Regulating electronic structure of CoN_(4)with axial Co-S for promoting oxygen reduction and Zn-air battery performance

Regulating the coordination environment of transition-metal based materials in the axial direction with heteroatoms has shown great potential in boosting the oxygen reduction reaction(ORR).The coordination configuration and the regulation method are pivotal and elusive.Here,we report a combined strategy of matrix-activization and controlled-induction to modify the CoN_(4)site by axial coordination of Co-S(Co1N_(4)-S_(1)),which was validated by the aberration-corrected electron microscopy and X-ray absorption fine structure analysis.The optimal Co1N_(4)-S_(1)exhibits an excellent alkaline ORR activity,according to the half-wave potential(0.897 V vs.reversible hydrogen electrode(RHE)),Tafel slope(24.67 mV/dec),and kinetic current density.Moreover,the Co1N_(4)-S_(1)based Zn-air battery displays a high power density of 187.55 mW/cm^(2)and an outstanding charge-discharge cycling stability for 160 h,demonstrating the promising application potential.Theoretical calculations indicate that the better regulation of CoN_(4)on electronic structure and thus the highly efficient ORR performance can be achieved by axial Co-S.

Controlling N-doping type in carbon to boost single-atom site Cu catalyzed transfer hydrogenation of quinoline

Single-atom site(SA)catalysts on N-doped carbon(CN)materials exhibit prominent performance for their active sites being M-Nx.Due to the commonly random doping behaviors of N species in these CN,it is a tough issue to finely regulate their doping types and clarify their effect on the catalytic property of such catalysts.Herein,we report that the N-doping type in CN can be dominated as pyrrolic-N and pyridinic-N respectively through compounding with different metal oxides.It is found that the proportion of distinct doped N species in CN depends on the acidity and basicity of compounded metal oxide host.Owing to the coordination by pyrrolic-N,the SA Cu catalyst displays an enhanced activity(two-fold)for transfer hydrogenation of quinoline to access the valuable molecule tetrahydroquinoline with a good selectivity(99%)under mild conditions.The higher electron density of SA Cu species induced by the predominate pyrrolic-N coordination benefits the hydrogen transfer process and reduces the energy barrier of the hydrogenation pathway,which accounts for the improved catalytic effeciency.

Convenient fabrication of BiOBr ultrathin nanosheets with rich oxygen vacancies for photocatalytic selective oxidation of secondary amines

Photocatalytic oxidation has been widely employed in organic synthesis,by virtue of the green,mild and simple reaction conditions as well as high selectivity.Introducing oxygen vacancies (OVs) with proper concentrations into the photocatalysts has been proven as an effective strategy to boost the catalytic performances.However,the currently used treatment method under high temperature at reducing atmosphere inevitably introduces a large number of OVs at the interior of the catalyst and serving as the recombination centers of carriers.To address this issue,here we develop a facile solvothermal process to prepare ultrathin BiOBr nanosheets with rich surface OVs.This method effectively decreases the bulk of the material and the ratio of interior OVs,rendering most of the OVs exposed on the surfaces which act as exposed catalytic sites and enhance the separation of carriers,therefore significantly elevates the photocatalytic performances.For the photo-oxidation reaction of secondary amines,under the conditions of visible light,ambient temperature and atmosphere,the BiOBr nanosheets featuring rich surface OVs deliver a doubled conversion compared to those with low OV concentrations,and a high selectivity of 99%,a high stability as the performance shows no reduction after 5 times of circular reaction.

PdAg bimetallic electrocatalyst for highly selective reduction of CO2 with low COOH^* formation energy and facile CO desorption

For electrocatalytic reduction of CO2 to CO,the stabilization of intermediate COOH^* and the desorption of CO^* are two key steps.Pd can easily stabilize COOH^*,whereas the strong CO^* binding to Pd surface results in severe poisoning,thus lowering catalytic activity and stability for CO2 reduction.On Ag surface,CO^* desorbs readily,while COOH^* requires a relatively high formation energy,leading to a high overpotential.In light of the above issues,we successfully designed the PdAg bimetallic catalyst to circumvent the drawbacks of sole Pd and Ag.The PdAg catalyst with Ag-terminated surface not only shows a much lower overpotential(-0.55 V with CO current density of 1 mA/cm^2)than Ag(−0.76 V),but also delivers a CO/H2 ratio 18 times as high as that for Pd at the potential of-0.75 V vs.RHE.The issue of CO poisoning is significantly alleviated on Ag-terminated PdAg surface,with the stability well retained after 4h electrolysis at-0.75 V vs.RHE.Density functional theory(DFT)calculations reveal that the Ag-terminated PdAg surface features a lowered formation energy for COOH^* and weakened adsorption for CO^*,which both contribute to the enhanced performance for CO2 reduction.

Mn调控NiFe LDH/rGO活性位点的电子结构作为高效水氧化催化剂

发展廉价、高效的水氧化(OER)催化剂对发展可持续能源具有重要意义.杂原子掺杂调节活性位点的电子结构提高催化剂的OER性能被认为是一种高效的策略.本文通过水热法制备得到Mn掺杂的层状镍铁氢氧化物/还原氧化石墨烯(Mn-NiFe LDH/rGO)作为高效、稳定的水氧化催化剂.实验和模拟计算研究都表明Mn能调整活性位点的电子结构,改善其对水氧化反应中中间产物的吸附能垒,从而减小OER反应中决速步骤的反应势垒.具体而言,最优的Mn-NiFe LDH/rGO复合材料在过电位仅为240 mV就能驱动10 mA cm^(-2)的电流密度,Tafel斜率低至40.0 mV dec^(-1),并且具有良好的稳定性.该催化剂优异的活性优于最近报道的OER电催化剂.本工作为制备用于能源转换领域的高活性、廉价的电催化剂提供了新的思路.

配位结构主导单原子Pt的烯烃反马氏硼氢化催化性能

单原子催化剂的高效合理设计具有十分重要的意义,但是目前对于结构和性能之间的关联关系认知不足,严重阻碍了催化剂的发展进程.因此,清晰阐释金属活性中心的配位结构对于其催化性能的影响将有利于单原子催化剂的高效设计.本文研究报道了单原子Pt催化剂的活性中心配位结构显著影响其在烯烃反马氏硼氢化反应中的性能表现.三个O原子配位的Pt单原子催化剂(Pt-O3)与另外两种配位结构(Pt-N4和Pt-O2)相比,表现出了更高的催化活性,在烯烃反马氏硼氢化反应中的转化数可达到3288.密度泛函理论计算表明,Pt-O3催化剂具有超高活性的主要原因是其在反应相图中具有最低的决速步能垒.

Biomass-assisted approach for large-scale construction ofmulti-functional isolated single-atom site catalysts

In recent years,the isolated single-atom site(ISAS)catalysts have attracted much attention as they are cost-effective,can achieve 100%atom-utilization efficiency,and often display superior catalytic performance.Here,we developed a biomass-assisted pyrolysis-etching-activation(PEA)strategy to construct ISAS metal decorated on N and B co-doped porous carbon(ISAS M/NBPC,M=Co,Fe,or Ni)catalysts.This PEA strategy can be applied in the universal and large-scale preparation of ISAS catalysts.Interestingly,the ISAS M/NBPC(M=Co,Fe,or Ni)catalysts show multi-functional features and excellent catalytic activities.They can be used to conduct different types of catalytic reactions,such as O-silylation(OSI),oxidative dehydrogenation(ODH),and transfer hydrogenation(THG).In addition,we used the transfer hydrogenation of nitrobenzene as a typical reaction and revealed the difference between ISAS Co/NBPC and ISAS Co/NPC(N-doped porous carbon)catalysts by density functional theory(DFT)calculations,and which showed that the decreased barrier of the ratedetermining step and the low-lying potential energy diagram indicate that the catalytic activity is higher when ISAS Co/NBPC is used than that when ISAS Co/NPC is used.These results demonstrate that the catalytic performance can be effectively improved by adjusting the coordination environment around the ISAS.

自组装多功能Fe_(3)O_(4)分级微球:高效的锂离子电池材料和加氢催化剂

本论文发展了一种简单、低成本的一步"同步还原-自组装(SRSA)"水热法并制备了自组装Fe_(3)O_(4)分级结构的微球(Fe_(3)O_(4)HMSs).在合成过程中,仅使用甘油、水和铁氰化钾作为反应物,而无需任何其他还原剂、表面活性剂或添加剂即可获得自组装Fe_(3)O_(4)HMSs.其中,K3[Fe(CN)6]和甘油是合成自组装Fe_(3)O_(4)HMSs的两个重要因素.自组装Fe_(3)O_(4)HMSs可以作为高性能的锂离子存储材料,在0.5Ag^(-1)的电流密度下,经过270次循环后比容量大于1000 mA hg^(-1).进一步充电和放电结果表明自组装Fe_(3)O_(4)HMSs表现出良好的可逆性能(放电比容量维持在1000mA h g^(-1)以上)和循环稳定性(700次循环).此外,作为多功能材料,自组装Fe_(3)O_(4)HMSs的饱和磁化强度达到99.5 emu g^(-1),其可以进一步作为高效、磁性可回收的催化剂用于高效的硝基化合物加氢反应.