Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

Abstract

Layered double hydroxides (LDHs) are low dimensional materials that act as benchmark catalysts for the oxygen evolution reaction (OER). Many LDH properties affecting the OER have been studied to reach the optimal efficiency but no systematic studies concerning the influence of the interlayer space have been developed. In this context, these materials allow a large tunability in their chemical composition enabling the substitution of the interlayer anion and therefore modifying exclusively the basal space. Here, we synthesize by anion exchange reactions a surfactantintercalated family of NiFe-LDHs with increasing basal spacing ranging from 8.0 to 31.6 (one of the largest reported so far for a NiFe-LDH) while the electrochemical OER performance of this family of compounds was explored to analyse the interlayer distance effect keeping similar morphology, dimensions and metallic composition. Results show the increase of the LDH basal space undergo to lower Tafel slopes, higher electrochemical surface area and a reduction of the resistance related to the chemisorption of oxygen leading to better kinetic behaviour, showing an optimum enhancement of the electrocatalytic performance for the NiFe-dodecyl sulphate (basal space of 25 ). Interestingly, the NiFe-dodecyl sulphate exhibits optimum proton diffusion values, indeed a further increment in the basal space compromises the onset potential, a fact that could be related to an increase in the hydrophobicity between the layers. Moreover, by judicious tuning of the interlayer space, it is possible to reach a Tafel slope value for the most spaced LDH (NiFe-octadecyl sulphate, basal space of 31.6 ), similar to the one obtained for exfoliated NiFe nanosheets, showing a much better long-time stability due to the three-dimensional robustness of the catalysts. This work illustrates the importance of molecular engineering in the design of novel highly active catalysts and provides important insights into the understanding of basic principles of oxygen evolution reaction in NiFe-LDHs.

Fundamental Insights into the Covalent Silane Functionalization of NiFe Layered Double Hydroxides

“…In order to allow for the insertion of APTES moiety and induce the covalent grafting, a previous enlargement of the basal space is mandatory. For this purpose, the incorporation of more labile dodecyl sulphate (DS) molecules (DS‐intercalated LDH) by anion exchange reaction is carried out prior to the final inclusion of APTES (Scheme ) . In addition, it is demonstrated that the organophilicity increases after the DS intercalation, hence favoring the insertion of the smaller APTES molecules into the interlayer space and their condensation with the ‐OH groups found on the LDH surface.…”

“…Taking this into account, it is expected that the reversibility of silane bonding should not affect the electrocatalytic behavior of NiFe‐LDHs . In this context, we tested the oxygen evolution reaction (OER) electrocatalytic performance of NiFe‐AQ and NiFe‐APTES in a basic medium (1 m KOH) in a standard three‐electrode cell (Figure and Table ).…”

“…Due to the ionic nature of the LDHs, covalent grafting remains a challenging yet attractive strategy in order to widen the scope of action of these clay materials by adding new functionalities. Among the different LDH compositions, NiFe‐LDH stands out as one of the best materials in electrocatalysis, and more concretely in the oxygen evolution reaction (OER) . In addition, its magnetic behaviour at low temperatures adds interest for the study of its properties after the functionalization.…”

“…Another key aspect of LDHs is their unparalleled anion exchange capacity, which allows the substitution of their interlayer anion thanks to anion exchange reactions . All this versatility from the point of view of metal composition, stoichiometry, anion exchange, and exfoliation properties positions LDHs as excellent candidates for application development in numerous fields of great interest, such as catalysis, sensing or magnetism, with special importance in the attention‐growing energy storage and conversion fields …”

Boosting the Supercapacitive Behavior of CoAl Layered Double Hydroxides via Tuning the Metal Composition and Interlayer Space

“…Taking into account that the nature of the interlayer anion (i. e., size, hydrophobicity, acidity, etc.) can influence the electrochemical properties, a systematic study exploring the supercapacitive performance with the progressive increase of the basal space would be desirable.…”