[en] The electrochemical reduction of WO₃ to W metal using a fluidised cathode process has been investigated. Voltammetry was compared with thermodynamic predictions using a predominance diagram for the system to help explain the reaction mechanism. The main reduction potential was located to be −2.14 V vs. Ag/Ag⁺. By performing near-exhaustive electroreduction at constant potential, the Faradaic current efficiency was estimated to be >82%. The metal is produced in the form of homogeneous particles bound to the substrate electrode, which can periodically spall off. The effects of metal oxide-to-salt ratio and of fluidisation conditions on the process were investigated. Higher loading of metal oxide particles resulted in an increase in the rate of metallic deposit growth and less current ‘noise’, while the rate of reduction was relatively insensitive to flow rate of the Ar agitation gas feed, up to a limit where transition to a different flow regime is expected to be the cause of increased reaction rate.

[en] The future need to recycle enormous quantities of Li-ion batteries is a consequence of the rapid rise in electric vehicles required to decarbonise the transport sector. Cobalt is a critical element in many Li-ion battery cathode chemistries. Herein, an electrochemical reduction and recovery process of Co from LiCoO₂ is demonstrated that uses a molten salt fluidised cathode technique. For the Li-Co-O-Cl system, specific to the experimental process, a predominance diagram was developed to aid in understanding the reduction pathway. The voltammograms indicate two 2-electron transfer reactions and the reduction of CoO to Co at −2.4 V vs. Ag/Ag⁺. Chronoamperometry revealed a Faradaic current efficiency estimated between 70-80% for the commercially-obtained LiCoO₂ and upwards of 80% for the spent Li-ion battery. The molten salt electrochemical process route for the recycling of spent Li-ion batteries could prove to be a simple, green and high-throughput route for the efficient recovery of critical materials.

[en] Flow batteries represent a possible grid-scale energy storage solution, having many advantages such as scalability, separation of power and energy capabilities, and simple operation. However, they can suffer from degradation during operation and the characteristics of the felt electrodes are little understood in terms of wetting, compression and pressure drops. Presented here is the design of a miniature flow cell that allows the use of x-ray computed tomography (CT) to study carbon felt materials in situ and operando , in both lab-based and synchrotron CT. Through application of the bespoke cell it is possible to observe felt fibres, electrolyte and pore phases and therefore enables non-destructive characterisation of an array of microstructural parameters during the operation of flow batteries. Furthermore, we expect this design can be readily adapted to the study of other electrochemical systems. (paper)

[en] Highlights: • Average grain size of 154 μm has been obtained in the Al-V alloys. • Equilibrium primary Al₁₀V particles form in-situ with cooling rate around 3.5 K/s. • HRTEM images show good lattice matching between Al₁₀V particles and Al grains. • Al₁₀V particles have two 3D morphologies: plate and octahedron. • Al₁₀V particles are responsible for the grain refinement via enhanced nucleation. Grain refinement of cast commercial purity aluminium by vanadium and the underlying mechanism have been investigated. Addition of 0.3 wt% and 0.4 wt% vanadium leads to columnar to equiaxed transition and the average grain sizes are refined to around 196 μm and 154 μm, respectively. Pro-peritectic equilibrium Al₁₀V particles are identified near the grain centres. These Al₁₀V particles have either octahedron or plate morphology with the bound planes belonging to {111} crystallographic planes. Three orientation relationships are also determined between the Al₁₀V particles and aluminium grains. Crystallographic analysis based on the experimental orientation relationships indicates that the Al₁₀V particles have relatively high nucleation potency for solid aluminium. Calculation of free growth undercooling based on the size distribution of the Al₁₀V particles reveals that the relatively large size of Al₁₀V particles facilitates the grain initiation of aluminium grains on these particles. Moreover, it is found that the level of vanadium added provides sufficient growth restriction effect in the aluminium melt as quantified by its growth restriction factor. All the three factors, i.e., sufficient potency of Al₁₀V particles, relatively large size of the Al₁₀V particles and adequate growth restriction effect by solute vanadium work in concert to achieve the grain refinement observed in Al-V alloys.

[en] Energy-dispersive X-ray diffraction was used to follow the reduction of UO₂ to U in LiCl–KCl eutectic. A novel electrochemical cell was designed and constructed in order to follow molten-salt electrochemical investigations in situ. A novel electrochemical cell has been designed and built to allow for in situ energy-dispersive X-ray diffraction measurements to be made during reduction of UO₂ to U metal in LiCl–KCl at 500°C. The electrochemical cell contains a recessed well at the bottom of the cell into which the working electrode sits, reducing the beam path for the X-rays through the molten-salt and maximizing the signal-to-noise ratio from the sample. Lithium metal was electrodeposited onto the UO₂ working electrode by exposing the working electrode to more negative potentials than the Li deposition potential of the LiCl–KCl eutectic electrolyte. The Li metal acts as a reducing agent for the chemical reduction of UO₂ to U, which appears to proceed to completion. All phases were fitted using Le Bail refinement. The cell is expected to be widely applicable to many studies involving molten-salt systems.

[en] Highlights: • Continuous hydrothermal synthesis production of Cu(I)oxide nanomaterials for CO₂ electroreduction. • Exclusive production of formate at up to 66% Faradaic efficiency. • Rotating ring-disc electrode effective means of studying CO₂ electroreduction process. A continuous hydrothermal flow synthesis method was used to produce copper(I) oxide nanoparticles, which were used as an electrocatalyst for the reduction of CO₂. A rotating ring-disc electrode (RRDE) system was used to study the electroreduction processes, including a systematic study (including quantitative NMR analysis) to identify product species formed at the disc and detected at the ring. In 0.5 M KHCO₃ electrolyte with a pH of 7.1, carbon dioxide was found to be exclusively reduced to formate. In the potential range −0.5 to −0.9 V vs the reversible hydrogen electrode (RHE), an active material/glassy-carbon disc electrode was shown to produce formate, with a maximum Faradaic efficiency of 66% (at −0.8 V vs RHE).

[en] While silicon-based negative electrode materials have been extensively studied, to develop high capacity lithium-ion batteries (LIBs), implementing a large-scale production method that can be easily transferred to industry, has been a crucial challenge. Here, a scalable wet-jet milling method was developed to prepare a silicon-graphene hybrid material to be used as negative electrode in LIBs. This synthesized composite, when used as an anode in lithium cells, demonstrated high Li ion storage capacity, long cycling stability and high-rate capability. In particular, the electrode exhibited a reversible discharge capacity exceeding 1763 mAh g⁻¹ after 450 cycles with a capacity retention of 98% and a coulombic efficiency of 99.85% (with a current density of 358 mA g⁻¹). This significantly supersedes the performance of a Si-dominant electrode structures. The capacity fade rate after 450 cycles was only 0.005% per cycle in the 0.05–1 V range. This superior electrochemical performance is ascribed to the highly layered, silicon-graphene porous structure, as investigated via focused ion beam in conjunction with scanning electron microscopy tomography. The hybrid electrode could retain 89% of its porosity (under a current density of 358 mA g⁻¹) after 200 cycles compared with only 35% in a Si-dominant electrode. Moreover, this morphology can not only accommodate the large volume strains from active silicon particles, but also maintains robust electrical connectivity. This confers faster transportation of electrons and ions with significant permeation of electrolyte within the electrode. Physicochemical characterisations were performed to further correlate the electrochemical performance with the microstructural dynamics. The excellent performance of the hybrid material along with the scalability of the synthesizing process is a step forward to realize high capacity/energy density LIBs for multiple device applications. (paper)

[en] Polypyrrole (PPy) has high electrochemical activity and low cost, so it has great application prospects in wearable supercapacitors. Herein, we have successfully prepared polypyrrole/reduced graphene oxide (PPy/rGO) nanocomposite cotton fabric (NCF) by chemical polymerization, which exhibits splendid electrochemical performance compared with the individual. The addition of rGO can block the deformation of PPy caused by the expansion and contraction. The as-prepared PPy-0.5/rGO NCF electrode exhibits the brilliant specific capacitance (9300 mF cm⁻² at 1 mA cm⁻²) and the capacitance retention with 94.47% after 10 000 cycles. At the same time, the superior capacitance stability under different bending conditions and reuse capability have been achieved. All-solid-state supercapacitor has high energy density of 167 μWh cm⁻² with a power density of 1.20 mW cm⁻². Therefore, the PPy-0.5/rGO NCF electrode has a broad application prospect in high-performance flexible supercapacitor fabric electrode. (paper)

[en] A combined X-ray diffraction and thermal imaging technique is described to investigate the effect of thermal gradients on high-temperature composite materials. A new technique combining in situ X-ray diffraction using synchrotron radiation and infrared thermal imaging is reported. The technique enables the application, generation and measurement of significant thermal gradients, and furthermore allows the direct spatial correlation of thermal and crystallographic measurements. The design and implementation of a novel furnace enabling the simultaneous thermal and X-ray measurements is described. The technique is expected to have wide applicability in material science and engineering; here it has been applied to the study of solid oxide fuel cells at high temperature

[en] Heteroatom-doped carbon materials with a high specific area, a well-defined porous structure is important to high-performance supercapacitors (SCs). Here, S and N co-doped three-dimensional porous graphene aerogel (NS-3DPGHs) have been synthesized in a facile and efficient self-assembly process with thiourea acting as the reducing and doping agent solution. Operating as a SC electrode, fabricated co-doping graphene, i.e. the sample of NS-3DPGH-150 exhibits the highest specific capacitance of 412.9 F g⁻¹ under 0.5 A g⁻¹ and prominent cycle stabilization with 96.4% capacitance retention in the back of 10 000 cycles. Furthermore, based on NS-3DPGH-150, the symmetrical supercapacitor as-prepared in 6 M KOH displays a superior energy density of 12.9 Wh kg⁻¹ under the power density of 249 W kg⁻¹. Hence, NS-3DPGHs could be considered as an excellent candidate for SCs. (paper)