Electrocatalytic water splitting is a promising strategy to generate hydrogen using renewable energy under mild conditions. Carbon-based materials have attracted attention in electrocatalytic water splitting because of their distinctive features such as high specific area, high electron mobility and abundant natural resources. Hydrogen produced by industrial electrocatalytic water splitting in a large quantity requires electrocatalysis at a low overpotential at a large current density. Substantial efforts focused on fundamental research have been made, while much less attention has been paid to the high-current-density test. There are many distinct differences in electrocatalysis to split water using low and high current densities such as the bubble phenomenon, local environment around active sites, and stability. Recent research progress on carbon-based electrocatalysts for water splitting at low and high current densities is summarized, significant challenges and prospects for carbon-based electrocatalysts are discussed, and promising strategies are proposed.
Electrocatalytic carbon dioxide (CO2) reduction is an important way to achieve carbon neutrality by converting CO2 into high-value-added chemicals using electric energy. Carbon-based materials are widely used in various electrochemical reactions, including electrocatalytic CO2 reduction, due to their low cost and high activity. In recent years, defect engineering has attracted wide attention by constructing asymmetric defect centers in the materials, which can optimize the physicochemical properties of the material and improve its electrocatalytic activity. This review summarizes the types, methods of formation and defect characterization techniques of defective carbon-based materials. The advantages of defect engineering and the advantages and disadvantages of various defect formation methods and characterization techniques are also evaluated. Finally, the challenges of using defective carbon-based materials in electrocatalytic CO2 reduction are investigated and opportunities for their use are discussed. It is believed that this review will provide suggestions and guidance for developing defective carbon-based materials for CO2 reduction.
Electrocatalysis is a key component of many clean energy technologies that has the potential to store renewable electricity in chemical form. Currently, noble metal-based catalysts are most widely used for improving the conversion efficiency of reactants during the electrocatalytic process. However, drawbacks such as high cost and poor stability seriously hinder their large-scale use in this process and in sustainable energy devices. Carbon-based metal-free catalysts (CMFCs) have received growing attention due to their enormous potential for improving the catalytic performance. This review gives a concise comprehensive overview of recent developments in CMFCs for electrosynthesis. First, the fundamental catalytic mechanisms and design strategies of CMFCs are presented and discussed. Then, a brief overview of various electrosynthesis processes, including the synthesis of hydrogen peroxide, ammonia, chlorine, as well as various carbon- and nitrogen-based compounds is given. Finally, current challenges and prospects for CMFCs are highlighted.
Producing organic electro-oxidation and hydrogen evolution reactions (HER) simultaneously in an electrolytic cell is an appealing method for generating valuable chemicals at the anode while also producing H2 at the cathode. Within this framework, the task of designing energy-saving electrocatalysts with high selectivity and stability is a considerable challenge. Carbon-based catalysts, along with their supports, have emerged as promising candidates due to their diverse sources, large specific surface area, high porosity and multidimensional characteristics. This review summarizes progress from 2012 to 2022, in the use of carbon-based catalysts and their supports for organic electrooxidation and HER. It delves into outer-sphere electrooxidation mechanisms involving molecule-mediated oxidation and oxidative radical coupling reactions, as well as inner-sphere electrooxidation mechanisms, encompassing both acidic and alkaline electrolytes. The review also explores prospective research directions within this domain, addressing various aspects such as the design of electrocatalytic materials, the study of the relationship between the structure and properties of electrocatalysts, as well as examining their potential industrial applications.
Because of the demand for clean and sustainable energy sources, nanocarbons, modified carbons and their composite materials derived from metal-organic frameworks (MOFs) are emerging as distinct catalysts for electrocatalytic energy conversion. These materials not only inherit the advantages of MOFs, like customizable dopants and structural diversity, but also effectively prevent the aggregation of nanoparticles of metals and metal oxides during pyrolysis. Consequently, they increase the electrocatalytic efficiency, improve electrical conductivity, and may play a pivotal role in green energy technologies such as fuel cells and metal-air batteries. This review first explores the carbonization mechanism of the MOF-derived carbon-based materials, and then considers 3 key aspects: intrinsic carbon defects, metal and non-metal atom doping, and the synthesis strategies for these materials. We also provide a comprehensive introduction to advanced characterization techniques to better understand the basic electrochemical catalysis processes, including mapping techniques for detecting localized active sites on electrocatalyst surfaces at the micro- to nano-scale and in-situ spectroscopy. Finally, we offer insights into future research concerning their use as electrocatalysts. Our primary objective is to provide a clearer perspective on the current status of MOF-derived carbon-based electrocatalysts and encourage the development of more efficient materials.
The reduction of carbon dioxide (CO2) by electrochemical methods for the production of fuels and value-added chemicals is an effective strategy for overcoming the global warming problem. Due to the stable molecular structure of CO2, the design of highly selective, energy-efficient and cost-effective electrocatalysts is key. For this reason, graphene and its derivatives are competitive for CO2 electroreduction with their unique and excellent physical, mechanical and electrical properties and relatively low cost. In addition, the surface of graphene-based materials can be modified using different methods, including doping, defect engineering, production of composite structures and wrapped shapes. We first review the fundamental concepts and criteria for evaluating electrochemical CO2 reduction, as well as the catalytic principles and processes. Methods for preparing graphene-based catalysts are briefly introduced, and recent research on them is summarized according to the categories of the catalytic sites. Finally, the future development direction of CO2 electroreduction technology is discussed.
Iron-chromium redox flow batteries (ICRFBs) use abundant and inexpensive chromium and iron as the active substances in the electrolyte and have great potential as a cost-effective and large-scale energy storage system. However, they are still plagued by several issues, such as the low electrochemical activity of Cr3+/Cr2+ and the occurrence of the undesired hydrogen evolution reaction (HER). We report the synthesis of amorphous bismuth (Bi) nanoparticles (NPs) immobilized on N-doped graphite felts (GFs) by a combined self-polymerization and wet-chemistry reduction strategy followed by annealing, which are used as the negative electrodes for ICRFBs. The resulting Bi NPs react with H+ to form intermediates and greatly inhibit the parasitic HER. In addition, the combined effect of Bi and N dopants on the surface of GF dramatically increases the electrochemical activity of Fe2+/Fe3+ and Cr3+/Cr2+, reduces the charge transfer resistance, and increases the mass transfer rate compared to plain GF. At the optimum Bi/N ratio of 2, a high coulombic efficiency of up to 97.7% is maintained even for 25 cycles at different current densities, the energy efficiency reaches 85.8% at 60.0 mA cm−2, exceeding many other reported materials, and the capacity reaches 862.7 mAh L−1 after 100 cycles, which is about 5.3 times that of bare GF.
The nitrate reduction reaction (NtRR) has been demonstrated to be a promising way for obtaining ammonia (NH3) by converting NO3− to NH3. Here we report the controlled synthesis of cobalt tetroxide/graphdiyne heterostructured nanowires (Co3O4/GDY NWs) by a simple two-step process including the synthesis of Co3O4 NWs and the following growth of GDY using hexaethynylbenzene as the precursor at 110 °C for 10 h. Detailed scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman characterization confirmed the synthesis of a Co3O4/GDY heterointerface with the formation of sp-C―Co bonds at the interface and incomplete charge transfer between GDY and Co, which provide a continuous supply of electrons for the catalytic reaction and ensure a rapid NtRR. Because of these advantages, Co3O4/GDY NWs had an excellent NtRR performance with a high NH3 yield rate (YNH3) of 0.78 mmol h−1 cm−2 and a Faraday efficiency (FE) of 92.45% at −1.05 V (vs. RHE). This work provides a general approach for synthesizing heterostructures that can drive high-performance ammonia production from wastewater under ambient conditions.
Designing efficient and robust catalysts for hydrogen evolution reaction (HER) is imperative for saline water electrolysis technology. A catalyst composed of CoxP nanowires array with N-doped carbon nanosheets (NC) was fabricated on Ni foam (NF) by an in-situ growth strategy. The material is designated as NC/CoxP@NF. In the preparation process, Co(OH)2 nanowires were transformed into a metal organic framework of cobalt (ZIF-67) on NF by the dissolution-coordination of endogenous Co2+ and 2-methylimidazole. The resulting cactus-like microstructure gives NC/CoxP@NF abundant exposed active sites and ion transport channels, which improve the HER catalytic reaction kinetics. Furthermore, the interconnected alternating nanowires and free-standing nanosheets in NC/CoxP@NF improve its structural stability, and the formation of surface polyanions (phosphate) and a NC nanosheet protective layer improve the anti-corrosive properties of catalysts. Thus, the NC/CoxP@NF has an excellent performance, requiring overpotentials of 107 and 133 mV for HER to achieve 10 mA cm−2 in 1.0 mol L−1 KOH and 1.0 mol L−1 KOH + 0.5 mol L−1 NaCl, respectively. This in-situ transformation strategy is a new way of constructing highly-efficient HER catalysts for saline water electrolysis.
The precise change of the electronic structure of active metals using low-active supports is an effective way of developing high-performance electrocatalysts. The electronic interaction of the metal and support provides a flexible way of optimizing the catalytic performance. We have fabricated an efficient hydrogen evolution reaction (HER) electrocatalyst, in which Ir nanoclusters are uniformly loaded on a nitrogen-doped carbon framework (Ir@NC). The synthesis process entails immersing an annealed zeolitic imidazolate framework-8 (ZIF-8), prepared at 900 °C as a carbon source, into an IrCl3 solution, followed by a calcination-reduction treatment at 400 °C under a H2/Ar atmosphere. The three-dimensional porous structure of the nitrogen-doped carbon framework exposes more active metal sites, and the combined effect of the Ir clusters and the N-doped carbon support efficiently changes the electronic structure of Ir, optimizing the HER process. In acidic media, Ir@NC has a remarkable HER electrocatalytic activity, with an overpotential of only 23 mV at 10 mA cm−2, an ultra-low Tafel slope (25.8 mV dec−1) and good stability for over 24 h at 10 mA cm−2. The high activity of the electrocatalyst with a simple and scalable synthesis method makes it a highly promising candidate for the industrial production of hydrogen by splitting acidic water.
超级电容器具有高功率密度、长循环寿命、良好的低温使用性能和安全性的优点,已经广泛应用到电子产品、能量回收和储能等领域。电极材料和电解液是决定超级电容器性能的两大关键因素,超级电容器常用的电极材料包括碳质材料(活性炭、碳纳米管、石墨烯、炭纤维、纳米洋葱碳等)、金属氧化物(金属氢氧化物)、导电聚合物及复合材料等;电解液主要有水系电解液、有机系电解液与离子液体。本文综述了超级电容器电极材料与电解液的研究现状,详细介绍了电极材料、电解液的性能及优缺点,并对新型电极材料和电解液的研究趋势提出展望。
研究了不同掺量下氧化石墨烯(GO)对水泥石以及胶砂微观结构和力学性能的影响。含16.5%水的水泥浆、0.05%GO及3倍于水泥的沙子共混物作为添加剂制备成砂浆。通过SEM、液氮吸附仪和一系列标准实验分别对水泥石的微观形态、孔隙结构、抗压抗折强度以及水泥净浆的流动度、黏度、凝结时间进行表征;考察不同GO掺量下水泥水化放热的变化情况。结果表明:GO对水泥浆有显著增稠和促凝作用;GO的掺入可以有效降低水泥的水化放热量;GO对水泥石有显著的增强增韧效果,28天龄期时,GO质量分数为0.05%的水泥石,3、7和28 d抗压强度和抗折强度同比对照组分别增加52.4%、46.5%、40.4%和86.1%、68.5%、90.5%,胶砂的抗压强度和抗折强度同比对照组分别增加43.2%、33%、24.4%和69.4%、106.4%、70.5%;GO在水泥硬化过程中对水泥石中晶体产物的产生有促进作用并能规整晶体的排布而形成针状晶体簇,改善水泥石中的孔结构,降低水泥石中微孔的体积,增加水泥石的密实度,对水泥石有显著地增强增韧效果。
磷酸活化法是植物纤维原料制备活性炭的主要化学活化方法。笔者系统综述了磷酸活化过程中活性炭孔隙结构的调控机制。从化学的观点,笔者提出植物纤维原料的磷酸活化在本质上是磷酸-生物高分子复合体的形成与热处理两个过程。基于这一概念,分析了植物纤维原料的组成与结构、浸渍条件等因素对磷酸-生物高分子复合体的组成与结构的影响,全面总结了植物纤维原料种类与预处理、植物细胞壁结构和结晶度、浸渍比、浸渍方式、温度和时间等组成、结构与条件对磷酸法活性炭孔隙结构的形成与发展的影响规律。在磷酸-生物高分子热处理过程中,系统总结了炭化温度、升温速率与中间停留温度等加热历程、惰性气体、氧化性气体和水蒸气等气氛对磷酸活化法活性炭孔隙结构的影响规律。最后概述了氧化性气氛和氧化试剂对磷酸活化过程的影响机理,以及磷酸活化过程中固相炭化和气相炭化对活性炭孔隙结构发展的贡献。
C/C复合材料因优异的高温性能被认为是高温结构件的理想材料。然而,C/C复合材料在高温高速粒子冲刷环境下的氧化烧蚀问题严重制约其应用。因此,如何提高C/C复合材料的抗烧蚀性能显得尤为重要。笔者综述C/C复合材料抗烧蚀的研究现状。目前,提高C/C复合材料抗烧蚀性能的途径主要集中于优化炭纤维预制体结构、控制热解炭织构、基体中陶瓷掺杂改性和表面涂覆抗烧蚀涂层等4种方法。主要介绍以上4种方法的研究现状,重点介绍基体改性和抗烧蚀涂层的最新研究进展。其中,涂层和基体改性是提高C/C复合材料抗烧蚀性能的两种有效方法。未来C/C 复合材料抗烧蚀研究的潜在方向主要集中于降低制造成本、控制热解炭织构、优化掺杂的陶瓷相以及将基体改性和涂层技术相结合。
评价了中国40多年来在航天、航空、光伏、粉末冶金、工业高温炉领域成功应用的针刺C/C,正交3D C/C、径编C/C、穿刺C/C、轴编C/C等五类C/C复合材料的物理、力学、热学、烧蚀、摩擦磨损、使用寿命等性能及特点,并与其他国家相应材料性能进行分析对比,为建立工程应用C/C复合材料共享的数据库平台奠定基础。揭示了炭纤维预制体、炭基体类型、界面结合状态与材料性能的关联度。指出炭纤维预制体结构单元精细化研究和其结构的梯度设计,以及炭基体的优化组合匹配技术,仍是C/C复合材料性能稳定化提升的重点研究方向。
利用化学氧化还原法制备出石墨烯。通过原位聚合法及溶液混合法制备出石墨烯/聚酰亚胺复合材料,考察不同复合材料制备方法对其机械性能及导电性能的影响,并对其作用机理进行探讨。结果表明,制备的石墨烯为二维的单层或寡层材料,加入到聚酰亚胺中能够增强其机械性能及电导率。相比溶液混合法,采用原位聚合法时石墨烯在聚酰亚胺基体中分散更均匀,对其团聚作用有更好的抑制作用,制备的复合材料性能更优异。采用该法加入石墨烯的量为1.0 wt%时,拉伸强度达到了132.5 MPa,提高了68.8%;加入量增加到3.0 wt%时,电导率达6.87×10-4S·m-1,提高了8个数量级,对聚酰亚胺的性能有显著的增强作用。
采用流变仪和激光共聚焦显微镜对不同氧化石墨烯(GO)掺量的新拌水泥浆体的流变参数以及浆体微观形态进行了定量化研究,并采用Modified-Bingham(M-B)模型和Herschel-Bulkley(H-B)模型对所测数据进行了拟合处理,提出了GO影响新拌水泥浆体的作用机理。结果表明,GO的掺入可以使新拌浆体中在减水剂作用下分散的水泥颗粒发生再次凝聚,形成重组絮凝结构,且随着GO掺量的增加,重组絮凝结构的数量越多,从而使得浆体流变性发生显著变化。一方面,新拌浆体的塑性粘度、屈服应力以及触变性随GO掺量的提高而显著增加。另一方面,GO的掺入提高了新拌浆体的临界剪切速率,使其在较大剪切速率下的流变行为仍然表现为剪切变稀;降低了浆体的剪切增稠程度,提高了浆体的稳定性。
碳纳米管优异的物理性质和可调的化学组成使其拥有广泛的应用前景。采用低温过程在碳骨架中引入磷原子预期带来可调的化学特性。本研究采用170℃下水热处理碳纳米管-磷酸混合物获得磷掺杂的碳纳米管。磷掺杂的碳管的磷含量为1.66%,比表面积为132 m2/g,热失重峰在纯氧环境下提升至694℃。当掺磷碳纳米管用于氧还原反应时,其起始电位为-0.20 V,电子转移数为2.60,反应电流显著高于无掺杂的碳纳米管。当其用作锂硫电池正极导电材料时,电极的起始容量为1106 mAh/g,电流密度从0.1 C提升至1 C时容量保留率为80%,100次循环的衰减率为每圈0.25%。
以新疆不粘煤为原料,三聚氰胺为氮源,硼酸为硼源,通过球磨和后续活化过程合成硼,氮掺杂及硼氮共掺杂煤基活性炭。氮吸附结果显示杂原子掺杂可提高活性炭中介孔的含量。红外和X光电子能谱结果显示,硼、氮原子存在于炭骨架中。循环伏安,恒流充放电及电化学阻抗分析说明硼、氮掺杂活性炭的电化学性能优于非掺杂活性炭。其中,硼氮共掺杂活性炭具有176 F·g-1的高比容量。循环20 000次容量保持率为96%。共掺杂活性炭优异的电化学性能归因于硼氮的协同作用。
随着石墨烯低成本宏量制备技术的突破,石墨烯的工业化应用进程已引起人们广泛关注。本文介绍了石墨烯在聚合物基复合材料领域的研究进展,侧重阐述石墨烯/聚合物复合材料在力学增强、导电/导热网络构建、防腐阻燃等方面的代表性研究成果,同时对商业化石墨烯产品及其复合材料应用进行了简单评述,探讨了石墨烯/聚合物复合材料领域目前存在的主要问题及未来发展趋势。
Editor-in-Chief: Chun-xiang Lu, Ph.D
Charged by:Chinese Academy of Sciences
Sponsored by:Institute of Coal Chemistry, Chinese Academy of Sciences
Published by:Science Press, Elsevier
CN 14-1407/TQ
ISSN 2097-1605
eISSN 1872-5805
Since 1985 Bimonthly
CiteScore: 6.1
IF: 5.7