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Co nanoparticle–graphene catalyst could replace Pt
News and Opinions The system could be made into an artificial photosynthesis system, says Artero, by adding photosensitizers. Ultimately, the advance could lead to the development of cheap systems based on earth-abundant elements to produce H2 from water, either electro- or photochemically, he suggests.
3 E-mail address: [email protected] 2211-2855/$ - see front matter http://dx.doi.org/10.1016/j.nanoen.2012.11.009
Co nanoparticle–graphene catalyst could replace Pt Cordelia Sealy A new generation of polymer membrane electrolyte fuel cells and metal–air batteries rely on Pt as a catalyst, which is both scarce and expensive. The search is on for a low-cost, abundant alternative and researchers from Brown University think they may have found it in the form of Co/CoO nanoparticles on graphene [S. Guo, et al., Angew. Chem. Int. Ed. (2012), http://dx.doi.org/10.1002/anie.201206152]. The new catalyst consists of Co/CoO nanoparticles, synthesized and self-assembled through thermal decomposition of precursors onto a graphene (G) surface (Fig. 1). The material performs as a catalyst for the O2 reduction reaction (ORR), which takes place on the cathode side of a fuel cell or battery. In the reaction, O2 acts as an electron sink, drawing away electrons from the H2 at the anode and creating the potential difference that drives the current. The researchers say that the G–Co /CoO material is the first non-precious metal catalyst that performs anywhere close to Pt. ‘‘The G–Co /CoO has comparable electrocatalytic activity, but higher stability than the commercial C/Pt catalyst for ORR in 0.5 M KOH solution,’’ says lead researcher Shouheng Sun. ‘‘To the best of our knowledge, this G–Co / CoO catalyst has the best kinetic process for ORR among all the reported non-noble metal catalysts.’’ Although the G–Co /CoO takes longer to get the ORR started, once it does the reaction goes at a faster pace than if catalysed by Pt. The new catalyst also appears to be remarkably stable, degrading somewhat less than Pt over time. After 17 h of testing, report the researchers, the G–Co /CoO was performing at 70% of its original capacity compared with 60% for a Pt catalyst under similar conditions. The researchers report that size and structure of the nanoparticles is essential to optimizing the catalyst. The best performing material comprises nanoparticles with an 8 nm Co core and a 1 nm CoO shell. The Co nanoparticles are first selfassembled onto the G surface and then allowed to form a layer of natural CoO under ambient conditions. This layer is essential to protect the Co from deep oxidation. Although there is more work to be done to perfect the catalyst, the researchers are optimistic that the combination of Co and G could prove a promising replacement in the future for Pt catalysts in fuel cells. ‘‘Developing new non-Pt nanocatalysts with high activity and stability for ORR is essential for future energy applications,’’ says Sun. ‘‘The present G–Co /CoO material is the most promising non-noble metal catalyst, whose performance comes close to, or matches, Pt.’’
Figure 1 Nanoparticles of Co attach themselves to a G substrate in a single layer. As a catalyst, the Co–G combination was a little slower getting the ORR going, but reduced O2 faster and lasted longer than Pt-based catalysts. Credit: Sun lab, Brown University.
Cordelia Sealy has many years’ experience as a scientific journalist and editor in areas spanning nanotechnology, energy, materials science and engineering, physics, chemistry and the environment. She is currently a freelance science writer for her own company, Oxford Science Writing, and serves as News and Opinions Editor of Nano Energy and Nano Today. She also writes on energy policy and business issues. In the past, Cordelia served as Editor of Materials Today and Nano Today and as Managing Editor of both titles. She also has experience in academic publishing as a books acquisitions editor and in business-to-business publishing as a journalist on European Semiconductor. She has a First in Physical Sciences (BSc) from University College London and a DPhil in Materials Science and Engineering from the University of Oxford, and is a Member of the Institute of Physics. E-mail address: [email protected] 2211-2855/$ - see front matter http://dx.doi.org/10.1016/j.nanoen.2012.11.007
3 E-mail address: [email protected] 2211-2855/$ - see front matter http://dx.doi.org/10.1016/j.nanoen.2012.11.009
Co nanoparticle–graphene catalyst could replace Pt Cordelia Sealy A new generation of polymer membrane electrolyte fuel cells and metal–air batteries rely on Pt as a catalyst, which is both scarce and expensive. The search is on for a low-cost, abundant alternative and researchers from Brown University think they may have found it in the form of Co/CoO nanoparticles on graphene [S. Guo, et al., Angew. Chem. Int. Ed. (2012), http://dx.doi.org/10.1002/anie.201206152]. The new catalyst consists of Co/CoO nanoparticles, synthesized and self-assembled through thermal decomposition of precursors onto a graphene (G) surface (Fig. 1). The material performs as a catalyst for the O2 reduction reaction (ORR), which takes place on the cathode side of a fuel cell or battery. In the reaction, O2 acts as an electron sink, drawing away electrons from the H2 at the anode and creating the potential difference that drives the current. The researchers say that the G–Co /CoO material is the first non-precious metal catalyst that performs anywhere close to Pt. ‘‘The G–Co /CoO has comparable electrocatalytic activity, but higher stability than the commercial C/Pt catalyst for ORR in 0.5 M KOH solution,’’ says lead researcher Shouheng Sun. ‘‘To the best of our knowledge, this G–Co / CoO catalyst has the best kinetic process for ORR among all the reported non-noble metal catalysts.’’ Although the G–Co /CoO takes longer to get the ORR started, once it does the reaction goes at a faster pace than if catalysed by Pt. The new catalyst also appears to be remarkably stable, degrading somewhat less than Pt over time. After 17 h of testing, report the researchers, the G–Co /CoO was performing at 70% of its original capacity compared with 60% for a Pt catalyst under similar conditions. The researchers report that size and structure of the nanoparticles is essential to optimizing the catalyst. The best performing material comprises nanoparticles with an 8 nm Co core and a 1 nm CoO shell. The Co nanoparticles are first selfassembled onto the G surface and then allowed to form a layer of natural CoO under ambient conditions. This layer is essential to protect the Co from deep oxidation. Although there is more work to be done to perfect the catalyst, the researchers are optimistic that the combination of Co and G could prove a promising replacement in the future for Pt catalysts in fuel cells. ‘‘Developing new non-Pt nanocatalysts with high activity and stability for ORR is essential for future energy applications,’’ says Sun. ‘‘The present G–Co /CoO material is the most promising non-noble metal catalyst, whose performance comes close to, or matches, Pt.’’
Figure 1 Nanoparticles of Co attach themselves to a G substrate in a single layer. As a catalyst, the Co–G combination was a little slower getting the ORR going, but reduced O2 faster and lasted longer than Pt-based catalysts. Credit: Sun lab, Brown University.
Cordelia Sealy has many years’ experience as a scientific journalist and editor in areas spanning nanotechnology, energy, materials science and engineering, physics, chemistry and the environment. She is currently a freelance science writer for her own company, Oxford Science Writing, and serves as News and Opinions Editor of Nano Energy and Nano Today. She also writes on energy policy and business issues. In the past, Cordelia served as Editor of Materials Today and Nano Today and as Managing Editor of both titles. She also has experience in academic publishing as a books acquisitions editor and in business-to-business publishing as a journalist on European Semiconductor. She has a First in Physical Sciences (BSc) from University College London and a DPhil in Materials Science and Engineering from the University of Oxford, and is a Member of the Institute of Physics. E-mail address: [email protected] 2211-2855/$ - see front matter http://dx.doi.org/10.1016/j.nanoen.2012.11.007