Abstract
The spin-spray-assisted layer-by-layer (LbL) assembly technique was used to prepare coordinative oxidative multilayers from Ce(IV), inorganic polyphosphate (PP), and graphene oxide (GO). The films consist of successive tetralayers and have a general structure (PP/Ce/GO/Ce)n. Such oxidative multilayers have been shown to be a general platform for the electrodeless generation of conducting polymer and melanin-type films. Although the incorporation of GO enhances the film growth, the conventional dip LbL method is very time consuming. We show that the spin-spray method reduces the time required to grow thick multilayers by the order of magnitude and the film growth is linear from the beginning, which implies a stratified structure. We have deposited poly(3,4-ethylenedioxothiophene), PEDOT, on the oxidative multilayers and studied these redox-active films as models for melanin-type capacitive layers for supercapacitors to be used in biodegradable electronics, both before and after the electrochemical reduction of GO to rGO. The amount of oxidant and PEDOT scales linearly with the film thickness, and the charge transfer kinetics is not mass transfer-limited, especially after the reduction of GO. The areal capacitance of the films grows linearly with the film thickness, reaching a value of ca. 1.6 mF cm–2 with 20 tetralayers, and the specific volumetric (per film volume) and mass (per mass of PEDOT) capacitances are ca. 130 F cm–3 and 65 F g–1, respectively. 5,6-Dihydroxyindole can also be polymerized to a redox-active melanin-type film on these oxidative multilayers, with even higher areal capacitance values.
Highlights
A successive layer-by-layer (LbL) self-assembly of charged components is an extremely versatile technique for the fabrication of thin films with a wide variety of materials.[1]
We have demonstrated that an oxidative multilayer based on coordinative bonding between a redox-active transition metal, for example, Ce(IV), and a polyanion, for example, inorganic polyphosphate (PP), can be used as a general platform to generate thin conducting polymer or polydopamine films on surfaces.[4−6] Incorporation of graphene oxide (GO) sheets into the multilayer greatly enhances its growth and allows it to bind a larger amount of oxidant in the multilayer, resulting in thicker polymer films.[7]
We have previously shown that GO enhances the mechanical properties of oxidative (PP/Ce)n multilayers formed by the dip LbL technique and that the formed (PP/ Ce/GO/Ce)n films grow much faster, reaching a thickness of ca. 230 nm already after five (PP/Ce/GO/Ce) tetralayers.[4,7]
Summary
A successive layer-by-layer (LbL) self-assembly of charged components is an extremely versatile technique for the fabrication of thin films with a wide variety of materials.[1]. Redox-active polymer films can be used as pseudocapacitive components in supercapacitors. Supercapacitors have many advantageous properties in energy storage.[8] They exhibit long cycle life and high power density because of fast charge and discharge rates. Simple electrochemical doublelayer capacitors (EDLCs) have a low energy density, which can be increased using high-surface-area carbon materials.[9] In EDLCs, the energy is stored electrostatically within the electrical double layer at the electrode−solution interface, but faradaic reactions can be used to increase the storage capacity. The fast redox reaction between the substrate electrode and the electroactive material is accompanied by ion flux in and out of the surface film. The highest storage density can be achieved in hybrid systems, which combine the high-surface-area EDLCs with effective pseudocapacitance. The capacitance of Received: March 24, 2020 Revised: May 12, 2020 Published: May 26, 2020
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