New evidence on the electroprecipitation of ceria

The electroprecipitation of ceria onto Ni electrodes from Ce(NO3)3 solutions has been studied by comparing deposits obtained with potentiostatic electrolysis of variable durations. The dependence on the deposition charge of (i) ceria layer thickness, (ii) apparent layer density, (iii) coverage of the Ni surface by CeO2 and (iv) layer resistance was determined. These quantities were respectively assessed using (i) cross-sectional SEM images, (ii) gravimetric measurements, (iii) cyclic voltammetry in alkaline solution and (iv) electrochemical impedance spectroscopy. Experimental data showed that a porous low-density oxide precipitated initially, leaving a substantial part of the Ni electrode surface in direct contact with the electrolyte. During successive phases of the film growth, the formation of new solid material at the layer|solution interface was progressively replaced by its formation within the layers' pores and at the Ni|layer interface.