Hunt Diego, Oestreicher Víctor, Mizrahi Martín, Requejo Félix G, Jobbágy Matías
Departamento de Física de la Materia Condensada, GIyA, CAC-CNEA, Instituto de Nanociencia y Nanotecnología, CNEA-CONICET, San Martin, Buenos Aires, B1650, Argentina.
INQUIMAE-DQIAQF, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pab. II, C1428EHA, Buenos Aires, Argentina.
Chemistry. 2020 Dec 18;26(71):17081-17090. doi: 10.1002/chem.202001944. Epub 2020 Nov 18.
Co- and Ni-based layered hydroxides constitute a unique class of two-dimensional inorganic materials with exceptional chemical diversity, physicochemical properties and outstanding performance as supercapacitors and overall water splitting catalysts. Recently, the occurrence of Co(III) in these phases has been proposed as a key factor that enhance their electrochemical performance. However, the origin of this centers and control over its contents remains as an open question. We employed the Epoxide Route to synthesize a whole set of α-NiCo layered hydroxides. The PXRD and XAS characterization alert about the occurrence of Co(III) as a consequence of the increment in the Ni content. DFT+U simulation suggest that the shortening of the Co-O distance promotes a structural distortion in the Co environments, resulting in a double degeneration in the octahedral Co 3d orbitals. Hence, a strong modification of the electronic properties leaves the system prone to oxidation, by the appearance of Co localized electronic states on the Fermi level. This work combines a microscopic interpretation supported by a multiscale crystallochemical analysis, regarding the so-called synergistic redox behavior of Co and Ni, offering fundamental tools for the controllable design of highly efficient electroactive materials. To the best of our knowledge, this is the first computational-experimental investigation of the electronic and structural details of α-NiCo hydroxides, laying the foundation for the fine tuning of electronic properties in layered hydroxides.
钴基和镍基层状氢氧化物是一类独特的二维无机材料，具有非凡的化学多样性、物理化学性质，作为超级电容器和全水解催化剂具有出色的性能。最近，有人提出这些相中钴（III）的存在是增强其电化学性能的关键因素。然而，这种中心的起源以及对其含量的控制仍然是一个悬而未决的问题。我们采用环氧化合物路线合成了一整套α-NiCo层状氢氧化物。PXRD和XAS表征表明，由于镍含量的增加，出现了钴（III）。DFT+U模拟表明，Co-O距离的缩短促进了Co环境中的结构畸变，导致八面体Co 3d轨道出现双重简并。因此，电子性质的强烈改变使系统易于氧化，这是由于在费米能级上出现了Co局域电子态。这项工作结合了多尺度晶体化学分析支持的微观解释，涉及所谓的Co和Ni的协同氧化还原行为，为高效电活性材料的可控设计提供了基本工具。据我们所知，这是首次对α-NiCo氢氧化物的电子和结构细节进行计算实验研究，为层状氢氧化物电子性质的微调奠定了基础。
