Speciation modelling of the electroprecipitation of rare-earth cuprate and nickelate materials Speciation of aqueous solutions not at equilibrium

Abstract

Films of insoluble metal hydroxide have been obtained by cathodic electroprecipitation from aqueous solutions containing the nitrate salts of a lanthanide (La³⁺ or Nd³⁺) and a transition-metal cation (Ni²⁺ or Cu²⁺). Manipulation of deposition parameters, such as deposition voltage, V_a and solution composition, allows for extensive variation in mole fractions, x, of each metal in the final bimetallic hydroxide product. The variations in x are attributed to changes in the chemical environment within the Nernst layer at the electrode/solution interface, occurring in tandem with differences in the solution- and solid-phase speciation characteristics of the two metals and their hydroxides.

The experimentally obtained compositions of the deposited solid oxyhydroxide have been correlated with thermodynamically derived overall formation constants, β, and calculations of concentration obtained using a full speciation analysis. This model can be used to correctly predict compositions, which is taken to verify the model of electroprecipitation used.