Featured paper: Graphene and nickel films, the best catalysts for hydrogen production.


[Paper: Nanocatalysts for hydrogen production from borohydride hydrolysis: graphene-derived thin films with Ag- and Ni-based nanoparticles. Leandro Hostert, Eduardo G. C. Neiva, Aldo J. G. Zarbin, Elisa S. Orth. J. Mater. Chem. A, 2018,6, 22226-22233. DOI 10.1039/C8TA05834B]

Graphene and nickel films, the best catalysts for hydrogen production

Thousands of vehicles powered by hydrogen gas already circulate in some regions of the world releasing only water through the exhaust pipes. As a fuel or source of energy, hydrogen is in fact an extremely clean (does not generate harmful emissions) and efficient option (it can produce more energy than any other fuel). However, pure hydrogen does not exist in nature on Earth. It needs to be produced, and most of the hydrogen-generating methods known to date have both economic and ecological drawbacks.

An alternative to these methods was recently presented by a team of researchers from the graduate program in Chemistry of the Brazilian Federal University of Paraná (UFPR). These scientists have proposed a clean, efficient, simple and inexpensive method to produce hydrogen. The team developed new catalysts (compounds that modify the speed of a chemical reaction without being consumed during the reaction), made of graphene and metal nanoparticles, which made hydrogen production feasible through the hydrolysis of borohydride – a chemical reaction still little used in hydrogen generation, notwithstanding its enormous potential as it is clean and very simple.

Photographs and representative schematics of H2 generation by hydrolysis of borohydride catalyzed with graphene and metallic nanoparticles thin films. The films, about 500 nm thick, cover the two sides of a glass plate, covering 15 cm2, which is immersed in a solution of sodium borohydride and water. The photos depict the bubbles of hydrogen gas generated on the surface of the catalyst.
Photographs and representative schematics of H2 generation by hydrolysis of borohydride catalyzed with graphene and metallic nanoparticles thin films. The films, about 500 nm thick, cover the two sides of a glass plate, covering 15 cm2, which is immersed in a solution of sodium borohydride and water. The photos depict the bubbles of hydrogen gas generated on the surface of the catalyst.

In this reaction, which is performed at room temperature, sodium borohydride (NaBH4) molecules, spontaneously react with water molecules generating hydrogen (H2) molecules. The process takes place in only one step, and is performed with catalyst materials, which accelerate the reaction rate.

“The main contribution of this work is the possibility of H2 generation through thin films of graphene nanocomposites,” says Professor Elisa Souza Orth, corresponding author of an article on the work, recently published in the Journal of Materials Chemistry A (impact factor = 9,931). “Nanocomposites of carbon-based materials and metallic nanoparticles have shown many promising applications and we have shown that for the less exploited borohydride hydrolysis they could also be used efficiently,” she adds.

Among the thin film catalysts produced by the UFPR team, the ones that presented better performance were those of reduced graphene oxide with nickel nanoparticles (rGO/Ni). In fact, this nanocomposite, produced with a relatively inexpensive metal, performed better than most of the catalysts previously reported in the scientific literature, including those prepared with noble metals, which cost much more.

In general, this means that small amounts of rGO/Ni (some tens of mg) generated large volumes of hydrogen (400 ml) in a short time (5 hours).

In addition, the films developed by the Brazilian team presented another important characteristic for a catalyst: they can be easily removed from the reaction vessel, washed and dried without damage, thus allowing their reuse. “In this work, we were able to reuse the same nanocatalyst in 10 consecutive cycles, without losing activity,” says Professor Orth.

The doctoral student Leandro Hostert in the laboratory of the postgraduate program of chemistry of UFPR.
The doctoral student Leandro Hostert in a laboratory of the postgraduate program in chemistry of UFPR.

These results were made possible by combining competencies in the production of carbon nanomaterials from the Materials Chemistry Group, coordinated by Professor Aldo José Gorgatti Zarbin, with expertise in catalysis processes of the Catalysis and Kinetics Group, led by Professor Orth. These two UFPR groups have a history of collaboration in the application of carbon materials; initially, in the study of pesticides and, currently, in the development of multifunctional materials with extraordinary catalytic activity.

In addition to the development of catalysts and their application in hydrogen production, the work published in the Journal of Materials Chemistry A included an analysis of the various ways of measuring the catalytic activity of a material. The authors were able to standardize criteria and compare several results obtained in the laboratory and found in the scientific literature. “We have developed a kinetic study that complements the discussion of these complex reactions and can help guide us to a more concise understanding of catalytic activity,” explains Elisa Orth.

The research was carried out under the doctoral program in progress of Leandro Hostert, guided by Professor Orth, and was funded by Brazilian agencies CNPq, CAPES, Araucária Foundation, INCT Nanocarbono, as well as L’Oréal-UNESCO-ABC through the Award for Women in Science (2015 ) and International Rising Talents (2016) received by Elisa Orth.

Featured paper: Taming the reactivity of nanoalloys.


[Paper: Charge transfer effects on the chemical reactivity of PdxCu1−x nanoalloys. M. V. Castegnaro, A. Gorgeski, B. Balke, M. C. M. Alves and J. Morais. Nanoscale, 2016,8, 641-647. DOI: 10.1039/C5NR06685A]

Taming the reactivity of nanoalloys

When, in 2009, the Electron Spectroscopy Laboratory (LEe-) group of the Federal University of Rio Grande do Sul (UFRGS) decided to start developing in-house metal nanoparticles required for their studies, they came across some issues. Many synthesis methods reported in the literature did not provide the expected results when made in the Brazilian laboratory.

Authors of the paper. From the top left: Marcus Vinicius Castegnaro, Andreia Gorgeski, PhD Benjamin Balke, Prof. Maria do Carmo Martins Alves and Prof. Jonder Morais.

Strongly motivated by curiosity, as usual, says professor Jonder Morais, LEe- researcher, the group members were able, after much dedication, to develop new routes of synthesis that, in addition to being reproducible, are environment-friendly, efficient and cost-effective. “The first articles were published in international journals in 2013, initially with palladium (Pd), platinum (Pt) and silver (Ag) nanoparticles applied to the catalytic decomposition of nitric oxide. Subsequently, we published some works focused in “in situ” studies aimed at determining the mechanisms of formation and growth of monometallic nanoparticles. We have recently started reporting the results obtained with more complex systems, such as palladium and copper (Pd-Cu) nanoalloys,” states Professor Morais.

The latter group includes the results recently reported in an article published in the journal Nanoscale, whose main authors are Professor Jonder Morais and Marcus Vinicius Castegnaro, a physics doctoral student at UFRGS, advised by Morais. The research covered the entire process from the production of nanomaterials to the survey of their applications. “It was important to have dedicated students, willing to face the challenge of preparing accurately their own samples, and correlating the electronic and structural properties to understand the final properties in terms of chemical reactivity,” says Morais.

In the article published in Nanoscale, nanoparticles composed of palladium and copper alloys were produced by applying a simple method developed by the LEe- team. This process is carried out under mild conditions to the environment and health (aqueous, ambient temperature and pressure, and use of cheap and innocuous substances, such as ascorbic acid and sodium citrate). Several samples were synthesized by this route, containing three different amounts of palladium and copper atoms.

The synthesized nanoparticles have undergone a series of analyses conducted at UFRGS, in Porto Alegre (Rio Grande do Sul State), they traveled to Campinas (São Paulo State) for another series of analyses on equipment of the National Center for Research in Energy and Materials (CNPEM) and crossed the ocean to Johannes Gutenberg University, in Germany, for some additional measures. From characterization, the authors concluded that the nanoparticles were approximately 4 nm in size and were highly crystalline, among other characteristics. In addition, through experiments conducted by the XANES in situ technique, the team of scientists exposed the nanoparticles to carbon monoxide (CO) at 450 ° C and surveyed the reactivity of the nanoalloys, i.e., their ability to react chemically.

After studying the results of the characterization, the authors of the article were able to conclude that the alloy composition affects the ability of nanoalloys to reduce (gain electrons) and to oxidize (lose electrons). In fact, the greater the amount of palladium, the easier the reduction, and the harder the oxidation.

Representative scheme of the correlation between the partial charge transfer between the Pd and Cu atoms (observed by XPS), and the reactivity after exposure to CO (surveyed by XANES in situ) for Pdx¬Cu1-x nanoalloys. It was observed that the higher is the amount of Pd present in nanoalloys, the greater is the reactivity of the sample after CO reduction, and the greater is the oxidation resistance of the atoms comprising it.

“The published results, obtained by the association of several experimental techniques are relevant to an understanding of the origin of high catalytic reactivity of palladium and copper (Pd-Cu) nanoalloys, as well as to elucidating similar behavior of other bimetallic systems”, highlights Jonder Morais. “Mostly, these results can be used in the “design “of new nanomaterials more efficient for various applications, such as in the petrochemical industry, in fuel cells or in the control of greenhouse gas emissions,” he concludes.

 

Inscrições abertas para Mestrado Profissional em Materiais e Catálise da Univap (São José dos Campos, SP).


O Programa de Pós-graduação em Materiais e Catálise da Universidade do Vale do Paraíba (Univap) está com inscrições abertas para o segundo semestre de 2014. O mestrado possui três linhas de pesquisa principais: (1) Desenvolvimento de materiais para suporte catalítico; (2) Processamento e caracterização de materiais metálicos; e (3) Processamento e caracterização de materiais compósitos, cerâmicos e poliméricos.

As inscrições podem ser feitas, pela internet, até 04/07. A prova de conhecimentos e entrevistas serão realizadas no dia 30/07, das 13:30h às 18:00h, no Instituto de Pesquisa e Desenvolvimento do campus Urbanova em São José dos Campos (SP). Podem participar do processo seletivo egressos de Engenharia, Química ou Física incluindo bacharéis e tecnólogos de áreas afins.

Mais informações em http://www.univap.br/ipd/proc_materiais_catalise/mestrado_proc_materiais_catalise/proc_seletivo.php ou pelo e-mail ivone@univap.br.

Chamada para bolsas de pós-doutorado da Dahlem Research School (Alemanha).


A Dahlem Research School, centro da Freie Universität Berlin para programas de excelência de doutorado e apoio para pós-doutorandos internacionais, estabeleceu um programa de bolsas de pesquisa, disponibilizando financiamento para que pesquisadores de pós-doutorado de destaque em todas as disciplinas possam realizar o seus próprios projetos de pesquisa na Freie Universität Berlin.

O programa é co-financiado pela Iniciativa de Excelência Alemã e pelo Programa Marie Curie da Comissão Europeia e tem como objetivo dar apoio a pós-doutorandos altamente qualificados com experiência de pesquisa internacional, além de integrá-los às redes de pesquisa da universidade na fase inicial de sua carreira.

Atualmente, são oferecidas 18 bolsas de pós-doutorado nas áreas de medicina, ciências naturais e exatas, ciências sociais e humanas e estudos regionais com uma duração de 18 meses.  Catálise é um dos temas de interesse.

A data-limite para a inscrição é o dia 15 de setembro de 2013.

Mais informações:

http://www.fu-berlin.de/pt/sites/brazil/cofund_point_regain2014.html.