Influence of Germanium Substitution on Phase Stability and Electrochemical Performance of Niobium Silicide

Abstract Supercapacitors are critical energy storage devices for rapid power delivery applications; however, achieving electrode materials with both high energy density and long‐term cyclic stability remains a significant challenge. In this study, a germanium (Ge) substitution strategy is employed to enhance the energy storage performance of niobium silicide electrodes. Ge is incorporated at varying concentrations, and its effects on microstructural and electrochemical properties are investigated in both as‐cast and annealed samples. Microstructural analysis reveals predominant formation of the Nb(Si,Ge) 2 phase, with a minor Nb 5 (Si,Ge) 3 phase (<5%), indicating high intermetallic phase stability in the ternary alloy system. Electrochemical characterization in a three‐electrode system using 1 M KOH electrolyte demonstrates that Ge‐substituted electrodes exhibit enhanced performance. Notably, as‐cast NbGe 2 achieves the highest specific capacitance of 5.93 F g −1 at 5 mV s −1 , along with excellent cyclic stability. Interestingly, the as‐cast Nb(Si 9 Ge 1 ) 2 , with a minor Ge substitution, displays an unexpected increase in both specific capacitance and cyclic stability compared to NbSi 2 . The enhanced performance is attributed to the high electrical conductivity of Ge, which facilitates efficient ion transport. While the micron‐scale structure imposes certain limitations, these results highlight the potential of Ge‐substituted NbSi 2 as a durable electrode material for high‐temperature and oxidative supercapacitor applications.