Crystallographic and geometrical dependence of water oxidation activity in Co-based layered hydroxides

Abstract

Cobalt-based layered hydroxides (LHs) stand out as one of the best families of electroactive materials for the alkaline oxygen evolution reaction (OER). However, fundamental aspects such as the influence of the crystalline structure and its connection with the geometry of the catalytic sites remains poorly understood. Thus, to address this we have conducted a thorough experimental and in silico study on the most essential Co-LHs (i.e.: ɑ-LH, β-LH and LDH) which allows us to understand the role of the layered structure and coordination environment of Co atoms on the OER performance. The ɑ-LH, containing both octahedral and tetrahedral sites, behaves as the best OER catalyst in comparison to the other phases, pointing out the role of the chemical nature of the crystalline structure. Indeed, density functional theory (DFT) calculations confirm the experimental results which can be explained in terms of both, the significant reduction of the Egap, due to the presence of tetrahedral sites, as well as the more favourable reconstruction of the ɑ-LH structure into active Co(III)-based oxyhydroxide-like phase. Furthermore, ex-situ X-ray diffraction and absorption spectroscopy reveal the permanent transformation of ɑ-LH phase into an unprecedented highly reactive oxyhydroxide-like structure under ambient conditions. Hence, our findings highlight the key role of tetrahedral sites on the electronic properties of the LH structure as well as their inherent reactivity towards OER catalysis, paving the way for the rational design of more efficient and low-maintenance electrocatalysts.

Influence of crystallographic structure and metal vacancies on the oxygen evolution reaction performance of Ni-based layered hydroxides

“…As we have recently reported for Co-based LHs, the role of crystallographic structure can play a crucial role in the OER performance, even in those phases containing exclusively Co II cations. [25] Thus, considering our last finding and the importance of nickel in the development of OER catalysts, we decided to perform a comprehensive study on the most important Ni-based LHs: brucite-like (β-LH), hydrotalcite-like (LDH), and turbostratic-like (ɑ-LH). In the case of the non-expanded β-LH phase, cations adopt octahedral environments, M II (O h ), exclusively, and exhibit basal space distances (d BS ) lower than 5 Å.…”

Upscaling the urea method synthesis of CoAl layered double hydroxides

“…Overall, a CoAl-LDH containing carbonate as interlayer anion is observed. Interestingly, in the case of sample x25M, a shift in the carbonate bending signal (from 775 to 740 cm −1 , denoted with a diamond) and the appearance of a shoulder at 581 cm −1 (denoted with an asterisk) indicate the presence of the impurity already observed by PXRD (see also Supporting Information File 1 , Figure S3) [ 48 ].…”