Effect of a magnetic field on the local pH value in front of the electrode surface during electrodeposition of Co

The change of the pH value, the hydrogen evolution reaction, and their effect on the electrodeposition of Co were investigated directly at the surface of a gold mesh with and without superimposition of a magnetic field of 1 T by cyclic voltammetry and chronoamperometry in 0.1 M Na2SO4 with and without addition of 0.01 CoSO4. The reduction of hydrogen ions is increased by superimposition of a magnetic field oriented parallel to the electrode surface. The increase of the pH value directly at the surface is lower in an applied magnetic field compared to the case without a magnetic field. This is likely to be due to the enhanced convection generated by the Lorentz force. The discharged hydrogen ions are rapidly compensated. The effect of a magnetic field on the limited current density as well as on the change of pH value is more significant at lower initial pH value. For initial pH values of 3 and 3.5 the deposition of Co under a superimposed magnetic field is improved and the increase of the pH value is low in front of the electrode. This leads to a suppression of the spontaneous formation of hydroxides.