The XPS spectra of Fe show that the peak change of Fe-P bond is very small (Fig. 5g), but the peaks of Fe 2+ and Fe 3+ have a certain positive displacement [52,61]. These phenomena indicate that a small amount of (NiFeCo)2P-PA has converted to MOOH on the surface of catalyst. Furthermore, M(OH)2 and MOOH formation is also confirmed by changes in XPS spectra of O 1 s (Fig. S20a).