Oxygen Vacancies Altering the Trapping in the Proton Conduction Landscape of Doped Barium Zirconate
Oxygen Vacancies Altering the Trapping in the Proton Conduction Landscape of Doped Barium Zirconate
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DOI：
10.1021/acs.jpcc.0c09461
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发表时间：
2020-12-24
影响因子：
3.7
通讯作者：
Gomez, Maria A.
中科院分区：
文献类型：
--
作者：
Lin, Ziqing;Lin, Shiyun;Gomez, Maria A.
受主掺杂锆酸钡是固定式氢燃料电池最有前途的质子导电材料之一。掺杂剂缺陷质子陷阱塑造了质子传导景观。受发现氧空位可减少在一些掺杂剂缺陷附近的俘获的启发（Chem.Mater. 2018，30，4919-4925），探索了在锆位点用铝、钪和钇掺杂剂掺杂12.5%时氧空位对锆酸钡的质子传导景观的影响。采用维也纳从头算模拟软件包（VASP）中的PBE泛函密度泛函理论（DFT）计算了锆酸钡晶体的电子能量。采用共轭梯度极小化方法寻找最低能量结构，采用爬升轻推弹性带（cNEB）方法寻找过渡态。随着掺杂剂（D）离子半径增加，晶格尺寸从4.24埃扩展到4.29埃，并且增加了锆酸钡中的DO 6八面体倾斜。氧空位的包含物加宽了ZrOD和ZrOZr角分布。虽然有三个不同的最小值的氧空位的位置，最小值和过渡态的相对能量表明，只有掺杂剂最近邻的氧空位是显着的铝和钪掺杂的锆酸钡。相比之下，钇掺杂的系统显示在800 K的掺杂剂最近和第二近邻氧空位的概率分别为67%和33%。最接近氧空位的掺杂剂使掺杂剂多面体中心电荷暴露。铝掺杂剂的小尺寸允许氧离子移动并部分屏蔽掺杂剂电荷。这与强氢键结合增加了质子捕获。对于较大的钪和钇离子，在具有最近邻氧空位的掺杂剂周围没有显著的氧离子重排。相反，由空位暴露的正掺杂剂电荷提高了几个掺杂剂最近邻质子位点的能量，从而降低了局部捕获。
Acceptor-doped barium zirconate is one of the most promising proton conducting materials for stationary hydrogen fuel cells. Dopant-defect proton traps shape the proton conduction landscape. Inspired by findings that oxygen vacancies may decrease trapping near some dopant defects (Chem. Mater. 2018, 30, 4919-4925), the effect of oxygen vacancies on the proton conduction landscape of barium zirconate is explored at 12.5% doping with aluminum, scandium, and yttrium dopant at the zirconium site. Density functional theory (DFT) with the PBE functional in the Vienna ab initio simulation package (VASP) was used to find the electronic energy for barium zirconate configurations. The conjugate-gradient minimization method is used to find the lowest energy structures and the climbing nudged elastic band (cNEB) method is used to find transition states. As the dopant (D) ion radius increases, the lattice size expands from 4.24 to 4.29 angstrom and increases DO6 octahedral tilting in barium zirconate. Inclusion of an oxygen vacancy broadens ZrOD and ZrOZr angle distributions. While there are three distinct minima for oxygen vacancy locations, relative energies of minima and transition states show that only the dopant nearest neighbor oxygen vacancy is significant for aluminum- and scandium-doped barium zirconate. In contrast, the yttrium-doped system shows 67% and 33% probabilities at 800 K for the dopant nearest and second nearest neighbor oxygen vacancies, respectively. The dopant nearest oxygen vacancy leaves the dopant polyhedral center charge exposed. The small size of the aluminum dopant allows oxygen ions to shift and partially screen the dopant charge. This coupled with strong hydrogen bonds increases proton trapping. For the larger scandium and yttrium ions, there is no significant oxygen ion rearrangement around the dopant with a nearest neighbor oxygen vacancy. Instead, the positive dopant charge exposed by the vacancy raises the energy of several dopant nearest neighbor proton sites decreasing trapping locally.