Electroanalysis based on stand-alone matrices and electrode-modifying films with silica sol-gel frameworks: a review

Abstract

Silica sol-gel matrices and its organically modified analogues that contain aqueous electrolytes, ionic liquids, or other ionic conductors constitute stand-alone solid-state electrochemical cells when hosting electrodes or serve as modifying films on working electrodes in conventional cells. These materials facilitate a wide variety of analytical applications and are employed in various designs of power sources. In this review, analytical applications are the focus. Solid-state cells that serve as gas sensors, including in chromatographic detectors of gas-phase analytes, are described. Sol-gel films that modify working electrodes to perform functions such as hosting electrochemical catalysts and acting as size-exclusion moieties that protect the electrode from passivation by adsorption of macromolecules are discussed with emphasis on pore size, structure, and orientation. Silica sol-gel chemistry has been studied extensively; thus, factors that control its general properties as frameworks for solid-state cells and for thin films on the working electrode are well characterized. Here, recent advances such as the use of dendrimers and of nanoscale beads in conjunction with electrochemically assisted deposition of silica to template pore size and distribution are emphasized. Related topics include replacing aqueous solutions as the internal electrolyte with room-temperature ionic liquids, using the sol-gel as an anchor for functional groups and modifying electrodes with silica-based composites.

The Influence of the Type of Electrolyte in the Modifying Solution on the Protective Properties of Vinyltrimethoysilane/Ethanol-Based Coatings Formed on Stainless Steel X20Cr13

“…Additionally, no formation of the blue colouring (Prussian Blue formation) was observed on the steel surface, confirming definitely that the obtained coating provides a compact and tight protective barrier. Moreover, the VTMS/EtOH/AcOH layer formed on the X20Cr13 steel blocked the transport of electrons to ferrocyanide ions, has manifested itself by the attenuation of the redox currents ( Figure 9 B) [ 49 , 50 ].…”

“…The following electrolytes were selected for testing: acetic acid (AcOH) by Chempur (the method of depositing the coating based on VTMS and acetic acid was developed in previous studies [ 36 ]); lithium perchlorate (LiClO 4 ) by Fluka Chemika, as a strongly oxidizing anion of inhibiting properties [ 37 , 38 , 39 , 40 , 41 , 42 ]; sulphuric acid (VI) (H 2 SO 4 ) by Chempur; an acid medium, with a passive film forming on the metal surface, containing sparingly soluble thermodynamically stable oxidation products [ 43 , 44 , 45 , 46 ]; ammonia (NH 3 )- P.P.H. by Polskie Odczynniki Chemiczne; a basic medium, for controlling the hydrolysis and condensation rates [ 47 , 48 , 49 , 50 , 51 , 52 ]. …”

“…ammonia (NH 3 )- P.P.H. by Polskie Odczynniki Chemiczne; a basic medium, for controlling the hydrolysis and condensation rates [ 47 , 48 , 49 , 50 , 51 , 52 ].…”

“…The water molecule combines with the silicon atom, which is followed by disintegration and the formation of silanols and alcohol. In acidic catalysis, we obtain transparent gels of low porosity [ 50 ].…”

“…An X20Cr13 steel sample uncovered and covered with a VTMS/EtOH/AcOH coating in a VTMS concentration of 3.16 mol dm −3 were immersed in potassium hexacyanoferrate (III) solution. Afterward, electrochemical measurements were taken by the cyclic voltammetry in the potential range from −0.6 V to 1.2 V vs. SCE [ 49 , 50 ].…”