Influence of magnetic field on hydrogen reduction and co-reduction in the Cu/CuSO4 system

Abstract

The effects of an applied magnetic field of up to 5 T on hydrogen evolution and cathodic overpotential were studied for H2SO4 and an acidic Cu/CuSO4 system. Cyclic voltammetry, potentiostatic and galvanostatic deposition as well as electrochemical noise measurements were used. The magnetic field simultaneously increases the rate of hydrogen evolution and modifies the hydrogen bubble size. The periodicity of bubble release from a microelectrode is strongly influenced by the field, which may change the characteristic frequency or make it aperiodic, depending on the field orientation relative to buoyancy. The magnetic field stabilizes a bubble growing on a microelectrode, especially at high current densities. For example, bubble volume increases by a factor four in 1.5 T when the Lorentz force acts downwards. The noise spectra around 1 kHz are characteristic of a coalescence phenomenon. Hydrogen co-reduction with copper was studied by scanning electron microscopy and the current efficiency was measured with a quartz crystal microbalance; at -1.0 V it decreases from 95% to 75% in a field of 1.5 T. Bubble release is no longer periodic, but the noise spectrum has a characteristic shape depending on whether the current density is greater than, equal to or less than the diffusion-limited copper current. The field reduces the roughness of the copper deposit, but the current efficiency can be maximized by controlling the system galvanostatically, which allows a high copper deposition rate at overpotential lower than 0.5 V in the applied field, with smooth deposit quality.