Barium-based Zintl-phase intermetallic supports (BaAlSi and BaSi₂) deliver significantly higher ammonia synthesis rates than their calcium-based counterparts (CaAlSi, CaSi₂, and CaSi), owing to their stronger electron-donating (lower work function) character. These Zintl compounds have low work functions, ranging from 2.6  – 3.5 eV as calculated by DFT, and below 3.0 eV when UPS is measured on Ar-sputtered powders. Under Haber-Bosch reaction conditions at 5 MPa, BaAlSi and CaAlSi form hydrides, but kinetic analysis reveals that this does not alter the catalytic mechanism. Reaction orders and activation energies remain essentially unchanged, and nonhydride-forming silicides (BaSi₂ and CaSi₂) show similarly high activity, indicating that hydride formation has minimal impact on catalysis. At 5 MPa, 400°C, Co/BaAlSi achieved activities of 55 mmol∙g⁻¹∙h⁻¹, exceeding the commercial Fe-based KM-1 catalyst (41 mmol∙g⁻¹∙h⁻¹). Moreover, the BaAlSi- and BaSi₂-supported Co and Ru catalysts achieved NH₃ production rates of 500–700 mmol∙g(Ru/Co)⁻¹∙h⁻¹, surpassing the performance of many previously reported ammonia synthesis catalysts. Previous intermetallic catalysts for ammonia synthesis focused on specific properties such as electride nature, electron-excess, or hydride formation; our results show that a wider range of Zintl compounds have adequately low work functions and reasonably high activities overall.