Electrochemical study of self-assembled monolayer of polyoxometalate on gold surface

The self-assembled organic monolayer chemistry has been paid intensive attention in the past 20 years, since Sagiv reported that alkanesilanes could be used to form a stable monolayer on glass or aluminum oxides [1]. The chemistry of SAMs provides an opportunity to control the film structure at the molecular level and enables tailoring of the surface properties through incorporation of various organic functional groups into the adsorbate molecules [2]. Although organic SAMs have been found to have potential utility in different fields [3], many undesirable features, such as their oxidization on exposure to air, instability in the typical thermal conditions, and desorption in organic solvents, preclude the practical use of the organic SAMs. Self-assembled inorganic monolayers will probably enjoy the popularity of the organic SAMs, due to the superior stability and mechanical properties of inorganic monolayers. Although much work on the adsorption of simple anions such as iodide, bromide, cyanide, and sulfate/bisulfate has been done, just recently pioneering studies on the SAMs of inorganic complexes have just been completed [4]. Polyoxometalates with welldefined primary structures are recently attracting much attention as building units of novel inorganic materials that may be useful in catalysis, medicine, biology, and devices [5]. In the present work the polyoxometalate anion, H3PW12O40 and (Cys)3PW12O40 were used to fabricate the inorganic SAMs by spontaneous adsorption of PW12O403- anions on gold surface from acidic aqueous solution. The electrochemical properties of the inorganic SAMs were studied in detail by electrochemistry. The voltammograms of the PW12O403- SAM on gold electrode showed two pairs of reversible peaks. Furthermore, electrochemical measurements prove that the H3PW12O40 and (Cys)3PW12O40 SAM on gold electrode maintains the same formal potential and exhibits better redox behavior compared with the PW12O403- anions in the solution, which is very favorable for electrocatalytical reaction of the polyoxometalate anions.