Electrochemical properties of mixed WC and Pt-black powders

Abstract

The electrochemical characteristics of a mixture of Pt-black and WC powders and its catalytic activity for methanol and formic acid oxidation were investigated in acid solution. XRD and AFM measurements revealed that the WC powder employed for the investigation was a single-phase material consisting of crystallites/spherical particles of average size of about 50 nm, which were agglomerated into much larger particles. Cyclic voltammetry showed that the WC underwent electrochemical oxidation, producing tungstate species. In the case of the mixed Pt + WC powders, the tungstate species were deposited on the Pt as a thin film of hydrous tungsten oxide. Enhanced hydrogen intercalation in the hydrous tungsten oxide was observed and it was proposed to be promoted in mixed powders by the presence of hydrogen adatoms on bare Pt sites. The determination of Pt surface area in the Pt + WC layer by stripping of underpotentially deposited Cu revealed that the entire Pt surface was accessible for underpotential deposition of Cu. Investigation of the electrochemical oxidation of methanol and formic acid on Pt + WC and pure Pt layers did not indicate electrocatalytic promotion due to the presence of WC.

U radu su ispitivane elektrohemijske karakteristike smeše prahova Pt i WC i njena katalitička aktivnost za reakcije oksidacije metanola i mravlje kiseline u kiselom rastvoru. Analiza rezultata difrakcije X-zraka (XRD) i mikroskopije atomskih sila (AFM) pokazuju da je prah WC jednofazni materijal sa prosečnom veličinom kristalita od oko 50 nm, koji su aglomerisani u mnogo veće čestice. Ciklična voltametrija ukazuje na to da WC podleže oksidaciji kojom nastaju volframatne vrste. U slučaju smeše prahova Pt i WC, volframatne vrste najverovatnije se talože na Pt u obliku tankog sloja hidratisanih oksida volframa. Primećeno je povećanje interkalacije vodonika u sloju hidratisanih volframata i pretpostavlja se da prisustvo adatoma vodonika na površini Pt potpomaže proces vodonične interkalacije. Određivanje površine Pt u sloju Pt + WC desorpcijom monosloja Cu taloženog na potpotencijalima ukazuje da je čitava površina Pt dostupna za taloženje atoma Cu. Ispitivanje elektrohemijskih reakcija oksidacije metanola i mravlje kiseline na sloju smeše Pt + WC i sloju čiste Pt ukazuje da prisustvo praha WC ne utiče na elektrokatalitička svojstva Pt.