Toward electrified CO2-free hydrogen production: A multiphysics model investigating microwave-driven methane pyrolysis in fluidized beds

Electrified methane pyrolysis using microwaves (MW) offers a promising pathway for CO2-free hydrogen production, effectively bridging fossil fuels to renewable energies. However, its optimization and scale-up remain largely underdeveloped. The progress is hindered primarily due to an inadequate understanding of its complex multiphysics, multiscale nature. Here, we develop a first-of-its-kind multiphysics model coupling electromagnetic fields with heterogeneous reacting multiphase fluidized bed (FB) dynamics to explore and optimize MW-driven methane pyrolysis. Results indicate that even minimal bubbling fluidization mitigates MW-induced thermal gradients by 54 %. At 1100 °C, a modest MW-induced thermal gradient of 35 °C boosts local hydrogen production rates by over 50 % along the reactor, highlighting the strong thermal sensitivity of the process. Interestingly, the thermal and hydrodynamic regimes evolve with operating temperature: below 1000 °C, MW-induced thermal gradients dictate the profile of methane conversion rates (CR), while above 1200 °C, fluidization (bubble) dynamics take precedence. Our energy analysis reveals the critical role of MW coupling efficiency, methane CR (operating temperature), and minimizing heat losses in optimizing system performance. Our findings show that at 1200 °C with a methane CR of ∼92 %, optimizing electromagnetic design and minimizing thermal radiation losses can reduce energy intensity from 84 to 5 kWh/kg H2, highlighting the importance of proper electromagnetic and thermal management design considerations. Finally, the simulations reveal that MW heating enables reactor-wide methane pyrolysis with radially uniform energy distribution, effectively mitigating carbon buildup on reactor walls compared to conventional heating. The present study provides actionable insights into unlocking the full potential of MW-driven methane pyrolysis, accelerating the adoption of efficient, scalable, and electrified CO2-free hydrogen production technologies.