Superior electrocatalytic nitrate-to-ammonia conversion activity on CuCo bimetals in neutral media

Abstract

Electrocatalytic recycling of waste nitrate (NO3-) to valuable ammonia (NH3) has been regarded as a sustainable and promising alternative to the unfriendly Haber-Bosch process. Nevertheless, it is still a challenge to achieve high production rate in a neutral media due to the multi-step electron and proton transfer process. Herein, a nonprecious CuCo tandem catalyst is facilely fabricated and the cooperative active sites enable efficient cascade NO3--to-NH3 conversion with outstanding Faradaic efficiency (FE) and high-rate NH3 generation (95 %, 710 μmol h−1 cm−2 at −0.65 VRHE) in neutral media. In-situ Fourier transform infrared spectroscopy (FTIR) is implemented to identify the reaction intermediates to figure out the tandem pathway. Further combined the density functional theory (DFT) calculations, the structure-activity relationship is unveiled. The introduction of Cu regulates the electronic structure of Co to boost the adsorption capacity of nitrate and shifts the d-band to lower the energy barrier. Moreover, the presence of Cu plays a vital role in inhibiting the binding of H*, which ensures the superior FE. To further maximize the energy utilization efficiency, a two-electrode electrolyzer (Cu45Co55||CuNi) is assembled by replacing the anodic oxygen evolution reaction (OER) with thermodynamically favored 5-hydroxymethylfurfural (HMF) oxidation to produce value-added 2,5-furandicarboxylic (FDCA), an important intermediate in the synthesis of bioplastics. These findings might guide the rational design of efficient and inexpensive electrocatalysts to produce value-added chemicals and hold the promise for contributing to carbon peaking and neutrality goals.