Vertically oriented graphene (VG) with three-dimensional architecture has been proved to exhibit unique properties, and its particular morphology has been realized by researchers to be crucial for its performance in practical applications. In this study, we investigated the morphology evolution of VG films synthesized by the plasma-enhanced chemical vapor deposition process, including porous graphene film, graphene wall, and graphene forest. This study reveals that the morphology of VG is controlled by a combination of the deposition and etching effects and tailored by the growth conditions, such as plasma source power and growth time and temperature. The plasma source power relates to the number of branches of VG, and the growth temperature relates to the thickness of each VG flake, whereas the growth time determines the height of VG. Finally, the electrochemical properties of VG films along with morphology evolution are investigated by fabricating as VG-based supercapacitor electrodes.
Combining
the advantages of a three-dimensional structure with
intrinsic properties of graphene, vertical graphene (VG) synthesized
by the plasma-enhanced chemical vapor deposition (PECVD) process has
shown great promise to be applied to energy-storage electrodes. However,
the practical application of the VG electrodes suffers from the limited
height, which is mostly in a scale of few hundreds of nanometers,
as shown in the previous studies. The reason for the unacceptable
thin VG film deposition is believed to be the height saturation, stemming
from the inevitable confluence of the VG flakes along with the deposition
time. In this study, we developed an oxygen-assisted “trimming”
process to eliminate the overfrondent graphene nanosheets thereby
surmounting the saturation of the VG thickness during growth. In this
approach, the height of the VGs reaches as high as 80 μm. Tested
as supercapacitor electrodes, a desirable capacitance of 241.35 mF
cm–2 is obtained by the VG films, indicating the
superior electrochemical properties and the potential for applications
in energy storage. It is worth noting, this thickness is by no means
the maximum that can be achieved with our synthesis technique and
higher capacitance can be achieved by conducting the circulating deposition–correction
process in our work.
Many practical applications require flexible high-sensitivity pressure sensors. However, such sensors are difficult to achieve using conventional materials. Engineering the morphology of the electrodes and the topography of the dielectrics has been demonstrated to be effective in boosting the sensing performance of capacitive pressure sensors. In this study, a flexible capacitive pressure sensor with high sensitivity was fabricated by using three-dimensional vertical graphene (VG) as the electrode and micro-pyramidal polydimethylsiloxane (PDMS) as the dielectric layer. The engineering of the VG morphology, size, and interval of the micro-pyramids in the PDMS dielectric layer significantly boosted the sensor sensitivity. As a result, the sensors demonstrated an exceptional sensitivity of up to 6.04 kPa−1 in the pressure range of 0–1 kPa, and 0.69 kPa−1 under 1–10 kPa. Finite element analysis revealed that the micro-pyramid structure in the dielectric layer generated a significant deformation effect under pressure, thereby ameliorating the sensing properties. Finally, the sensor was used to monitor finger joint movement, knee motion, facial expression, and pressure distribution. The results indicate that the sensor exhibits great potential in various applications, including human motion detection and human-machine interaction.
Cobalt oxide (CoOx) nanowires have been broadly explored as advanced pseudocapacitive materials owing to their impressive theoretical gravimetric capacity. However, the traditional method of compositing with conductive nanoparticles to improve their poor conductivity will unpredictably lead to a decrease in actual capacity. The amelioration of the aspect ratio of the CoOx nanowires may affect the pathway of electron conduction and ion diffusion, thereby improving the electrochemical performances. Here, CoOx nanowires with various aspect ratios were synthesized by controlling hydrothermal temperature, and the CoOx electrodes achieve a high gravimetric specific capacity (1424.8 C g−1) and rate performance (38% retention at 100 A g−1 compared to 1 A g−1). Hybrid supercapacitors (HSCs) based on activated carbon anode reach an exceptional specific energy of 61.8 Wh kg−1 and excellent cyclic performance (92.72% retention, 5000 cycles at 5 A g−1). The CoOx nanowires exhibit great promise as a favorable cathode material in the field of high-performance supercapacitors (SCs).
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