Nanoporous high-entropy alloys fabricated by liquid metal dealloying and surface anodizing for enhanced electrochemical performance in capacitors

Three-dimensional nanoporous (3DNP) TiVNbMoTa high-entropy alloys (HEAs) were developed as potential high-performance electrode materials for metal capacitors. The alloys were fabricated by liquid metal dealloying of a (TiVNbMoTa) 25 Ni 75 precursor in molten Mg at 600 °C and 900 °C, producing ligament sizes of approximately 10 nm and 250 nm, respectively. Anodizing in phosphoric acid formed amorphous oxide layers enriched with Nb and Ta. The thickness of these layers increased linearly with anodizing duration. Structural and compositional analyses confirmed that anodizing changed the chemical states of the amorphous oxides, modified their oxidation states, and increased the concentration of oxygen vacancies. Capacitance measurements using an LCR meter at 1 V and 120 Hz showed that the specimen prepared at 600 °C exhibited a high mass-specific capacitance of 58.3 F/g, which is attributed to its large surface area. However, anodizing reduced its capacitance because pore blockage occurred in the oxide layer. In contrast, the specimen prepared at 900 °C showed a significant capacitance increase after anodizing. This was attributed to preserved pore connectivity and a thicker dielectric layer. Compared with 3DNP Nb, the HEAs showed higher mass-specific capacitance at the same ligament size. This improvement was mainly due to favorable multicomponent oxide chemistry. In addition, the high thermal stability of HEAs allowed the formation of finer ligament structures, which increased the specific surface area and capacitance. These results demonstrate that anodized 3DNP HEAs combine structural stability with tunable surface chemistry. They provide a promising pathway toward optimized capacitor electrode materials.