Magnetic Effect during Copper Electrodeposition: Diffusion Process Considerations

Magnetic forces in paramagnetic fluids

An overview of the effect of a magnetic field gradient on fluids with linear magnetic susceptibilities is given. It is shown that two commonly encountered expressions, the magnetic field gradient force and the concentration gradient force for paramagnetic species in solution are equivalent for incompressible fluids. The magnetic field gradient and concentration gradient forces are approximations of the Kelvin force and Korteweg-Helmholtz force densities, respectively. The criterion for the appearance of magnetically induced convection is derived. Experimental work in which magnetically induced convection plays a role is reviewed.

Effect of a Magnetic Field on the Electrode Process of Al Electrodeposition in a [Emim]Cl-AlCl3 Ionic Liquid

The magnetohydrodynamic (MHD) effect was usually used to improve the mass transport during electrodeposition in a solution electrolyte. Herein, we reported the effect of a magnetic field on the electrode process of Al electrodeposition in a [Emim]Cl-AlCl₃ ionic liquid composed of pure ions. Under a uniform and perpendicular magnetic field to the Cu electrode plane, electrochemical impedance spectroscopy (EIS) of the circuit, the cyclic voltammetry (CV) curves, and the different capacitances at the potential of zero charge (PZC) were measured, and the electrodeposition of aluminum was carried out at a constant current density. The results indicated that a vertical magnetic field significantly reduced the resistance (activation energy) for charge transfer of electrochemical reduction of Al₂Cl₇^-; meanwhile, the capacitance of an electric double layer (EDL) and the density of the electrodeposited aluminum layer were increased.

Characterisation of Complex Electrode Processes using Simultaneous Impedance Spectroscopy and Electrochemical Nanogravimetric Measurements

The methodology and illustrative examples of application are presented for a technique that simultaneously combines electrochemical impedance spectroscopy (EIS) and nanogravimetric measurements; the latter are implemented using a so-called electrochemical quartz crystal nanobalance (EQCN). The combination of EIS and EQCN provides a powerful method for the characterisation of many complex processes at electrochemical interfaces. This method gives in one relatively simple experiment more detailed information than is available from conventional electrochemical techniques. The combined measurements can be performed either as a function of time, at a constant electrode potential, or under potentiodynamic conditions, as a function of the electrode potential. Herein, we show how this can be applied to enable more accurate investigation of processes that occur at boundaries between electrodes and electrolytes. The application examples range from eletrocatalysis, in which evaluation of a catalyst is performed simultaneously with its formation, and the intercalation and electrodeposition of thin metal films to in situ characterisation of non-electroactive self-assembled monolayers during their formation.

Nature of inclined growth in thin-layer electrodeposition under uniform magnetic fields

Electrochemical deposition (ECD) in thin cells in a vertical position relative to gravity, subject to an external uniform magnetic field, yields a growth pattern formation with dense branched morphology with branches tilted in the direction of the magnetic force. We study the nature of the inclined growth through experiments and theory. Experiments in ECD, in the absence of magnetic forces, reveal that a branch grows by allowing fluid to penetrate its tip and to be ejected from the sides through a pair of symmetric vortices attached to the tip. The upper vortices zone defines an arch separating an inner zone ion depleted and an outer zone in a funnel-like form with a concentrated solution through which metal ions are carried into the tip. When a magnetic field is turned on, vortex symmetry is broken, one vortex becoming weaker than the other, inducing an inclination of the funnel. Consequently, particles entering the funnel give rise to branch growth tilted in the same direction. Theory predicts, in the absence of a magnetic force, funnel symmetry induced through symmetric vortices driven by electric and gravitational forces; when the magnetic force is on, it is composed with the pair of clockwise and counterclockwise vortices, reducing or amplifying one or the other. In turn, funnel tilting modifies particle trajectories, thus, growth orientation.

Magnetic structuring of electrodeposits

Metal electrodeposition reflects the pattern of the magnetic field at the cathode surface created by a magnet array. For deposits from paramagnetic cations such as Co²⁺ or Cu²⁺, the effect is explained in terms of magnetic pressure which modifies the thickness of the diffusion layer, that governs their mass transport. An inverse effect allows deposits to be structured in complementary patterns when a strongly paramagnetic but nonelectroactive cation such as Dy³⁺ is present in the electrolyte, and is related to inhibition of convection of water liberated at the cathode, in the inhomogeneous magnetic field. The magnetic structuring depends on the susceptibility of the electroactive species relative to that of the nonelectroactive background.

Investigations on the Kinetics of Electron Transfer Reactions in Magnetic Fields

There is a controversial debate if a magnetic field can influence the rate of electron transfer (ET) reactions. In this paper, we report kinetic measurements of the ET rate constants for the redox couples [IrCl6]2-/[IrCl6]3-, [Fe(CN)6]3-/[Fe(CN)6]4-, and [Fe(H2O)6]3+/[Fe(H2O)6]2+ in magnetic fields up to 1 T. To reduce effects arising from magnetically induced mass transport (magnetohydrodynamic effect), disk microelectrodes with a diameter of 50 microm were used in potentiodynamic (cyclic and linear sweep voltammetry) and in electrochemical impedance spectroscopy experiments. None of the investigated redox couples showed a magnetic field effect on the ET rate constant.