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The size-distribution, coverage, electrochemical impedance, and mass-transport properties of H 2 gas-bubble films were measured for both planar and microwire-array platinized n + -Si cathodes performing the hydrogen-evolution reaction in 0.50 M H 2 SO 4 (aq). Inverted, planar n + -Si/Ti/Pt cathodes produced large, stationary bubbles which contributed to substantial increases in ohmic potential drops. In contrast, regardless of orientation, microwire array n + -Si/Ti/Pt cathodes exhibited a smaller layer of bubbles on the surface, and the formation of bubbles did not substantially increase the steady-state overpotential for H 2 (g) production. Experiments using an electroactive tracer species indicated that even when oriented against gravity, bubbles enhanced mass transport at the electrode surface. Microconvection due to growing and coalescing bubbles dominated effects due to macroconvection of gliding bubbles on Si microwire array cathodes. Electrodes that maintained a large number of small bubbles on the surface simultaneously exhibited low concentrations of dissolved hydrogen and small ohmic potential drops, thus exhibiting the lowest steady-state overpotentials. The results indicate that microstructured electrodes can operate acceptably for unassisted solar-driven water splitting in the absence of external convection and can function regardless of the orientation of the electrode with respect to the gravitational force vector.
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This content will become publicly available on November 24, 2026
Computational Modeling of Methane Pyrolysis in a Fixed-Bed Reactor for CO₂-Free Hydrogen Production”
Understanding the dynamics of a methane bubble in a liquid metal bubble column reactor is important for optimizing the reactor design and improving efficiency. To better understand methane bubble dynamics and the reaction to produce hydrogen, we employ ANSYS Fluent to investigate the gas-liquid interface, to relate the surface area where reaction occurs to bubble size, and to determine coalescing behavior as a function of dimensionless numbers. Once the simulation is verified by comparing bubble velocity [1], shape [2], and coalescing distance [3] for a water-air system, a methane bubble in liquid bismuth at 1000 k is examined [4] [5]. Experimentally obtained kinetic parameters for the reaction are used in the computations. The bubble interfacial area to volume ratio is maximized at a diameter of 4mm and does not induce breakage of the bubble. The coalescing distance for two bubbles of methane in bismuth is a third of the distance for air in water bubbles. REFERENCES 1. S. Baz-Rodríguez, A. Aguilar-Corona, and A. Soria, Rev. Mex. Ing. Quím. 8, 213 (2009). 2. R. Clift, J. R. Grace, and M. E. Weber, Bubbles, Drops, and Particles (Academic Press, New York, 1978). 3. T. Otake, S. Tone, K. Nakao, and Y. Mitsuhashi, Chem. Eng. Sci. 32, 377 (1977). 4. M. J. Assael, K. Gialou, K. Kakosimos, and I. Metaxa, High Temp. High Press. 41, 101 (2012). 5. Engineering ToolBox (2004), https://www.engineeringtoolbox.com/methane-d_1420.html. Funding acknowledgement The support of the US National Science Foundation under grant number 2317726 is gratefully acknowledged.
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- Award ID(s):
- 2317726
- PAR ID:
- 10653012
- Publisher / Repository:
- American Physical Society, Division of Fluid Dynamics
- Date Published:
- Format(s):
- Medium: X
- Location:
- Houston, TX
- Sponsoring Org:
- National Science Foundation
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