Effect on electrochemical reduction of nitrogen to ammonia under ambient conditions: Challenges and opportunities for chemical fuels

The nitrogen cycle plays an important role in nature,but N-containing products cannot meet human needs.The electrochemical synthesis of ammonia under ambient conditions has attracted the interest of many researchers because it provides a clean and pollution-free synthesis method;however,it has certain difficulties,including a high activation energy,multiple electron transfer,and hydrogenation.Thermodynamic factors limit the selectivity and activity of ammonia synthesis techniques.This review summarizes progress in the electrochemical synthesis of ammonia from theory and experiment.Theoretically,the reduction of nitrogen molecules is analyzed using orbit theory and the thermodynamic reaction pathways.Experimentally,we first discuss the effect of the experimental setup on the nitrogen reduction reaction,and then the four critical of catalysts,including size,electronic,coordination,and orientation effects.These issues must be considered to produce highly-efficient catalysts for electrochemical nitrogen reduction(eNRR).This review provides an overview of the eNRR to enable future researchers to design rational catalysts.

超声医学质量控制与住院医师规范化培训相结合的实践探讨

目的探讨超声医学质量控制与住院医师规范化培训的实践结合效果。方法纳入2022年至2023年间中国医学科学院肿瘤医院超声医学科住院医师规范化培训的在培学员10名为研究对象。通过建立质量控制/住院医师规范化培训管理实践小组,开展规范报告书写、标准切面教学、临床工作中实时质量控制、病例追随及阶段性总结评价等多项质量控制管理措施,通过上机操作、超声诊断及报告书写模拟考核及无记名问卷调查评价效果。采用Mann-Whitney U检验比较学员考核成绩的差异。结果质量控制方案实施后学员上机操作和超声诊断及报告书写评分均较实施前提高[88.25(84.25,91.25)分vs 82.50(77.50,85.75)分;86.00(82.75,92.50)vs 81.50(76.13,84.50)],差异均具有统计学意义(Z=-2.118、-2.005,P=0.034、0.045)。调查问卷统计显示学员报告规范性、操作标准度、临床思维能力、诊断准确性及综合工作能力均有不同程度提高,以操作标准度提升最为明显。结论超声医学质量控制与住院医师规范化培训结合能够形成良性循环,有效提高超声住院医师规范化培训学员的操作、诊断和报告书写能力。

Surface hydrophobic modification enhanced catalytic performance of electrochemical nitrogen reduction reaction

Electrocatalytic nitrogen reduction reaction(NRR)is a sustainable approach for NH_(3)production with low energy consumption.However,competing hydrogen reduction reaction(HER)in aqueous solution results in low NH_(3)production and Faraday efficiency(FE).Here,MoS_(2)nanostructures with a hydrophobic surface are synthesized by alkyl thiols modification.Aerophilic and hydrophobic surface facilitates an efficient three-phase contact of N_(2),H_(2)O,and catalyst.Thus,localized concentrated N_(2)molecules can overcome the mass transfer limitation of N2 and depress the HER due to lowering the proton contacts.Although the active-sites decrease with the increase of the alkyl chain since the thiol may cover the active site,the optimized electrocatalyst achieves NH_(3)yield of 12.86×10^(-11)mol·cm^(-2)·s^(-1)at-0.25 V and 22.23%FE,which are 4.3 and 24 times higher than those of MoS2-CP electrocatalyst,respectively.The increased catalytic performance is attributed to the high N_(2)adsorption and depressed HER.

Tuning the performance of nitrogen reduction reaction by balancing the reactivity of N_(2) and the desorption of NH_(3)

Electrochemical reduction of nitrogen to ammonia under mild conditions provides an intriguing approach for energy conversion. A grand challenge for electrochemical nitrogen reduction reaction (NRR) is to design a superior electrocatalyst to obtain high performance including high catalytic activity and selectivity. In the NRR process, the three most important steps are nitrogen adsorption, nitrogen activation, and ammonia desorption. We take MoS_(2) as the research object and obtain catalysts with different electronic densities of states through the doping of Fe and V, respectively. Using a combination of experiments and theoretical calculations, it is demonstrated that V-doped MoS_(2) (MoS_(2)-V) shows better nitrogen adsorption and activation, while Fe-doped MoS_(2) (MoS_(2)-Fe) obtains the highest ammonia yield in experiments (20.11 µg·h^(−1)·mg^(−1)cat.) due to its easier desorption of ammonia. Therefore, an appropriate balance between nitrogen adsorption, nitrogen activation, and ammonia desorption should be achieved to obtain highly efficient NRR electrocatalysts.

Fe_(2)Mo_(3)O_(8)/XC-72 electrocatalyst for enhanced electrocatalytic nitrogen reduction reaction under ambient conditions

To perform the electrochemical nitrogen reduction reaction(NRR)under milder conditions for sustainable ammonia production,electrocatalysts should exhibit high selectivity,activity,and durability.However,the key restrictions are the highly stable N≡N triple bond and the competitive hydrogen evolution reaction(HER),which make it difficult to adsorb and activate N2 on the surface of electrocatalysts,leading to a low ammonia yield and Faraday efficiency.Inspired by the enzymatic nitrogenase process and using the Fe-Mo as the active center,here we report supported Fe_(2)Mo_(3)O_(8)/XC-72 as an effective and durable electrocatalyst for the NRR.Fe_(2)Mo_(3)O_(8)/XC-72 exhibited NRR activity with an NH3 yield of 30.4μg·h^(−1)·mg^(−1)(−0.3 V)and a Faraday efficiency of 8.2%(−0.3 V).Theoretical calculations demonstrated that the electrocatalytic nitrogen fixation mechanism involved the Fe atom in the Fe_(2)Mo_(3)O_(8)/XC-72 electrocatalyst acting as the main active site in the enzymatic pathway(*NH2→*NH3),which activated nitrogen molecules and promoted the NRR performance.