理论探究水溶液条件对TMN_(x)C_(y)催化氮还原性能的增强机制

在电化学氮还原(NRR)合成氨过程中,为了认识真实水环境对过渡金属掺杂氮碳材料催化NRR活性的影响,并筛选出实际催化性能最佳的构型,本研究通过密度泛函理论(DFT)和从头算分子动力学(AIMD)相结合的方法,对一系列不同配位形式的过渡金属掺杂氮碳催化剂(TMN_(x)C_(y), TM=Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn;x=1~4;y=4-x,总共40种构型)催化NRR的热力学稳定性和实际氮还原催化活性进行了系统研究.计算结果表明,本工作所研究的40种催化剂结构均具有较高的热力学稳定性,可作为实际的NRR候选催化剂.其中,利用隐性+显性水溶剂模拟真实水环境时,过渡金属V掺杂形成的VN3C1结构催化NRR酶机制过程的最大吉布斯自由能变值仅为0.35eV(在U=0 V vs. RHE时),表现出最佳的NRR催化性能.总体而言,本研究采用DFT与AIMD相结合的方法,深入地阐述了TMN_(x)C_(y)催化剂的实际NRR催化过程,为实验过程做出了更为贴切的理论预测.

氧空位Co_(3)O_(4)纳米线阵列的制备及其高效电催化合成氨

室温下的电化学氮还原反应(NRR)为合成氨提供了一条温和的途径。然而,常温常压下电化学NRR的活性和选择性较差。过渡金属氧化物上的氧空位可以为N;分子的吸附和活化提供独特的活性位点。制备了一种氧空位Co_(3)O_(4)(V-Co_(3)O_(4))纳米线阵列。喇曼光谱和X射线光电子能谱(XPS)测试显示氧空位可以稳定地存在于V-Co_(3)O_(4)纳米线阵列上。电化学测试表明,V-Co_(3)O_(4)具有高效的电化学氮还原反应活性和选择性。在工作电极上施加-0.3 V时,氨的产量高达10.9μg·h;·cm^(-2),法拉第效率为6.3%。这种低成本的过渡金属氧化物是有前途的固氮催化剂之一。

Transition metal-nitrogen sites for electrochemical carbon dioxide reduction reaction

Electrochemical CO2 reduction reaction(CO2RR)powered by renewable electricity has emerged as the most promising technique for CO2 conversion,making it possible to realize a carbon‐neutral cycle.Highly efficient,robust,and cost‐effective catalysts are highly demanded for the near‐future practical applications of CO2RR.Previous studies on atomically dispersed metal‐nitrogen(M‐Nx)sites constituted of earth abundant elements with maximum atom‐utilization efficiency have demonstrated their performance towards CO2RR.This review summarizes recent advances on a variety of M‐Nx sites‐containing transition metal‐centered macrocyclic complexes,metal organic frameworks,and M‐Nx‐doped carbon materials for efficient CO2RR,including both experimental and theoretical studies.The roles of metal centers,coordinated ligands,and conductive supports on the intrinsic activity and selectivity,together with the importance of reaction conditions for improved performance are discussed.The mechanisms of CO2RR over these M‐Nx‐containing materials are presented to provide useful guidance for the rational design of efficient catalysts towards CO2RR.

Photoelectrochemical nitrogen reduction:A step toward achieving sustainable ammonia synthesis

Industrial NH3 production mainly employs the well‐known Haber‐Bosch(H‐B)process,which is associated with significant energy consumption and carbon emissions.Photoelectrochemical nitro‐gen reduction reaction(PEC‐NRR)under ambient conditions is considered a promising alternative to the H‐B process and has been attracting increasing attention owing to its associated energy effi‐ciency and environmentally friendly characteristics.The performance of a PEC‐NRR system,such as the NH_(3) yield,selectivity,and stability,is essentially determined by its key component,the photo‐cathode.In this review,the latest progress in the development of photocathode materials employed in PEC‐NRR is evaluated.The fundamental mechanisms and essential features required for the PEC‐NRR are introduced,followed by a discussion of various types of photocathode materials,such as oxides,sulfides,selenides,black silicon,and black phosphorus.In particular,the PEC‐NRR reac‐tion mechanisms associated with these photocathode materials are reviewed in detail.Finally,the present challenges and future opportunities related to the further development of PEC‐NRR are also discussed.This review aims to improve the understanding of PEC‐NRR photocathode materials while also shedding light on the new concepts and significant innovations in this field.

A combinatorial descriptor for volcano relationships of electrochemical nitrogen reduction reaction

Though touted as a potential way to realize clean ammonia synthesis,electrochemical ammonia synthesis is currently limited by its catalytic efficiency.Great effort has been made to find catalysts with improved activity toward electrochemical nitrogen reduction reaction(eNRR).Rational screening of catalysts can be facilitated using the volcano relationship between catalytic activity and adsorption energy of an intermediate,namely,the activity descriptor.In this work,we proposeΔG^(*)_(NH_(2))+ΔG^(*)_(NNH)as a combinatorial descriptor,which shows better predictive power than traditional descriptors using the adsorption free energies of single intermediates.The volcano plots based on the combinatorial descriptor exhibits peak activity fixedly at the descriptor value corresponding to the formation free energy of NH3,regardless of the catalyst types;while the descriptor values correspond to the top activities for eNRR on volcano plots based on single descriptors usually vary with the types of catalysts.