Layered double hydroxides (LDHs) have been combined with graphene and/or carbon nanotubes to prepare new composite materials with fascinating electrochemical features. For the first time, this work describes the development of an electrosynthesis protocol that allows the deposition of thin films of a Ni/Al LDH on glassy carbon electrodes previously modified with carbon nanomaterials. Three different approaches (potentiostatic, galvanostatic and potentiodynamic) were investigated in order to identify the best procedure. In all cases the potentiodynamic synthesis exhibits better reproducibility than the potentiostatic one which is the most used in literature. The reliability of the synthesis protocol was evaluated by performing the LDH electrodeposition using glassy carbon electrodes modified with multiwalled carbon nanotubes and/or electrochemically reduced graphene oxide arranged in five configurations. XRD and SEM analysis confirmed the LDH formation. Cyclic voltammetry shows the graphene presence ensured a large electrochemically active area with values 3 times higher than the one observed for an LDH deposited on a bare glassy carbon.Moreover, impedance electrochemical spectroscopy highlights that carbon nanomaterials play a key role in reducing the charge transfer resistance. In fact, it decreases from 2800 KΩ recorded for LDH deposited on bare glassy carbon to about 600 Ω for the best composite material. The materials were tested for glucose electrooxidation which was exploited for the fabrication of a sensor with high sensitivity (2.6 A M -1 cm -2 for the best device) and low limit of detection (0.6 µM for the best device).

A novel and reproducible protocol allows the electro-synthesis of LDHs for electro-catalytic applications.

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Layered double hydroxides (LDHs) are anionic clays which have found applications in a wide range of fields, including electrochemistry. In such a case, to display good performances they should possess electrical conductivity which can be ensured by the presence of metals able to give reversible redox reactions in a proper potential window. The metal centers can act as redox mediators to catalyze reactions for which the required overpotential is too high, and this is a key aspect for the development of processes and devices where the control of charge transfer reactions plays an important role. In order to act as redox mediator, a material can be present in solution or supported on a conductive support. The most commonly used methods to synthesize LDHs, referring both to bulk synthesis and in situ growth methods, which allow for the direct modification of conductive supports, are here summarized. In addition, the most widely used techniques to characterize the LDHs structure and morphology are also reported, since their electrochemical performance is strictly related to these features. Finally, some electrocatalytic applications of LDHs, when synthesized as nanomaterials, are discussed considering those related to sensing, oxygen evolution reaction, and other energy issues.

Prussian Blue analogues (PBAs) are a promising class of electrode active materials for batteries. Among them, copper nitroprusside, Cu[Fe(CN)5NO], has recently been investigated for its peculiar redox system, which also involves the nitrosyl ligand as a non-innocent ligand, in addition to the electroactivity of the metal sites, Cu and Fe. This paper studies the dynamics of the electrode, employing surface sensitive X-ray Photoelectron spectroscopy (XPS) and bulk sensitive X-ray absorption spectroscopy (XAS) techniques. XPS provided chemical information on the layers formed on electrode surfaces following the self-discharge process of the cathode material in the presence of the electrolyte. These layers consist mainly of electrolyte degradation products, such as LiF, LixPOyFz and LixPFy. Moreover, as evidenced by XAS and XPS, reduction at both metal sites takes place in the bulk and in the surface of the material, clearly evidencing that a self-discharge process is occurring. We observed faster processes and higher amounts of reduced species and decomposition products in the case of samples with a higher amount of coordination water.