Multielectrocatalysis by Layer-by-Layer Films Based on Pararosaniline and Vanadium-Substituted Phosphomolybdate

Abstract

Hybrid multilayer films based on the two molecular species pararosaniline (PR) and Keggin-type polyoxometalate K5[PMo11VO40)] (PMo11V) were prepared on different substrates using the electrostatic layer-by-layer (LbL) self-assembly method. The film buildup, monitored by electronic spectroscopy, showed a regular stepwise growth, and X-ray photoelectron spectroscopy data confirmed the presence of both molecular components within the LbL films. Scanning electron microscopy images revealed a completely covered surface with a nonuniform distribution of film components, and atomic force microscopy images confirmed a rough surface. The film electrochemical responses and permeability were studied by cyclic voltammetry. Films revealed three Mo-based redox processes (Mo(VI) → Mo(V)) and one V-based redox process (V(V) → V(IV)) in the potential range between 0.8 and -0.4 V vs Ag/AgCl. Studies with the redox probes [Fe(CN)6](3-/4-) and [Ru(NH3)6](3+/2+) showed that the films maintain the permeability even after six bilayers. Furthermore, the {PR/PMo11V}n multilayer films exhibit excellent Mo-based electrocatalytic activity toward reduction of iodate and V-based electrocatalytic activity toward ascorbic acid oxidation, thus acting as a versatile multielectrocatalyst.

Statistical evaluation of an electrochemical probe for the detection of chlorate

“…Given these favorable characteristics, we fabricated PMo 11 V/PR films on PEI-coated quartz and ITO slides for chlorate electrocatalysis studies using 2 mg/mL (i.e., 1.09 mM) PMo 11 V and 0.14 mM PR solutions in 0.10 M acetate buffer pH 4 with 10 min substrate treatment times corresponding approximately to the optimum deposition conditions identified by Fernandes, et. al [45]. We observed broadened absorbance spectra consistent with previous reports in Figure 1A for our films on quartz as functions of the number of PMo 11 V/PR bilayers, n, for n = 1  20.…”

“…However, our absorbance changes exhibit two linear regions with increasing numbers of PMo 11 V/PR bilayers, rather than a single nearly linear growth behavior, as shown in the Figure 1B. In addition, we note that the 535 nm absorbance of our Quartz/PEI/(PMo 11 V/PR) 20 film was ~0.38, which is somewhat smaller than the ~0.46 value found for the corresponding film in the literature [45].…”

“…al. [45] described a composite electrode prepared via layer by layer (LbL) alternate electrostatic deposition of the Keggin-type polyoxometalate anion, [PMo 11 VO 40 ] 5 (PMo 11 V), and the cationic dye, p-rosaniline acetate (PR) (note Scheme 1). The resulting stable electrode films were permeable to large anions, such as ferrocyanide, and exhibited electrocatalytic oxidation of ascorbate and reduction of iodate.…”

POM & MOF‐based Electrocatalysts for Energy‐related Reactions

“…Aw ide range of charged materials have been used to fabricate POM-based LbL films, which include biopolymers (chitosan), [72] polycations, such as poly(ethylenimine) (PEI), [61,64,73] poly(allylamine hydrochloride) (PAH), [74] and poly(diallyldimethylammoniumc hloride) (PDDA), [75] transition metal complexes, [63] and to am uch lower extent dye molecules. [76][77][78] However,m ost of these examples are used for sensinge lectrocatalysis rather than energy-related applications. In fact, only few examples have been published regarding the use of this technique for the preparation of POM-based electrocatalysts for energy reactions or energy conversion and storagedevices.…”

“…This method was widely used due to several advantages: 1) it is a simple, low‐cost, eco‐friendly technique that enables the fabrication of films/nanocomposites; 2) allows the control of the final product functionality and structure; 3) an almost infinite range of materials can be used; 4) allows the assembly of multi‐materials without the need for chemical modification. A wide range of charged materials have been used to fabricate POM‐based LbL films, which include biopolymers (chitosan), polycations, such as poly(ethylenimine) (PEI), poly(allylamine hydrochloride) (PAH), and poly(diallyldimethylammonium chloride) (PDDA), transition metal complexes, and to a much lower extent dye molecules . However, most of these examples are used for sensing electrocatalysis rather than energy‐related applications.…”