Finding new materials for energy storage or conversion devices at a low cost has become crucial to addressing the current energy crisis in the modern world. Sulfide materials are gaining more interest in battery and supercapacitor electrode materials because of their significant electrochemical reactivity, higher electrical conductivity, weaker metal-sulfur bonds, and superior thermal stability compared to oxide materials. In this work, we first introduce a scalable “heat-up” method to colloidally synthesize NixCo3-xS4 nanoparticles that are smaller than 15 nm in diameter with less than 15% in size dispersion as an effective material for supercapacitor electrodes. These Ni0.8Co2.2S4 electrodes deliver a high energy density of 37.6 Wh/kg at a power density of 1867.7 W/kg. Another critical technology in energy conversion is water splitting, and developing materials that exhibit both high activity and stability in the oxygen evolution reaction (OER) is crucial to improving the efficiency of water splitting. The high entropy transition metal sulfide (HES) catalyst is a promising candidate for enhancing OER rates due to its intrinsic activity and robust stability. In this work, spinel-phase NiCoFeMnInS nanoparticles with an average diameter of 10 nm and NiCoCuMnCrS nanodiscs with an average diameter of 14 nm were successfully synthesized and electrochemically tested. The results show that NiCoFeMnInS nanoparticles achieved a low overpotential of 287 mV, and NiCoCuMnCrS nanodiscs achieved an overpotential of 343 mV.