Unveiling high-yield dinitrogen-to-green ammonia production via highly defective Cu4Bi5S10/Mn4V2O9 electrocatalysts in alkaline H-cell and stack-cell reactors

Abstract

This study unveils a novel and highly defective Cu₄Bi₅S₁₀/Mn₄V₂O₉ composite catalyst tailored for the electrochemical nitrogen reduction reaction (eNRR). The quaternary catalyst VCuMnBi(2 : 3 : 2 : 2) demonstrated an impressive performance, achieving a high ammonia yield rate of 4356 μg h⁻¹ cm⁻² and a notable faradaic efficiency of 46.1% at −0.6 V vs. RHE in an H-type cell with a 0.5 M KOH solution. In contrast, ternary and binary metal catalysts, CuMnBi(3 : 2 : 2) and CuMn(2 : 3), exhibited lower ammonia yield rates of 3604 μg h⁻¹ cm⁻² and 446 μg h⁻¹ cm⁻², respectively. A two-terminal stack-cell reactor exhibited an average NH₃ yield rate of 1711 μg h⁻¹.cm², 37.2% faradaic efficiency, 46.5% energy efficiency, and 24.2 kW h kg_NH3⁻¹ energy consumption at 1.9 V, achieving innovation in design with the promise of greater efficiency and commercial viability for nitrogen reduction technologies. The excellent conversion due to the quaternary catalyst is ascribed to abundant defects in both cation and anion sites, created by including vanadium (V) as the fourth metal into the ternary CuMnBi system. The proposed mechanisms for the bottleneck reaction in inert N₂ trapping involve the dipole-assisted oxygen vacancy in Mn₄V₂O₉, Bi⁵⁺ in Cu₄Bi₅S₁₀, and the two-phase interface trapping mechanisms. This study underscores the potential of highly defective Cu₄Bi₅S₁₀/Mn₄V₂O₉ catalysts as an efficient and sustainable alternative for electrochemical nitrogen fixation, presenting a greener approach to ammonia production and highlighting its mass-production potential with a stack-cell design.