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Ni/Carbon hybrids were prepared by hydrothermal carbonization at 200 ºC for 48 h using glucose as carbon source, NiCl2.6H2O as oxidizing agent and catalyst of the carbonization process. The materials were prepared in the absence and in the presence of cetyltrimetylammoniun bromide (CTAB) using an CTAB:glucose molar ratios of 1:10. The obtained carbonaceous materials were further treated at 900 ºC under Argon and PtRu nanoparticles were deposited on these materials using an alcohol reduction process. The resulting PtRu/C electrocatalysts were characterized by EDX, thermogravimetrics analysis, X-ray diffraction and transmission electron microscopy and they were tested for methanol electro-oxidation using chronoamperometry. The PtRu/C electrocatalyst prepared using as support Ni/Carbon with CTAB showed superior performance for methanol electro-oxidation.

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A factorial design study was performed to evaluate the influence of the BH4-:PtRu molar ratio (5 and 15) and the solvent (water or isopropyl alcohol) in the preparation of PtRu/C electrocatalysts for Direct Methanol Fuel Cell (DMFC) anodes. The obtained materials were characterized by Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and transmission electron microscopy (TEM). For both solvents increasing the BH4-:PtRu molar ratio from 5 to 15 leads to a decrease of the mean nanoparticle sizes and, using water as solvent, it was observed better distributions of the nanoparticles on the carbon support than using isopropyl alcohol. The DMFC maximum power density was obtained using a electrocatalyst prepared with a BH4-:PtRu molar ratio of 15 and water as solvent. The analysis of the effect of interaction of the two parameters showed that the variations of the maximum power density was more dependent of the BH4-:PtRu molar ratio than of the solvent used.

RESUMO Neste trabalho, híbridos Ni/Carbono foram preparados em duas etapas (carbonização hidrotérmica e tratamento térmico a 900 °C sob argônio) a partir de diferentes fontes de carbono: glicose, amido e celulose. Eletrocatalisadores PtRu/C foram preparados pelo método da redução por álcool utilizando os híbridos como suportes. Os materiais foram caracterizados por espectroscopia por energia dispersiva de raios-X (EDX), análise termogravimétrica (TGA), espectroscopia no infravermelho com transformada de Fourier (FTIR), isotermas de B.E.T., difração de raios-X (DRX), microscopia eletrônica de transmissão (TEM) e voltametria cíclica em meio ácido. A eletro-oxidação do metanol foi estudada por cronoamperometria. O eletrocatalisador PtRu/C preparado utilizando o híbrido sintetizado a partir da celulose apresentou uma eletroatividade levemente superior aos demais materiais obtidos.

Híbridos PtRu/Carbono com diferentes cargas metálicas (5, 10 e 20% em massa) foram preparados por carbonização hidrotérmica utilizando celulose como fonte de carbono e agente redutor e H 2PtCl6.6H2O e RuCl3.xH2O como fontes de metais e catalisadores do processo de carbonização. Os materiais comosintetizados foram tratados sob atmosfera de Argônio a 900 °C e caracterizados por espectroscopia por energia dispersiva de raios-X, análise termogravimétrica, difração de raios-X, microscopia eletrônica de transmissão e voltametria cíclica em meio ácido. A eletro-oxidação do methanol foi estudada por cronoamperometria. O material preparado utilizando uma carga metálica de 5% em massa apresentou a melhor eletroatividade para a eletro-oxidação do metanol comparado aos outros materiais provavelmente devido ao menor tamanho de partículas e conteúdo de óxidos superficiais.

Background: PtRu/C electrocatalysts present good results in methanol electo-oxidation. The activity of these electrocatalysts is strongly dependent on the synthesis method. Additionally, the use of mesoporous carbons or nanostructured carbons increases the performance of electrocatalysts applied in alcohol electro-oxidation. The hydrothermal carbonization method is an alternative to obtain different nanoarchitectures without involving harsh conditions. Aims: Thus, this work aimed to evaluate the influence of synthesis time on the properties of PtRu/Carbon hybrids prepared by the hydrothermal carbonization method. Methods: PtRu/Carbon hybrids were prepared by hydrothermal carbonization at different times of synthesis (6 h and 12 h). It used cellulose as a carbon source and reducing agent and H2PtCl6.6H2O and RuCl3.xH2O as metal sources and catalysts of the carbonization process. The materials were treated at 900 °C and characterized by energy-dispersive X-ray spectroscopy, thermogravimetric analysis, B.E.T isotherms, X-ray diffraction, transmission electron microscope and cyclic voltammetry. The electro-oxidation of methanol was studied by chronoamperometry. Results: The increase in synthesis time from 6 to 12 hours, apparently, resulted in an increase in mean particle size, reduction of mesoporous volume and increase in superficial area and total pore volume. The chronoamperometry of methanol electro-oxidation on these PtRu/Carbon hybrids indicated a higher electroactivity to the material prepared in 6 hours. Discussion: Probably, the higher electroactivity of material prepared in 6 h is associated with smaller particle size, mesoporous structure and surface oxides content. Conclusions: Therefore, it is possible to affirm that the synthesis time is an important parameter that affects the physical-chemical properties of metal/carbon hybrids obtained by the hydrothermal carbonization method.