This work unfolds novel electrocatalytic effects of tin for all-vanadium redox flow batteries (VRFBs). By the introduction of Sn²⁺ ions into the electrolyte, tin nanoparticles are in situ electrodeposited on a carbon felt electrode. The effectiveness of the two tin species (Sn²⁺ and Sn⁴⁺) as well as their impact on the kinetics of cathode (VO₂ ²⁺/VO₂ ⁺) and anode (V³⁺/V²⁺) half-reactions are also evaluated comprehensively. Cyclic voltammetry reflects the excellent improvement in reaction kinetics, particularly for the anode half-reaction (i.e. V³⁺/V²⁺ reduction) by reducing its peak potential separation from 1011 to 589 mV, owing to the deposition of tin nanoparticles in its vicinity. The electrocatalytic effects of tin cause a significant improvement in key performance parameters of voltage efficiency, energy efficiency (EE), specific discharge capacity, discharge energy density and cycling stability for VRFBs. The VRFBs employing Sn²⁺ ions in the anolyte exhibit an EE of 77.3% at a high current density of 150 mA cm⁻² while the corresponding specific discharge capacity and discharge energy density are increased by 26.2 and 32.0%, respectively, as compared to the pristine system. Thus, electrolyte utilization is also increased at faster charge/discharge rates due to the reduction of overpotentials. Various characterization techniques confirm the deposition and effectiveness of tin at the electrodes. EIS studies reveal remarkable acceleration in the charge transfer process for the V³⁺/V²⁺ redox couple which is considered as a performance limiting reaction for VRFBs nowadays. Therefore, the convenience in its application coupled with effectiveness for VRFBs, makes tin a commercially feasible electrocatalyst for this technology.

Lithium–sulfur (Li–S) batteries are one of the most promising next generation secondary batteries due to high energy capacity and low cost. However, they suffer from the loss of active material, insulating nature of sulfur, degradation of the lithium anode and fast capacity fading due to polysulfide shuttling. In this work, a novel approach has been made to improve the performance of the Li–S battery by using functional separators that are modified using a plasma technique. The plasma-modified functional separator is made by firstly irradiating a polymer separator with a plasma, secondly followed by coating it with a thin carbon layer which is then thirdly subjected to an additional plasma treatment to modify the carbon layer. The plasma treatment generates various functional groups on the surfaces of the polymer separator and the carbon layer. The plasma-modified functional separator is found to provide more wettability, electric conduction paths and active sites that could facilitate the redox reactions and lithium ion transport as well as reduce the polysulfide shuttling, ultimately leading to a dramatic improvement in the performance of the Li–S battery. Among various plasma gases tested, such as CO₂, N₂ and O₂, the CO₂ plasma is found to be the most effective in improving the electrochemical properties of the functional separators. The polysulfide permeation rate through the CO₂-plasma-modified functional separator is reduced by about 70 times and the Li–S battery employing the functional separator displays an initial capacity of 1204 mA h g⁻¹ and a remaining capacity of 802 mA h g⁻¹ after 100 cycles at 0.2C rate, which account for 57% and 61% increments, respectively, as compared with those of the cell using a pristine separator. In-depth physicochemical and electrochemical analyses have also been carried out to characterize the modified separators and carbon layers and to interpret the reasons for the improved performance of the Li–S batteries employing the functional separators. Accordingly, these functional separators modified with plasma are confirmed to be very promising for the development of high performance Li–S batteries.

We explore a phase engineering strategy to improve the electrochemical performance of transition metal sulfides (TMSs) in anode materials for lithium-ion batteries (LIBs). A one-pot hydrothermal approach has been employed to synthesize MoS₂ nanostructures. MoS₂ and MoO₃ phases can be readily controlled by straightforward calcination in the (200–300) °C temperature range. An optimized temperature of 250 °C yields a phase-engineered MoO₃@MoS₂ hybrid, while 200 and 300 °C produce single MoS₂ and MoO₃ phases. When tested in LIBs anode, the optimized MoO₃@MoS₂ hybrid outperforms the pristine MoS₂ and MoO₃ counterparts. With above 99% Coulombic efficiency (CE), the hybrid anode retains its capacity of 564 mAh g⁻¹ after 100 cycles, and maintains a capacity of 278 mAh g⁻¹ at 700 mA g⁻¹ current density. These favorable characteristics are attributed to the formation of MoO₃ passivation surface layer on MoS₂ and reactive interfaces between the two phases, which facilitate the Li-ion insertion/extraction, successively improving MoO₃@MoS₂ anode performance.