Study on Charge Transfer Reactions in Electrodeposition

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(1)Charge transfer reactions in the Helmholtz layer in electrodepositionElectrochemical impedance spectroscopy measurements under a small alternating current density were performed to make investigations into electrochemical reactions on (110) single-crystalline nickel surfaces in nickel sulfamate electrolyte. The reaction impedance shows a power law of the ac modulation frequency and two exponents for the reaction resistance and reaction capacitance are found to agree with the values predicted by a homogeneous charge-transfer reaction model. In addition, the Nyquist diagrams exhibit the absence of inductive loops. A condition for the existence of inductive loops derived in this study suggests that the electrocrystallization of Ni^<2+> ions may take place in the slow reaction step Ni^<2+>+e^-→Ni^+_<abs> and in the fast reaction step Ni^+_<abs>+e^-→Ni.(2)Transient process in the Helmholtz layer in electrodepositionA method is described for the study of the kinetics of electrode reaction … More s on the basis of analytical solutions of three transient electrochemical processes comprising the diffusion of ions, charge-transfer reactions and a charging process of an electrochemical double-layer. Multi-pulse currents are applied to a working electrode and the potentials are recorded. The measured potential-time curves agree with those predicted by the analytical solution. The kinetic constant, exchange current density and double-layer capacitance are determined from the measured potential-time curves using the analytical solution.(3)Surface nucleation and growth in electrodepositionVoltage-time curves in surface growth on single crystalline nickel electrodes in nickel sulfamate have been measured under a fixed current density with a nanosecond rise-time. The transient voltage-time curves in a two-electrode system exhibit three continuous regions that correspond to the reduction of nickel ions by two-step electrochemical reactions, the crystallization process such as nucleation and growth, and steady state surface growth. The measured voltage-time curves are well consistent with the calculation results predicted by phenomenological equations proposed in this study. Less