Scaled-up industrial water electrolysis equipment that can be used with abundant seawater is key for affordable hydrogen production. The search for highly stable, dynamic, and economical electrocatalysts could have a significant impact on hydrogen commercialization. Herein, we prepared energy-efficient, scalable, and engineering electronic structure modulated Mn-Ni bimetal oxides (Mn0.25Ni0.75O) through simple hydrothermal followed by calcination method. As-optimized Mn0.25Ni0.75O displayed enhanced oxygen and hydrogen evolution reaction (OER and HER) performance with overpotentials of 266 and 115 mV at current densities of 10 mA cm−2 in alkaline KOH added seawater electrolyte solution. Additionally, Mn-Ni oxide catalytic benefits were attributed to the calculated electronic configurations and Gibbs free energy for OER, and HER values were estimated using first principles calculations. In real-time practical application, we mimicked industrial operating conditions with modified seawater electrolysis using Mn0.25Ni0.75O∥Mn0.25Ni0.75O under various temperature conditions, which performs superior to the commercial IrO2∥Pt-C couple. These findings demonstrate an inexpensive and facile technique for feasible large-scale hydrogen production.