Understanding the Influence of the Biomass-Derived Alcohols on the Activity and Stability of Pt Nanoparticles Supported on Graphene Nanoribbons

We produced Pt/GNRs by a one-step synthesis procedure and evaluated their electroactivity and stability towards glycerol electrooxidation reaction (GEOR) for the first time. We compared the electrocatalytic performance of GEOR with methanol and ethanol electrooxidation on Pt/GNRs at identical experimental conditions. The activities and stabilities for the electrooxidation of these biomass-derived alcohols on Pt/GNRs were compared to commercial Pt/C. The synthesis of the Pt/GNRs was confirmed by transmission electron microscopy, x-ray diffractometry, ultraviolet spectrophotometry, and Raman spectroscopy. We found that the activities of Pt/GNRs for these reactions are comparable to Pt/C, with improvement in terms of current density for methanol electrooxidation. Comparing potentiostatic measurements, we found that glycerol produces lower pseudo-stationary current densities than ethanol and methanol on both catalysts, with greatest values found for methanol electrooxidation on Pt/C. Otherwise, the GNRs remarkably enhance the stability of the catalyst for all the reactions, by increasing the stability of the current density during successive potential cycles, and by preventing the loss of electrochemically active surface area by avoiding carbon corrosion and Pt detachment. Moreover, we showed that the stability of the NPs depends on the biomass-derived alcohol used. The solution containing methanol reveals itself the most aggressive electrochemical environment to the catalyst, impacting in the decrease of surface area, while glycerol is less aggressive. Hence, the different products formed at the interface electrode/solution might lead to a different electrochemical environment, which plays an important role on the stability of the catalysts.The authors acknowledge financial assistance from CNPq (grant no. 454516/2014-2), FUNDECT (grant no. 026/2015), FAPESP (grant no. 2016/01365-0), CAPES, FINEP, and FAPESP.Peer reviewe

The oxygen reduction reaction on palladium with low metal loadings:The effects of chlorides on the stability and activity towards hydrogen peroxide

Hydrogen peroxide is considered one of the most important commodity chemicals worldwide but its main production method, the anthraquinone process, poses serious logistical, environmental and safety challenges. Electrocatalytic synthesis through the reduction of molecular oxygen is a promising H2O2 production route. However, the reduction of molecular oxygen is kinetically hindered and stable electrocatalysts with a high activity and selectivity towards the 2-electron transfer reaction are needed. In this work, we evaluated the influence of chloride on catalysts with low palladium loadings on the ORR selectivity towards H2O2. We report the factors and dynamics that influence H2O2 production and highlight synthesis strategies to obtain close to 100% selectivity. By probing the electrode surface after various degradation cycles, we evaluate the role of adsorbing species and the catalysts oxidation states on the hydrogen peroxide selectivity. We systematically modified the catalyst synthesis using different Pd-precursors that were reduced and supported on high surface area graphene nanoribbons. Identical location transmission electron microscopy was used to probe catalyst dynamics during reaction and the activities and selectivities were measured by a rotating ring disk electrode. We probe the potential boundary conditions that lead to catalyst degradation during accelerated stress tests and potentiostatic polarisation and demonstrate how the catalytically active surface can be revived after degradation. The obtained insights can be used as guideline for the development of active, selective and stable catalysts with low noble metal loadings.</p

The oxygen reduction reaction on palladium with low metal loadings:The effects of chlorides on the stability and activity towards hydrogen peroxide

Hydrogen peroxide is considered one of the most important commodity chemicals worldwide but its main production method, the anthraquinone process, poses serious logistical, environmental and safety challenges. Electrocatalytic synthesis through the reduction of molecular oxygen is a promising H2O2 production route. However, the reduction of molecular oxygen is kinetically hindered and stable electrocatalysts with a high activity and selectivity towards the 2-electron transfer reaction are needed. In this work, we evaluated the influence of chloride on catalysts with low palladium loadings on the ORR selectivity towards H2O2. We report the factors and dynamics that influence H2O2 production and highlight synthesis strategies to obtain close to 100 selectivity. By probing the electrode surface after various degradation cycles, we evaluate the role of adsorbing species and the catalysts oxidation states on the hydrogen peroxide selectivity. We systematically modified the catalyst synthesis using different Pd-precursors that were reduced and supported on high surface area graphene nanoribbons. Identical location transmission electron microscopy was used to probe catalyst dynamics during reaction and the activities and selectivities were measured by a rotating ring disk electrode. We probe the potential boundary conditions that lead to catalyst degradation during accelerated stress tests and potentiostatic polarisation and demonstrate how the catalytically active surface can be revived after degradation. The obtained insights can be used as guideline for the development of active, selective and stable catalysts with low noble metal loadings. © 2020 Elsevier Inc

New microsatellite markers developed from an enriched microsatellite common bean library Novos marcadores microssatélites desenvolvidos a partir de uma biblioteca genômica enriquecida em feijão-comum

The objective of this work was to develop new microsatellite markers in common bean. Ninety nine new microsatelitte loci were developed from a microsatellite enriched library for (CT)8 and (GT)8 motifs, from CAL-143 line. The majority of microsatellite sequences (51%) was related to cellular metabolism. The remaining sequences were associated to transcription functions. Only 17.2% of the sequences presented some level of similarity with other plant species genes.<br>O objetivo deste trabalho foi desenvolver novos marcadores microssatélites para feijão-comum. Noventa e nove novos locos de microssatélites foram desenvolvidos a partir de uma biblioteca enriquecida com motivos (CT)8 e (GT)8, proveniente da linhagem CAL-143. A maioria dos microssatélites (51%) esteve relacionada ao metabolismo celular. As demais seqüências estiveram associadas a funções de transcrição. Apenas 17,2% das seqüências apresentaram alguma semelhança com genes de outras espécies