Extended Data Fig. 4: Surface chemical states of C, N, Rb and Ir in Rb-PHI, Ir0.5-PHI and Ir0.5Rb-PHI.

a-c, High-resolution XPS spectra of N 1 s (a), C 1 s (b) and Rb 3 d (c) for Rb-PHI and Ir0.5Rb-PHI. d, High-resolution XPS spectra of Ir 4 f for Ir0.5-PHI and Ir0.5Rb-PHI. The almost no shift in the Rb 3 d XPS spectrum is attributed to the notably large content of Rb (~7% wt.%) species in Ir0.5Rb-PHI, which cannot be remarkably affected by the Ir species with a low concentration (~0.5 wt.%). On the other hand, the shift of the Ir 4 f XPS spectrum is notable for Ir0.5Rb-PHI as compared to that for Ir0.5-PHI.