Search

Enzyme immobilization method in packaged freestanding microfluidic channel is developed for biomolecule assembly of biosensor in this research. A new micro fluidic fabrication method is proposed to fabricate freestanding fluidic structure by MEMS technology. The SU-8 polymer channel is treated by plasma treatment to change hydrophobic surface to hydrophilic property which can automatically drive the liquid into the channel by capillary force. The electro click chemistry method is carried out in hydrophilic SU-8 micro channel by capillary effect. The results show that enzyme immobilization can be immobilized by electro click chemistry in completely packaged freestanding channel. The proposed enzyme immobilization method in micro channel is capable of minimizing biosensor device for healthcare application.

The microstructures and strength of pure Ni ball after high speed collision process were investigated. The elongated and equiaxed nanocrystallines with high angle grain boundaries and random grain orientation were formed near the interface position due to high strain and strain rate. Sufficient intragranular recrystallization occurred due to shock induced storage energy. Sufficient recrystallization in the grain interior facilitated to activate dislocation in the process of subsequent deformation and resulted in ameliorated hardness. Moreover, the high angle grain boundaries could effectively impede the dislocation movement, which also significantly enhanced the strength of Ni ball near the interface.

The ratio of the twin decreased after thermomechanical process for the CoCrNi medium-entropy alloy. The grain refinement decreased the passive current and increased the breakdown potential of the CoCrNi medium-entropy alloy in sodium chloride solution. The electrochemical impedance spectroscopy analysis showed that the grain refinement of the CoCrNi medium-entropy alloy facilitated to form thicker passive films and larger passive film resistance, which thus resulted into better corrosion resistance in sodium chloride solution. More nucleation sites after the grain refinement could enhance diffusion rate of alloying element and promote to form thicker and more stable passive films on refined grain CoCrNi medium-entropy alloy. Moreover, sufficient recrystallization level within refined grains for the CoCrNi MEA also improved its corrosion resistance.

The ultrafine grained pure Ni and Ni-W alloy were obtained by electrodeposition technique and subsequent annealing treatment. The effects of annealing on the microstructures, the mechanical properties and the corrosion resistance of pure nickel and Ni-W alloy were investigated. The EBSD analyses showed that annealed pure Ni displayed preferred grain orientation, while annealed Ni-W alloy showed relatively more random grain orientation. Moreover, abnormal grain growth was observed in annealed pure Ni, while annealed Ni-W alloy displayed a more uniform grain size distribution. It could be predicted that solid solution of tungsten significantly suppressed grain growth and induced uniform grain size distribution during low temperature annealing process. Moreover, comparing with annealed pure Ni, the tungsten in annealed Ni-W alloy changed the semiconducting characteristic of surface passive films. Annealed Ni-W alloy showed higher corrosion resistance than annealed pure Ni in 3.5 wt% NaCl solution and in borate buffer solution.

The effects of the ball milling on microstructures of the graphene/Ni composites and subsequent hydrogen evolution reaction in acidic solution were investigated. Ni nanoparticles with average grain size of 4 nm were uniformly dispersed on the graphene surface after short time ball milling. While amorphous characteristic was observed due to long time ball milling. The graphene/Ni composites with amorphous structure exhibited higher electrocatalytic performance than the graphene/Ni composites with nanocrystalline structure. The Volmer-Heyrovsky mechanism was found for the graphene/Ni composites with nanocrystalline structure, while the graphene/Ni composites with amorphous structure showed evident Heyrovsky mechanism. The excellent hydrogen evolution reaction and stability of the graphene/Ni composites could be attributed to superior interfacial contact, amorphous Ni, and synergistic effect between amorphous Ni and high conductive graphene.

NiMoO4 nanoparticles and quantum dots were uniformly distributed on the surface of reduced nanohole graphene oxide (rNHGO). NiMoO4@rNHGO exhibited a higher specific capacitance and better cycling stability than NiMoO4@reduced graphene oxide (rGO), which were attributed to the large surface area and high electrical conductivity. NiMoO4 nanoparticles and quantum dots (QDs) had high surface to volume ratio, which would not result in change in volume during the electro–chemical operation and induced better supercapacitor performance. Moreover, synergistic effect between NiMoO4 and the rNHGO also improved undoubtedly high specific capacitance and cycle stability.

Few layer graphene was formed on the surface of Ni foam using the chemical vapor deposition technique, which effectively decreased flaws and inhibited stack of graphene. The CoS nanorods were synthesized on the surface of bare Ni foam after hydrothermal method, while graphen on Ni foam facilitated to form CoS nanowires with porosity surface structure and large specific surface area. The CoS nanowires on Ni foam coated with graphene showed an high specific capacitance of 1506 F g−1 at 1 A g−1 and 88.2% capacity retention at a current density of 1 A g−1 after 5000 cycles charge-discharge test. The improved electronic conductivity of current collector Ni foam by graphene and porous microstructure of CoS nanowires catalyzed by graphene enhanced significantly supercapacitors performance. This was attributed to large CoS nanowires electrode-electrolyte contact area and reduced volume change during the charge-discharge process.

Aligned NiCo 2 S 4 nanotubes on Ni foam were obtained by the complete sulfidation of NiCo-precursor which was synthetized by hydrothermal process. The NiCo 2 S 4 nanotubes on Ni foam delivered a higher specific capacitance than NiCo 2 O 4 nanowires on Ni foam. The NiCo 2 S 4 nanotubes on Ni foam exhibited the high capacitance of 1936.2 F g −1 at 1 A g −1 . The porous NiCo 2 S 4 nanotubes on Ni foam provided a huge number of exposed active sites for electrochemical reaction. Moreover, the NiCo 2 S 4 nanotubes on Ni foam with large specific surface area facilitated the diffusion and penetration of electrolyte and improved electrochemical reaction. Therefore, after 5000 continuous charge–discharge cycles, only about 7.9% degradation in specific capacitance was observed for NiCo 2 S 4 nanotubes on Ni foam.

3D MoS 2 hollow spheres were successfully fabricated by hydrothermal process. Commercial bulk MoS 2 had quite large grain size and preferential (002) grain orientation, while as-prepared MoS 2 hollow spheres had refined grain and random grain orientation. Meanwhile, the hydrogen evolution reaction of the commercial bulk MoS 2 and as-prepared MoS 2 hollow spheres was systematically investigated in acidic solution. The as-prepared MoS 2 hollow spheres catalyst exhibited a lower onset overpotential for hydrogen evolution reaction than bulk MoS 2 . The superior hydrogen evolution reaction activity could be attributed to the unique 3D MoS 2 hollow spheres which provided more active edge sites. In addition, 3D MoS 2 hollow spheres also exhibited excellent high chemical stability after 1000 potential cycles.

Cotton-like NiO is formed on the surface of bare Ni foam after hydrothermal process and calcination process, while ultrathin NiO nanoflakes occur on Ni foam coated with graphene. The high specific capacitance of 1782 F g− 1 at 1 A g− 1 and 90.2% capacity retention at 1 A g− 1 after 5000 cycles charge-discharge test are found. The graphene induces the high electrical conductivity and excellent interfacial contact, in addition, the graphene facilitates the forming of ultrathin NiO nanoflakes which result in huge pseudocapacitance due to large surface area and abundant mesoporous. The unique microstructure characteristic promotes interfacial electron transport in the electrode material and improves ion diffusion during the electrochemical reaction process.