Unipolar pulse electrodeposition of nickel hexacyanoferrate thin films with controllable structure on platinum substrates

Unipolar pulse electrodeposition was used to prepare nickel hexacyanoferrate (NiHCF) films on platinum substrates with controllable structure. The unipolar pulse waveforms consisted of an applied cathodic potential during the on-period and the open-circuit potential during the off-period. The effects of the pulse deposition parameters on the electrochemical properties of NiHCF films were investigated by potential cycling in K+-containing electrolytes. The morphology and composition of NiHCF films were characterized using scanning electron microscopy and energy dispersive X-ray spectroscopy. The charge transfer and the stability of the film electrodes were also examined by cyclic voltammetry (CV). Experimental results show that the cathodic pulse potential is the primary factor influencing the composition of the NiHCF films. The structure of NiHCF films prepared with a pulse potential of 0.7 V SCE appears close to that of the "insoluble" form with a single reversible CV peak at lower voltage and a unit cell with a stoichiometry close to KNi4II [Fe-III(CN)(6)](3). These films exhibit good stability and high dynamics for charge transport. The application of more negative cathodic potential pulses produces less dense and robust NiHCF films, with a structure closer to the "soluble" form and an approximate stoichiometry K8Ni4II[Fe-II(CN)(6)](4). (C) 2011 Elsevier B.V. All rights reserved.