Metal–organic frameworks (MOFs), known as porous coordination polymers, have attracted intense interest as electrode materials for supercapacitors (SCs) owing to their advantageous features including high surface area, tunable porous structure, structural diversity, etc. However, the insulating nature of most MOFs has impeded their further electrochemical applications. A common solution for this issue is to transform pristine MOFs into more stable and conductive metal compounds/porous carbon materials through pyrolysis, which however losses the inherent merits of MOFs. To find a consummate solution, recently a surge of research devoted to improving the electrical conductivity of pristine MOFs for SCs has been carried out. In this review, the most related research work on pristine MOF‐based materials is reviewed and three effective strategies (chemical structure design of conductive MOFs (c‐MOFs), composite design, and binder‐free structure design) which can significantly increase their conductivity and consequently the electrochemical performance in SCs are proposed. The conductivity enhancement mechanism in each approach is well analyzed. The representative research works on using pristine MOFs for SCs are also critically discussed. It is hoped that the new insights can provide guidance for developing high‐performance electrode materials based on pristine MOFs with high conductivity for SCs in the future.
As a newly emerging excellent energy storage device, supercapacitors have been widely studied due to their unique advantages. Electrode material is one of the key components that determine the performance of a supercapacitor. Among the various electrode materials of supercapacitors, RuO 2 has attracted great attention in the scientific community due to its high theoretical energy storage capability and excellent stability. However, most RuO 2 materials suffer the problem of low specific surface area, causing a much lower actual capacitance value compared to the theoretical performance of the material. In this work, a mulberry-like RuO 2 electrode material with large specific surface area (159.4 m 2 Ág -1 ) was successfully synthesized by a facial hydrothermal method. The electrochemical characterization has shown that the RuO 2 possesses a high specific capacitance of 400 FÁg -1 at a current density of 0.2 AÁg -1 and good capacitance retention rate of 84.7% after 6000 charge/discharge cycles under a current density of 10 AÁg -1 . The energy densities and power densities of the RuO 2 -AC supercapacitor vary from 25.0 to 11.7 WhÁkg -1 and 160 to 10,560 WÁkg -1 at current density ranging from 0.2 to 10.0 AÁg -1 , respectively.
Three-dimensional
(3D) printing technologies are widely applied
in various industries and research fields and are currently the subject
of intensive investigation and development. However, high-performance
materials that are suitable for 3D printing are still in short supply,
which is a major limitation for 3D printing, particularly for biomedical
applications. The physicochemical properties of single constituent
materials may not be sufficient to meet the needs of modern biotechnology
development and production. To enhance the materials’ performance
and broaden their applications, this work designed and tested a series
of titanate nanofiller (nanowire and nanotube)-enhanced polycaprolactone
(PCL) composites that were 3D-printable and provided superior mechanical
properties. By grafting two different functional groups (phenyl- and
thiol-terminated ligands), the nanofiller surface showed improved
hydrophobicity, which significantly improved their dispersion in the
PCL matrix. After characterizing the surface modification, we evaluated
the significance of the homogeneity of the ceramic nanofiller in terms
of printability, formability, and mechanical strength. Melt electrowriting
additive manufacturing was used to fabricate microfibers of PCL and
PCL/nanofiller composites. Improved nanofiller dispersion enabled
intact and uniform sample morphology, and in contrast, nanofiller
aggregation greatly varied the viscosity during the printing process,
which could result in poorly printed structures. Importantly, the
modified ceramic/PCL composite delivered enhanced and stable mechanical
properties, where its Young’s modulus was measured to be 1.67
GPa, which is more than 7 times higher compared to that of pristine
PCL (0.22 GPa). Retaining the cell safety properties (comparable to
PCL), the concept of enhancing biocompatible polymers with modified
nanofillers shows great potential in the field of customized 3D printing
for biomedicine.
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