MnO<sub>2</sub>-Ir Nanowires: Combining Ultrasmall Nanoparticle Sizes, O-Vacancies, and Low Noble-Metal Loading with Improved Activities towards the Oxygen Reduction Reaction
Scarllett L. S. de Lima,
Fellipe S. Pereira,
Roberto B. de Lima,
Isabel C. de Freitas,
Julio Spadotto,
Brian J. Connolly,
Jade Barreto,
Fernando Stavale,
Hector A. Vitorino,
Humberto V. Fajardo,
Auro A. Tanaka,
Marco A. S. Garcia,
Anderson G. M. da Silva
Affiliations
Scarllett L. S. de Lima
Departamento de Engenharia Química e de Materiais-DEQM, Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rua Marquês de São Vicente, 225 Gávea, Rio de Janeiro 22453-900, RJ, Brazil
Fellipe S. Pereira
Departamento de Química, Centro de Ciências Exatas e Tecnologias, Universidade Federal do Maranhão (UFMA), Av. dos Portugueses, 1966 Vila Bacanga, São Luís 65080-805, MA, Brazil
Roberto B. de Lima
Departamento de Química, Centro de Ciências Exatas e Tecnologias, Universidade Federal do Maranhão (UFMA), Av. dos Portugueses, 1966 Vila Bacanga, São Luís 65080-805, MA, Brazil
Isabel C. de Freitas
Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, São Paulo 05508-000, SP, Brazil
Julio Spadotto
Department of Materials, Henry Royce Institute, University of Manchester, Manchester M13 9PL, UK
Brian J. Connolly
Department of Materials, Henry Royce Institute, University of Manchester, Manchester M13 9PL, UK
Jade Barreto
Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180, RJ, Brazil
Fernando Stavale
Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180, RJ, Brazil
Hector A. Vitorino
South American Center for Education and Research in Public Health, Universidad Norbert Wiener, Lima 15108, Peru
Humberto V. Fajardo
Departamento de Química, Instituto de Ciências Exatas e Biológicas, Universidade Federal de Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto 35400-000, MG, Brazil
Auro A. Tanaka
Departamento de Química, Centro de Ciências Exatas e Tecnologias, Universidade Federal do Maranhão (UFMA), Av. dos Portugueses, 1966 Vila Bacanga, São Luís 65080-805, MA, Brazil
Marco A. S. Garcia
Departamento de Química, Centro de Ciências Exatas e Tecnologias, Universidade Federal do Maranhão (UFMA), Av. dos Portugueses, 1966 Vila Bacanga, São Luís 65080-805, MA, Brazil
Anderson G. M. da Silva
Departamento de Engenharia Química e de Materiais-DEQM, Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rua Marquês de São Vicente, 225 Gávea, Rio de Janeiro 22453-900, RJ, Brazil
Although clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can be considered a promising strategy, this approach remains challenging by the dependence on high loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or alloying) or replace them completely in these systems. The present investigation shows that high catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs) deposited onto MnO2 nanowires surface under low Ir loadings (1.2 wt.%). Interestingly, we observed that the MnO2-Ir nanohybrid presented high catalytic activity for the ORR close to commercial Pt/C (20.0 wt.% of Pt), indicating that it could obtain efficient performance using a simple synthetic procedure. The MnO2-Ir electrocatalyst also showed improved stability relative to commercial Pt/C, in which only a slight activity loss was observed after 50 reaction cycles. Considering our findings, the superior performance delivered by the MnO2-Ir nanohybrid may be related to (i) the significant concentration of reduced Mn3+ species, leading to increased concentration of oxygen vacancies at its surface; (ii) the presence of strong metal-support interactions (SMSI), in which the electronic effect between MnOx and Ir may enhance the ORR process; and (iii) the unique structure comprised by Ir ultrasmall sizes at the nanowire surface that enable the exposure of high energy surface/facets, high surface-to-volume ratios, and their uniform dispersion.
