Researches On Electrodeposition Of Pd-Ag Alloy Nanowire Arrays On The Surface Of Highly Oriented Pyrolytic Graphite

Palladium alloy nanowires composed of 16% 25% silver can increase the dynamic reversibility of metal palladium absorbing hydrogen and prevent the alloy from hydrogen damnification. So Pd-Ag alloy nanowires are more practical valuable materials of hydrogen sensors. Pd-Ag alloy nanowire arrays were electrodeposited on the surface of Highly Oriented Pyrolytic Graphite (HOPG) which served as template. Morphologies, composition, crystal structures of the nanowires and their dependences on baths composition and processes parameters were characterized and investigated by SEM, EDX, AES, XRD. Behaviors of co-deposition were theoretically calculated by Nernst equation and experimental investigated by dynamical potential scanning. Mechanisms of electrodeposition were investigated by electrochemical techniques such as: electrochemical impendence spectrum and double potential pulse. In this work three different methods of fabrication Pd-Ag alloy nanowires were preformed: "triple pulse", "alkanethiol assembled"and "one step direct electrodeposition". Characterizations and deposition conditions of these methods are investigated. The main results are gained as following:1. Results of electrochemical polarization experiments show that: polarization of silver curve is larger than that of palladium, Pd promotes Ag deposition obviously.2. Co-deposition can take place in the bath of simple ions and NH3 ionized from NH4NO3 as ligant. The NH4NO3 in the plating solution plays an important role in terms of complexing and conducting. Mechanism of Pd-Ag co-deposition is ascribed to abnormal co-deposition. Ag underpotential deposition on surface of Pd is the main causes resulting in abnormal co-deposition. The optimal concentration of NH4NO3 is 2 mol·dm^-3, and pH ranges from 2 to 3, and in the bath with Pd / Ag ion concentration ratio of 15:1 20:1, Ag content ranging from 23% to 18% mass fraction in Pd-Ag nanowire arrays can be obtained.3. Modified "Triple pulse" method: oxidation and nucleation voltage pulse and growth current pulse" is a more effective method for fabrication Pd-Ag alloy nanowires. The optimal parameters values of the method are: oxidation pulse 0.8 1.1V, nucleation pulse -1.4 V -1.5 V for 5ms 1000ms and growth pulse -20 ^-60μA·cm^-2. The alloy nanowire arrays fabricated by this method are continuous, parallel, ordered, and well-aligned with narrow diameter dispersion.4. Deposition potential of Pd-Ag alloy will not be changed after assembling...