Oxygen reduction in nanoporous metal–ionic liquid composite electrocatalysts

Abstract

The improvement of catalysts for the four-electron oxygen-reduction reaction (ORR; O2+4H++4e→2H2O) remains a critical challenge for fuel cells and other electrochemical-energy technologies. Recent attention in this area has centred on the development of metal alloys with nanostructured compositional gradients (for example, core–shell structure) that exhibit higher activity than supported Pt nanoparticles (Pt–C; refs 1,2,3,4,5,6,7). For instance, with a Pt outer surface and Ni-rich second atomic layer, Pt3Ni(111) is one of the most active surfaces for the ORR (ref. 8), owing to a shift in the d-band centre of the surface Pt atoms that results in a weakened interaction between Pt and intermediate oxide species, freeing more active sites for O2 adsorption2,9. However, enhancements due solely to alloy structure and composition may not be sufficient to reduce the mass activity enough to satisfy the requirements for fuel-cell commercialization10, especially as the high activity of particular crystal surface facets may not easily translate to polyfaceted particles. Here we show that a tailored geometric and chemical materials architecture can further improve ORR catalysis by demonstrating that a composite nanoporous Ni–Pt alloy impregnated with a hydrophobic, high-oxygen-solubility and protic ionic liquid has extremely high mass activity. The results are consistent with an engineered chemical bias within a catalytically active nanoporous framework that pushes the ORR towards completion.

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Figure 1: Cross-sectional TEM of np-NiPt foil.
Figure 2: Potentiostatic ORR curves and half-wave as a function of roughness factor.
Figure 3: Tafel plots.
Figure 4: Kinetic activities for np-NiPt and np-NiPt + [MTBD][beti] electrodes.

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Acknowledgements

We gratefully acknowledge support for this work by the US Department of Energy, Office of Basic Energy Sciences, under grant DE-FG02-05ER15727, and V. Stamenkovic (Argonne National Laboratory) for discussion and technical assistance in verifying the activity of np-NiPt for the ORR. We also acknowledge 3M, who generously supplied us with a sample of Li bis(perfluoroethylsulphonyl)imide.

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T.F. and M.W.C. carried out TEM characterization of the dealloyed np-NiPt material. Otherwise, J.S. and J.E. contributed equally in conceiving the new material, carrying out electrochemical characterization, data analysis and manuscript preparation.

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Correspondence to J. Erlebacher.

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The authors declare no competing financial interests.

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Snyder, J., Fujita, T., Chen, M. et al. Oxygen reduction in nanoporous metal–ionic liquid composite electrocatalysts. Nature Mater 9, 904–907 (2010). https://doi.org/10.1038/nmat2878

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