Nitrate reduction on platinum (111) surfaces modified with Bi: single crystals and nanoparticles

Nitrate reduction on well-oriented platinum surfaces modified with Bi adatoms has been studied. The quantification of the electrocatalytic enhancement of the reaction rate due to the presence of Bi at different coverages was made on Pt(111) and the vicinal surfaces Pt(554) and Pt(332). These contain 9 and 5 atoms-width (111) terraces, respectively, separated by (110) monoatomic steps. The study was then extended to preferentially {111}Pt oriented nanoparticles. In all cases, Bi catalyzes nitrate reduction at high potentials, but the catalytic current suddenly drops when Bi is reduced. The analysis of the variation of catalytic activity with Bi coverage reveals the participation of a third body effect, meaning that Bi impedes the NO formation on the surface that acts as a poison for the nitrate reduction. The poisoning effect was also quantified by measuring the stripping of adsorbed NO spontaneously formed by contacting with nitrate solutions electrodes with different Bi coverage. The results of both single crystals and preferentially oriented nanoparticles agree with the participation of a third body effect. The comparison of Pt nanoparticles with the stepped surfaces, Pt(554) and Pt(332), suggests that the main differences are related to the size of the terraces and not to the existence of defects/steps that do not seem to play any significant contribution to the catalysis.