Catalytic effect of L-proline on the reduction of Ni(II) ions during nickel electrodeposition from a Watts-type nickel bath

Abstract

Many chemical entities have been proposed as additives to enhance the properties and structure of electro deposited nickel. In this work, considerable improvements have been found by using L-proline as a complexing agent in a Watts-type nickel bath. This study determined the influence of L-proline concentrations on the cathodic efficiency, cathodic polarization, anodic linear stripping voltammetry, current-time transients, mac rothrowing power and Wagner number. The presence of L-proline leads to a great shift in the polarization curve and the deposition potential towards more noble potentials, indicating the catalytic effect of L-proline on the reduction of Ni(II) ions. The kinetic data confirmed that the exchange current density is greatly enhanced with increasing L-proline concentration. The Tafel slopes in the presence of L-proline are higher (141–160 mV decade−1 ) than that without L-proline (130.7 mV decade−1 ). The constant values of αc, proposes that the Ni electrodeposition mechanism is not influenced by the presence of L-proline. The corrosion property of nickel coatings prepared from Watts-type nickel bath in the absence and presence of L-proline was tested in 3.5% NaCl solution. In the presence of L-proline a surface morphology consisting of fine and homogeneous tightly packed non-porous grains covering the entire cathode surface was obtained as detected by SEM.