Multiscale confinement nitridation in molybdenum carbide for efficient hydrogen production

The molybdenum carbide(Mo_(2)C)has been regarded as one of the most cost-efficient and stable electrocatalyst for the hydrogen evolution reaction(HER)by the virtue of its Pt-like electronic structures.However,the inherent limitation of high density of empty valence band significantly reduces its catalytic reactivity by reason of strong hydrogen desorption resistance.Herein,we propose a multiscale confinement synthesis method to design the nitrogen-rich Mo_(2)C for modulating the band structure via decomposing the pre-coordination bonded polymer in a pressure-tight tube sealing system.Pre-bonded c/N-Mo in the coordination precursor constructs a micro-confinement space,enabling the homogeneous nitrogenization in-situ happened during the formation of Mo_(2)C.Simultaneously,the evolved gases from the precursor decomposition in tube sealing system establish a macro-confinement environment,preventing the lattice N escape and further endowing a continuous nitridation.Combining the multiscale confinement effects,the nitrogen-rich Mo2C displays as high as 25%N-Mo concentration in carbide lattice,leading to a satisfactory band structure.Accordingly,the constructed nitrogen-rich Mo_(2)C reveals an adorable catalytic activity for HER in both alkaline and acid solution.It is anticipated that the multiscale confinement synthesis strategy presents guideline for the rational design of electrocatalysts and beyond.

China Survey Report on High Schools'Online Learning Status During the Pandemic

●We examined the results of a large-scale national survey of online secondary education in China.The online survey of 33,194 high school students and 5,667 teachers has provided comprehensive and representative data regarding the quality of online education and its implementation during the pandemic.●Questionnaire surveys administered to students and teachers in different grades and comparative analysis of different cohorts revealed group heterogeneity of the online learning effect.●The findings have elucidated the emergency teaching situation in China during the pandemic,yielding targeted suggestions for school education following the resumption of classes.

氢键有机框架材料在电化学能源存储和转换中的研究进展

作为一种新型的多孔材料,氢键有机框架(hydrogen-bonded organic frameworks,HOFs)结构因其丰富的孔道分布、可控的晶体构型以及易于调节的分子组成而表现出诸多优异的电化学特性,如快速的离子传输、特异性的离子筛分、可观的电化学活性面积、高暴露的催化活性位点等.这些特性促使研究者越来越多地关注其在电化学能源存储和转换技术中的应用,是能源领域研究的前沿和热点.尽管这些HOFs相关材料的结构和组成各不相同,总体上却可以分为HOFs和HOFs衍生物两大类.本文详细地介绍了HOFs及其衍生物作为电极材料或电催化剂在电化学领域,包括可充电离子电池、电化学超级电容器、电催化析氢、电催化析氧和氧还原反应中的应用原理与最新研究进展.在此基础上,重点阐述了HOFs相关材料的纳米形貌、晶体结构、孔道结构和分子组成对其电化学性能的影响,总结了克服HOFs相关材料氢键骨架稳定性和导电性差的相关方法,凝练了它们在该领域发展中的优势和挑战.基于上述讨论,希望对HOFs相关材料在电化学能源存储和转换技术中的发展提供新的研究方向.

Supramolecular assembly-derived carbon-nitrogen-based functional materials for photo/electrochemical applications: progress and challenges

Supramolecular chemistry during the synthesis of carbon-nitrogen-based materials has recently experienced a renaissance in the arena of photocatalysis and electrocatalysis.In this review,we start with the discussion of supramolecular assemblies-derived carbon-nitrogen-based materials’regulation from the aspect of morphology,chemical composition,and micro/nanostructural control.Afterwards the recent advances of these materials in energy and environment related applications,including degradation of pollutants,water splitting,oxygen reduction reactions,CO_(2) reduction reactions along with organic synthesis are summarized.The correlations between the structural features and physicochemical properties of the carbonnitrogen-based materials and the specific catalytic activity are discussed in depth.By highlighting the opportunities and challenges of supramolecular assembly strategies,we attempt an outlook on possible future developments for highly efficient carbon-based photo/electrocatalysts.

Supplementary Tutoring for Compulsory Education Students in China:Status and Trends

Purpose-The purpose of this paper is to explore the current status of,and developmental trends affecting,the participation in supplementary tutoring by compulsory education students in China.Design/Approach/Methods-Based on the data from the China Family Panel Study(CFPS)conducted by the Peking University Institute of Social Science Survey in 2010,2012,2014,and 2016,the paper uses the method of multilevel linear model to comprehensively analyze problems involving a multilevel data structure.Findings-The paper finds that the proportion of compulsory education students participating in supplementary tutoring(and the expenditure on such tutoring)increased annually before declining in 2016.Students with higher socioeconomic status,higher school quality,and better academic performance have a higher tutoring participation rate and also spend more on tutoring.Students in China’s three northeastern provinces and eastern coastal areas have higher participation rates in tutoring and higher tutoring expenditures.Originality/Value-Supplementary tutoring in China already has its own developmental patterns and trends;however,few scholars have empirically studied the developmental patterns and trends of supplementary tutoring in compulsory education based on longitudinal survey data.