Comparative evaluation of porous materials for catalyst-free hydrogen generation from ethanol under variable heating conditions

Catalyst-free hydrogen generation from ethanol, without added steam, offers a simplified and scalable route for compact reactor systems. In this study, two porous ceramics with sharply contrasting properties (C1 and AZPW40) were directly compared under identical conditions using internal microheating and passive capillary fueling. Once the heating power exceeded ∼200 W, C1 exhibited a sharp increase in hydrogen output, reaching 8.1 × 10 −6 m3 s −1 at 250 W, whereas AZPW40 produced only negligible amounts comparable to C1 at 100 W. This contrast arose because C1, characterized by high porosity, fine multiscale pores, and low thermal conductivity (0.44 W m −1 K −1 ), retained ethanol and confined heat locally, while AZPW40, with lower porosity, larger pores, and high thermal conductivity (14.1 W m −1 K −1 ), dissipated heat rapidly and failed to sustain pyrolysis. Throughout all tests, CO 2 remained undetected, confirming that ethanol decomposition proceeded via non-oxidative dehydrogenation and decarbonylation pathways rather than reforming with in-situ steam. These findings demonstrate that hydrogen yield under catalyst-free conditions is governed primarily by thermal confinement and pore morphology, rather than by chemical composition. The demonstrated microheater-integrated, capillary-fed configuration establishes design principles for achieving hydrogen generation near 300 °C under dry, catalyst-free conditions, and suggests that anisotropic or hierarchical porous architectures could further enhance confinement for next-generation compact hydrogen generators. • Direct comparison of two porous ceramics (C1 vs. AZPW40) under identical conditions. • Catalyst-free hydrogen generation was achieved by C1 at ∼300 °C without external steam. • AZPW40 failed to sustain pyrolysis due to insufficient ethanol retention and heat dissipation. • DSC analysis demonstrated confined evaporation as a prerequisite for decomposition. • Thermal confinement offers a quantitative design principle for compact hydrogen generators.