金属纳米催化剂高效催化制氢概述

金属纳米催化剂由于其优异的催化性能、可控的微观结构等优点而备受关注。综述了从NH3BH3、N2H4及NaBH4等液相化学储氢材料中催化制氢的研究现状,并提出了金属纳米催化剂在催化制氢研究领域中存在的问题及以后的研究发展方向。     

MOF(Co)/功能化石墨烯制备高效Co-N-C型氧还原催化剂研究

以六水合硝酸钴为金属源,苯并咪唑为有机配体,对苯二胺改性氧化石墨烯(PGO)为碳载体,采用一步溶剂热法合成金属有机骨架(MOF)-PGO前躯体,经过高温处理制备了多孔Co-N-PGO催化剂。采用比表面积孔隙度分析仪、扫描电子显微镜、透射电子显微镜、X射线衍射、拉曼光谱和X射线光电子能谱等物理表征手段对催化剂形貌、结构以及元素形态进行表征,同时利用线性扫描伏安法和计时电流法对催化剂在碱性电解液中的氧还原(ORR)性能进行测试。结果表明,Co-N-PGO催化剂具有较高的比表面积和电化学活性面积,良好的结晶程度以及丰富的孔洞结构。此外,Co-N-PGO催化剂表现出优异的ORR催化活性,半波电位与商业Pt/C催化剂相比仅相差10mV,同时拥有更好的稳定性及抗甲醇毒化性能。根据K-L方程,Co-N-PGO催化剂在ORR过程中主要为四电子途径,与Pt/C催化剂反应机理相似。     

功能化石墨烯多层膜载金催化剂的制备及其对肼的电催化氧化

以聚二甲基二烯丙基氯化铵功能化石墨烯(PDDA-GNs)和磷钼酸功能化石墨烯(PMo₁₂-GNs)为原料,利用层层自组装法制备了功能化石墨烯多层膜({PDDA-GNs/PMo₁₂-GNs}),以此多层膜为载体,通过恒电位电沉积法制备功能化石墨烯多层膜载金催化剂(Au/{PDDA-GNs/PMo₁₂-GNs}_n)。采用XRD、XPS和SEM等表征Au/{PDDA-GNs/PMo₁₂-GNs}_n催化剂的组成、结构和形貌。结果表明:实验成功制备了Au/{PDDA-GNs/PMo₁₂-GNs}_n催化剂,且多层膜载体改善了Au粒子的分散性。利用循环伏安(CV)、计时电流(It)和交流阻抗(EIS)等评价催化剂对肼氧化的电催化性能。结果表明,Au/{PDDA-GNs/PMo₁₂-GNs}_n催化剂使肼氧化的电催化活性和稳定性得到很大提高。与Au/玻碳电极(GCE)相比,Au/{PDDA-GNs/PMo₁₂-GNs}_n催化肼氧化反应的峰电流密度从0.46 mA/cm2提高到0.87 mA/cm2,600 s时的稳态电流密度是Au/GCE的2.5倍。      

Pd-P/g-C3N4催化剂的优化制备及在甲酸分解制氢中的应用

以氮化碳(g-C₃N₄)为载体,采用液相还原法制备了一系列Pd-P/g-C₃N₄催化剂用于甲酸分解制氢,通过优化还原温度和活性组分负载量可以显著提高催化剂性能。采用X射线衍射仪、透射电子显微镜和X射线光电子能谱仪对催化剂的晶相结构、微观形貌、活性组分分布以及价态进行分析,并通过甲酸分解制氢实验测试了催化剂的甲酸分解制氢活性。结果表明：使用次磷酸钠还原剂需要在较高还原温度(90℃)才能实现Pd-P活性组分在g-C₃N₄载体表面的高度分散,获得较小的纳米粒子,过高或过低的还原温度都不利于制备高性能催化剂。当Pd负载量为8.0%(质量分数)时,2-Pd-P/g-C₃N₄催化剂表现出最佳催化性能,通过动力学研究和Arrhenius方程计算得到该催化剂的甲酸分解活化能为33.83kJ/mol。     

基于分子动力学方法模拟硅功能化石墨烯纳米压痕过程

基于分子动力学方法, 采用Tersoff势函数与Lennard-Jones势函数, 结合速度形式的Verlet算法, 首先对单层石墨烯薄膜的分子动力学模型进行了纳米压痕力学过程的模拟.通过模拟得到单层石墨烯薄膜的荷载-位移曲线, 并对其进行最小二乘法拟合, 得到了单层石墨烯薄膜的弹性模量和强度, 通过和已有研究结论进行对比, 验证了模型的有效性.最后建立了由双层石墨烯薄膜构成的硅功能化石墨烯分子动力学模型, 进行了纳米压痕力学过程的模拟.采用同样的计算方法和过程, 得到了硅碳比 (硅原子数与碳原子数之比) 为0.65%的双层硅功能化石墨烯材料的弹性模量和强度分别为0.98 TPa和247.33 GPa.     

功能化石墨烯纳米带-纳米碳纤维/热塑性聚氨酯薄膜的制备及性能

利用溶液涂覆成膜工艺在涂膜机上制得功能化石墨烯纳米带-纳米碳纤维/热塑性聚氨酯(FGNRs-CNFs/TPU)复合材料薄膜。采用红外光谱、X射线衍射、X射线光电子能谱、透射电镜对所得FGNRs-CNFs的结构与性能进行表征,并结合复合材料薄膜的氧气透过率和体积电阻率测试以及断面形貌观察,研究了不同含量的FGNRs-CNFs对TPU复合材料薄膜阻隔和抗静电性能的影响。结果显示,KH-550成功接枝在GNRs上,并且FGNRs附着在骨架CNFs上形成稳定的FGNRs-CNFs网络结构,这有利于其在TPU中均匀分散;相比于纯TPU薄膜,当FGNRs-CNFs质量分数为1%时,FGNRsCNFs/TPU复合材料薄膜的氧气透过率降低了68.8%,阻隔性能得到大幅度提升;石墨烯纳米带与纳米碳纤维构建导电网络,当添加量为0.6%时,复合材料薄膜导电性能提升了7个数量级,表现出优良的室温导电性能。     

纳米功能化石墨烯/室温硫化硅橡胶复合材料的制备与表征

用KH-550对氧化石墨进行改性, 再对其进行还原, 获得功能化石墨烯(FG), 未经干燥的FG经超声处理后可以稳定分散在质量比9∶1的丙酮/水混合液中; 在高速搅拌和超声分散条件下, 将FG分散液分散到室温硫化(RTV)硅橡胶中, 固化后得到纳米FG(nano-FG)/RTV硅橡胶复合材料。采用FTIR、TEM、SEM、XRD和DSC分析了FG及复合材料的结构和形貌。结果表明: KH-550连接到石墨烯片层表面上, 使其片层起皱、折叠, 部分发生了剥离, 层间距增大到3.46 ; FG经过超声处理后剥离成透明至半透明的片层; nano-FG/RTV硅橡胶复合材料的断面结构为褶皱结构, 不同于纯硅橡胶, 也未出现微观相分离; 与硅橡胶相比, 复合材料的T_g、T_m和结晶度均有所提高。复合材料的力学性能测试结果表明, nano-FG对RTV硅橡胶具有明显的补强效果, 当nano-FG质量分数为0.5 %时, nano-FG/RTV硅橡胶复合材料的拉伸强度比纯RTV硅橡胶提高了一倍多, 达到了0.43 MPa; 断裂伸长率也提高了52%, 达到了265%。      

基于分子动力学方法模拟硅功能化石墨烯纳米压痕过程北大核心CSCD

基于分子动力学方法,采用Tersoff势函数与Lennard-Jones势函数,结合速度形式的Verlet算法,首先对单层石墨烯薄膜的分子动力学模型进行了纳米压痕力学过程的模拟.通过模拟得到单层石墨烯薄膜的荷载-位移曲线,并对其进行最小二乘法拟合,得到了单层石墨烯薄膜的弹性模量和强度,通过和已有研究结论进行对比,验证了模型的有效性.最后建立了由双层石墨烯薄膜构成的硅功能化石墨烯分子动力学模型,进行了纳米压痕力学过程的模拟.采用同样的计算方法和过程,得到了硅碳比(硅原子数与碳原子数之比)为0.65%的双层硅功能化石墨烯材料的弹性模量和强度分别为0.98 TPa和247.33 GPa.     

可见光响应的三维石墨烯/氧化钴复合催化剂及其光解水制氢性能

以新型二维材料氧化石墨烯和金属有机框架化合物ZIF-67为前驱体,通过溶剂热反应和高温焙烧过程,制备了一种三维交联石墨烯负载CoO纳米粒子(3D G/CoO)的复合催化剂材料。XRD、XPS、紫外可见漫反射、SEM和TEM等结构和形貌分析结果表明：平均粒径约为34.5 nm的CoO粒子均匀负载在三维交联石墨烯体相骨架中。三维石墨烯特有的光致热电子发射性能及两种材料间的协同作用,赋予了复合材料优异的光催化分解水制氢性能。在300 W氙灯照射下,催化分解水制氢速率为10.1 mmol·gcat^-1·h^-1;在520 nm波长可见光照射下,获得了7.77%的表观量子效率。催化剂循环使用5次,活性保持率为88%。此高性能可见光响应的三维复合催化剂材料的研究,对光催化领域中新型高效催化剂的开发和应用具有重要意义。     

3D Graphene Hollow Nanospheres@Palladium‐Networks as an Efficient Electrocatalyst for Formic Acid Oxidation

Graphene has served widely as a support material for noble metal nanoparticle electrocatalysts in fuel cells. During the synthesis of electrocatalysts, however, the intense stacking and folding of graphene nanosheets decreases the utilization and activity of electrocatalysts, owing to the following aspects: i) the noble metal wrapped by the winding graphene cannot be fully utilized; ii) the structural destruction of graphene decreases the specific surface area and increases electrical resistance; and iii) the hydrophobicity and wrinkles of graphene greatly increase the mass transfer resistance of fuel molecules and electrolytes. In this work, 3D graphene oxide hollow nanospheres are designed to minimize wrinkles, maximize specific surface area, and realize the regular clipping of 2D graphene oxide. The 3D‐reduced graphene oxide hollow nanosphere supported Pd‐network nanohybrids (3D‐RGO/Pd‐NWs) are then obtained using 3D graphene oxide hollow nanospheres as a reaction precursor. The skeleton of 3D‐RGO not only acts as an exclusive inner conducting shell to promote electron and ion kinetics but is also crucial for enhancing the permeation of fuel molecules and electrolytes. Therefore, 3D‐RGO/Pd‐NWs exhibit enhanced electrocatalytic activity and durability for the formic oxidation reaction in an acidic medium compared to 2D graphene supported Pd nanoparticles and commercial Pd/C electrocatalysts.     

MOF-Derived In2O3/CuO p-n Heterojunction Photoanode Incorporating Graphene Nanoribbons for Solar Hydrogen Generation

Solar-driven photoelectrochemical (PEC) water splitting is a promising approach toward sustainable hydrogen (H₂) generation. However, the design and synthesis of efficient semiconductor photocatalysts via a facile method remains a significant challenge, especially p-n heterojunctions based on composite metal oxides. Herein, a MOF-on-MOF (metal-organic framework) template is employed as the precursor to synthesize In₂O₃/CuO p-n heterojunction composite. After incorporation of small amounts of graphene nanoribbons (GNRs), the optimized PEC devices exhibited a maximum current density of 1.51 mA cm⁻² (at 1.6 V vs RHE) under one sun illumination (AM 1.5G, 100 mW cm⁻²), which is approximately four times higher than that of the reference device based on only In₂O₃ photoanodes. The improvement in the performance of these hybrid anodes is attributed to the presence of a p-n heterojunction that enhances the separation efficiency of photogenerated electron-hole pairs and suppresses charge recombination, as well as the presence of GNRs that can increase the conductivity by offering better path for electron transport, thus reducing the charge transfer resistance. The proposed MOF-derived In₂O₃/CuO p-n heterojunction composite is used to demonstrate a high-performance PEC device for hydrogen generation.     

Nanopore-Supported Metal Nanocatalysts for Efficient Hydrogen Generation from Liquid-Phase Chemical Hydrogen Storage Materials

Hydrogen has emerged as an environmentally attractive fuel and a promising energy carrier for future applications to meet the ever-increasing energy challenges. The safe and efficient storage and release of hydrogen remain a bottleneck for realizing the upcoming hydrogen economy. Hydrogen storage based on liquid-phase chemical hydrogen storage materials is one of the most promising hydrogen storage techniques, which offers considerable potential for large-scale practical applications for its excellent safety, great convenience, and high efficiency. Recently, nanopore-supported metal nanocatalysts have stood out remarkably in boosting the field of liquid-phase chemical hydrogen storage. Herein, the latest research progress in catalytic hydrogen production is summarized, from liquid-phase chemical hydrogen storage materials, such as formic acid, ammonia borane, hydrous hydrazine, and sodium borohydride, by using metal nanocatalysts confined within diverse nanoporous materials, such as metal–organic frameworks, porous carbons, zeolites, mesoporous silica, and porous organic polymers. The state-of-the-art synthetic strategies and advanced characterizations for these nanocatalysts, as well as their catalytic performances in hydrogen generation, are presented. The limitation of each hydrogen storage system and future challenges and opportunities on this subject are also discussed. References in related fields are provided, and more developments and applications to achieve hydrogen energy will be inspired.     

Highly Selective Metal-Free Electrochemical Production of Hydrogen Peroxide on Functionalized Vertical Graphene Edges

Electrochemical generation of hydrogen peroxide (H₂O₂) is an attractive alternative to the energy-intensive anthraquinone oxidation process. Metal-free carbon-based materials such as graphene show great promise as efficient electrocatalysts in alkaline media. In particular, the graphene edges possess superior electrochemical properties than the basal plane. However, identification and enhancement of the catalytically active sites at the edges remain challenging. Furthermore, control of surface wettability to enhance gas diffusion and promote the performance in bulk electrolysis is largely unexplored. Here, a metal-free edge-rich vertical graphene catalyst is synthesized and exhibits a superior performance for H₂O₂ production, with a high onset potential (0.8 V versus reversible hydrogen electrode (RHE) at 0.1 mA cm^?2) and 100% Faradaic efficiency at various potentials. By tailoring the oxygen-containing functional groups using various techniques of electrochemical oxidation, thermal annealing and oxygen plasma post-treatment, the edge-bound in-plane ether-type (C? O? C) groups are revealed to account for the superior catalytic performance. To manipulate the surface wettability, a simple vacuum-based method is developed to effectively induce material hydrophobicity by accelerating hydrocarbon adsorption. The increased hydrophobicity greatly enhances gas transfer without compromising the Faradaic efficiency, enabling a H₂O₂ productivity of 1767 mmol g_catalyst^?1 h^?1 at 0.4 V versus RHE.     

Pd/PMo12-GN复合膜的制备及其对甲酸氧化的电催化性能

以紫外光还原法将氧化石墨(GO)还原成石墨烯(GN), 同时将磷钼酸(PMo₁₂)修饰到石墨烯上, 形成磷钼酸功能化的石墨烯PMo₁₂-GN, 并以此为基底利用电化学还原法制备了Pd/PMo₁₂-GN复合膜催化剂。运用X射线粉末衍射、X射线光电子能谱、扫描电镜、透射电镜等对复合膜的组成、结构、形态进行表征, 结果表明: 实验成功制备了Pd/PMo₁₂-GN复合膜催化剂, 且Pd颗粒均匀分散在PMo₁₂-GN基底上。采用CV、计时电流法、CO溶出伏安法、交流阻抗法等电化学方法研究了Pd/PMo₁₂-GN复合膜的电催化性能。研究结果表明: 制备的复合膜催化剂对甲酸氧化反应的催化活性、催化稳定性、抗CO毒化能力和电子传递能力显著优于商品化的Pd/C催化剂。Pd/PMo₁₂-GN复合膜电催化性能的提高主要是由于Pd纳米颗粒在PMo₁₂-GN基底上均匀分散, 以及PMo₁₂的强氧化能力从而使钯表面一氧化碳等中间产物能迅速氧化去除。     

水解制氢材料研究进展

水解制氢是一种常温常压下的现场制氢方式。由于水解制氢材料氢含量高,储存容易,运输方便,安全可靠,一直受到研究者们的关注。本文综述了近年来水解制氢材料的总体发展情况,介绍了三类主要的水解制氢材料,包括硼氢化物(NaBH4, NH3·BH3)、金属(Mg, Al)以及金属氢化物(MgH2),对不同材料的制氢原理、主要问题、催化剂与材料设计进行了详细介绍,比较了不同体系的特点与制氢成本,并对水解制氢及水解制氢材料的现状和商业化面临的困难做了评价,最后对未来的发展方向进行了展望。     

Memristive Devices with Highly Repeatable Analog States Boosted by Graphene Quantum Dots

Memristive devices, having a huge potential as artificial synapses for low‐power neural networks, have received tremendous attention recently. Despite great achievements in demonstration of plasticity and learning functions, little progress has been made in the repeatable analog resistance states of memristive devices, which is, however, crucial for achieving controllable synaptic behavior. The controllable behavior of synapse is highly desired in building neural networks as it helps reduce training epochs and diminish error probability. Fundamentally, the poor repeatability of analog resistance states is closely associated with the random formation of conductive filaments, which consists of oxygen vacancies. In this work, graphene quantum dots (GQDs) are introduced into memristive devices. By virtue of the abundant oxygen anions released from GQDs, the GQDs can serve as nano oxygen‐reservoirs and enhance the localization of filament formation. As a result, analog resistance states with highly tight distribution are achieved with nearly 85% reduction in variations. In addition the insertion of GQDs can alter the energy band alignment and boost the tunneling current, which leads to significant reduction in both switching voltages and their distribution variations. This work may pave the way for achieving artificial neural networks with accurate and efficient learning capability.     

A Simple and Effective Principle for a Rational Design of Heterogeneous Catalysts for Dehydrogenation of Formic Acid

Efficient and selective dehydrogenation of formic acid is a key challenge for a fuel‐cell‐based hydrogen economy. Though the development of heterogeneous catalysts has received much progress, their catalytic activity remains insufficient. Moreover, the design principle of such catalysts are still unclear. Here, experimental and theoretical studies on a series of mono‐/bi‐metallic nanoparticles supported on a NH₂‐N‐rGO substrate are combined for formic acid dehydrogenation where the surface energy of a metal is taken as a relevant indicator for the adsorption ability of the catalyst for guiding catalyst design. The AuPd/NH₂‐N‐rGO catalyst shows record catalytic activity by reducing the energy barrier of rate controlling steps of formate adsorption and hydrogen desorption. The obtained excellent results both in experiments and simulations could be extended to other important systems, providing a general guideline to design more efficient catalysts.     

In Situ Exfoliated,Edge‐Rich,Oxygen‐Functionalized Graphene from Carbon Fibers for Oxygen Electrocatalysis

Metal‐free electrocatalysts have been extensively developed to replace noble metal Pt and RuO₂ catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in fuel cells or metal–air batteries. These electrocatalysts are usually deposited on a 3D conductive support (e.g., carbon paper or carbon cloth (CC)) to facilitate mass and electron transport. For practical applications, it is desirable to create in situ catalysts on the carbon fiber support to simplify the fabrication process for catalytic electrodes. In this study, the first example of in situ exfoliated, edge‐rich, oxygen‐functionalized graphene on the surface of carbon fibers using Ar plasma treatment is successfully prepared. Compared to pristine CC, the plasma‐etched carbon cloth (P‐CC) has a higher specific surface area and an increased number of active sites for OER and ORR. P‐CC also displays good intrinsic electron conductivity and excellent mass transport. Theoretical studies show that P‐CC has a low overpotential that is comparable to Pt‐based catalysts, as a result of both defects and oxygen doping. This study provides a simple and effective approach for producing highly active in situ catalysts on a carbon support for OER and ORR.     

氨硼烷水解制氢催化剂载体的研究进展

氢由于具有高效率和高功率密度而被认为是一种出色的清洁能源。化学储氢材料要求具有高的氢储存量。氨硼烷具有高氢含量(19.6%),且在普通贮存条件下稳定,被认为是有吸引力的储氢材料之一。由于氨硼烷在常温下不易放氢,故放氢催化剂成为氨硼烷放氢研究的核心技术和主要方向。金属催化剂可以显著提高水解放氢速度,是影响氨硼烷水解放氢的关键因素,但是金属颗粒催化剂一般都存在颗粒粒径生长过快、易团聚等缺点。为了解决这一问题,研究者选择不同的载体来分散催化剂,使催化剂金属分散在载体表面,防止团聚和过快增长,从而暴露更多活性位点,使催化氨硼烷放氢速率更快。文章将针对不同催化剂载体对氨硼烷水解的催化效果进行阐述。