Electrochemical Nitrogen Reduction Kinetics on a Copper Sulfide Catalyst for NH₃ Synthesis at Low Temperature and Atmospheric Pressure

We studied the electrochemical synthesis of NH₃ on Fe-CuS/C catalysts in an alkaline aqueous solution under ambient conditions. The metal chalcogenide catalyst is active in the nitrogen reduction reaction (NRR) for approximately 45 min with an NH₃ production yield of 16 μg h^-1 cm^-2 at -0.4 V_RHE, while it decomposes to CuO. The rapid degradation of the catalyst hinders the precise investigation of the NH₃ production activity in longer time measurements. Herein, the electrochemical NH₃ production rate is enhanced with increased overpotentials when the degradation effect is mitigated in the measurement, which was difficult to observe in the NRR reports. In the Tafel analysis, the exchange current density, heterogeneous rate constant, and transfer coefficient of the Fe-CuS/C catalyst on the NRR were estimated. When the electrode degradation is mitigated, one of the best NH₃ production activities among the reported metal sulfide electrochemical NRR catalysts is obtained, which is 42 μg h^-1 cm^-2 at -0.6 V_RHE.