Local structure characterization of Mn in NGn and NG1a. (a) Experimental Mn K-edge XANES spectra of NG1, NG2, NG1a and the standard references (bulk Mn, MnO and MnO2). No Mn signal is detected in NG 3-6. (b) Fourier transformed magnitudes of the experimental Mn K-edge EXAFS spectra for NG1, NG2, NG1a and the standard references (bulk Mn and MnO2).