N₂O Decomposition on Singly and Doubly (K and Li)-Doped Co₃O₄ Nanocubes─Establishing Key Factors Governing Redox Behavior of Catalysts

The intimate mechanism of N₂O decomposition on bare and redox-tuned Co₃O₄ nanocubes (achieved by single (Li or K) and double (Li and K) doping) was elucidated. The catalysts synthesized by the hydrothermal method were characterized by X-ray electron absorption fine structure measurements, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and Kelvin Probe techniques. TPSR and steady-state isothermal catalytic tests reveal that the N₂O turnover frequencies are critically sensitive to the work function of the catalysts, adjusted purposely by doping. For the catalysts obtained by one-pot hydrothermal synthesis, lithiation of the Co₃O₄ nanocubes leads to the formation of {Li'_8a, Co·_16d} species, decreasing steadily the work function and the activity, while for the catalysts prepared by postsynthesis impregnation, formation of {Li'_8a, Co'_16d, Co··_16c} species leads to a volcano-type dependence of the catalytic activity and the work function in parallel. The beneficial effect of potassium was discussed in terms of mitigation of surface potential buildup due to the accumulation of ionosorbed oxygen intermediates (surface electrostatics), which hinders the interfacial electron transfer. Analysis of the catalytic activity response to the redox tuning of Co₃O₄, substantiated by DFT calculations, allowed for a straightforward conceptualization of the redox nature of the N₂O decomposition in terms of the lineup of frontier orbitals of the N₂O/N₂O^- and O₂^-/O₂ reactants with the surface DOS structure and the resultant molecular orbital interactions. The positions of the virtual bonding 3π_g⁰(N₂O)-α-3d_<i>z</i>2 and the occupied 2π_g¹(O₂^-)-α-3d_<i>z</i>2 states relative to the Fermi energy level play a crucial role in the regulation of the forward and backward interfacial electron transfer events, which drive the redox process.