Using a Mediating Effect in the Electroreduction of Aryldiazonium Salts To Prepare Conducting Organic Films of High Thickness

Abstract

Usually, electrografting of aryldiazonium salts results in the formation of covalently attached films <10 nm thick. In this work, we report on an electrografting procedure by which thick conducting films, even in the micrometer size range, can be formed on glassy carbon, gold, or stainless steel in a controlled manner. It is a prerequisite that the aryldiazonium salt contains a redox active moiety such as nitrobenzene, anthraquinone, or benzophenone to maintain charge propagation in the growing layer. In addition, electrografting proceeds only efficiently by way of using potential sweeping rather than electrolysis at a fixed potential. Sweeping is essential to continuously desorbing any physisorbed species that otherwise would clog the channels in the film and make it insulating. Cyclic voltammetry, polarization modulation infrared reflection absorption spectroscopy, ellipsometry, and profilometry are used to characterize the surfaces and, through this, explain the growth mechanism. Elucidation of the role of the substrate, solvent, and supporting electrolyte is included in the investigation.

Electrochemical Behaviour of HOPG and CVD‐Grown Graphene Electrodes Modified with Thick Anthraquinone Films by Diazonium Reduction

“…Thick conducting layers have also very important applications in a wide range of areas, including protection of surfaces and chemical sensors [48]. Recently, a new method called redox grafting was proposed for formation of thick covalently attached conducting organic layers on different substrates (GC, gold, and stainless steel) via electrochemical reduction of various aryldiazonium salts (e.g., 9,10-dioxo-9,10-dihydroanthracene-1-diazonium salt) [48][49][50].…”

“…Recently, a new method called redox grafting was proposed for formation of thick covalently attached conducting organic layers on different substrates (GC, gold, and stainless steel) via electrochemical reduction of various aryldiazonium salts (e.g., 9,10-dioxo-9,10-dihydroanthracene-1-diazonium salt) [48][49][50]. A prerequisite for redox grafting is that the aryldiazonium salt used should contain a redox active functionality.…”

“…Furthermore, employment of high sweep rate in cyclic voltammetry is pertinent to avoid clogging of the physisorbed species in the electrolyte channels in the film that would, otherwise, easily prevent the charge propagation in the growing film. Finally, the switching potential should be carefully selected to encompass the reduction of the redox moiety in the growing film during grafting to exploit the repulsion effect to get rid of noncovalently attached material [48][49][50].…”

“…To our knowledge, the modification of such graphene materials by redox grafting has not been studied until now. Large differences in these films would be expected originating from the different nature of the substrates [48]. In fact, the research area of preparing hybrid materials of graphene nanosheets and redox polymers is in its very infancy and needs further development.…”

“…Based on the principles of redox grafting, thick conductive AQ films on GC, HOPG, Ni-Gra and Cu-Gra were prepared [48]. First, the redox grafting of AQD on GC was performed applying potential cycling between 0.6 and À1.6 V vs. SCE for 10 cycles at a sweep rate, v, of 1 Vs…”