A high-entropy oxide, Mg₀.₂Co₀.₂Ni₀.₂Cu₀.₂Zn₀.₂O (RS-20), was used to enhance electrochemical ammonia generation from nitrate. The study found that the spin state of Co plays a crucial role in the Cu-Co synergistic effect for ammonia production. RS-20, which contains a high-spin Co, showed significantly higher ammonia production rates and Faradaic efficiencies compared to other samples, including those with Li incorporation, which reduced the Co spin state and thus hindered ammonia generation. The Cu-Co pair in RS-20 facilitated ammonia generation, while a low-spin Co in Li-incorporated samples decreased the synergistic effect. The study also revealed that the Co spin state is essential for achieving high ammonia production, as a high-spin Co enhances the catalytic activity. The results indicate that the spin-related Cu-Co synergistic effect is important for selective catalysis in ammonia synthesis, both in electrocatalysis and thermal catalysis. The high-entropy oxide RS-20 demonstrated excellent performance in converting nitrate to ammonia, with a Faradaic efficiency of 99.3% and a yield rate of 26.6 mg mg⁻¹ h⁻¹. The study also showed that the surface reconstruction of RS-20 during nitrate reduction was limited to a few nanometers, and the Co spin state was crucial for maintaining high ammonia production. The findings highlight the importance of spin states in designing efficient electrochemical processes for ammonia generation.A high-entropy oxide, Mg₀.₂Co₀.₂Ni₀.₂Cu₀.₂Zn₀.₂O (RS-20), was used to enhance electrochemical ammonia generation from nitrate. The study found that the spin state of Co plays a crucial role in the Cu-Co synergistic effect for ammonia production. RS-20, which contains a high-spin Co, showed significantly higher ammonia production rates and Faradaic efficiencies compared to other samples, including those with Li incorporation, which reduced the Co spin state and thus hindered ammonia generation. The Cu-Co pair in RS-20 facilitated ammonia generation, while a low-spin Co in Li-incorporated samples decreased the synergistic effect. The study also revealed that the Co spin state is essential for achieving high ammonia production, as a high-spin Co enhances the catalytic activity. The results indicate that the spin-related Cu-Co synergistic effect is important for selective catalysis in ammonia synthesis, both in electrocatalysis and thermal catalysis. The high-entropy oxide RS-20 demonstrated excellent performance in converting nitrate to ammonia, with a Faradaic efficiency of 99.3% and a yield rate of 26.6 mg mg⁻¹ h⁻¹. The study also showed that the surface reconstruction of RS-20 during nitrate reduction was limited to a few nanometers, and the Co spin state was crucial for maintaining high ammonia production. The findings highlight the importance of spin states in designing efficient electrochemical processes for ammonia generation.