Figure 59.

Normalized XANES spectra at different potential (a) at Co K-edge, (b) at Fe K-edge, (c) at Co K-edge in the presence of oxygen or nitrogen, (d) at Fe K-edge in the presence of oxygen or nitrogen, and (e) different model structures of Co–N–C material with O₂ bounded to Co center with the corresponding fitting. The spectra were measured in the presence of 0.5 M H₂SO₄. Δμ spectra in (a) and (b) are obtained by subtracting normalized XANES spectra at every potential to the spectrum measured at 0.2 V potential versus RHE. Δμ spectra in (c) and (d) are obtained by subtracting normalized XANES spectra recorded in the presence of O₂ to the one recorded in N₂. Color code in (e): purple (cobalt), red (oxygen), blue (nitrogen), and gray (carbon). Adapted with permission from ref (401) under Creative Commons CC BY license http://creativecommons.org/licenses/by/4.0/.