for NH3 synthesis. However, to date, this technology still suffers from low yield and low selectivity ...associated with the catalyst. Herein, inspired by the activation of N2 by lithium metal, a highly reactive defective black phosphorene (D−BPene) is proposed as a lithium‐like catalyst for boosting electrochemical N2 activation. Correspondingly, we also report a strategy for producing environmentally stable D−BPene by simultaneously constructing defects and fluorination protection based on topochemical reactions. Reliable performance evaluations show that the fluorine‐stabilized D−BPene can induce a high NH3 yield rate of ≈70 μg h−1 mgcat.−1 and a high Faradaic efficiency of ≈26 % at −0.5 V vs. RHE in an aqueous electrolyte. This work not only exemplifies the first stable preparation and practical application of D−BPene, but also brings a new design idea for NRR catalysts.
A novel and feasible strategy is proposed for obtaining environmentally stable defective black phosphorene via simultaneously constructing defects and fluorination protection. Due to the inherent high chemical reactivity, the fluorine‐stabilized defective black phosphorene as a nitrogen reduction electrocatalyst induces a high NH3 yield rate of ≈70 μg h−1 mgcat.−1 and a high Faradaic efficiency of ≈26 % at −0.5 V vs. RHE under ambient conditions.
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