Deriving highly-enhanced mass activity of electrochemical catalyst for oxygen evolution reaction with stack of ordered Iridium nanowire arrays

Abstract

Selecting highly efficient catalyst for oxygen evolution reaction in acidic electrolytes is a challenge for producing environmentally friendly hydrogen with highly compactable and efficient polymer electrolyte membrane water electrolysis(PEMWE). Here, we suggest a woodpile-nanostructured Ir thin film, fabricated by stacking periodically-arrayed nanowires through solvent-assisted nanotransfer printing, exhibiting exceptional enhancement of mass activity and stability. The woodpile nanostructure enables complete utilization of iridium in the catalyst from top to bottom because ordered and interconnected pores with size of meso (~50nm) and macro(>200 nm) pores have propensity to flood. Low tortuosity of the pores within the woodpile structure facilitates dioxygen product to escape the catalyst layer. These characteristics are related to increase of the surface area of the interface between the catalyst and the water reactant and the quantity of the reaction per unit area per unit time. These properties result woodpile-nanostructured Ir thin film to show 4.8 times advanced mass activity relative to a conventional nanoparticle-type iridium catalyst. In addition, it sustains 80% of activity after 500 start/stop cycles in contrast to 60% sustainability of the nanoparticles. Furthermore, we demonstrated ~36 times enhancement of mass activity in real PEMWE device. The woodpile nanostructured Ir thin film are meant to guide further research to improve orderability of stacking nanowire array for optimized electrochemical OER catalyst.