Application of porous flow through electrodes: IV. Hydrogen evolution on packed bed electrodes of iron spheres in flowing alkaline solutions

Packed bed electrodes of small iron spheres have been used for the electrolytic production of hydrogen from alkaline solutions at different temperatures under conditions of electrolyte flow. The effects of temperature, electrolyte type, concentration and flow rate on the polarization behavior of the electrode were evaluated and analyzed. It was shown that increases in the conductivity of the electrolyte or the operating temperature decreases the potential required to support the reaction. The generated gas bubbles disperse in the pore electrolyte, resulting in an increase in its resistivity and, subsequently, an increase in the potential. It was shown that some gas bubbles are trapped within the porous electrode. The implications of the trapped gas bubbles on the behaviour of the electrode are discussed.Nomenclature A geometrical cross-sectional area (cm²) - a empirical constant (cm³ C^–1) - b RT/F in volt, withR the gas constant,T the absolute temperature - E ₀ electrode potential at the entry face (V) - E _L electrode potential at the exit face (V) - F Faradays's constant - i ₀ exchange current density of the electrode reaction (A cm^–2) - i _L experimentally measured current density at the exist face (A cm^–2) - L bed thickness (cm) - q tortuosity - Q electrolyte volume flow rate (cm³ s^–1) - V electrolyte flow rate,V=Q/A (cm s^–1) - S specific surface area of the bed (cm^–1) - x position in the electrode - transfer coefficient - gas void fraction - ₀ polarization at the entry face (V) - _L polarization at the exit face (V) - porosity - pore electrolyte resistivity ( cm) - ₀ resistivity of the bubble-free pore electrolyte ( cm) - ₀ ^b resistivity of the bulk electrolyte ( cm)