Efficient hydrogen production via ammonia decomposition over iron-cobalt catalysts supported on nitrogen-doped carbon derived from a metal-organic framework heterostructure.

Ammonia (NH3), as a high-density and carbon-free hydrogen carrier, effectively addresses the challenges associated with the storage and long-distance transportation of hydrogen. Thermochemical ammonia decomposition is a key step for hydrogen production. However, the most efficient catalysts currently available are Ru-based, which are high cost and limit large-scale application. Therefore, there is an urgent need to develop non-noble-metal catalysts that combine high catalytic activity with low cost. In this study, a bimetallic alloy catalyst confined within a porous carbon framework was developed using a composite metal-organic framework-on-metal-organic framework (MOF-on-MOF), specifically MIL-101(Fe)/ZIF-67(Co) as the precursor. Two catalysts were successfully synthesized via different pyrolysis strategies: an iron-cobalt alloy supported on nitrogen-doped carbon (FeCo/NC) by direct high-temperature pyrolysis and a urea-assisted iron-cobalt alloy supported on nitrogen-doped carbon (U-FeCo/NC) by urea-assisted pyrolysis. The experimental results show that: (1) FeCo/NC exhibits excellent catalytic performance due to the spatial confinement effect of the carbon framework and the synergy between Fe and Co; (2) U-FeCo/NC displays a thin-layer morphology, which not only significantly enhances the spatial dispersion of the alloy nanoparticles but also markedly increases the density of surface basic sites; (3) in ammonia decomposition tests, U-FeCo/NC achieves an NH3 conversion of 95.9% at 550 °C (with a hydrogen production rate of 32.13 mmol H2 g-1 cat min-1) and nearly complete conversion at 600 °C; (4) after 100 h of continuous operation at 600 °C, no noticeable deactivation of U-FeCo/NC is observed, demonstrating excellent high-temperature stability. This study validates the feasibility of the MOF-on-MOF strategy for constructing bimetallic catalysts and provides important guidance for the future design of low-cost ammonia-to‑hydrogen conversion catalysts.