fig2

Figure 2. Structure and composition of the samples. (A) XRD patterns comparing the TNO array and N-C@TNO array; (B) Survey XPS spectra, and high-resolution XPS spectra of (C) C 1s, (D) N 1s, (E) Nb 3d, and (F) O 1s. TNO: TiNb₂O₇, titanium niobium oxide; N-C: N-doped carbon; XRD: X-ray diffraction; XPS: X-ray photoelectron spectroscopy.