• Energy Research

Supercapacitors have gained prominence as a cutting‐edge energy storage technology. However, the performance of conventional transition metal oxide electrodes is hindered by their poor electrical conductivity, insufficient ion‐accessible surface area, and complex synthesis processes. Herein, a firsthand demonstration of carbon doping in a crystalline NiCuMn trimetallic alloy, followed by dealloying in an oxygen‐rich environment, is presented. This process produces a highly uniform, 3D flaky nanoporous microstructure with exceptional electrochemical energy storage capabilities. The synthesized electrode demonstrates a remarkable specific capacitance of 1835 F cm−3 at an ultrahigh current density of 10 A cm−3 along with an excellent rate capability of ≈62%. In contrast, the carbon‐free NiCuMn alloy shows 900 F cm−3 capacitance with only 35% retention under similar test conditions. A symmetric supercapacitor showcases an impressive energy density of 120.4 Wh L−1 at a power density of 850 W L−1. It also exhibits remarkable rate capability of ≈50% and excellent cyclic stability, maintaining 96.5% of its capacity after 10000 cycles. The exceptional performance of the developed electrode is attributed to its carbon‐doped unique hierarchical microstructure that ensures efficient and rapid charge transport due to large surface area and high electrical conductivity.