Synthesis and Characterization of Ligand-Linked Pt Nanoparticles: Tunable,Three-Dimensional,Porous Networks for Catalytic Hydrogen Sensing

Porous networks of Pt nanoparticles interlinked by bifunctional organic ligands have shown high potential as catalysts in micro-machined hydrogen gas sensors. By varying the ligand among p-phenylenediamine, benzidine, 4,4‘‘-diamino-p-terphenyl, 1,5-diaminonaphthalene, and trans-1,4-diaminocyclohexane, new variants of such networks were synthesized. Inter-particle distances within the networks, determined via transmission electron microscopy tomography, varied from 0.8 to 1.4 nm in accordance with the nominal length of the respective ligand. While stable structures with intact and coordinatively bonded diamines were formed with all ligands, aromatic diamines showed superior thermal stability. The networks exhibited mesoporous structures depending on ligand and synthesis strategy and performed well as catalysts in hydrogen gas microsensors. They demonstrate the possibility of deliberately tuning micro- and mesoporosity and thereby transport properties and steric demands by choice of the right ligand also for other applications in heterogeneous catalysis.     

Adaptive Bifunctional Electrocatalyst of Amorphous CoFe Oxide @ 2D Black Phosphorus for Overall Water Splitting

Water electrolysis offers a promising green technology to tackle the global energy and environmental crisis, but its efficiency is greatly limited by the sluggish reaction kinetics of both the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). In this work, by growing amorphous multi-transition-metal (cobalt and iron) oxide on two-dimensional (2D) black phosphorus (BP), we develop a bifunctional electrocatalyst (CoFeO@BP), which is able to efficiently catalyze both HER and OER. The overpotentials for the hybrid CoFeO@BP catalyst to reach a current density of 10 mA cm⁻² in 1 m KOH are 88 and 266 mV for HER and OER, respectively. Based on a series of ex-situ and in situ investigations, the excellent catalytic performance of CoFeO@BP is found to result from the adaptive surface structure under reduction and oxidation potentials. CoFeO@BP can be transformed to CoFe phosphide under reduction potential, in situ generating the real active catalyst for HER.     

Making Use of the Direct Process Residue: Synthesis of Bifunctional Monosilanes

The industrial production of monosilanes Me_nSiCl_4−n (n=1–3) through the Müller–Rochow Direct Process generates disilanes Me_nSi₂Cl_6−n (n=2–6) as unwanted byproducts (“Direct Process Residue”, DPR) by the thousands of tons annually, large quantities of which are usually disposed of by incineration. Herein we report a surprisingly facile and highly effective protocol for conversion of the DPR: hydrogenation with complex metal hydrides followed by Si−Si bond cleavage with HCl/ether solutions gives (mostly bifunctional) monosilanes in excellent yields. Competing side reactions are efficiently suppressed by the appropriate choice of reaction conditions.     

Sulfur Chemistry for Stable and Electroactive Metal-Organic Frameworks: The Crosslinking Story

The versatile sulfur chemistry, as exemplified by the reactive yet tractable thiol group (-SH), offers unique opportunities for bypassing the obstacles in accessing stable and electroactive metal-organic frameworks. Of particular interest are recent advances in assembling MOF materials equipped with free-standing thiol functions: metal guests can be conveniently inserted to install electroactive metal-sulfur bonds, which, as crosslinks, also stabilize the host coordination net. Here the historical development of the bifunctional, two-step design embodied by the thiol-tagged MOF solids is traced, in order to highlight the underlying spirit that has driven research efforts in the past two decades. Going forward, broad new horizons are foreseen in solid-state materials synthesis, for example, arising from various sulfur-based hard-and-soft combinations, in synergy with the crystalline and modular MOF structural platform.     

Engineering Bifunctional Host Materials of Sulfur and Lithium-Metal Based on Nitrogen-Enriched Polyacrylonitrile for Li–S Batteries

Lithium–sulfur batteries (LSBs) still suffer from the shuttle effect on the cathode and the lithium dendrite on the anode. Herein, polyacrylonitrile (PAN) is developed into a bifunctional host material to simultaneously address the challenges faced on both the sulfur cathode and lithium anode in LSBs. For the sulfur cathode, PAN is bonded with sulfur to produce sulfurized PAN (SPAN) to avoid the shuttle effect. The SPAN is accommodated into a conductive 3D CNTs-wrapped carbon foam to prepare a self-supporting cathode, which improves the electronic and ionic conductivity, and buffers the volume expansion. Thereby, it delivers reversible capacity, superb rate capability, and outstanding cycling stability. For the Li-metal anode, PAN aerogel is carbonized to give macroporous N-doped cross-linked carbon nanofiber that behaves as a lithiophilic host to regulate Li plating and suppress the growth of Li dendrite. Combining the improvements for both the cathode and anode realizes a remarkable long-term cyclability (765 mAh g⁻¹ after 300 cycles) in a full cell. It provides new opportunity to propel the practical application of advanced LSBs.     

碳模板诱导生长Fe-Nx活性位点

能源危机和环境恶化是当今社会面临的巨大挑战. 燃料电池作为一种高效、清洁的发电装置,受到了社会各界特别是新能源行业的高度关注. 尤其是, 日本丰田推出Mirai燃料电池汽车量产上市计划, 把燃料电池及其关键技术发展推向了一个新的发展纪元. 然而, 制约燃料电池走向大规模商业化的核心问题依然是其综合性能不具竞争力. 其中, 氧电极的缓慢动力学以及贵金属Pt的有限资源、高昂成本等是关键所在, 因此, 亟待实现高性能非贵金属催化剂的突破.近年来, 大量研究表明, Fe-Nx掺杂的碳催化剂具有极大的代Pt潜力, 研究者们尝试各种手段进行开发,如: 调控Fe化合物及N前驱体的类型与添加量, 改变温度、压力等合成条件, 采用轴向配位体连接、共价接枝、球磨等非热解路线, 构建核壳、有序介孔碳、阵列、类石墨烯薄片、多孔碳等碳纳米结构, 制备石墨烯/碳纳米管、石墨烯/碳黑、碳纳米带/碳纳米管、碳纳米颗粒/碳纤维、碳球/碳纳米管/石墨烯等复合材料, 进行酸洗、造孔、二次加热等后处理, 调控不同类型Fe物种相生成等. 此外, EXAFS及M?ssbauer等谱学技术已经证实Fe-Nx特别是Fe-N4为强活性位点. 因此, 有待提出合理策略以促进非贵金属碳催化剂中Fe-Nx强活性位点的高密度掺杂.本文提出了一种碳模板诱导Fe-Nx活性位点生长的方法即通过高温热解含有Fe盐的三聚氰胺前驱体混合物, 成功制备 了Fe-Nx掺杂的碳催化剂, 并结合多种表征技术证实了碳模板对制备碳催化剂结构组成及电化学性能的影响. 形貌结果说明, 碳模板的引入有利于Fe、N化合物的均匀吸附以至于Fe基纳米颗粒的均一成核, 促使竹状碳纳米管在碳模板表面以及中间均一生长; 氮气吸脱附及孔径分布曲线显示, 引入碳模板形成的复合材料较单一的碳纳米管和碳黑材料具有提高的比表面积和总孔体积, 说明复合材料中存在两种单体的有效协同; M?ssbauer、XPS及XRD测试数据证实, 碳模板可以调控Fe、N两种元素的耦合方式, 能够抑制金属Fe和Fe碳化物等非活性Fe物种的生成、诱导Fe-N4和其它Fe氮化物等强活性Fe-Nx物种的生长. 电化学测试数据表明, 复合材料具有提升的面积活性和质量活性, 且TOF值明显提高, 说明碳模板的引入增强了Fe-Nx位点的本征活性; 此外, 复合材料的氧还原过程为高效的4e-途径, 且较商业Pt/C催化剂表现出了优异的循环稳定性和甲醇耐受性.     

High‐Performance Sodium Metal Anodes Enabled by a Bifunctional Potassium Salt

Developing Na metal anodes that can be deeply cycled with high efficiency for a long time is a prerequisite for rechargeable Na metal batteries to be practically useful despite their notable advantages in theoretical energy density and potential low cost. Their high chemical reactivity with the electrolyte and tendency for dendrite formation are two major issues limiting the reversibility of Na metal electrodes. In this work, we introduce for the first time potassium bis(trifluoromethylsulfonyl)imide (KTFSI) as a bifunctional electrolyte additive to stabilize Na metal electrodes, in which the TFSI^? anions decompose into lithium nitride and oxynitrides to render a desirable solid electrolyte interphase layer while the K⁺ cations preferentially adsorb onto Na protrusions and provide electrostatic shielding to suppress dendritic deposition. Through the cooperation of the cations and anions, we have realized Na metal electrodes that can be deeply cycled at a capacity of 10 mAh cm^?2 for hundreds of hours.     

浆态床合成二甲醚复合催化剂失活原因探索

在反应温度260℃、压力5.0MPa的条件下,对浆态床反应器中二甲醚合成复合催化剂的失活规律进行了研究。结果表明, Cu基催化剂失活较快是导致浆态床二甲醚合成催化剂不稳定的主要原因。通过分析Cu基催化剂在浆态床反应器和固定床反应器中的活性变化规律,发现在浆态床反应器中不能及时导出反应体系的H2O对催化剂的毒副作用导致了浆态床Cu基催化剂快速失活。对失活催化剂进行的TPR、XRD和SEM EDS表征结果可以看出,Cu粒子的长大和积炭是Cu基催化剂失活的重要原因,与已有文献报道不同的是并未发现明显的Cu元素流失。