Efficient Electrocatalytic Ammonia Synthesis via Spirulina Biomass Based on High-Entropy Alloy

To address persistent challenges of low ammonia yield and Faradaic efficiency (FE) in electrocatalytic nitrogen reduction, this work pioneers a breakthrough strategy utilizing nitrogen-enriched spirulina biomass as the nitrogen source coupled with high-entropy alloy (HEA) catalysts. This novel electrocatalytic synthesis route establishes a sustainable pathway for green ammonia production. The MnFeNiCuAl and MnFeNiCuCo HEAs were synthesized via a coprecipitation method. Structural analysis reveals that MnFeNiCuAl exhibits a pure face-centered cubic (FCC) phase, and the Al element incorporation suppresses high-temperature sintering and mitigates compositional segregation. Its oxygen vacancy concentration is higher than that of the MnFeNiCuCo HEO, which can optimize the multielectron transfer kinetics, thereby enhancing the electrocatalytic performance. Electrocatalytic tests using four amino acid model compounds from spirulina (glutamate, histidine, leucine, and phenylalanine) revealed superior activity of the MnFeNiCuAl catalyst compared to that of MnFeNiCuCo. The MnFeNiCuAl HEA catalyst was then employed for the spirulina electrolysis, which achieved a high NH₃ yield of 1783.9 μg/(h cm²) at -0.9 V vs RHE and an FE up to 80.27% at -0.6 V vs RHE. Meanwhile, cycling stability tests validate the robust stability and durability of the MnFeNiCuAl catalyst. The mechanism analysis showed that the carboxyl groups (-COOH) dissociate to generate H⁺ as proton sources under the action of Cu/Al sites, while the amino groups (-NH₂) are adsorbed and activated at the Fe sites. Subsequently, the activated amino groups undergo continuous hydrogenation to form *NH₃, which then desorbs from the Fe sites.