Department of Chemistry, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
Phys Chem Chem Phys. 2018 Nov 21;20(45):28685-28698. doi: 10.1039/c8cp02137f.
We present a Hubbard-corrected density functional theory (DFT+U) study of the adsorption and reduction reactions of oxygen on the pure and 25% Ca-doped LaMnO3 (LCM25) {100} and {110} surfaces. The effect of oxygen vacancies on the adsorption characteristics and energetics has also been investigated. Our results show that the O2 adsorption/reduction process occurs through the formation of superoxide and peroxide intermediates, with the Mn sites found to be generally more active than the La sites. The LCM25{110} surface is found to be more efficient for O2 reduction than the LCM25{100} surface due to its stronger adsorption of O2, with the superoxide and peroxide intermediates shown to be energetically more favorable at the Mn sites than at the Ca sites. Moreover, oxygen vacancy defect sites on both the {100} and {110} surfaces are shown to be more efficient for O2 reduction, as reflected in the higher adsorption energies calculated on the defective surfaces compared to the perfect surfaces. We show from Löwdin population analysis that the O2 adsorption on the pure and 25% Ca-doped LaMnO3 surfaces is characterized by charge transfer from the interacting surface species into the adsorbed oxygen πg orbital, which results in weakening of the O-O bonds and its subsequent reduction. The elongated O-O bonds were confirmed via vibrational frequency analysis.
我们提出了一个修正后的 Hubbard 密度泛函理论（DFT+U），研究了纯 LaMnO3（LCM25）{100}和{110}表面以及 25%Ca 掺杂的 LaMnO3（LCM25）{100}和{110}表面上氧气的吸附和还原反应。我们还研究了氧空位对吸附特性和能量学的影响。我们的研究结果表明，O2 的吸附/还原过程是通过超氧化物和过氧化物中间体的形成来进行的，Mn 位通常比 La 位更活跃。LCM25{110}表面比 LCM25{100}表面更有利于 O2 还原，因为它对 O2 的吸附更强，而超氧化物和过氧化物中间体在 Mn 位比在 Ca 位更有利于能量学。此外，我们还发现{100}和{110}表面上的氧空位缺陷位对于 O2 还原更为有效，因为与理想表面相比，缺陷表面上计算出的吸附能更高。我们通过 Löwdin 布居分析表明，O2 在纯 LaMnO3 和 25%Ca 掺杂的 LaMnO3 表面上的吸附是通过相互作用表面物种向吸附氧 πg 轨道转移电荷来表征的，这导致 O-O 键变弱，随后发生还原。通过振动频率分析证实了 O-O 键的伸长。
