The origin of electrochemical promotion in heterogeneous catalysis: Photoelectron spectroscopy of solid state electrochemical cells

WILLIAMS, F J; PALERMO, A; TIKHOV, M S; LAMBERT, R M

JOURNAL OF PHYSICAL CHEMISTRY B - (Print)

AMER CHEMICAL SOC

Año: 2000 vol. 104 p. 615 - 621

1520-6106

Electropumping of Na from or to a Na-􏱆′′ alumina solid electrolyte contacted with a thin film porous copper electrode results in fully reversible transport of Na to or from the vacuum-exposed Cu surface. The extent of pumping is controlled by the potential of the catalyst film (VWR), measured with respect to a reference electrode. The time constants of these spill over and reverse spill over processes are short compared with 1 min. Photoelectron microscopy suggests that the spatial distribution of Na is fairly uniform. Over an extended range of catalyst potential (∆VWR ∼ 1 V), both the Na coverage (θNa) and the Cu work function (φ) scale linearly with VWR. This is the same regime over which the rate and nitrogen selectivity of the Cu-catalyzed CO+NO reactions are greatly increased. The maximum Na coverage achieved by electro-pumping is ∼0.06 monolayer, commensurate with the corresponding catalytic response of the system. At sufficiently high positive values of VWR, this quantity becomes uncoupled from ∆φ, θNa, and the catalytic behavior. The possible origin of this uncoupling effect is discussed and a consistent explanation offered for the phenomenon of electrochemical promotion.