This study investigates the modification of materials by doping with foreign elements to enhance electrocatalytic activity and focuses on the engineering of an inorganic material composed of transition heterometal-rich pentlandite (Fe3Co3Ni3S8, FCNS) doped with silicon (FCNSSi) as a bifunctional catalyst for the overall electrochemical water splitting process. The FCNSSi electrode exhibits remarkable catalytic activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The OER performance of FCNSSi was evaluated in a 1.0 M KOH solution, achieving an overpotential of 313 mV at 10 mA cm-2. The FCNSSi electrode exhibits a current density of -10 mA cm-2 at a remarkably low overpotential of 164 mV with a Tafel slope of 80.7 mV/dec in HER. Density functional theory (DFT) calculation suggests that Si doping adjusts the binding energies of intermediates on the surface, which weakened the *OH, *O, and *OOH adsorption energies, resulting in enhanced activity for both OER and HER. Moreover, Si doping enhances the hydrogen adsorption activity of all sites. Finally, a two-electrode zero-gap cell assembly was used to investigate the durability of FCNSSi catalyst towards efficient and durable alkaline water electrolysis, demonstrating the promising potential of this catalyst for practical applications at 500 mA cm-2.