Revealing the Ambience-Dependent Structural Evolutions of Mo–Based Metal–Organic Frameworks with in Situ TEM for Efficient Electrocatalytic N2 Reduction to NH3

Abstract

The electrocatalytic nitrogen reduction reaction (NRR) has been demonstrated to be the potential alternative strategy for NH3 production in the clean and sustainable manner. Various materials have been widely adopted for the NRR in recent years, and metal-based zeolite imidazole framework-8 (ZIF-8) and their derivatives have been extensively utilized. In this study, we used in situ TEM to probe the structural evolution of Mo-based zeolite imidazole framework-8 (Mo-ZIF-8) and provide the decomposition mechanism under various pyrolysis conditions [Figure 1a]. Upon pyrolyzing Mo-ZIF-8 under oxidative, inactive, and reductive environments, the ZIF-derived ZnO, Mo2C, and Mo nanoparticles (Mo-NPs) in porous N-doped carbon (PNC) are formed, respectively [Figure 1b]. At a lower concentration of Mo, Mo single atoms (Mo-SAs) were formed in the inactive environment, whereas Mo nanoclusters (Mo-NCs) were obtained under the reductive conditions [Figure 1b]. Furthermore, the Mo-related materials/PNC were served as the catalysts for the electrochemical NRR [Figure 1c]. Among all of the Mo-related materials, Mo-SA/PNC achieves a maximum NH3 yield rate [Figure 1d] and outstanding Faradic efficiency (FE) [Figure 1e] at -0.2 V ( vs. RHE), which is 1.4-fold and 8-fold higher than that of the Mo-NP/PNC, respectively. Our findings suggest some new guidelines for the rational design of the derivatives of metal-based metal–organic frameworks and their feasible application in various field. Figure 1