Admixing palladium nanoparticles with tungsten oxide nanorods toward more efficient electrocatalytic oxidation of formic acid

•Hybrid electrocatalysis was obtained by combining hexagonal tungsten oxide nanorods and Pd nanoparticles.•HxWO3, WO3−y and Pd nanoparticles are expected to exist at electrocatalytic interface.•Enhancement of oxidation of formic acid at potential as low as 0.04 V vs. RHE was observed.

By depositing nanorods of tungsten oxide over catalytic palladium nanoparticles (dispersed onto glassy carbon substrate), enhancement of the overall electrocatalytic activity toward oxidation of formic acid in acid medium was observed. The effect was particularly evident from the increase of chronoamperometric currents at a fairly low potential of 0.04 V vs. RHE. Under such conditions, tungsten oxide nanorods seem to be partially and reversibly reduced not only to nonstoichiometric hydrogen tungsten(VI,V) oxide bronzes (HxWO3, 0 < x < 1) but also substoichiometric lower tungsten (VI,IV) oxides (WO3−y, 0 < y < 1). Mutual interactions between tungsten oxides with Pd nanoparticles affect electrochemical characteristics of both components. The metal–oxide interactions, as well as high population of hydroxyl groups at the electrocatalytic interface (favoring oxidative removal of passivating CO adsorbates), are most likely responsible for the overall enhancement effect. In comparison to conventional electrodeposited microporous tungsten oxides, WO3 nanorods, despite their small dimensions, are more robust and less hydrated. Electrochemical diagnostic experiments were supported with microscopic measurements aiming at monitoring morphology of catalytic surfaces with use of transmission (TEM) and scanning (SEM) electron microscopies. The palladium nanoparticles were of the sizes 10–20 nm, and the tungsten oxide nanorods had diameters of 50–70 nm while being approximately 5 μm long.

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