This study investigates the improvement of spinel SnMn$_2$O$_4$ catalysts for the oxygen evolution reaction (OER) in water electrolysis through the incorporation of Sm doping during the hydrothermal synthesis process. The Sm-doped SnMn$_2$O$_4$ catalyst exhibits enhanced OER performance, with a remarkable overpotential of 212 mV at 10 mA cm$^{-2}$ and a Tafel slope of 37 mV dec$^{-1}$. The catalyst also demonstrates exceptional stability after 5000 cycles and lower impedance characteristics. The addition of Sm dopant increases the surface area and conductivity, significantly improving the OER activity. This research provides a cost-effective and efficient method to enhance the performance of spinel-based OER catalysts, offering broader perspectives for their application in energy generation devices.This study investigates the improvement of spinel SnMn$_2$O$_4$ catalysts for the oxygen evolution reaction (OER) in water electrolysis through the incorporation of Sm doping during the hydrothermal synthesis process. The Sm-doped SnMn$_2$O$_4$ catalyst exhibits enhanced OER performance, with a remarkable overpotential of 212 mV at 10 mA cm$^{-2}$ and a Tafel slope of 37 mV dec$^{-1}$. The catalyst also demonstrates exceptional stability after 5000 cycles and lower impedance characteristics. The addition of Sm dopant increases the surface area and conductivity, significantly improving the OER activity. This research provides a cost-effective and efficient method to enhance the performance of spinel-based OER catalysts, offering broader perspectives for their application in energy generation devices.