Coalescence and counterflow of droplets on needle electrode with negative corona discharge

The coalescence of droplets on the discharge electrode surface in high humidity environments has rarely been studied, which may affect discharge characteristics. Meanwhile, directional transport of droplets is of great significance for many applications ranging from fluidic processing to thermal management. Here, corona discharge in needle-plate electrode is adopted to explore the coalescence rule of droplets attached on the discharge electrode surface in high-humidity environment, and realize the counterflow of droplets. The experimental results show that the amount of coalesced droplets on the needle electrode surface reaches the maximum under -7.5 kV at relative humidity ~ 94% and ambient temperature ~ 20 ℃. When the applied voltage increases from -6 kV to -11 kV, the droplet moves up 2.76 mm in 5 s. The size of attached droplet depends on the balance of coalescence and evaporation. The coalescence is mainly attributed to the dielectrophoretic force caused by the high electric field gradient. The evaporation is related with the ionic wind generated by the corona discharge. As for the counterflow phenomenon of droplet, we speculate that the high concentration gradient of positive ions near the needle electrode provides a driving force for the negatively charged droplets. Meanwhile, the electrons and negative ions below the needle tip offer a repulsive force to the droplet. The shape and moving direction of the droplet attached on the needle surface can be manipulated by changing the voltage applied to the needle electrode, which shows the potential application value in realizing self-cleaning of electrode, liquid lens and so on.

Electrocatalytic Properties of Ni(II) Schiff Base Complex Polymer Films

Platinum electrodes were modified with polymers of the (±)-trans-N,N′-bis(salicylidene)-1,2-cyclohexanediaminenickel(II) ([Ni(salcn)]) and (±)-trans-N,N′-bis(3,3′-tert-Bu-salicylidene)-1,2-cyclohexanediaminenickel(II) ([Ni(salcn(Bu))]) complexes to study their electrocatalytic and electroanalytical properties. Poly[Ni(salcn)] and poly[Ni(salcn(Bu))]) modified electrodes catalyze the oxidation of catechol, aspartic acid and NO2−. In the case of poly[Ni(salcn)] modified electrodes, the electrocatalysis process depends on the electroactive surface coverage. The films with low electroactive surface coverage are only a barrier in the path of the reducer to the electrode surface. The films with more electroactive surface coverage ensure both electrocatalysis inside the film and oxidation of the reducer directly on the electrode surface. In the films with the most electroactive surface coverage, electrocatalysis occurs only at the polymer–solution interface. The analysis was based on cyclic voltammetry, EQCM (electrochemical quartz crystal microbalance) and rotating disc electrode method.

Influence of Diffusion through a Porous Film under Electrode Surface in Chronoamperometry Problems

In the presented work on chronoamperometry, the Cottrell model has been generalized by taking into account a thin porosity layer covering the surface of the electrode and Tafel kinetics of an electrode reaction. The effective diffusion coefficient inside a porosity layer is calculated by Bruggeman’s law. It is shown that in the quasi-stationary approximation of diffusion inside a thin porous layer, the chronoamperometry problem can be solved analytically. The obtained solution has been compared with the results of direct numerical simulations and a good agreement is shown. Limiting cases of the solution related to low and high porosity are considered.

Optimization of Resistance Spot Welding with Inserted Strips via FEM and Response Surface Methodology

Resistance spot welding (RSW) with inserted strips, a recent variant of traditional RSW, was usually adopted in joining thin gage steels to lower the temperature developed at the electrode surface and to extend electrode life. In order to understand the influencing mechanism how the inserted strips affect the heat transfer behavior and to optimize the selection of suitable strips, an approach integrated with FEM and response surface methodology (RSM) was employed. FEM results showed that the inserted strips would not only lead to earlier initiation of weld and bigger weld size in both diameter and thickness but also lower the electrode surface temperature. Based on FEM, uniform design and RSM were further employed to build a regression model between the strip properties (i.e., electrical/thermal conductivity, thickness) and the responses (i.e., electrode tip temperature, weld diameter, and temperature at strip/sheet interface). A graphical optimization was conducted to identify a preferable strip, and a Cu55Ni45 strip with a thickness of 0.12 mm was recommended for a 0.4 mm steel sheet.

Li Plating on Carbon Electrode Surface Probed by Low-Field Dynamic Nuclear Polarization 7Li NMR

Lithium deposition on graphite electrode not only reduces fast-charging capability of lithium ion batteries but also causes safety trouble. Here, a low-field 7Li dynamic nuclear polarization (DNP) is used to probe Li plating on the surfaces of three types of carbon electrodes: hard carbon, soft carbon and graphite. Owing to the strong Fermi contact interaction between 7Li and conduction electrons, the 7Li nuclear-magnetic-resonance (NMR) signal of Li metal deposited on electrode surface could be selectively enhanced by DNP. It is suggested that low-field 7Li DNP spectroscopy is a sensitive tool for investigating Li deposition on electrodes during charging/discharging processes.