Circulating nitrogen is crucial to the sustainability of our living system. Urea is a central form of nitrogen species that sustains our food supply, but its natural abundance in fertilizing effluent and human metabolite demands circulating technology back to innocuous dinitrogen (N2), while it would otherwise pollute the environment. Electrochemical urea reforming can fragment the urea molecule into N2 and dihydrogen (H2) using renewable electricity, and N2 can be formed directly via oxidative intramolecular N-N coupling on catalytic surfaces. However, this reforming technology remains elusive due to the low N2 selectivity. Herein, we uncovered a urea oxidation pathway that selectively splits urea into N2, driven by nickel oxide (NiO) lattices with adjacent Ni sites. The double-ended urea coordination on NiO facilitates intramolecular N-N coupling and suppresses C-N cleavage toward undesired overoxidation products. Further lattice engineering via Al substitution creates the optimal performance of near-unity N2 selectivity toward N-based products and a 1 order of magnitude higher N2 production rate compared to those of most reported catalysts. The electrochemical urea reforming devices can effectively split urea into N2 and H2 using both synthetic urea and artificial urine, reviving this technology as a bridge of sustainable energy and environmental treatment toward the water-energy-food nexus.
Chen et al. (Sun,) studied this question.