Europium phosphomolybdate and osmium metallopolymer multi-functional LbL films: Redox and electrocatalytic properties

• Layer-by-layer hybrid films {Os-poly/Eu(PMo11)2}n were sucessfully prepared.
• UV–Vis was used to monitor film build-up and showed regular stepwise film growth.
• XPS confirmed successful {Os-poly/Eu(PMo11)2}n film fabrication.
• Films showed Mo- and Os-based reduction processes attributed to POM and Os-poly.
• Films showed excellent electrocatalytic activity towards NO2- and IO3- reduction.

Hybrid multilayer films composed by osmium metallopolymer [Os(bpy)2(PVP)10Cl]Cl (Os-poly) and europium phosphomolybdate, K11[EuIII(PMo11O39)2]K11[EuIII(PMo11O39)2] (Eu(PMo11)2), were prepared using the electrostatic layer-by-layer (LbL) self-assembly method. The film build-up, monitored by electronic spectroscopy, showed a regular stepwise growth indicating a strong interaction between layers. The XPS measurements corroborated the successful fabrication of the hybrid films with the Os-poly/Eu(PMo11)2 composition. SEM images revealed a completely covered surface with a highly roughened texture. Electrochemical characterisation of films by cyclic voltammetry revealed three Mo-based reduction processes (MoVI → MoV) in the potential range between −0.4 and 0.1 V and one Os reduction process (OsIII → OsII) at ≈0.270 V. The cyclic voltammograms of two electroactive probes, [Fe(CN)6]3-/4-[Fe(CN)6]3-/4- and [Ru(NH3)6]3+/2+[Ru(NH3)6]3+/2+ on {Os-poly/Eu(PMo11)2}n modified electrodes revealed redox mediation between film and the probes. Furthermore, the {Os-poly/Eu(PMo11)2}n multilayer films also showed excellent Mo-based electrocatalytic activity towards reduction of nitrite and iodate, confirming the multi-functional properties of the hybrid europium phosphomolybdate – osmium metallopolymer LbL films.

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