Deconvoluting the XPS spectra for nitrogen-doped chars: An analysis from first principles

Quantifying the content of surface nitrogen and oxygen containing functional groups in amorphous nitrogen doped carbons via deconvolution of C 1s x-ray photoelectron (XPS) spectra remains difficult due to limited information in the literature. To improve the interpretation of XPS spectra of nitrogen-doped carbons, the C 1s, N 1s and O 1s core level energy shifts have been calculated for various nitrogenated carbon structures via DFT. Furthermore, we propose an expanded method to improve the self-consistency of the XPS interpretation based on a seven-peak C 1s deconvolution (3 C–C peaks, 3 C–N/-O peaks, and π-π∗ transition peaks). With the DFT calculations, spectral components arising from surface-defect carbons could be distinguished from aromatic sp2 carbon. The deconvolution method proposed provides C/(N + O) ratios in very good agreement (error less than 5%) with those obtained from total C 1s, N 1s and O 1s peaks. Our deconvolution strategy provides a simple guideline for obtaining high-quality fits to experimental data on the basis of a careful evaluation of experimental conditions and results.