A Study about Bimetallic and Coreshell Structured Nanomaterials

A Study about Bimetallic and Coreshell Structured Nanomaterials as Catalysts on ORR Reaction Bárbara Quaiato Gomes Research Conducted at University of ABC, Santo André, São Paulo, Brazil. Professor: Mauro Coelho dos Santos Subject: Nanomaterials Science Professor: Kovács Imre Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

Aim of this project • This project aims to discovery an ideal nanomaterial which can be applied as catalyst on the Oxygen Reduction Reaction, increasing the amount of Hydrogen Peroxide produced and applying this Hydrogen on the contaminated efluents recovery. • The material has to be efficient, cheap and easy to produce. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

Oxygen Reduction Reaction • The 2 electrons way is used for hydrogen peroxide production and it is represented by the equations 3 and 4 above. The equations 1 and 2 represent the 4 electrons way, which is applied, for example, in some fuel cells. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

The Chosen Materials and Designs • Studies with samples of Sn-Ni by the technique of physical vapor deposition showed that the main phase formed in the prepared materials was Ni 3 Sn 4, with many changes to its network parameters, generating a large concentration of defects, which could trigger a fast diffusion of oxygen. • Also, it was reported that the reduction of particle size results in an increase in the adsorption of oxygen species on the catalyst surface, since these species can provide increased hydrophilicity, facilitating the formation of H 2 O 2. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

• The electrocatalysts with core shell structure type are a new class of nanostructured materials that have been developed in recent years and are also suitable for this type of study, since it modifies the interaction between the metals present. • Great alternative to control the reactivity and catalytic activity of the element that makes up the shell, and the interaction between the two metals can improve catalytic activity of the final material. • Costs can be reduced when working with noble metals, as non-noble metal can be used to form the core, decreasing the amount of noble metal used. Scheme of a core-shell structure Ru@Pt Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

• Based on previous studies, gold was the first chosen material for this structure in this project, but the cost of this material is high. • Studies employing catalysts WO 3/Ti. O 2 compounds and thin films of WO 3 for catalysis of RRO and subsequent application of these catalysts in the degradation of organic pollutants were positive, showing improvements due to the addition of the tungsten oxide. • By this results, tungsten was applied as shell, expecting to increase the characteristics of the material and decrease the costs. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

Methods • The binary materials were produced using the polymers precursor method, reaching the proportions of 50% Ni and 50% Sn; 25% Ni and 75% Sn; 75% Ni and 25% Sn; 15% Ni and 85% Sn; 85% Ni and 15% Sn, respecting the proportion of 1% metal on carbon. For all proportions carbon XC 72 R was added as the base material. • The core-shell materials were prepared by an adapted method, and consisted of steps adding WCl 4, water, Au, ascorbic acid and carbon XC 72 R. The proportions were 1% and 2% of metals on carbon. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

Results X-ray diffractograms to Sn. Ni electrocatalysts supported on Vulcan XC 72 R carbon. X-ray diffractograms to W@Au electrocatalysts supported on Vulcan XC 72 R carbon. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

Average crystallite size of the electrocatalysts Electrocatalyst Phase Average Size (nm) Sn. Ni/C 6: 1 Ni. O 1. 8 Sn. Ni/C 3: 1 Ni 3 Sn 4 1. 7 Sn. Ni/C 1: 3 Sn. Ni/C 1: 6 Ni 3 Sn 4 1. 8 2. 6 1% W@Au/C Au 280. 0 2% W@Au/C Au 44. 3 1% W@Au/C 2% W@Au/C Au Nemzeti Tehetség 2 O 3 Program Tehetségútlevél Program „NTP-TÚP-13 -002” Au 2 O 3 82. 6 31. 8

Polarization curve of ORR electrocatalysts with Sn. Ni/C in Na. OH 1 mol / L. (a) ring current Ea = +0. 2 V, (b) current disk at 1600 rpm. Scan rate 5 m. V / s. Polarization curve of ORR electrocatalysts with W@Au/C in Na. OH 1 mol / L. (a) ring current Ea = +0. 2 V, (b) current disk at 1600 rpm. Scan rate 5 m. V / s. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

Number of Electrons Transferred and Percentage of Generated Peroxide Electrocatalyst nt p(H 2 O 2) (%) Sn. Ni/C 1: 1 2. 3 86 Sn. Ni/C 3: 1 2. 7 67 Sn. Ni/C 1: 3 2. 8 62 Sn. Ni/C 6: 1 3. 5 23 Sn. Ni/C 1: 6 3. 9 4 W@Au/C 1% 2. 2 90 W@Au/C 2% 2. 5 73 Vulcan XC-72 R Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002” 2. 7 63

Conclusions • Among the synthesized and studied materials, the coreshell W @ Au / C 1% exceeded all proportions and structures, generating the best results for the ORR via 2 electrons, thus suggesting that it may be an excellent material to be applied in gas diffusion electrodes to further degradation of persistent organic pollutants. • It has a lower production cost when compared to other materials, due to lower proportions of metal on carbon used, and given the enhanced ring current obtained. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”

References • J. C. M. Silva, R. F. B. De Souza, L. S. Parreira, E. Teixeira Neto, M. L. Calegaro, M. C. Santos. Applied Catalysis B: Environmental, 99 (2010) 265– 271 • M. Giomo, A. Buso, P. Fier, G. Sandonà, B. Boye, G. Farnia. Electrochimica Acta, 54 (2008) 808– 815. • Y. Ando, T. Tanakab. International Journal of Hydrogen Energy, 29 (2004) 1349– 1354. • J. W Shabaker, G. W Huber, J. A Dumesic. Journal of Catalysis, 222(2004) 180– 191. • S. Kim, D. C. Johnson. Journal of Alloys and Compounds, 392(2005) 105 -111. Nemzeti Tehetség Program Tehetségútlevél Program „NTP-TÚP-13 -002”