A review of 3D graphene materials for energy storage and conversion

Electrochemical energy storage and conversion are currently one of the most critical challenges due to the increasing energy demand. Therefore, discovering novel materials to develop low-cost and more efficient energy storage technologies is urgently necessary. Among various novel materials, two-dimensional (2D) materials have attracted intensive research activities in multiple fields due to their fascinating physical and chemical properties. The 2D materials having a higher surface-to-volume ratio are beneficial to developing low-cost and large-scale energy storage systems for practical applications. There have been many promising concepts of 2D material-based real-life energy applications recently in batteries, supercapacitors, fuel cells, solar cells, thermoelectric, triboelectric generators, etc. Despite recent progress, significant efforts are still needed to investigate the fundamentals of 2D materials for electrochemical energy storage and conversion. Over the past few years, there has been substantial progress in modeling, theories, and experimental characterizations of 2D materials for energy storage and conversion. This timely Special Section issue addressed some recent advances in this critical area. We have selected eight papers covering a gamut of electrochemical-centric research in 2D materials for energy storage and conversion.In this issue, Qu et al. reported the electrochemical evaluation of helical carbon nanofibers (HCNFs) prepared by the ethanol flame method as anode materials of lithium-ion batteries. Their results show that HCNFs possess high reversible capacity, good rate performance, and excellent cycling stability. Farma et al. investigated a simple and cost-effective method to generate porous carbon activation from Palmae plant waste biomass, namely, areca leaf midrib (ALM). They showed that the electrochemical properties of activated carbon supercapacitor cells derived from ALM biomass have the highest specific capacitance value and scan rate in a two-electrode system. Arumugam et al. discussed a ternary composite made up of graphene oxide, polyaniline, and zinc oxide as an electrode material for supercapacitors with its structural and electrochemical properties. The ternary composite exhibited the highest specific capacitance. Metzger et al. focused on using graphene-coated proton exchange membrane (PEM) to reduce fuel crossover. They found that the adhesion of graphene on PEMs is insufficient for prolonging fuel cell operation, resulting in graphene delamination at high temperatures and higher fuel crossover values compared to lower temperature testing. Zaidi et al. reported the superior performance of graphene nanosheet (GNS) materials over Vulcan XC incorporated as a cathode catalyst in Li-O2 battery. The GNS catalysts demonstrated promising performance at higher current densities and with various organic electrolytes. Pandey et al. synthesized a mechanically stable, proton-conducting, and very cost-effective nanocomposite membrane using a simple and scalable phase-inversion approach. The synthesized proton-conducting nanocomposite membrane was demonstrated as a potential advanced functional solid electrolyte for possible application in proton exchange membrane fuel cells. Fauzi et al. reported the thermophysical properties of N,N-diethylethanolammonium chloride/ethylene glycol-DES (deep eutectic solvent) for the replacement of ionic liquid. They studied the physical properties of DES, which are thermal conductivity, viscosity, and surface tension. Finally, the review article by Zeng et al. provided an overview of the application of conductive diamond in electrocatalytic reduction and outlined the improvement of electrochemical properties by employing metal particles to modify the surface.We believe that this Special Section issue will be a valuable contribution to the energy storage and conversion literature and open new frontiers for researchers. The interdisciplinary field of 2D material-based energy storage is rapidly evolving. Our Special Section issue will motivate many researchers to implement novel techniques, such as artificial intelligence, digital twins, and automated advanced manufacturing, in this field and initiate new collaborations between experimentalists, theorists, and modelers. We would like to thank all contributors to this Special Section issue for submitting their latest high-impact work. Also, special thanks would go out to the invited reviewers for helping us further enhance the quality of the articles.

Applications of metal–organic framework-derived N, P, S doped materials in electrochemical energy conversion and storage

Sp2-carbon dominant carbonaceous materials for energy conversion and storage

Flexible engineering of advanced phase change materials

Sustainability is highly desired for human beings due to a rapidly changing global climate and numerous environmental issues. In past decades, state-of-the-art studies have been extensively conducted to achieve sustainable energy conversion and storage. However, the remaining challenges in the commercialization of energy conversion and storage devices are to develop novel materials and advanced manufacturing processes. Furthermore, the engineering of nanostructures and device-architectures is of great importance for the energy conversion and storage flat forms. This Special Issue “Novel Materials for Sustainable Energy Conversion and Storage” aims the state-of-the-art research reports of novel nanomaterials and the engineering of device architectures for divergent energy conversion and storage applications with high sustainability involving solar energy systems, electrochemical cells, artificial photosynthesis or secondary (rechargeable) batteries, as highlighted in this editorial.

With the ever-growing global energy demands and environmental pollution issues, developing high-performance energy storage and conversion materials has become a hot topic in the material science community. In this regard, substantial progress has been made in theoretically predicting new materials for energy-related fields, experimentally synthesizing these materials, and further improving their properties for high performance in energy storage and conversion devices. In particular, two-dimensional (2D) materials have shown great potential in the field of energy storage and conversion. However, it remains challenging to explore 2D materials that render high efficiency of energy storage and conversion while guarantee long-term stability and safety. Over the past decades, theoretical calculations based on density functional theory (DFT) have become a practical toolkit to address this issue by revealing the reaction mechanism at an atomic scale and screening high-performance energy storage and conversion materials on a large scale. In particular, DFT calculations enable us to establish the relationships between the intrinsic properties of materials and their performance for energy storage and conversion, and provide theoretical guidance for screening and experimentally synthesizing the promising materials. In this review, we summarize the DFT calculations’ applications in recent studies of developing high-performance and reliable energy-related 2D materials for Li-ion battery (LIB), water splitting, fuel cells, and electrochemical carbon dioxide reduction (CRR). First, we introduce the reaction mechanism of LIB, hydrogen evolution reaction (HER), oxygen evolution reaction/oxygen reduction reaction (OER/ORR), and CRR in detail and the application of 2D material in these fields. Then, we highlight the role of DFT calculations in unveiling the intrinsic relationships between the electronic structure and the performance of 2D materials by comprehensively discussing the descriptors in predicting the performance of 2D materials. For example, the occupancy of d orbital and energy required to fill empty states serve as descriptors to predict the electrochemical performance of the electrode in ion intercalation battery. The d orbital center, lowest unoccupied states, and oxygen vacancy formation energy serve as descriptors to predict the catalytic performance of electrode in HER. The energy difference between the lowest valance electron orbital center and Fermi level, occupancy of p z orbital, and the energy difference between p z and p x /p y orbital center serve as descriptors to predict the catalytic performance of electrode in ORR. Even though these descriptors can help to further understand the relationships between the electronic structure and the performance of the electrochemical electrode, they are only reliable to specific materials and inapplicable to the electrode with a complex structure or complex reaction path, such as the electrode in CRR. Newly developed machine learning methods may bring a breakthrough to the exploration of a universal descriptor, which is a key factor in the large-scale screening of potential electrode materials with excellent performance and the dependable guidance to experimental synthesis. Finally, we summarize the disadvantage of DFT calculation, such as the underestimation of bandgap and incorrect description of van der Waals interaction, and give a perspective of DFT calculations in the study of new energy-related materials. The method to simulate the ambient environment of the electrode (including the electrolyte, external electric field, and non-cooperative transfer of proton and electron) based on DFT calculation is needed to be developed, which is vital to reflect the actual working condition of the electrode. The universal descriptor applicable to the electrode with a complex structure is also needed to explore to overcome the poor versatility of single intrinsic property of the material in predicting the performance of the electrochemical electrode.

With the rapid development of modern society, the efficient development and utilization of new energy have become more and more important. The development of high-performance energy storage and conversion devices has a decisive impact on the sustainable and efficient use of energy. In the foreseeable future, the exploration of high-quality functional materials for energy storage and conversion will continue to be the main goal pursued by the scientific and application fields. Metal organic frameworks (MOFs) have the merits of adjustable porosity and a stable structure. Moreover, the metal elements in the MOFs could play a role as active sites during the electrochemical process. Thus, various kinds of MOFs and their derivatives have been prepared and used as functional materials for energy storage and conversion. In this work, the applications and potentials of cobalt-based MOFs (Co-MOFs) and their derivatives in supercapacitors, advanced batteries, and electrochemical catalysts have been reviewed and summarized. The electrochemical properties, energy storage and conversion mechanisms, and the effects on performance were described in depth. A large number of Co-MOFs with unique structures, as well as numerous Co-MOF derivatives and composites, have been developed, and excellent application performance has been achieved, which have already become some of the most advantageous functional materials in the energy storage and conversion field. In addition, the current research status, difficulties, and prospects of Co-based MOFs and their derivatives as energy storage and conversion functional materials were comprehensively summarized at the end of this study.

In this review, the recent progress in the application of an important category of materials, i.e. ABO3 perovskite‐type compounds in the fields of energy storage and conversion, is reviewed. Four main areas, as materials for oxygen transporting membrane toward the application in oxy‐fuel combustion, as key material for solid oxide fuel cells for efficient power generation from fuels, as room‐temperature electrocatalysts for oxygen reduction reaction and oxygen evolution reaction, and as material for solar cells for solar energy harvest, are referred. Our past efforts in these research areas are emphasized. Some prospects about the future development in the application of perovskite materials in energy storage and conversion is proposed. Copyright © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Advanced Materials for Sustainable Energy and a Greener Environment

2020 roadmap on two-dimensional materials for energy storage and conversion

Materials with hierarchical porosity and structures have been heavily involved in newly developed energy storage and conversion systems. Because of meticulous design and ingenious hierarchical structuration of porosities through the mimicking of natural systems, hierarchically structured porous materials can provide large surface areas for reaction, interfacial transport, or dispersion of active sites at different length scales of pores and shorten diffusion paths or reduce diffusion effect. By the incorporation of macroporosity in materials, light harvesting can be enhanced, showing the importance of macrochannels in light related systems such as photocatalysis and photovoltaics. A state‐of‐the‐art review of the applications of hierarchically structured porous materials in energy conversion and storage is presented. Their involvement in energy conversion such as in photosynthesis, photocatalytic H2 production, photocatalysis, or in dye sensitized solar cells (DSSCs) and fuel cells (FCs) is discussed. Energy storage technologies such as Li‐ions batteries, supercapacitors, hydrogen storage, and solar thermal storage developed based on hierarchically porous materials are then discussed. The links between the hierarchically porous structures and their performances in energy conversion and storage presented can promote the design of the novel structures with advanced properties.

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

The fast development of modern technology requires matured energy storage and conversion devices to meet the demands of the ever-growing portable electronic and electric vehicle industries. As a result, electrochemical energy strategies including energy storage and electrocatalysis have attracted broad attention lately. Thanks to the fast development of nanoscience and nanotechnology, various structures and materials have been proposed with outstanding electrochemical performance. Two-dimensional layered materials including graphene, transition metal dichalcogenides, and MXene, etc., have demonstrated enormous potential as electrode materials for energy storage and conversion due to their robust properties of high electrical conductivity, large surface area, and superior chemical stability. In this talk, the electrochemical property of two-dimensional layered materials will be introduced. Advanced two-dimensional materials and their hybrids for the applications of electrochemical energy storage and electrocatalysis will be discussed.

The hybridization between energy conversion and energy storage materials in a single cell (HECS) is proposed in this work. The HECS cell consists of photoactive cobalt oxide (Co3O4) positive electrode as the energy conversion material and N-doped reduced graphene oxide aerogel (N-rGOAE) as the energy storage material. The photoactive Co3O4 nanosheets were prepared by using various calcination temperatures for which the in situ electrochemical XAS suggests that the Co3O4 nanosheets calcined at 300oC exhibit the highest change in oxidation state compared to other conditions. The HECS cell using photoactive Co3O4 film calcined at 300oC and N-rGOAE exhibits 1.7-fold higher specific capacitance under LED light illumination than that of the dark condition. Under white LED light illumination, the photovoltaic effect can be generated in the Co3O4 electrode with electron-hole pairs, while the N-rGOAE can balance all the charges generated from the Co3O4 via both electrochemical double-layer and pseudocapacitive behaviours.

The development of two‐dimensional (2D) materials is experiencing a renaissance since the adventure of graphene. 2D materials typically exhibit strong in‐plane covalent bonding and weak out‐of‐plane van der Waals interactions through the interlayer gap. Opening 2D materials is an effective way to alter the physical and chemical properties, such as band gap, conductivity, optical property, thermoelectric property, photovoltaic property and superconductivity. A larger interlayer distance means more accessible active sites for catalysis, an ion‐accessible surface in the interlayer space, which may greatly enhance the performance of 2D materials for energy conversion and storage. Moreover, opening 2D materials by intercalation can change the band filling state and the Fermi level. This review mainly focuses on the opening of 2D materials and their subsequent applications in energy conversion and storage fields, expecting to promote the development of such a new class of materials, namely expanded 2D materials. The exciting progresses of these expanded materials made in both energy conversion and storage devices including solar cells, thermoelectric devices, electrocatalyst, supercapacitors and rechargeable batteries, is presented and discussed in depth. Furthermore, prospects and further developments in these exciting fields of the expanded 2D materials are also commented.