RESUMEN
Electrocatalytic urea synthesis via coupling N2 and CO2 provides an effective route to mitigate energy crisis and close carbon footprint. However, the difficulty on breaking N≡N is the main reason that caused low efficiencies for both electrocatalytic NH3 and urea synthesis, which is the bottleneck restricting their industrial applications. Herein, a new mechanism to overcome the inert of the nitrogen molecule was proposed by elongating N≡N instead of breaking N≡N to realize one-step C-N coupling in the process for urea production. We constructed a Zn-Mn diatomic catalyst with axial chloride coordination, Zn-Mn sites display high tolerance to CO poisoning and the Faradaic efficiency can even be increased to 63.5 %, which is the highest value that has ever been reported. More importantly, negligible N≡N bond breakage effectively avoids the generation of ammonia as intermediates, therefore, the N-selectivity in the co-electrocatalytic system reaches100 % for urea synthesis. The previous cognition that electrocatalysts for urea synthesis must possess ammonia synthesis activity has been broken. Isotope-labelled measurements and Operando synchrotron-radiation Fourier transform infrared spectroscopy validate that activation of N-N triple bond and nitrogen fixation activity arise from the one-step C-N coupling process of CO species with adsorbed N2 molecules.
RESUMEN
Electrocatalytic urea synthesis emerged as the promising alternative of Haber-Bosch process and industrial urea synthetic protocol. Here, we report that a diatomic catalyst with bonded Fe-Ni pairs can significantly improve the efficiency of electrochemical urea synthesis. Compared with isolated diatomic and single-atom catalysts, the bonded Fe-Ni pairs act as the efficient sites for coordinated adsorption and activation of multiple reactants, enhancing the crucial C-N coupling thermodynamically and kinetically. The performance for urea synthesis up to an order of magnitude higher than those of single-atom and isolated diatomic electrocatalysts, a high urea yield rate of 20.2 mmol h-1 g-1 with corresponding Faradaic efficiency of 17.8% has been successfully achieved. A total Faradaic efficiency of about 100% for the formation of value-added urea, CO, and NH3 was realized. This work presents an insight into synergistic catalysis towards sustainable urea synthesis via identifying and tailoring the atomic site configurations.
RESUMEN
Ammonia oxidation reaction (AOR) via electrocatalysis is one of the most efficient ways of utilizing ammonia (a zero-carbon fuel with high hydrogen content) for renewable energy systems. However, AOR seriously suffers from the slow kinetics, and low durability due to its multi-electron transfer process and the poison of the reaction intermediates (Nads and NOads) to precious metal catalysts. Herein, hyperbranched concave octahedral nanodendrites of PtIrCu (HCOND) with high-index facets of {553}, {331} and {221} were developed for the first time using a solvothermal method. The HCOND possesses PtIr-rich edges and exhibit highly efficient AOR activity and stability in alkaline media, wherein their onset potential is 0.35 V vs.RHE, which is 60 mV and 160 mV lower than that of the PtIrCu nanoparticles (NPs) (0.41 V) and commercial Pt/C (0.51 V), respectively, and its high mass activity of 40.6 A gPtIr-1 at the 0.5 V vs.RHE is 10.3 times, 2.34 times higher than that of commercial Pt/C (3.9 A gPt-1) and PtIrCu NPs (17.3 A gPtIr-1), respectively. In addition, its peak current density (122.9 A gPtIr-1) is only reduced by 17.7% after 2000-cycles accelerated durability test. Meanwhile, the performance of PtIrCu HCOND is also better than that of other previously reported morphologies of Pt based catalysts (eg. nanoparticles, nanocubes, nanofilm, nanoflowers). The improvement is critically ascribed to unique advantages of the specific HCOND structure including PtIr rich surface, high-index faceted nanodendrites, strong lattice strain and electronic effects. These characteristics endow the HCOND with great promise to reduce Pt and Ir loading dramatically in the practical application of direct ammonia fuel cells.