Experimental FeL-edge sXAS spectra of Prussian White (PW, Na₂Fe^II[Fe^II(CN)₆]) and Berlin Green (BG, Fe^III[Fe^III(CN)₆]). Panel (a) shows the lattice structure of the iron HCF materials. Panel (b) displays the two electrochemical potential plateau corresponding two redox reactions. (c) The resolved experimental features could be clearly assigned to Fe atoms at different sites with the specified formal valences. The lithiation (discharge) process introduces electrons into the lowest energy electron state in the BG Fe^IIIspectrum (red arrow), which corresponds to the Fe^IIIat the carbon coordinated site. This combined spectroscopic and theoretical study clarifies the mechanism of the high (low) electrochemical plateau from the low (high) spin Fe at the C (N) coordinated site.^[36]