Research progress of the electrode materials for electrochemical capacitors

超级电容器是一种利用界面双电层储能或在电极材料表面及近表面发生快速可逆氧化还原反应而储能的装置,因其高比功率和长循环寿命等特点而具有广阔的应用前景,高性能电极材料是当前超级电容器研究的重点.本文简单介绍了超级电容器电极材料的分类,并对碳素材料,过渡金属氧化物,导电聚合物等三类超级电容器电极材料及其复合材料的研究进展进行了简单论述.     

Synergistic interaction of biocatalyst with bio-anode as a function of electrode materials

Comprehensive study was performed to understand the synergistic interaction between the biocatalyst and anode in terms of electron discharge (ED) pattern and microbial growth by varying electrode (bio-anode) materials viz., graphite, aluminum, brass, copper, nickel and stainless steel. Experiments were performed in bio-electrochemical cell consisting of three electrodes (bio-anode as working electrode, carbon rod as counter electrode and Ag/AgCl(S) as reference electrode) employing anaerobic mixed culture as anodic biocatalyst. Voltammetric and chronoamperometric analysis were used to enumerate the ED and redox reactions. Presence of higher microbial population and dominance of Gram positive bacteria with higher ED supported graphite function as a good bio-anode material. Nickel and stainless steel showed higher ED after graphite associated with dominance of Gram positive bacterial population. Although higher ED was noticed with brass, metal oxidation and decrement in ED with time doesn’t support its function as bio-anode. In spite of higher ED than nickel and stainless steel, aluminum and copper showed significant metal oxidation leading to change in both physical and electrochemical properties along with dominant growth of Gram negative bacteria. This study gives a comprehensive idea on biocatalyst interaction with anode in extracellular electron transfer which is important in improving the anode performance. Juxtaposing the results, it can be deduced that the outcome of the present study can be extended to all bio-electrochemical systems including microbial fuel cell (MFC).     

Graphene‐based ternary composites for supercapacitors

The research on electrode materials for supercapacitor application continues to evolve as the request of high‐energy storage system has increased globally due to the demand for energy consumption. Over the past decades, various types of carbon‐based materials have been employed as electrode materials for high‐performance supercapacitor application. Among them, graphene is 1 of the most widely used carbon‐based materials due to its excellent properties including high surface area and excellent conductivity. To exploit more of its interesting properties, graphene is tailored to produce graphene oxide and reduced graphene oxide to improve the dispersibility in water and easy to be incorporated with other materials to form binary composites or even ternary composites. Nowadays, ternary composites have attracted enormous interest as 2 materials (binary composites) cannot satisfy the requirement of the high‐performance supercapacitor. Thus, many approaches have been employed to fabricate ternary composites by combining 3 different types of electroactive materials for high‐performance supercapacitor application. This review focuses on the supercapacitive performance of graphene‐based ternary composites with different types of active materials, ie, conducting polymers, metal oxide, and other carbon‐based materials.     

Compact energy storage: Opportunities and challenges of graphene for supercapacitors

碳纳米储能材料发展迅速,质量容量性能不断刷新。但通常碳纳米材料的密度较低,导致其体积比容量有限,在很多时候很难将材料水平上的优异性能反映到最终的器件上。发展高体积能量密度储能材料,在器件水平上实现致密储能,对推动储能材料和器件的实用化至关重要。作为其它sp2碳质材料的基本结构单元和一种柔性二维材料,石墨烯通过组装可以实现纳米结构致密化,在致密储能方面具有先天优势。本文以石墨烯在超级电容器中的应用为主,分别从材料、电极、器件3个层次讨论了实用化储能器件的设计原则,梳理了高体积能量密度碳基储能材料的研究进展,重点介绍了高体积容量碳电极材料的致密化设计理念,强调了从器件角度考虑储能材料设计的重要性,并对致密储能面临的机遇和挑战作了分析。     

Recent progress on self-supported two-dimensional transition metal hydroxides nanosheets for electrochemical energy storage and conversion

Transition metal hydroxides (TMHs) nanosheets have attracted wide attention in electrochemical energy storage and conversion because of their superior surface area, highly tunable composition, and low cost. Moreover, the self-supported electrode has been extensively studied for electrochemical devices due to its fast electron transfer and mass transport, resulting in enhanced stability and electrode performance. Hence, reviewing the recent advances in self-supported TMHs nanosheets is crucial for developing high-performance electrodes for electrochemical devices. In this review, we first introduce the fundamental properties of TMHs in terms of layered single metal hydroxides (LSHs) and layered double hydroxides (LDHs). Then, we review various synthetic approaches utilized to construct self-supported TMHs nanosheets with tunable compositions and structures. Afterwards, the electrode performance and durability of self-supported TMHs nanosheets in various electrochemical applications (water electrolysis, zinc-air battery and supercapacitor) are comprehensively summarized. Finally, the further perspectives on current challenges and research directions of self-supported TMHs nanosheets towards electrochemical energy storages and conversion applications are proposed.     

Progress of electrochemical capacitor electrode materials: A review

The electrode is the key part of the electrochemical capacitors (ECs), so the electrode materials are the most important factors to determine the properties of ECs. In this paper, the storage principles and characteristics of electrode materials, including carbon-based materials, transition metal oxides and conductive polymers for ECs are depicted briefly. Among them, more work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and organic electrolytes. But the composites of pseudocapacitive and carbonaceous materials are promising electrode materials for ECs because of their good electrical conductivity, low cost and high mass density.     

金属有机框架及其衍生金属氧化物在锂和钠离子电池中的应用

高性能锂和钠离子电池是未来便携电子设备、电动汽车和大规模储能电站的重要组成部分,受到了各行业的广泛关注。目前商用的锂离子电池和研发中的钠离子电池都面临着一些技术瓶颈,主要表现为能量密度低、充放电慢等,导致无法满足市场的需求。具有独特结构、高比表面积的金属有机框架及其衍生金属氧化物可作为电化学储能器件新型电极材料,满足高性能锂和钠离子电池的要求。本文综述了近年来金属有机框架及其衍生金属氧化物作为锂和钠离子电池电极材料的研究进展,同时指出了金属有机框架及其衍生金属氧化物在实际应用中的不足及未来可能的一些改进措施。     

Transition metal nanoparticles doped carbon paper as a cost-effective anode in a microbial fuel cell powered by pure and mixed biocatalyst cultures

The poor wettability and high cost of the carbonaceous electrodes materials prohibited the practical applications of microbial fuel cells (MFCs) on large scale. Here, a novel nanoparticles of metal sheathed with metal oxide is electrodeposited on carbon paper (CP) to introduce as high-performance anodes of microbial fuel cell (MFC). This thin layer of metal/metal oxide significantly enhance the microbial adhesion, the wettability of the anode surface and decrease the electron transfer resistance. The investigation of the modified CP anodes in an air-cathode MFCs fed by various biocatalyst cultures shows a significant improving in the MFC performance. Where, the generated power and current density was 140% and 210% higher as compared to the pristine CP. Mixed culture of exoelectrogenic microorganism in wastewater exhibited good performance and generated higher power and current density compared to yeast as pure culture. The excellent capacitance with a distinctive nanostructure morphology of the modified-CP open an avenues for practical applications of MFCs.     

Synthesis of composite electrode materials of FeOOH-based particles/carbon powder and their high-rate charge-discharge performance in lithium cells

Composite electrode materials of FeOOH-based particles and carbon powder were prepared with and without heat treatment of composite powder. The composite powder was obtained by hydrolyzing mixed aqueous solutions of FeCl₃, Ti(SO₄)₂ and electron conducting carbon powder as acetylene black (AB) or Ketjen black (KB). FeOOH-based materials formed in the presence of Ti(IV) ions became amorphous and/or low crystalline structure. The composite powder worked as lithium insertion electrode materials in lithium cells using nonaqueous electrolytes including lithium ions. The electrodes exhibited a good cycle performance at large charge-discharge current densities over 5 mA cm⁻² (4 A g⁻¹ per weight of active material). In addition, it was found that the cycle performance was effective process to be improved by the heat treatment of the composite materials. The composite materials such as amorphous FeOOH, α-Fe₂O₃, TiO₂ and electron conductive powder obtained by the heat treatment are one of the promising candidates as electrode materials for energy storage devices, such as lithium-ion batteries and hybrid electrochemical supercapacitors.     

Electronically conducting hybrid material as high performance catalyst support for electrocatalytic application

The electronically conducting hybrid material based on transition metal oxide and conducting polymer has been used as the catalyst support for Pt nanoparticles. The Pt nanoparticles loaded hybrid organic (polyaniline)–inorganic (vanadium pentoxide) composite has been used as the electrode material for methanol oxidation, a reaction of importance for the development of direct methanol fuel cells (DMFC). The hybrid material exhibited excellent electrochemical and thermal stability in comparison to the physical mixture of conducting polymer and transition metal oxide. The Pt nanoparticles loaded hybrid material exhibited high electrocatalytic activity and stability for methanol oxidation in comparison to the Pt supported on the Vulcan XC 72R carbon support. The higher activity and stability is attributed to the better CO tolerance of the composite material.     

Bioelectrochemical element conversion reactions towards generation of energy and value-added chemicals

In the past decades, the bioelectrochemical system (BES) has developed into a versatile platform to sustain the conversion of various substances for the generation of energy and energy-efficient production of chemicals. Taking advantage of microbial extracellular electron transfer, the BES is able to perform a variety of value-added element conversion reactions, including production of electric energy from organic carbon, synthesis of chemicals from carbon dioxide, oxidation of sulfide into element sulfur, reduction of nitrate/nitrite into nitrous oxide and reduction of metal ions into solid metals and/or metal oxides. While the potential for using BES as an energy and resource factory has been fully recognized, governing the element conversion pathways into the desired energy and products in BES is still a great challenge. This review provides comprehensive insights into the microbial extracellular electron transfer principles as well as behaviors of key chemical elements in BESs. Individual element conversion processes and their integrations on the BES platform are analyzed. The physicochemical, chemical and microbial mechanisms involved in these processes are explored, and the coupling patterns of electron transfer and element conversion reactions are elucidated. Furthermore, the challenges to design, construct and operate a BES with improved electron transfer efficiency and product specificity are discussed, and research needs are proposed. Additionally, BES technologies from the perspectives of waste remediation, energy production, resource recovery and chemical synthesis are envisaged.     

In-situ modified titanium suboxides with polyaniline/graphene as anode to enhance biovoltage production of microbial fuel cell

Microbial fuel cell (MFC) has been the focus of much investigation in the search for harvesting electricity from various organic matters. The electrode material plays a key role in boosting MFC performance. Most studies, however, in the field of MFC electrode material has only focused on carbonaceous materials. The finding indicates that titanium suboxides (Ti₄O₇, TS) can provide a new alternative for achieving better performance. Polyaniline (PANI) together with graphene is chosen to in-situ modify TS (TSGP). The MFC reactor with TSGP anode achieves the highest voltage with 980 mV, and produces a peak power density of 2073 mW/m², which is 2.9 and 12.7 times those with the carbon cloth control. The rather intriguing result could be due to the fact that TSGP has the high conductivity and large electrochemical active surface area, greatly improving the charge transfer efficiency and the bacterial biofilm loading. This study has gone some way towards exploring the conducting ceramics materials in MFC.     

A critical review on improving hydrogen storage properties of metal hydride via nanostructuring and integrating carbonaceous materials

Hydrogen-based economy has a great potential for addressing the world's environmental concerns by using hydrogen as its future energy carrier. Hydrogen can be stored in gaseous, liquid and solid-state form, but among all solid-state hydrogen storage materials (metal hydrides) have the highest energy density. However, hydrogen accessibility is a challenging step in metal hydride-based materials. To improve the hydrogen storage kinetics, effects of functionalized catalysts/dopants on metal atoms have been extensively studied. The nanostructuring of metal hydrides is a new focus and has enhanced hydrogen storage properties by allowing higher surface area and thus reversibility, hydrogen storage density, faster and tunable kinetics, lower absorption and desorption temperatures, and durability. The effect of incorporating nanoparticles of carbon-based materials (graphene, C60, carbon nanotubes (CNTs), carbon black, and carbon aerogel) showed improved hydrogen storage characteristics of metal hydrides. In this critical review, the effects of various carbon-based materials, catalysts, and dopants are summarized in terms of hydrogen-storage capacity and kinetics. This review also highlights the effects of carbon nanomaterials on metal hydrides along with advanced synthesis routes, and analysis techniques to explore the effects of encapsulated metal hydrides and carbon particles. In addition, effects of carbon composites in polymeric composites for improved hydrogen storage properties in solid-state forms, and new characterization techniques are also discussed. As is known, the nanomaterials have extremely higher surface area (100–1000 time more surface area in m²/g) when compared to the bulk scale materials; thus, hydrogen absorption and desorption can be tuned in nanoscale structures for various industrial applications. The nanoscale tailoring of metal hydrides with carbon materials is a promising strategy for the next generation of solid-state hydrogen storage systems for different industries.     

Solvent treatment inducing ultralong cycle stability poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) fibers as binding-free electrodes for supercapacitors

As one kind of conducting polymer composite, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) has been widely used as an electrode for energy storage and conversion devices because of its optical transmittance, flexibility, and high electrical conductivity etc. Here, we prepared binding-free PEDOT:PSS fibers (PFs) electrodes with high capacitive performance for supercapacitors via a facile method followed by various solvent treatments. Dimethyl sulfoxide (DMSO)-treated electrodes displayed a better specific capacitance (C_s) of 202 F/g at 0.5 A/g with higher elongation at break, flexibility, and conductivity of 140.7 S/cm, compared to those of pristine PEDOT:PSS materials. More importantly, the DMSO-treated fibers possessed improved stability, which retained 105% of the initial C_s after 22 000 long cycles at 10 A/g. It is believed that the fabricated PFs will be promising organic electrodes for portable supercapacitors and other flexible electronic devices in the near future.     

Recent progress in the application of carbon materials to supercapacitors and lead-carbon batteries

新型炭材料是电化学储能领域中非常重要的一类储能材料,目前广泛应用于各种电化学储能器件.本文综述了具有电容特性的高比表面积炭材料在超级电容器与铅炭电池中的应用.采用不同的方法合成具有高比表面积的新型炭材料作为超级电容器电极材料,能够得到较高的比容量.适量高比表面积的炭材料应用于铅酸电池负极,形成铅炭电池,极大地提高了电池的储能特性.论文最后探讨了新型炭材料在超电容以及铅炭电池中应用的发展方向.     

Research progress on heat transfer enhancement technology of phase change energy storage

相变储能是通过相变材料吸/放热过程来实现能量储存的技术,它能够解决热量供需时间、空间和强度上的不匹配,并以其高储能密度成为储能领域的研究热点,但由于相变材料的热导率较低,使其应用受到限制。针对相变储能材料熔化/凝固过程中热导率低引起的传热速率慢的问题,从优化储能设备结构、添加剂提高相变材料热导率以及联合强化传热技术三方面综述国内外相变材料储能强化传热技术的最新进展。通过比较各种强化传热方式的优劣,实验和模拟均显示复合强化传热即可解决相变材料热导率低,又增大传热面积,从而提高相变材料的传热性能;多孔金属作为导热添加剂增强导热效果更好;并提出了相变储能强化传热技术未来需要解决的相关技术难题。     

Supported bimetallic nanoparticles as anode catalysts for direct methanol fuel cells: A review

Direct methanol fuel cell (DMFC) is an environment friendly energy source that transforms chemical energy of methanol oxidation into electrical energy. The Pt- and non-Pt based bimetallic nanoparticles (BMNPs) with electrocatalyst support materials are employed as anode electrocatalysts for methanol oxidation. These supported BMNPs have drawn prominent consideration due to their incredible physical and chemical properties. This article reviews the advancements in the field of supported BMNPs of varied structures, compositions and morphologies, using innumerable carbonaceous support materials such as carbon black, carbon nanotubes, carbon nanofibers, graphene, mesoporous carbon as well as non-carbonaceous supports like inorganic oxides, graphitic carbon nitride, metal nitrides, conducting polymers and hybrid support materials. The performance of electrocatalysts on the basis of support material, structure, composition and morphology of BMNPs, and pros and cons of various support materials have been discussed.     

Effect of NiO on organic framework functionalized ZnO nanoparticles for energy storage application

Functionalization of metal oxides nanomaterial by different organic and inorganic species could considerably enhance the electrochemical performance of a supercapacitor. Here, we have synthesized and functionalized ZnO nanoparticles (NPs) via organic compounds of E. cognate and then doped the synthesized nanomaterials by NiO following hydrothermal route involving the bioactive compounds. As synthesized ZnO@NiO was analyzed by field emission-scanning electron microscopy at nanoscale. The organic functional groups were delineated by X-ray photoelectron spectroscopy as well as by Fourier transform infrared spectroscopy. What is more, Tauc plot revealed drastically decreased band gap energy of ZnO@NiO to 2.48 eV resulting in an enhanced electrochemical properties. Therefore, organic framework derived ZnO@NiO nanomaterial was scrutinized as an electrode for supercapacitor by galvanostatic charge-discharge, cyclicvoltammetry and electrochemical impedance spectroscopy. ZnO@NiO electrode demonstrated specific capacitance of 185 Fg⁻¹ by cyclicvoltammetry, proposing its potential towards supercapacitor due to nanoscale particles and incorporated C, O, and N atoms of organic compounds.     

Biomimetic molecular water splitting catalysts for hydrogen generation

During the last few decades, the scientific community has been striving hard to develop new and alternative sources for renewable energy and fuel. Hydrogen or carbon free fuels obtained from catalytic water splitting using sunlight offer an attractive solution for a cleaner and greener future. In this pursuit, to establish effective molecular catalytic systems for efficient water oxidation is considered to be a bottleneck, hampering the design, implementation and exploitation of electrochemical and photo-electrochemical modular devices for light driven energy conversion into hydrogen-based storable fuels. From metal oxides to composite materials, noble metal complexes to transition metal organometallics, multinuclear to mono-site catalysts, various water oxidation complexes (WOCs) have been investigated both in a homogeneous environment and on surfaces in photo- or electrochemical conditions. However, a truly biomimetic catalytic system that matches the performance of photosystem-II for efficient water splitting, operating with four consecutive proton coupled electron transfer (PCET) steps to generate oxygen and hydrogen for hundred thousands of cycles at high rate is yet to be achieved. We here present an overview of biomimetic molecular complexes that have been investigated recently for water oxidation catalysis in homogeneous solution using chemical oxidants, or as heterogeneous species for catalytic electrochemical systems.