Heterometallic cluster-based organic frameworks as highly active electrocatalysts for oxygen reduction and oxygen evolution reaction:a density functional theory study

Recently,metal–organic frameworks are one of the potential catalytic materials for electrocatalytic applications.The oxygen reduction reaction and oxygen evolution reaction catalytic activities of heterometallic cluster-based organic frameworks are investigated using density functional theory.Firstly,the catalytic activities of heterometallic clusters are investigated.Among all heterometallic clusters,Fe_(2)Mn–Mn has a minimum overpotential of 0.35 V for oxygen reduction reaction,and Fe_(2)Co–Co possesses the smallest overpotential of 0.32 V for oxygen evolution reaction,respectively 100 and 50 mV lower than those of Pt(111)and RuO_(2)(110)catalysts.The analysis of the potential gap of Fe_(2)M clusters indicates that Fe_(2)Mn,Fe_(2)Co,and Fe_(2)Ni clusters possess good bifunctional catalytic activity.Additionally,the catalytic activity of Fe_(2)Mn and Fe_(2)Co connected through 3,3′,5,5′-azobenzenetetracarboxylate linker to form Fe_(2)M–PCN–Fe_(2)M is explored.Compared with Fe_(2)Mn–PCN–Fe_(2)Mn,Fe_(2)Co–PCN–Fe_(2)Co,and isolated Fe_(2)M clusters,the mixed-metal Fe_(2)Co–PCN–Fe_(2)Mn possesses excellent bifunctional catalytic activity,and the values of potential gap on the Mn and Co sites of Fe_(2)Co–PCN–Fe_(2)Mn are 0.69 and 0.70 V,respectively.Furthermore,the analysis of the electron structure indicates that constructing a mixed-metal cluster can efficiently enhance the electronic properties of the catalyst.In conclusion,the mixed-metal cluster strategy provides a new approach to further design and synthesize high-efficiency bifunctional electrocatalysts.

Macroporous 3D carbon-nitrogen(CN)confined MoO_(x) catalyst for enhanced oxidative desulfurization of dibenzothiophene

Macroporous 3D carbon doped with nitrogen confined Mo catalyst(MoO_(x)@CN)had been prepared by a facile one-step pyrolysis technique using silica as a template and was employed for oxidative desulfurization(ODS)of dibenzothiophene(DBT)in model fuel with H2O_(2) as oxidant.The effect of different ope rating conditions(i.e.,reaction te mperature and time,catalyst dosage,H2O_(2)/DBT(O/S)molar ratio)were also systematic investigated.Under the optimal reaction condition,MoO_(x)@CN catalyst exhibited highly excellent ODS performance toward DBT,the highest sulfur removal efficiency can be up to 99.9%and sulfur content was wiped out from 800 ppm to 10 ppm.Due to the robust 3D structure promoting rapid transfer,in addition to the increased number of active sites induced by the Mo vacancies,the catalyst,prepared using chitosan and ammonium heptamolybdate in a mass ratio of 1:0.5,displayed rapid kinetics and low activation energy in the oxidation of dibenzothiophene.Moreover,it exhibited excellent recyclability after five cycles without any obvious decrease in catalytic activity for the oxidative desulfurization reaction.

Probing the catalytic activity of M-N_(4−x)O_(x) embedded graphene for the oxygen reduction reaction by density functional theory

In this work,the detailed oxygen reduction reaction(ORR)catalytic performance of M-N_(4−x)O_(x)(M=Fe,Co,and Ni;x=1−4)has been explored via the detailed density functional theory method.The results suggest that the formation energy of M-N_(4−x)O_(x)shows a good linear relationship with the number of doped O atoms.The adsorption manner of O_(2)on M-N_(4−x)O_(x)changed from end-on(x=1 and 2)to side-on(x=3 and 4),and the adsorption strength gradually increased.Based on the results for binding strength of ORR intermediates and the Gibbs free energy of ORR steps on the studied catalysts,we screened out two highly active ORR catalysts,namely Co-N_(3)O_(1)and Ni-N_(2)O_(2),which possess very small overpotentials of 0.27 and 0.32 V,respectively.Such activities are higher than the precious Pt catalyst.Electronic structure analysis reveals one of the reasons for the higher activity of Co-N_(3)O_(1)and Ni-N_(2)O_(2)is that they have small energy gaps and moderate highest occupied molecular orbital energy levels.Furthermore,the results of the density of states reveal that the O doping can improve the electronic structure of the original catalyst to tune the adsorption of the ORR intermediates.

Ultra-smooth CsPbI_(2)Br film via programmable crystallization process for high-efficiency inorganic perovskite solar cells

CsPbI_(2)Br is an ideal inorganic perovskite material with a reasonable bandgap for solar cell applications because of its advantage of superior thermal and phase stability. However, the performance of CsPbI2Br based solar cells highly relied on the perovskite crystallization process along with the interfacial contact engineering process between CsPbI_(2)Br perovskite and charge-transporting layers. In this work, a programmable crystallization method is developed to obtain ultra-smooth CsPbI_(2)Br perovskite film with a well-engineered contact interface in perovskite solar cells. This method combines a pre-stand-by process with a programmable gradient thermal engineering process, which mediates the crystal growth dynamics process of CsPbI2Br perovskite by controlling the release of dimethyl sulfoxide(DMSO) from its coordinates with the perovskite film, leading to high-quality CsPbI_(2)Br film with large-scale crystalline grains, reduced surface roughness, and low trap density. Fabricated perovskite devices based on CsPbI_(2)Br film obtained by this method deliver power conversion efficiency of 14.55 %;meanwhile, the encapsulated CsPbI_(2)Br perovskite device achieves a maximum efficiency of 15.07 %. This decent solar conversion efficiency demonstrates the effectiveness of the programmable crystallization method used in this work,which shows great potential as a universal approach in obtaining high-quality CsPbI_(2)Br perovskite films for fabricating high-efficiency inorganic perovskite solar cells.

缺陷富集型钌基电催化剂在强碱和强酸析氢反应中的高质量比活性研究

合理的设计策略以提高贵金属电催化剂在析氢反应(HER)中的利用率,对于简化HER的工艺流程,促进未来能源循环经济的发展至关重要.本文在约2.4 nm的Ru纳米颗粒上设计了大量的缺陷,使其在苛刻的酸性和碱性电解质中具有超高质量比反应活性.在过电势为100 m V时,所制备的缺陷富集型Ru基电催化剂DR-Ru表现出超高的HER翻转频率(碱性:16.4 s^(-1);酸性:20.6 s^(-1))和超低的过电势(碱性:η10=28.2 m V;酸性:η10=25.1 mV),明显优于其他Ru基电催化剂.此外,低配位的Ru活性位和表面部分晶格氧削弱了DR-Ru的Ru–H结合能,促进了酸性HER进行;同时有利于H2O分子分解,缓解了碱性HER过程中水分子的解离迟滞,导致其具有与酸性HER相当的高质量比活性.