Inkjet printed multilayer bifunctional electrodes for proton exchange membrane unitized regenerative fuel cells

A multilayer arrangement configuration was evaluated for low-loading bifunctional oxygen electrodes (BOEs) for PEM unitized regenerative fuel cells (URFCs). The Pt to IrOx x ratio was studied in two distinct multilayer catalyst-coated membrane configurations, i.e., with the IrOx x layer near the GDL or the PEM. A novel approach to fabricate the Pt black catalyst layer (CL) was used with a Pt nanoparticle ink printed first and then impregnated with ionomer by inkjet printing a Nafion dispersion. The electrodes were characterized via scanning electrode microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The results show that the performance of the multilayer electrodes is highly dependent on the position of the CLs in the electrode and that the Pt to IrOx x ratio is critical for the successful operation of the electrode when the Pt layer is in contact with the PEM. At high catalyst loadings, the poorly conductive IrOx layer, in contact with the GDL, acted as a barrier for the electrons to reach the Pt layer, increasing the high-frequency impedance of the cell and leading to a second semicircle. The catalyst ratio study showed that, at lower IrOx loadings, the multilayer approach outperforms the mixed catalyst BOEs when the Pt CL is in contact with the PEM reaching a round-trip (RT) efficiency of 51.2% at 500 mA/cm2 2 and 43.8% at 1000 mA/cm2 2 with a catalyst loading of only 0.56 mg/cm2 2 and a 9:1 Pt:IrOx x ratio. Once the CLs position and the catalyst ratio are optimized, the electrodes fabricated in this work achieved the highest RT efficiency for a multilayer arrangement and one of the highest by the amount of catalysts of any constant gas BOE reported in the literature.