Highly Accelerated Mass Transport within Jungle-Gym-Type Ir Electrocatalyst for Water Electrolyzers

Abstract

Hydrogen is an efficient and clean energy carrier, as well as a fuel for transportation and various other applications. Polymer electrolyte membrane water electrolysis (PEMWE) has shown to be a promising method for producing pure hydrogen without significant additional compression.[1] However, understanding the relationship between nanostructure and activity is one of the current challenges faced by water electrolysis for analyzing and improving IrOx-based catalysts for the OER. Herein, in order to confirm the effect of controlling the nanostructure, jungle-gym-structured Ir OER catalysts were fabricated using solvent-assisted nanotransfer printing (S-nTP). They are composed of vertically stacked nanowire array with a periodicity. They showed 4 higher mass activity than that of iridium black powder(2-4 nm in diameter). To measure the electrochemically active surface area, the integrated surface charge was calculated from the cyclic voltammetry in the range of 1.0 – 1.4 V vs RHE. The jungle-gym-type Ir catalyst recorded 2.3 times higher integrated surface charge compared to that of iridium black powder. If the mass activity is normalized by the integrated surface charge, turnover frequency (TOF) can be calculated, which is associated with the specific current density per electrochemically active surface area. [2] TOF values 1.8 times higher than iridium black were observed in the case of jungle-gym-structured one. The efficiency of the catalyst utilization has been maximized due to the novel structure, achieving a high ratio of surface area to the mass of the structure as high as that of Ir Black catalysts. Moreover, the jungle-gym nanostructure within the catalyst layer enhanced the intrinsic activity of the catalyst due to the accelerated mass transport within the catalyst layer. Reference [1] Aricò, A. S., et al. "Polymer electrolyte membrane water electrolysis: status of technologies and potential applications in combination with renewable power sources." Journal of Applied Electrochemistry2 (2013): 107-118. [2] Abbott, Daniel F., et al. "Iridium oxide for the oxygen evolution reaction: correlation between particle size, morphology, and the surface hydroxo layer from operando XAS." Chemistry of Materials18 (2016): 6591-6604.