Figure 4. X-ray absorption spectra of MnO_x standards and experimental specimens.

X-ray absorption measurements of as-prepared three samples and reference Mn oxide materials. (a) XANES spectra of reference materials MnO, Mn₃O₄, Mn₂O₃ and MnO₂. (b) XANES spectra of protonated MnO₂, pH=2 and 4 treated reassembled MnO₂. The reference materials of Mn₂O₃ and MnO₂ from (a) are also shown for of ease comparison. (c) First derivative curves corresponding to the samples shown in b. (d) Average oxidation state of Mn for the samples and standards derived from the K-edge energy.