Fig. 4. (a) HR-TEM of the FeAs electro(pre)catalyst after OER forming a nanostructure with a lattice spacing of ∼0.25 nm (110). The SAED (a, inset) displayed two broad diffraction rings indicative of 2-line ferrihydrite (see Fig. S57a†). The XPS spectra of the FeAs compared to FeAs after OER for (b) Fe 2p, (c) As 3d and (d) O 1s.