(Invited) Towards the Development of Active, Stable and Abundant Catalysts for Oxygen Evolution in Acid

Of the different water splitting technologies, polymer electrolyte membrane (PEM) electrolysers are the most amenable towards small-scale delocalized storage of renewable electricity.  In order for these devices make a significant impact to the global energy landscape, they will need to be scaled to the TW level. State-of the art PEM electrolysers employ IrO_x, which is both expensive and scarce, to catalyse oxygen evolution.(1) Around a decade’s worth of Ir production would be required to scale up PEM electrolysis to the TW scale: this is clearly untenable.(2)  It turns out that RuO_x has a higher catalytic activity than IrOx, but is more prone to dissolution.(3-5)  All other surfaces are completely inactive or unstable. We recently demonstrated that mass-selected RuO_x nanoparticles exhibited an order of magnitude improvements in both mass activity and turnover frequency over the state of the art. Should this activity be stabilised for instance, by utilising a more stable oxide such as TiO_x or IrO_x,(6, 7) PEM electrolysis could indeed be scalable to the TW level.

Alternatively, the precious metal catalysts could be eliminated altogether and replaced by abundant, active and stable catalysts.  However, this is not a trivial task, given the highly oxidising and corrosive environment under reaction conditions. Herein, we attempt to address this problem by stabilising MnO_x with TiO_x.  Density functional theory calculations suggest that the undercoordinated surface sites on MnOx, which are inactive and also most prone to dissolution, could be stabilised by TiO_x. We test this notion by performing oxygen evolution on Mn-TiO_x thin films. We probe the composition using X-ray photoelectron spectroscopy measurements and dissolution with inductively coupled plasma mass spectroscopy.  We confirm that TiO_x does indeed engender MnO_x with modest stability.  Further development of this strategy opens up the possibility of developing active, stable and abundant non-precious metal oxides for oxygen evolution in acid.

References

1.             M. K. Debe, S. M. Hendricks, G. D. Vernstrom, M. Meyers, M. Brostrom, M. Stephens, Q. Chan, J. Willey, M. Hamden, C. K. Mittelsteadt, C. B. Capuano, K. E. Ayers and E. B. Anderson, J. Electrochem. Soc., 159, K165 (2012).

2.             E. A. Paoli, F. Masini, R. Frydendal, D. Deiana, C. Schlaup, M. Malizia, T. W. Hansen, S. Horch, I. E. L. Stephens and I. Chorkendorff, Chemical Science, DOI: 10.1039/c4sc02685c (2015).

3.             T. Reier, M. Oezaslan and P. Strasser, ACS Catalysis, 2, 1765 (2012).

4.             S. Cherevko, A. R. Zeradjanin, A. A. Topalov, N. Kulyk, I. Katsounaros and K. J. J. Mayrhofer, ChemCatChem, 6, 2219 (2014).

5.             R. Frydendal, E. A. Paoli, B. P. Knudsen, B. Wickman, P. Malacrida, I. E. L. Stephens and I. Chorkendorff, ChemElectroChem, DOI: 10.1002/celc.201402262 (2014).

6.             S. Trasatti, Electrochimica Acta, 45, 2377 (2000).

7.             N. Danilovic, R. Subbaraman, K. C. Chang, S. H. Chang, Y. Kang, J. Snyder, A. P. Paulikas, D. Strmcnik, Y. T. Kim, D. Myers, V. R. Stamenkovic and N. M. Markovic, Angewandte Chemie International Edition,  (2014).