Structural optimization of TiO2 supported IrO2 catalyst for proton exchange membrane water electrolysis

• TiO 2 supported IrO 2 catalysts are optimized using a nominal IrO 2 shell thickness. • The optimized catalyst outperforms a commercial catalyst at 0.1 mg Ir cm −2 . • Catalyst powder conductivity and high frequency resistance strongly correlate. Reducing the iridium loading in proton exchange membrane water electrolysis (PEMWE) is essential, and catalysts with a low iridium content are one viable approach to reach this goal. This study investigates a series of TiO 2 supported IrO 2 catalysts with three different TiO 2 support-particle sizes (3, 14, and 56 m 2 g −1 ) and three different iridium oxide contents (30, 50, and 70 wt%). We demonstrate that, for optimal iridium utilization, the nominal IrO 2 shell thickness should be maximized, which is readily achieved by employing low-surface area supports. Following this strategy, a TiO 2 @IrO 2 catalyst with 50 wt% IrO 2 is designed, whose single-cell performance exceeds a commercial reference catalyst (88 wt% IrO 2 ) by 43 mV at 2 A cm −2 at a low iridium loading of 0.1 mg Ir cm −2 . Furthermore, we find a strong correlation between powder conductivity measurements and single-cell high frequency resistance, underlining the importance of catalyst conductivity.