Strongly coupled Ag/Cu with MXene for efficient tandem nitrate reduction reaction and zinc–nitrate batteries†

The electrochemical conversion of nitrate ions into valuable ammonia represents a sustainable alternative to the traditional Haber–Bosch process. However, ammonia electrosynthesis from nitrate reduction is still limited by the low catalytic activity and faradaic efficiency. This work puts forward a two-step tandem strategy for nitrate reduction to ammonia by integrating charge polarized Ag nanoparticles and Cu nanoclusters on MXene to boost the electrocatalytic performance. The strongly coupled Ag nanoparticles/Cu clusters with MXene result in polarized Ag^δ+/Cu^δ+, which preferentially catalyzes NO₃⁻ → NO₂⁻ and NO₂⁻ → NH₃ conversions, respectively. The synthesized Ag/Cu/MXene composite sample achieves an ammonia yield rate of 10.3 mol g_cat.⁻¹ h⁻¹ and a faradaic efficiency of 87.7% at −1.0 V versus a reversible hydrogen electrode, as well as good cycling stability. The composite was assembled into a zinc–nitrate battery as the cathode; the open-circuit voltage of the battery reaches 1.81 V, with a maximum output power density of 5.75 mW cm⁻², demonstrating potential application value.