Extended Data Fig. 5: AES observations.
From: Vacancy-enabled N2 activation for ammonia synthesis on an Ni-loaded catalyst
a–f, AES spectra for N (a, d), La (b, e) and Ni (c, f), for fresh Ni/LaN, H2-pretreated Ni/LaNV and used Ni/LaN. Panels a–c (left) compare the spectra between fresh Ni/LaN and H2-pretreated Ni/LaNV; d–f compare the spectra between fresh and used Ni/LaN. To determine the location of VN, Ar plasma was used to etch the sample surface during the AES measurement (a–c, right). After Ar spattering, the N content became almost the same as that in the LaN bulk, showing that the VN were generated only on the surface of LaN. By contrast, the signals of La remained largely unchanged between the surface and the bulk. The change in the Ni concentration was obvious because it was deposited only on the surface of LaN (c). The depth composition variation of used Ni/LaN bulk shows that the N peak (about 387 eV) also remains largely unchanged after reaction (d), demonstrating that the surface VN generated in situ should be occupied by N2 molecules during ammonia synthesis. La and Ni peaks also remains largely unchanged after reaction (e, f).
