Development of porous Pt/IrO2/carbon paper electrocatalysts with enhanced mass transport as oxygen electrodes in unitized regenerative fuel cells

• Novel oxygen electrode was developed for unitized regenerative fuel cell (URFC).
• Pt was sprayed on IrO2-coated carbon paper (CP) to prepare the porous Pt/IrO2/CP.
• The loadings of Pt and IrO2 were 0–0.3 mg cm− 2 and 0.1 mg cm− 2, respectively.
• Porous Pt/IrO2/CP showed high URFC performance with low electrocatalyst loading.
• High URFC performance was due to facile mass transport in open structured electrode.

The oxygen electrodes in unitized regenerative fuel cells (URFC) must have high activities towards oxygen reduction reaction (ORR) as well as oxygen evolution reaction (OER), thus requiring high loading of noble metal electrocatalysts. In this study, porous Pt/IrO2/carbon paper (CP) electrocatalysts were developed to reduce the metal loading. The Pt/IrO2/CP electrodes were fabricated by sequential formation of IrO2 layers (loading 0.1 mg cm− 2) and porous Pt layers (0–0.3 mg cm− 2) on CP substrates by electrodeposition and spraying techniques, respectively. The fuel cell (FC) performances increased linearly up to 0.69 A cm− 2 with increasing Pt loading (up to ~ 0.3 mg cm− 2) at 0.6 V, whereas the water electrolysis (WE) activity was highest at Pt loading of 0.2 mg cm− 2. The current densities in the FC and WE modes and round-trip efficiency of the developed Pt/IrO2/CP electrodes with the oxygen electrocatalysts loadings of 0.3 and 0.4 mg cm− 2 were higher or comparable to previously reported values with higher loading (1.5–4.0 mg cm− 2). These high performances with low loading are probably due to the facile oxygen and water transport through well-developed macropores originating from the open CP structures, providing effective utilization of the IrO2 and Pt electrocatalysts towards OER and ORR, respectively.