(Invited) Towards the Development of Active, Stable and Abundant Catalysts for Oxygen Evolution in Acid
Authors: Stephens Ifan Erfyl Lester , Paoli Elisa Antares , Frydendal Rasmus , Rossmeisl Jan , Chorkendorff Ib 
Published: February 2020

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 RuOx 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 RuOx 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 TiOx or IrOx,(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 MnOx with TiOx. 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-TiOx 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 MnOx 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.

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