Bifunctional CuNi-x nano-alloys for electrocatalytic nitrate reduction and HPAM oxidation coupling reactions

Abstract

Electrochemical synthesis of ammonia (NH₃) through cathodic nitrate reduction presents an effective alternative to the Haber–Bosch process, enabling efficient ammonia production without significant environmental pollution. The electrocatalytic degradation strategy is an efficient and environmentally friendly tool for the treatment of oily wastewater containing partially hydrolized polyacrylamide (HPAM). Thus, coupling cathodic nitrate reduction with anodic HPAM oxidation can further enhance ammonia synthesis efficiency and HPAM degradation efficiency. Here, we reported an N-doped carbon nanotube loaded with CuNi-x (x = 0.5, 1, 2) as an electrocatalyst for cathodic nitrate reduction coupled with anodic HPAM oxidative degradation. Notably, the CuNi-1 variant achieved the highest ammonia yield of 4962.76 ± 40.22 μg h⁻¹ mg_cat⁻¹ and a faradaic efficiency of 85.91 ± 0.42%. Furthermore, the oxidative degradation rate of HPAM reached a maximum of 81.91 ± 0.36% within 2 h. Anodic HPAM oxidation not only promotes cathodic nitrate reduction but also enables the acquisition of valuable anodic products. Using in situ ATR-SEIRAS, in situ DEMS, and DFT calculations, we thoroughly analyzed reaction intermediates and the critical role of the CuNi bimetallic system in electrocatalytic nitrate reduction. The coupled reaction system was established to achieve both efficient ammonia synthesis and HPAM degradation.