Exploring the application potential of ZnAl layered double hydroxides in electrosynthesis of urea with nitrate and CO2

The combination of nitrogen oxides adsorbed from industrial flue gas or nitrate generated from industrial wastewater with carbon dioxide for the synthesis of urea represents a dual strategy for reducing atmospheric and aqueous pollutants and valorizing these waste products. In this study, ZnAl-layered double hydroxides (ZnAl-LDH) catalysts were prepared via different methods to explore their potential for C-N coupling electrochemical urea synthesis in low-concentration (≤10 mM) nitrate wastewater. It was found that the ZnAl-LDH catalyst prepared by the reverse microemulsion method (ZnAl RME), which maintains the special layered structure and properties of LDH with oxygen defects and ZnO component, can significantly enhance urea selectivity, with the corresponding urea yield being 2.45 times that of the ZnAl-LDH prepared by co-precipitation (ZnAl CP). Experimental and theoretical analyses indicated that the smaller negative potential and the temporal separation of intermediates before CO and ammonia formation are the roots of the enhanced electrochemical urea synthesis activity. Although there is still much room for improvement in the performance of ZnAl-LDH for urea electrosynthesis compared with the reported catalysts, this study provides valuable insights and directions for the application of this material in the field of urea electrosynthesis and the future design and optimization of catalysts. ZnAl layered double hydroxides (ZnAl-LDH), enriched with oxygen defects and ZnO, significantly enhance urea selectivity in C-N coupling electrosynthesis, achieving a 2.45-fold increase in urea yield compared to traditional ZnAl-LDH. • ZnAl-LDH with oxygen defects and ZnO components enhances urea yield. • LDH layered structure and properties preserved. • Smaller potential and temporal decoupling intermediates boost activity.