Electrochemical hydrogen storage: Critical parameters and performance drivers

Electrochemical hydrogen storage has emerged as a promising route for safe and reversible hydrogen storage under ambient conditions. However, its performance is highly sensitive to the interplay of electrode design, electrolyte composition, and applied current density. This review systematically evaluates chronopotentiometry studies published from 2010 to 2025, highlighting how experimental parameters govern kinetics, reversibility, and gravimetric capacity. The analysis reveals that over 70 % of high-performing systems employed Ag/AgCl or saturated calomel electrodes, with alkaline electrolytes in the range of 6–7 M KOH offering high ionic conductivity and stability. The reported current densities ranged from 50 to 600 mA/g, with asymmetric charge-discharge protocols improving power output and extending cycle life. Under optimized conditions, gravimetric storage capacities approaching 2.5 wt% were achieved, corresponding to 1500–14000 mAh/g depending on the active material, which is comparable to intermetallic hydrides under milder operating conditions. In addition to the well-known effects of current density and electrolyte concentration, factors such as electrode coating, mixing methods, and cell design can modify storage capacity by more than 20 % in otherwise similar systems. By linking material design, electrolyte selection, and system parameters, this review presents a quantitative roadmap to guide the optimization and future development of electrochemical hydrogen storage solutions.