Tuning the Composition and Structure of Metallic Nanotubes for Electrocatalysis

Recent trends in the design of electrocatalysts for power generation systems have highlighted the usefulness of supportless extended surfaces, surface-segregated alloys, and shape-controlled particles for activity enhancement¹.  Multiple synthetic schemes have been devised to produce these materials with varying degrees of versatility and scalability. 

            We have investigated templated vapor deposition as an addition to the already wide array of synthetic strategies, and applied these methods to problems in low-temperature electrocatalysis.  In our approach, metalorganic precursors are used to deposit conformal nanoparticulate films within the internal channels of porous anodic alumina templates.  By sequentially depositing multiple species, layered structures can be formed.  Subsequent thermal treatments can then be used to drive crystallite growth, alloying (or phase separation) and mesostructural evolution.  The template structure is then dissolved to release high-aspect ratio nanotubes that can be implemented as electrocatalysts (Figure 1).

            By rationally selecting the constituent metals, relative compositions, and heat treatment temperatures, we synthesized highly active electrocatalysts for multiple reactions of technological interest.  These include the use of pure Pt nanotubes² for acidic oxygen reduction, Bi-decorated Pd nanotubes for formic oxidation, Pt-Ru nanotubes for methanol oxidation³and, recently, Ru-Pt nanotubes for hydrogen oxidation in alkaline electrolytes.

            In this contribution we examine the unique characteristics of the novel class of electrocatalysts emerging from our templated vapor deposition methods.  Comprehensive characterization of the catalysts using chemical and structural probes including advanced transmission electron microscopy are used to gain insight into the structure-property relationships governing nanotube activity.  Finally, future prospects for the synthesis of additional functional nanostructures for electrochemical systems will be discussed.

References

¹ M. K. Debe, Nature 486, 43–51 (2012).

² A. B. Papandrew, R. W. Atkinson, G. a. Goenaga, S. S. Kocha, J. W. Zack, B. S. Pivovar, and T. A. Zawodzinski, J. Electrochem. Soc. 160, F848–F852 (2013).

³ R. W. Atkinson, R. R. Unocic, K. A. Unocic, G. M. Veith, T. A. Zawodzinski, and A. B Papandrew, ACS Appl. Mater. Interfaces DOI: 10.1021/am508228b (2015).