Abstract
Here we report the first study on the electrochemical energy storage application of a surface-immobilized ruthenium complex multilayer thin film with anion storage capability. We employed a novel dinuclear ruthenium complex with tetrapodal anchoring groups to build well-ordered redox-active multilayer coatings on an indium tin oxide (ITO) surface using a layer-by-layer self-assembly process. Cyclic voltammetry (CV), UV-Visible (UV-Vis) and Raman spectroscopy showed a linear increase of peak current, absorbance and Raman intensities, respectively with the number of layers. These results indicate the formation of well-ordered multilayers of the ruthenium complex on ITO, which is further supported by the X-ray photoelectron spectroscopy analysis. The thickness of the layers can be controlled with nanometer precision. In particular, the thickest layer studied (65 molecular layers and approx. 120 nm thick) demonstrated fast electrochemical oxidation/reduction, indicating a very low attenuation of the charge transfer within the multilayer. In situ-UV-Vis and resonance Raman spectroscopy results demonstrated the reversible electrochromic/redox behavior of the ruthenium complex multilayered films on ITO with respect to the electrode potential, which is an ideal prerequisite for e.g. smart electrochemical energy storage applications. Galvanostatic charge-discharge experiments demonstrated a pseudocapacitor behavior of the multilayer film with a good specific capacitance of 92.2 F g(-1) at a current density of 10 μA cm(-2) and an excellent cycling stability. As demonstrated in our prototypical experiments, the fine control of physicochemical properties at nanometer scale, relatively good stability of layers under ambient conditions makes the multilayer coatings of this type an excellent material for e.g. electrochemical energy storage, as interlayers in inverted bulk heterojunction solar cell applications and as functional components in molecular electronics applications.
Highlights
The multilayer thin films were prepared with the novel redoxactive dinuclear ruthenium complex [Ru2(tppz)(LPOH)2](PF6)[4] (Ru–N) on an indium tin oxide (ITO) substrate employing an aqueous-based layer-by-layer (LBL) assembly process (Fig. 1)
We describe the structure of the multilayers as ITO|(Ru–N)n, where “n” represents the number of ruthenium complex [Ru2(tppz)(LPOH)2](PF6)4 (Ru–N) layers
Characterisation of the ruthenium complex multilayer ITO| (Ru–N)[65] in an electrochemical energy storage application Further we present a proof of principle application of ITO|(Ru– N)[65] multilayer for electrochemical energy storage
Summary
Recent developments in portable consumer electronics, such as transparent and/or flexible electronic devices and integrated microsystems, demand generation energy storage devices, which must meet the requirements of high performance (rapid charge/discharge) and high stability (low performance loss) during the charging–discharging cycles as well as low cost.[1,2,3,4,5] Conventional electrochemical energy storage devices, such as batteries, are known to suffer from slow charge–discharge rates and difficulties in maintaining their efficiency upon scaling-down in size.[1,6] This creates a strong demand for small, flexible, high performance and low cost portable energy storage solutions.[4,7,8,9,10,11,12]It was suggested that electrochemical supercapacitors, which store the electric energy by charging the electric double layer, may suit this purpose. The multilayer thin films were prepared with the novel redoxactive dinuclear ruthenium complex [Ru2(tppz)(LPOH)2](PF6)[4] (Ru–N) on an indium tin oxide (ITO) substrate employing an aqueous-based layer-by-layer (LBL) assembly process (Fig. 1).
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