Chakraborty Arup, Kunnikuruvan Sooraj, Zitoun David, Major Dan T
Department of Chemistry, Institute for Nanotechnology & Advanced Materials, Bar-Ilan University Ramat-Gan 52900 Israel
RSC Adv. 2020 Aug 6;10(49):29175-29180. doi: 10.1039/d0ra02577a. eCollection 2020 Aug 5.
Lithium transition metal olivine phosphates are well known Li-ion battery cathode materials, but these materials can also be used as electrocatalyst. Recent experimental studies showed that olivine phosphates with mixed alkali metals (Li and Na) and mixed transition metals (Ni and Fe) provide better electrocatalytic activity compared to single alkali and transition metal alternatives. In the current work, we analyzed the role of alkali metals, transition metals and vacancies on the reactivity of a series of olivine phosphates with different stoichiometries using first principles calculations. To this end, we investigated the adsorption of water at the surface of these materials. We found that water binds preferably at Ni surface sites for materials devoid of alkali ion vacancies. We further found correlation between the calculated adsorption energy with experimentally measured overpotentials for a series of olivine phosphates. Additionally, we found correlation between the adsorption energy of the systems with the total charge polarization of surface and adsorbate. To explain the computed trends, we analyzed the occupancies of the partial density of states of the Ni and Fe 3d states and Bader atomic charges.
锂过渡金属橄榄石磷酸盐是众所周知的锂离子电池正极材料，但这些材料也可用作电催化剂。最近的实验研究表明，与单一碱金属和过渡金属的替代物相比，具有混合碱金属（锂和钠）和混合过渡金属（镍和铁）的橄榄石磷酸盐具有更好的电催化活性。在当前的工作中，我们使用第一性原理计算分析了碱金属、过渡金属和空位对一系列不同化学计量比的橄榄石磷酸盐反应活性的作用。为此，我们研究了这些材料表面水的吸附情况。我们发现，对于没有碱离子空位的材料，水优先吸附在镍表面位点。我们还发现了一系列橄榄石磷酸盐的计算吸附能与实验测量的过电位之间的相关性。此外，我们发现体系的吸附能与表面和吸附质的总电荷极化之间存在相关性。为了解释计算得到的趋势，我们分析了镍和铁3d态的部分态密度占有率以及巴德原子电荷。
