Synthesis of Co ₃O ₄ thin films by chemical bath deposition in the presence of different anions and application to H ₂O ₂ sensing

Co ₃O ₄ modified electrode was prepared by directly growing layered cobalt carbonate hydroxide (LCCH) on a conducting fluorine-doped tin oxide (FTO) substrate using a simple chemical bath deposition (CBD) technique and then by transforming the LCCH into Co ₃O ₄ through pyrolysis. Cobalt sources with various anions, including cobalt chloride, cobalt nitrate, cobalt acetate, and cobalt sulfate, were used in the bath solutions of CBD to prepare the LCCH thin films with various morphologies. The composition and grain size of these films were verified by X-ray diffraction (XRD); their morphologies were examined by scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images. Observed from the SEM images, the Co ₃O ₄ films synthesized from cobalt chloride (C-Co ₃O ₄), cobalt nitrate (N-Co ₃O ₄), cobalt acetate (A-Co ₃O ₄), and cobalt sulfate (S-Co ₃O ₄) were composed of straight acicular nanorods, bending acicular nanorods, nanosheets, and net-shaped nanosheets, respectively. The four kinds of modified electrodes were applied to detect H ₂O ₂, and the C-Co ₃O ₄ modified electrode showed the best electrocatalytic activity toward H ₂O ₂. The pertinent sensor could be successfully used for the quantification of H ₂O ₂ by amperometric method. The sensing performance parameters include a linear range up to 2.0 mM, a sensitivity of 66.29 μA/cm ²-mM, a remarkable low detection limit of 0.36 μM, and a low applied potential of 0.50 V vs. Ag/AgCl/sat'd KCl.