Reduced water activity in aqueous electrolytes affects oxygen evolution kinetics, expanding electrochemical stability via increased overpotential, but with conductivity and viscosity trade-offs in high-voltage aqueous electrolytes.

Supercapacitors are widely acknowledged as crucial devices for storing and converting electrical energy, alongside batteries and fuel cells. Their ability to rapidly charge and discharge, typically within seconds or even milliseconds, makes them ideal for high-power applications. This feature provides significant advantages for electric vehicles, such as regenerative braking and hill-climbing, where quick energy transfer is essential. To optimize the power performance of supercapacitor cells, it is essential to focus not only on the active material but also on the inactive components, including binders, conductive agents, and separators. The latter functions as an electronic insulating barrier between the cathode and the anode while facilitating optimal ionic transport across the cell. Therefore, particularly in high-power devices, selecting suitable separators is crucial to ensure fast charging kinetics and minimal cell resistance. Despite significant progress in developing high-power electrode materials, relatively few studies have been dedicated to membranes and their impact on the cell's electrochemical behavior. Herein, we provide a practical guide for choosing appropriate membranes for high-power supercapacitor applications. A comprehensive description of the main characterization methods for reliable evaluation of separators, alongside practical experimental examples, is given below. A special discussion is devoted to the evaluation of membrane impedance by various analytical approaches.

Citrate-EDTA-H ₂ O ₂ buffering system recovers Li/Co/Ni/Mn from battery black mass at pH 5.0 using a dual chelation mechanism.

In the evolving landscape of energy storage technologies, nickel-metal hydride (Ni-MH) batteries maintain significant market relevance despite the prominence of lithium-ion systems. The global Ni-MH market continues to grow steadily, reflecting their continued importance in applications demanding safety, environmental compatibility, and reliability. This review provides a critical analysis of electrochemical techniques used to investigate metal hydride electrodes for Ni-MH batteries. We examine the thermodynamic and kinetic phenomena of hydrogen storage in intermetallic compounds, focusing on the correlation between gas-phase hydrogen interactions and electrochemical processes. The review systematically analyzes various methods including cyclic voltammetry, chronopotentiometry, chronoamperometry, galvanostatic and potentiostatic intermittent titration techniques (GITT and PITT), and electrochemical impedance spectroscopy (EIS). For each method, we discuss theoretical foundations, practical applications, and fundamental limitations when applied to metal hydride systems. Our analysis reveals significant challenges in the direct application of methodologies originally developed for liquid-phase electrochemical systems to solid-state metal hydride electrodes. This methodological transfer without appropriate modifications has resulted in inconsistent data interpretation and discrepancies in reported parameters, particularly for hydrogen diffusion coefficients determined by different techniques. We identify common methodological errors and provide guidelines for more accurate experimental design and data analysis. The critical examination presented in this review demonstrates the necessity for researchers to carefully consider the fundamental differences between liquid-phase and solid-state electrochemical processes when selecting and applying characterization methods. Given the continued importance of Ni-MH batteries in energy infrastructure, establishing reliable characterization protocols is important for advancing the fundamental understanding and technological development of metal hydride electrode materials.

A coaxial flow electrolyser generates peroxodisulfuric acid at 180 g L ⁻¹ concentration with 1.5 Wh g ⁻¹ energy consumption. Applied to spent battery black mass, the acid extracts lithium quantitatively but shows limited transition metal recovery.