Redox-mediated metal deposition

Redox-Mediated Metal Deposition. A reduced polyimide surface can function as a reducing substrate for subsequent deposition of metal ions from solution. For metal reduction to occur at a polymer surface, the electron transfer reaction must be kinetically uninhibited and thermodynamically favored, i.e., the reduction potential of the dissolved metal complex must be more positive than the oxidation potential of the reduced film. Redox-mediated metal deposition results in oxidation of the polymer film back to the original neutral state. The reduction and oxidation peak potential values for different metal complexes and metal deposits in nonaqueous solvents as measured by cyclic voltammetry are listed in Table III. 

The above studies suggest that electrochemical deposition provides a versatile, yet simple route for immobilizing proteins, enzymes, and bacteria in silane sol-gel films. The biological species remained active in the electrodeposited composite films, allowing their applications for biosensing. More sophisticated films with redox mediators, metal nanoparticles, and CNTs have also been constructed via the sol-gel co-electrodeposition approach. 

Scheme II. Proposed Charge Transfer Reactions for Redox-Mediated Pd Metal Deposition on Polyimide.

Solid-state redox mediators or hole conductor materials would make it possible to construct completely solid-state DSSCs that will probably have considerable added commercial value. One of the main difficulties in substituting liquid electrolytes is the need for an interpenetration of the sensitised metal oxide by the electrolyte, in order to have efficient contact between the sensitiser cation (the hole) and the mediator. Additionally, prospective solid hole collectors should have the following properties the valence band of the hole collector material must be located above the bottom of the sensitiser dye ground state it must be transparent throughout the visible spectrum, where the dye absorbs fight and the deposition of the solid material should be done without degrading the monolayer of sensitiser dye adsorbed on Ti02. 

The SECM studies of nanoparticles are of great interest and diversity. Metal nanoparticles can serve as redox mediators in solution to investigate their redox activities at solid-liquid and liquid-liquid interfaces by using SECM as discussed in Chapter 3. By contrast, this section is focused on the SECM studies of monolayers and multilayers of metal nanoparticles formed at various interfaces. In these studies, SECM was employed to quantitatively investigate the lateral conductivity and interfacial electroactivity of nanoparticle films. In addition, new experimental setups were developed to address the electrocatalytic and photocatalytic activities of nanoparticle films. Moreover, significant progresses were made to deposit and pattern nanoparticles on various substrates by using SECM. 

Details of the CEE method applied here to Step I-B to recover and purify RMFP obtained from Step 1A were discussed elsewhere [7]. In principle, Pd (or Fc ) would accelerate electro-deposition of the other ions as a promoter (i.e., Pd, ,.,.,.) at the electrode surface or as a mediator in the bulk solution. As for a typical example of CEE of RMFP from simulated HLLW, the galvanostatic electrolysis resulted in the quantitative deposition, where metal ions with E >0.7V tended to deposit on the cathode, and the deposition ratio seemed to be proportional to the order of the redox potential Pd>Te>Se>Rh>Ru>Re. Molybdenum and Zr can be recovered as co-precipitation at H <1.5 mol/dm . 

The incorporation of metals in multilayer thin films significantly extends the scope of useful characteristics associated with these films. By employing, for instance, polymeric Ru(II) complexes as polycationic species and poly(sodium acrylate) as polyanions in the layer-by-layer deposition process, efficient fight-emitting solid-state devices could be fabricated [91]. In another example, a ferrocene-containing redox-active polycation was combined with an enzyme to produce electrocatalyticaUy active enzyme/mediator multilayer structures [92]. Multilayers composed of poly(4-vinylpyridine) complexed with [Os(bpy)2Cl] / and poly(sodium 4-styrenesulfonate), for example, were used to accomplish the electrocatalytic reduction of nitrite [93]. 

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