Integrated ultra-low PtIr catalyst coated membrane toward efficient proton exchange membrane water electrolyzers

Catalyst coated membrane (CCM) is the core component of proton exchange membrane water electrolyzers (PEMWEs) and confronts the challenge of unaffordable Ir loading of 2-4 mg cm-2, polarization loss and inferior stability closely correlated with low-activity disordered thick catalyst layers (CLs, 3-10 mu m) frequently fabricated by catalyst ink painting. We report wet-chemical direct growth of semi-ordered PtIr nanoflowers array as CLs on both sides of membrane, leading to an integrated ultra-low PtIr CCM (IUCCM) with a single-side PtIr loading of 62.7 mu g (1.8 mu g Pt+60.9 mu g Ir) cm- 2 and a CL thickness of 429.1 +/- 62.9 nm. Remarkably, the IUCCM exhibits 20.8 %, 34.8 % and 23.8 % attenuation of activation, ohmic and mass transfer polarization relative to a house-made CCM, respectively, and a current density of 2 A cm-2 at 1.77 V as well as the highest specific power of 21.5 kW gIr- 1 at 1.6 V in the literature. The improvement of activation polarization is primarily arising from the electronic effect between Pt and Ir as evidenced by the d-band center downshift of 0.80 eV. The thin and semiordered CL largely accounts for the mitigation of mass transfer and ohmic polarization. Notably, the IUCCM displays a good long-term stability with a degradation rate of ca. 44.4 mu V h-1 during 300 h of electrolysis at 0.5 A cm-2. The superior stability can be attributed to strong CL/membrane interfacial interaction with the CL rooted down into the membrane matrix analogous to teeth as well as structural robustness of PtIr CL.