Electrocatalytic Sensing of Carbon Dioxide, Oxygen and Inert Inorganic Analytes at Network Films of Transition Metal Complexes
Authors: Kulesza Pawel J , Wadas Anna , Ozimek Weronika , Frik Malgorzata , Rutkowska Iwona Agnieszka 
Published: February 2020

There has been growing interest in electrocatalytic sensing of inert reactants that exhibit totally irreversible behavior at common electrode substrates. For example, catalytic reductive transformations of carbon dioxide (CO2) to fuels and to commodity chemicals are important contemporary energy and environmental challenges. Because CO2 is very stable, the direct electroreduction of CO2 to CO requires large over-potentials. On analytical grounds, there is a need to develop new methods for the determination of arsenic (electrochemically very inert basically at all oxidation states) due to its high toxicity and increasing population in the environment. At present chromatographic and spectroscopic approaches are the most common. Electrochemical methods for determination of arsenic are often considered as complimentary ones because they are fairly simple and they do not required generation of toxic AsH3. Our interests also concern electrochemical performance and electroanalysis of bromate (slow complex reduction) as well as electroreduction and sensing of oxygen.

In the process of developing of new micro- and nanostructured electrocatalytic systems, we have concentrated on the network films yielding nanostructured metallic palladium via reduction of the complex of palladium(II), [Pd(C14H12N2O3)Cl2]2∙MeOH. The catalytic activity of CO2 reduction was estimated from the oxidation charge of the adsorbed products. The adsorbed products obviously interfere with the formation of the oxide film on the Pd surface. The concept of generation and utilization of metallic (Pt, Ru, Au, Pd) nanostructures within the supramolecular organic networks will also be extended to the formation of electrocatalytic interfaces of importance to probing the redox behavior of arsenic(III), arsenic(V), bromate(V) and dioxygen. The rotating ring (platinum)-disk (glassy carbon) electrode methodology is employed for the characterization of different catalysts during the electrode processes mentioned above. For example, with respect to oxygen reduction, the rotating ring disk electrode has been employed for the studies in 0.1 M KHCO3 and 0.1 mol dm-3 KH2PO4/K2HPO4 (pH = 6.8) solutions. The results revealed that the specific activity of palladium nanocenters generated within the coordination architecture of tridentate Schiff-base-ligands by electrodeposition from the supramolecular complex of palladium(II), [Pd(C14H12N2O3)Cl2]2∙MeOH is higher than that of commercial Pd particles.

Having in mind systems resulting in the enhancement of the electrooxidation of arsenic (III), we will consider various noble metals nanoparticles for example Pt, PtRu, Rh, Au, Pd that are capable of inducing the arsenic (III) oxidation in acidic medium. The recorded currents will be compared to those observed previously at the electrodes modified with a thin film of oxocyanorutheneate that is probably the most potent system so far for the electrocatalytic oxidation of As(OH)3. Reduction of arsenic (V) is even more inert but we have observed promising results in acidic medium at platinum and platinum-ruthenium nanoparticles. In other words, both processes, oxidation and reduction of arsenic species, can be successfully investigated at bare or modified (e.g. polyoxometallate functionalized) platinum nanoparticles. Network films of metal nanoparticles also permit preconcentration of arsenic species on their surfaces. The stripping steps would allow determination of low concentrations of arsenic (10-6 mol/dm-3 or lower). All effects are particularly evident from the increases of currents with increases of concentration of arsenic species in the solution.