Interleaved Electroactive Molecules into LDH Working on Both Electrodes of an Aqueous Battery-Type Device.

By selecting two electroactive species immobilized in a layered double hydroxide backbone (LDH) host, one able to act as a positive electrode material and the other as a negative one, it was possible to match their capacity to design an innovative energy storage device. Each electrode material is based on electroactive species, riboflavin phosphate (RF) on one side and ferrocene carboxylate (FCm) on the other, both interleaved into a layered double hydroxide (LDH) host structure to avoid any possible molecule migration and instability. The intercalation of the electroactive guest molecules is demonstrated by X-ray diffraction with the observation of an interlayer LDH spacing of about 2 nm in each case. When successfully hosted into LDH interlayer space, the electrochemical behavior of each hybrid assembly was scrutinized separately in aqueous electrolyte to characterize the redox reaction occurring upon cycling and found to be a rapid faradic type. Both electrode materials were placed face to face to achieve a new aqueous battery (16C rate) that provides a first cycle-capacity of about 7 mAh per gram of working electrode material LDH/FCm at 10 mV/s over a voltage window of 2.2 V in 1M sodium acetate, thus validating the hybrid LDH host approach on both electrode materials even if the cyclability of the assembly has not yet been met.

Effect of electrolyte flow on a gas evolution electrode.

In this study, the effect of flow of the electrolyte on an electrolysis cell and a zinc cell is investigated. The gain of energy brought by the flow is discussed and compared to the viscous losses in the cells. We point out that the balance between the gained electrical power and the viscous loss power is positive only if the hydrodynamic resistance of the circuit is correctly designed and further comment on the economical viability of the whole process. A model of the studied phenomena is proposed in the last section. This analytical model captures the dynamics of the process, gives the optimal flowing conditions and the limits of the energetical rentability of the process. This study shows that the use of flowing electrolyte in zinc-air batteries can be energetically profitable with the appropriate flowing conditions.

Ni(OH)2 and NiO Based Composites: Battery Type Electrode Materials for Hybrid Supercapacitor Devices.

Nanocomposites of Ni(OH)2 or NiO have successfully been used in electrodes in the last five years, but they have been falsely presented as pseudocapacitive electrodes for electrochemical capacitors and hybrid devices. Indeed, these nickel oxide or hydroxide electrodes are pure battery-type electrodes which store charges through faradaic processes as can be shown by cyclic voltammograms or constant current galvanostatic charge/discharge plots. Despite this misunderstanding, such electrodes can be of interest as positive electrodes in hybrid supercapacitors operating under KOH electrolyte, together with an activated carbon-negative electrode. This study indicates the requirements for the implementation of Ni(OH)2-based electrodes in hybrid designs and the improvements that are necessary in order to increase the energy and power densities of such devices. Mass loading is the key parameter which must be above 10 mg·cm−2 to correctly evaluate the performance of Ni(OH)2 or NiO-based nanocomposite electrodes and provide gravimetric capacity values. With such loadings, rate capability, capacity, cycling ability, energy and power densities can be accurately evaluated. Among the 80 papers analyzed in this study, there are indications that such nanocomposite electrode can successfully improve the performance of standard Ni(OH)2 (+)//6 M KOH//activated carbon (−) hybrid supercapacitor.

Hybrid Li Ion Conducting Membrane as Protection for the Li Anode in an Aqueous Li-Air Battery: Coupling Sol-Gel Chemistry and Electrospinning.

Aqueous lithium-air batteries have very high theoretical energy densities, which potentially makes this technology very interesting for energy storage in electric mobility applications. However, the aqueous electrolyte requires the use of a watertight layer to protect the lithium metal, typically a thick NASICON glass-ceramic layer, which adds ohmic resistance and penalizes performance. This article deals with the replacement of this ceramic electrolyte by a hybrid organic-inorganic membrane. This new membrane combines an ionically conducting inorganic phase for Li ion transport (Li1.3Al0.3Ti1.7(PO4)3 (LATP) and a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer for water tightness and mechanical properties. The Li ion transport through the membrane is ensured by an interconnected 3-D network of crystalline LATP fibers obtained by coupling an electrospinning process with the sol-gel synthesis followed by thermal treatment. After an impregnation step with PVDF-HFP, hybrid membranes with different volumetric fractions of PVDF-HFP were synthesized. These membranes are watertight and have Li ion conductivities ranging from 10-5 to 10-4 mS/cm. The conductivity depends on the PVDF-HFP volume fraction and the fibers' alignment in the membrane thickness, which in turn can be tuned by adjusting the water content in the electrospinning chamber during the process. The alignment of fibers parallel to the membrane surface is conductive to poor conductivity values whereas a disordered fiber mat leads to interesting conductivity values (1 × 10-4 mS/cm) at ambient temperature.