Self-discharge is known to have considerable adverse effects on the performance and application of electrochemical capacitors (ECs). Thus, obtaining an understanding of EC self-discharge mechanism(s) and subsequent derivation and solution of EC models, subject to a particular mechanism or combination of mechanisms during charging, discharging and storage of the device, is the only way to solve problems associated with EC self-discharge. In this review, we summarize recent progress with respect to EC self-discharge by considering the two basic types, electric double-layer capacitors (EDLC) and pseudocapacitors, and their hybrids with their respective charge storage mechanisms, distinguishable self-discharge mechanisms, charge redistribution and charge/energy loss during self-discharge. It was clearly observed that most of the voltage reduction is not purely due to the self-discharge effect but is basically due to redistribution of charge carriers deep inside pores and can therefore be retrieved from a capacitor during long-time discharging. Tuning the self-discharge rate is therefore feasible for single-walled carbon nanotube (SWNT) ECs and can be achieved by simply adjusting the surface chemistry of the nanotubes. The effects of surface chemistry modification on EC self-discharge are very important in studying and suppressing the self-discharge process and will benefit potential applications of ECs with respect to energy retention. Self-discharge can be averted by the use of redox couples that are transformed to insoluble species via electrolysis and adsorbed onto the activated carbon electrode in redox-couple EDLCs, thus transforming the EDLC electrolyte into a material that can store charge. Self-discharge in ECs can also be successfully suppressed by utilizing an ion-interchange layer (ion-exchange membrane), separator or CuSO4 mobile electrolyte that can be converted into an insoluble species by electrolysis during the charge/discharge process. This will help in producing a modern-day blueprint for ECs with high capacitance and improved energy sustainability.

Flower-like MoS2 modified with carbon nanospheres (CNS) displays energy-storage capability when used as an aqueous symmetric pseudocapacitor.

The energy storage performance of one of the lightest-known MXenes, Ti 2 CT x (MX) combined with carbon nanospheres (CNS) has been investigated as a symmetric electrode system in an aqueous electrolyte (1 M Li 2 SO 4 ). The energy storage properties were interrogated using cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL), electrochemical impedance spectroscopy (EIS) and voltage-holding tests. The combined material (MX/CNS) demonstrated a higher specific capacity compared to each of the individual components. The material was fabricated with relatively high and low mass loadings, assembled into a symmetric device and performance compared. Specific capacitance, specific power and specific energy for the lower electrode mass loading of 180 F·g −1 , 37.6 kW·kg −1 and 14.1 W·h·kg −1 were all higher than 86 F·g −1 , 20.1 kW·kg −1 and 6.7 W·h·kg −1 for the higher mass loading. A wide voltage window of 1.5 V was obtained, but with limited long-term cycling behavior, suggesting the need for future improvement. Mathematical modelling and simulation of the supercapacitor showed good correlation with the experimental results, validating the model. The results reveal the potential of the Ti 2 CT x to be employed as a viable energy storage system for lightweight applications. As part of the increasing role of clean energy technologies, electrochemical capacitors (ECs) are continuously evolving components that contribute to meeting the demands of electronic apparatuses and systems and are projected to be even more significant in the future.1 In 2011, Gogotsi and co-workers, 2 first synthesized a two-dimensional (2-D) layered material called MXene, by selectively etching aluminum (Al), using hydrofluoric acid (HF) from the MAX phase material. MAX phase materials are layered ternary carbide and nitride materials with the general chemical formula of M n+1 AX n (where 'M' represents an early transition metal, 'A' represents a group IIIA or IVA element, 'X' is C and/or N, and n may equal 1, 2, or 3). There are more than 70 different MAX phase compositions currently known. 3,4 MXenes are formed when the 'A' element is etched out of the MAX phase material, and subsequently have a general formula of M n+1 X n T x (where T represent surface functional groups such as F, OH or O, and x is the number of functional groups that are attached to the surface following the etching process).5 This newly discovered family of materials has similar properties to graphene with good electronic conductivity and different surface terminations enabling the possibility to manipulate their properties to fit different applications. 2-D materials potentially have large electroactive surfaces and therefore attract research attention. MXenes are currently studied, both theoretically and experimentally, as potential electrode materials for energy storage devices such as batteries [6][7][8][9][10][11][12][13][14][15][16] and ECs 9,14,17-32 as well as other uses. 33,34Although the MXene materials do not possess such a high surface ...

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Typical silicate bioactive glasses are known to crystallize readily during the processing of porous scaffolds. While such crystallization does not fully suppress the bioactivity, the presence of significantly large amounts of crystals leads to a decrease in the rate of reaction of the glass and an uncontrolled release of ions. Furthermore, due to the non-congruent dissolution of silicate glasses, these materials have been shown to remain within the surgical site even 14 years postoperation. Therefore, a need for bioactive materials that can dissolve with higher conversion rates and more effectively are required. Within this work, boron was introduced, in the FDA approved S53P4 glass, at the expense of SiO2. The crystallization and sintering-ability of the newly developed glasses were investigated by differential thermal analysis. All the glasses were found to crystallize primarily from the surface, and the crystal phase precipitating was dependent upon the quantity of B2O3 incorporated. The rate of crystallization was found to be lower for the glasses were 25, 50 and 75 % of the SiO2 was replaced with B2O3. These glasses were further sintered into porous scaffolds using simple heat sintering. The impact of glass particles size and heat treatment temperature on the scaffolds porosity and average pore size was investigated. Scaffolds with porosity ranging from 10 to 60 % with compressive strength ranging from 1 to 35 MPa, were produced. The scaffolds remained amorphous during processing and their ability to rapidly precipitate hydroxycarbonated apatite was maintained. This is of particular interest in the field of tissue engineering as the scaffolds degradation and reaction was generally faster and offers higher controllability as opposed to current partially/fully crystallized scaffolds obtained from the FDA approved bioactive glasses. IntroductionAs of today, autografts are still the gold standard for the repair of large bone defects. However, with the aging and growing population, the number of surgical intervention to regenerate bone defects are increasing. The limited supply and patient site morbidity is a well-known disadvantage and problem [1][2]. Allografts are an option. However, the limited tissue bank as well as the higher risk for infection and cellular and humoral immune reactions limits their usage [3]. The quest for synthetic biomaterials to replace the autografts is more than two decades old. However, as of today no materials have shown as promising a result as autografts. Q. Chen et al. have reported the optimum characteristic that the synthetic materials should have to find great potential as bone grafts [4]. The bone graft should be a 3D construct (3D scaffold) not only biocompatible, but ultimately biodegradable and osteoconductive with highly interconnected porosity. Pore size should be no less than 100 µm to allow cell and fluid penetration as well as angiogenesis. In general, interconnected pores of at least 100 µm and an open porosity of over 50% is considered the minimum requirement for ti...

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