Gas Bubble Behaviour during Water Electrolysis
Due to the presence of hydrogen and oxygen bubbles in the electrolyte during water electrolysis, the potential drop between the cathode and the anode in the two phase mixture electrolyte-gas bubbles will be increased. To reduce this negative effect of the bubbles on the energy efficiency of the process, the bubble behaviour is studied and potential drop measurements have been carried out.
The bubble behaviour is characterized by the bubble nucleation, growth, population, departure radius, frequency and tendency to coalesce. These quantities have been studied at natural and forced convection in dependence of current density, pressure and flow velocity.
The potential drop was measured at forced convection, using nickel expanded metal gauze electrodes of 500 × 20 mm2. The potential drop is lowest at the middle of the electrode. It decreases at increasing flow velocity, from 0.05–0.30 m/s significantly, above 0.30 m/s only weakly. The specific resistance increases at increasing current density. A first step for obtaining a dimensionless relationship between the specific resistance and the gas fraction has been taken.
Investigations of the gas bubble behaviour during water electrolysis at a zero distance between electrodes and diaphragm at natural convection showed, that the bubble behaviour in the gaps of the electrode is influenced essentially by the electrode geometry and, even more, by the chemical composition and texture of the diaphragm.
KeywordsFree Convection Forced Convection Potential Drop Large Bubble Perforated Plate
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