(Invited) New Synthesis Approaches to Nanostructured Complex Functional Metal Oxides

2D materials have attracted a great deal of attention for their unique electrical and magnetic properties, but may also play important roles in energy storage applications. Lithium-ion batteries and supercapacitors are widely used to power mobile devices, but the energy and power densities of the electrode materials still need improvement. Many conventional battery materials have layered structures, and hence can be readily exfoliated into 2D nanosheet materials. The high surface area and short ionic diffusion distances in the 2D nanosheets may improve the charging/discharging rates and result in more lithium insertion or surface adsorption. Furthermore, hybrid electrode materials composed layers of different cathode materials may be possible by reassembling different nanosheets. These sandwich structures could potentially result in unique synergistic effects and novel redox behavior due to the interactions from different sheets. Finally, we can obtain better understanding of the structure of complex layered cathode materials through exfoliation and high resolution ex-situ microscopy studies. Here we present our synthesis of 2D nanosheets of two common lithium-ion battery materials, LiCoO2 (LCO) and LiNi1/3Mn1/3Co1/3O2 (NMC). Nanosheets were obtained by exfoliation of LCO and NMC particles using traditional osmotic swelling with tetraethylammonium (TEA). TEM, SEM and AFM analysis showed that the particles were successfully exfoliated nanosheets with around 2 nm thickness. XRD and SADP[CKC1] analysis showed that these materials had hexagonal structures with good crystallization. A reassembly process was developed and applied to obtain LCO, NMC, and LCO/NMC hybrid particles. Electrochemical evaluation of the particles as electrodes for lithium-ion batteries and supercapacitors were performed. Our work is a firm step forward on improving understanding of osmotic swelling processes for the synthesis of nanosheets from complex metal oxides as well as the design and fabrication of high performance hybrid electrodes for energy storage applications.

Optimising the fabrication of 3D binder-free graphene electrode for electrochemical energy storage application

Polyacrylonitrile (PAN)-based carbon precursor is a well-established and researched material for electrodes in energy storage applications due to its good physical properties and excellent electrochemical performance. However, in the fight of preserving the environment and pioneering renewable energy sources, environmentally sustainable carbon precursors with superior electrochemical performance are needed. Therefore, bio-based materials are excellent candidates to replace PAN as a carbon precursor. Depending on the design requirement (e.g. carbon morphology, doping level, specific surface area, pore size and volume, and electrochemical performance), the appropriate selection of carbon precursors can be made from a variety of biomass and biowaste materials. This review provides a summary and discussion on the preparation and characterization of the emerging and recent bio-based carbon precursors that can be used as electrodes in energy storage applications. The review is outlined based on the morphology of nanostructures and the precursor’s type. Furthermore, the review discusses and summarizes the excellent electrochemical performance of these recent carbon precursors in storage energy applications. Finally, a summary and outlook are also given. All this together portrays the promising role of bio-based carbon electrodes in energy storage applications.Graphic abstract

Mixed matrix membrane development progress and prospect of using 2D nanosheet filler for CO2 separation and capture

Conducting polymers such as polyaniline (PAni) show a great potential as pseudocapacitor materials for electrochemical energy storage applications. Yet, the cycling instability of PAni resulting from structural alteration is a major hurdle to its commercial application. Here, the development of nanostructured PAni–RuO2 core–shell arrays as electrodes for highly stable pseudocapacitors with excellent energy storage performance is reported. A thin layer of RuO2 grown by atomic layer deposition (ALD) on PAni nanofibers plays a crucial role in stabilizing the PAni pseudocapacitors and improving their energy density. The pseudocapacitors, which are based on optimized PAni–RuO2 core–shell nanostructured electrodes, exhibit very high specific capacitance (710 F g−1 at 5 mV s−1) and power density (42.2 kW kg−1) at an energy density of 10 Wh kg−1. Furthermore, they exhibit remarkable capacitance retention of ≈88% after 10 000 cycles at very high current density of 20 A g−1, superior to that of pristine PAni‐based pseudocapacitors. This prominently enhanced electrochemical stability successfully demonstrates the buffering effect of ALD coating on PAni, which provides a new approach for the preparation of metal‐oxide/conducting polymer hybrid electrodes with excellent electrochemical performance.

Enhanced capacitance of nickel ferrite decorated laser-induced graphene nanocomposite for symmetric supercapacitor device

Carbon-coated Zn2GeO4 on Ni foam as lithium ion battery anodes with exceptional long cycling stability

Extensive investigations have been carried out on spinel mixed transition metal oxide-based materials for high-performance electrochemical energy storage applications. In this study, mesoporous Mn-substituted MnxZn1−xCo2O4 (ZMC) ternary oxide microspheres (x = 0, 0.3, 0.5, 0.7, and 1) were fabricated as electrode materials for supercapacitors through a facile coprecipitation method. Electron microscopy analysis revealed the formation of microspheres comprising interconnected aggregates of nanoparticles. Furthermore, the substitution of Mn into ZnCo2O4 significantly improved the surface area of the synthesized samples. The electrochemical test results demonstrate that the ZMC3 oxide microspheres with an optimal Mn substitution exhibited enhanced performance, displaying the largest specific capacitance of 589.9 F g−1 at 1 A g−1. Additionally, the ZMC3 electrode maintained a capacitance retention of 92.1% after 1000 cycles and exhibited a significant rate capability at a current density of 10 A g−1. This improved performance can be ascribed to the synergistic effects of multiple metals resulting from Mn substitution, along with an increase in the surface area, which tailors the redox behavior of ZnCo2O4 (ZC) and facilitates charge transfer. These findings indicate that the incorporation of Mn into mixed transition metal oxides holds promise as an effective strategy for designing high-performance electrodes for energy storage applications.

Recent advances in using biological scaffolds for nanoparticle synthesis have proven to be useful for preparing various nanostructures with uniform shape and size. Proteins are significant scaffolds for generating various nanostructures partly because of the presence of many functional groups to recognize different chemistries. In this endeavor, cocosin protein, an 11S allergen, is prepared from coconut fruit and employed as a potential scaffold for synthesizing Mn3O4 materials. The interaction between protein and manganese ions is studied in detail through isothermal calorimetric titration. At increased scaffold availability, the Mn3O4 material adopts the exact hexamer structure of the cocosin protein. The electrochemical supercapacitive properties of the cocosin-Mn3O4 material are found to have a high specific capacitance of 751.3 F g-1 at 1 A g-1 with cyclic stability (92% of capacitance retention after 5000 CV cycles) in a three-electrode configuration. The Mn3O4//Mn3O4 symmetric supercapacitor device delivers a specific capacitance of 203.8 F g-1 at 1 A g-1 and an outstanding energy and power density of 91.7 W h kg-1 and 899.5 W kg-1, respectively. These results show that cocosin-Mn3O4 could be considered a suitable electrode for energy storage applications. Moreover, the cocosin protein to be utilized as a novel scaffold in protein-nanomaterial chemistry could be useful for protein-assisted inorganic nanostructure synthesis in the future.

The Li‐ion hybrid capacitor (LIHC) system explores the possibility of achieving both high energy and power density in a single energy storage system with an intercalation anode and capacitive cathode. However, to achieve a high power and energy‐based system, the properties of the cathode electrode material are vital. Here, bio‐waste plant stem‐derived activated porous carbon is explored as a cathode for LIHC application. A specific surface area of 1826 m2 g−1, enhanced degree of crystallinity, and graphitization results for porous carbon from activation by potassium hydroxide. When employed as supercapacitor material, the device exhibits good rate capability, energy, and power attributes with a specific capacitance of 116 F g−1 (1 A g−1). Simultaneously when tested for LIHC application the formulated device shows good capacity retention for 2500 cycles with a high energy density of 125 Wh kg−1 at a power density of 69 W kg−1. The work demonstrates unique, cost‐effective strategy to develop a crystalline high surface area carbon from any such bio‐waste sources to be employed as potential electrodes for energy storage applications.

Nanostructured cobalt oxide and cobalt sulfide for flexible, high performance and durable supercapacitors

Interest in novel energy storage and conversion methods has prompted a broad interest in potential applications of conductive, complex materials such as graphene oxide slurries. Investigating the complex rheological, material, and chemical properties of chemically exfoliated graphene oxide suspensions is a potential means to address that interest. The morphological size and clustering, rheology, and electronic conductivity are determined to characterize the properties of graphene oxide (GO) suspensions from variable centrifugation speeds. The evolution of viscosity is then analyzed under oscillatory shear, steady shear, and transient shear characteristics. The resulting microstructure is then analyzed via neutron scattering analysis and imaged with scanning electron microscopy. Small-Angle Neutron Scattering (SANS) of a 500g centrifuged GO suspension determined that particle structure is locally flat sheet-like at lengths below 100 nm, crumpled aggregates of GO sheets with surface roughness at length scales from 200 nm to 2 μm, and a dense mass fractal of overlapping GO sheets extending up to length scales of 20 μm. Increased centrifugation force of the 1000g GO suspension corresponded with lower zero-shear viscosity, yield stress, and less pronounced thixotropic behavior. Rheo-dielectric measurements were conducted on 1000g and 500g GO suspensions to determine the ohmic resistance, electronic conductivity, and specific capacitance. The more fluid-like microstructure of 1000g with smaller monodispered thinning GO sheets in suspension had lower ohmic resistance and higher electronic conductivity compared to the 500g GO suspension with more polydispersed larger aggregates. The 1000g GO suspension had the highest specific capacitance of 4.63 mF cm-2 at the highest shear rate of 700 s-1 due to the higher frequency of particle-particle collisions during shear within the network of smaller and more intrinsically conductive GO sheets to store charge. Therefore, the results of this study have implications for future studies in flowable carbon nanomaterials in flow battery and flow capacitor technologies.

Nanostructured materials afford a promising potential for many energy storage applications because of their extraordinary electrochemical properties. However, the remarkable electrochemical energy storage performance could only be harvested at a relatively low mass‐loading via the traditional electrode fabrication process, and the scale of these materials into commercial‐level mass‐loading remains a daunting challenge because the ion diffusion kinetics deteriorates rapidly along with the increased thickness of the electrodes. Very recently, three‐dimensional (3D) printing, a promising additive manufacturing technology, has been considered as an emerging method to address the aforementioned issues where the 3D printed electrodes could possess elaborately regulated architectures and rationally organized porosity. As a result, the outstanding electrochemical performance has been widely observed in energy storage devices made of 3D printed electrodes of high‐mass loading. In this review, we systemically introduce the basic working principles of various 3D printing technologies and their practical applications to manufacture high‐mass loading electrodes for energy storage devices. Challenges and perspectives in 3D printing technologies for the construction of electrodes at the current stage are also outlined, aiming to offer some useful opinions for further development for this prosperous field.image

Performance of sunflower petal shaped CuCo2S4 wrapping on GO asymmetric capacitor for energy storage applications

We report a novel photonic processing technique as a next-generation cost-effective technique to instantaneously synthesize nanostructured manganese-cobalt mixed oxide reduced graphitic oxide (Mn-Co-rGO) for supercapacitor electrodes in energy storage applications. The active material was prepared directly on highly conductive Pt–Si substrate, eliminating the need for a binder. Surface morphological analysis showed that the as-prepared electrodes have a highly porous and resilient nanostructure that facilitates the ion/electron movement during faradaic redox reactions and buffers the volume changes during charge–discharge processes, leading to the improved structural integrity of the electrode. The presence of distinct redox peaks, due to faradaic redox reactions, at all scan rates in the cyclic voltammetry (CV) curves and non-linear nature of the charge–discharge curves suggest the pseudocapacitive charge storage mechanism of the electrode. The electrochemical stability and the life cycle were examined by carrying out galvanostatic charge–discharge (GCD) measurements at 0.40 mA cm−2 constant areal current density for 80 000 cycles, and the electrode showed 95% specific capacitance retention, exhibiting excellent electrochemical stability and an ultra-long cycle life. Such remarkable electrochemical performance could be attributed to the enhanced conductivity of the electrode, the synergistic effect of metal ions with rGO, and the highly porous morphology, which provides large specific surface area for electrode/electrolyte interaction and facilitates the ion transfer.