Electrochemical Preparation Of Bismuth And Bismuth Oxide Nanomaterials

Bismuth nanomaterials with very large magnetoresistance (MR) and excellent thermoelectric properties are widely used in magnetic field sensor, thermoelectric cooler or batteries materials. Bismuth oxides with marked photoconductivity and photoluminescence also find wide applications in catalysts, ceramic materials, solid oxide fuel cells and sensors. So the preparation and application of their nanostructures are attracting a lot of interests. What's more, our group has proposed a physical model, i.e., bistability coupled with positive and negative feedbacks, and a universal criterion based on this model for the oscillatory electrochemical systems from the viewpoint of the electrode processes. It has been proved that the cylic-voltammetry-based criterion has a wider range of application. In this paper, bismuth nano and porous materials and bismuth oxides have been prepared by new electrochemical methods and new current oscillations have been observed and investigated in the electro-oxidation of bare bismuth electrode in sulfuric acid with cysteine. The main contents are summarized as follows:1. Bismuth nanoparticles (NPs) ca. 20～40 nm have been facilely prepared by novel cathodic dispersion of bulk bismuth electrodes in an alkaline solution at room temperature, requiring no any precursor ions and protective agents. The fabrication process involves the formation and decomposition of unstable bismuth hydrides and aggregation of atomic bismuth from the decomposition. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscrope (SEM) have been employed to character the as-prepared Bi nanoparticles. Moreover, Bi₂O₃ NPs can be also achieved by heating the precursor Bi NPs. While the bismuth nanoparticles were assembled into a thin nanoporous film on a glass carbon electrode (GCE), the Bi NPs modified GCE demonstrated sensitive electrocatalytic response to the reduction of 4-nitrophenol (4-NP).2. Micro/nano-porous bismuth films and nano-porous bismuth films have been prepared by electrodeposition with hydrogen bubble dynamic templates and by redox potential pulses, respectively. The morphology, structure and component of the two kinds of films were characterized by SEM and XRD, respectively. These films demonstrated high activity to the electrochemical reduction of 4-NP.3. Composite nanorods of bismuth oxide/sulfate and nanoneedles of bismuth oxide have been prepared by potentiostatic cathodic polarization in H2SO4 solution and H₂SO₄ + cysteine solution. With the guidance of crossing cycle criterion, current oscillations have been observed and investigated for the first time during the electro-oxidation of bare bismuth electrode in sulfuric acid with cysteine. The interfacial phase transition between bismuth oxide and sulfate is the main reason for the current oscillations and the crossing cycle in the cyclovoltammogram.