Abstract
The combined promotional effect of electrochemically-supplied O2− and chemically-supplied Na+ promoters, was studied for the case of CO oxidation on Pt/YSZ. Four different sodium coverages (0.16, 1.6, 8 and 40%) were loaded onto the catalyst surface and the catalytic behaviour was compared with a nominally ‘clean’ catalyst under a wide range of reactants’ ratios under open-circuit and polarised conditions. Sodium generally increased oxygen adsorption by lowering the work function of the catalyst. However, sodium promoted the catalytic rate only at coverages up to 1.6% and worked synergistically with O2− promoting species to an increased overall promotion of the catalytic rate. At higher sodium coverages, i.e. θNa ≥ 8%, the catalytic behaviour was strongly affected by the interactions between the sodium species, the catalyst, the reactants and oxygen ions promoting species. The postulated formation of stable sodium oxide species on the catalyst pores reduced the active catalytic area which resulted in poisoning the catalytic rate and suppressing EPOC effect, respectively. It is suggested that these stable sodium oxide species which also induced a permanent EPOC effect by oxygen storage, were formed by the migrated oxygen ions.
Highlights
Electrochemical promotion of catalysis (EPOC) is a phenomenon where the application of small currents or potentials causes significant activity and selectivity modification of catalysts supported on ionic or mixed ionic-electronic conductors [1]
Where ΔΦ is the variation of catalyst work function and ΔUWR is the change of the potential between the catalyst and the reference electrode [3]
The electrocatalytic system used in this work was a threeelectrode Pt/YSZ/Au pellet, consisting of a platinum catalyst film acting as the working electrode, an yttria-stabilised zirconia (YSZ) pellet and gold counter and reference electrodes
Summary
Electrochemical promotion of catalysis (EPOC) is a phenomenon where the application of small currents or potentials causes significant activity and selectivity modification of catalysts supported on ionic or mixed ionic-electronic conductors [1]. Where ΔΦ is the variation of catalyst work function and ΔUWR is the change of the potential between the catalyst and the reference electrode [3]. In EPOC, promoters are supplied to the catalyst electrochemically, in situ and reversibly. The latter is the main difference between electrochemical and conventional chemical promotion of catalysts where only ex situ addition of promoters can take place, during the catalyst preparation. Despite of this operational difference, the promotional function in both cases is identical and the phenomena are relied on the same promotional rules [5].
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