Reduction of silver cations followed by nanoparticle (Ag-NPs) synthesis is a model process to understand the reduction mechanism induced by a discharge over an aqueous surface, termed electrochemical plasma. This work aims at studying the silver reduction reaction steered by electrochemical plasma in the presence of other chemically active plasma-related interfaces, namely the plasma-gas and the liquid-gas interfaces. As no other plasma-induced species are able to reduce silver cations, the reduction of silver cations is employed as strategy to selectively detect the presence of hydrated electrons (e-h). The results demonstrate that the global rise of pH (increase in the content of OH-), observed for discharge in the helium gas phase, occurs in connection with the silver reduction, which is interpreted as a vivid experimental evidence of the second-order recombination reaction of the e h − 2 e aq − + 2 H 2 O → H 2 + 2 OH −. On the other hand, the global decrease of pH (increase in the content of H+) observed for discharge in mixed oxygen and nitrogen gas phase, is an event primarily driven by the Birkeland-Eyde process, and it is concomitant but spatially distinct from the electron injection. The acidification interferes in the NP formation, as NPs promptly dissolve in presence of HNO3. Only in complete suppression of the acidification, an experimental evidence of the reaction pathways for hydrated electron could be captured: e-h is competitively consumed through a scavenger-like reaction (reduction of silver cations in this work) and through the second-order recombination reactions of the e-h. The kinetic model proposed in this work further corroborates this interpretation.

Neste trabalho, a eletrooxidação oscilatória de ácido fórmico (FA) é investigada sobre paládio policristalino e comparada a resultados obtidos sobre platina policristalina; as principais diferenças entre ambas as superfícies são atribuídas a diferentes cinéticas da sub-rede química tanto quanto a rotas preferenciais admitidas sobre a superfície de paládio. Com o intuito de presumir a taxa cinética de acumulação de veneno sobre paládio, eletrooxidação de FA foi conduzida na presença e ausência de hidrogênio dissolvido na rede cristalina do paládio. As rotas preferenciais foram presumidas a partir do padrão temporal (série temporal). Notoriamente, oscilações de potencial durante a eletrooxidação de FA possuem mínimo de potencial em 0,2 V, o que é associado a uma rápida taxa de desidrogenação direta; além disso, períodos de indução (ca. 60 min) e oscilação (20 min) estão entre os mais compridos já observados em eletroquímica, pois o hidrogênio incluso na rede cristalina do paládio reduz a taxa de acumulação de CO sobre a superfície.

Herein, oscillatory formic acid (FA) electrooxidation on polycrystalline palladium is investigated and compared with the one on polycrystalline platinum; major differences between both are attributed to differences on the kinetics of sub-set chemical network as well as to preferential routes admitted on palladium surface. To presume the kinetic rate of poison accumulation on palladium, FA oxidation was accomplished in presence of occluded hydrogen and hydrogen-free electrodes. The preferential routes were presumed from the temporal pattern. Markedly, oscillations during FA electrooxidation have minimum potential at 0.2 V, which is linked to the fast rate of direct dehydrogenation; moreover, it has one of the largest induction period (ca. 60 min) and oscillatory period (20 min) observed in electrochemistry, since subsurface hydrogen slows down the rate of CO accumulation on the surface.