Intensification of alkaline water electrolysis using 3D electrodes, forced electrolyte flow and pulsed voltage

The study presented here investigated the effects of a pulsed voltage in alkaline water electrolysis using 3D Nickel electrodes. The electrolyzer was operated with a solution of 1M of KOH, at room temperature, atmospheric pressure, and an anion exchange membrane. The pulses had a square shape and widths of 200ms, 20ms, and 2ms. Voltage varied from a base value of 1.23V to a peak value between 1.33V-2.23V. Two main parameters were investigated: hydrogen production rate and LHV efficiency. The former was measured using a graduated cylinder, which stored the produced hydrogen, while the former is the ratio between the recoverable energy by hydrogen burning and the consumed energy to produce it. During a pulse, there is the on-time defined as the time at which voltage is at peak value and the off-time, defined as the time when the voltage returns to the baseline value of 1.23V. It was observed that when the pulses were applied, the current at on-time was higher than the current of the DC electrolysis. During off-time, a change in polarization was observed, which indicates a reversible reaction going backwards or the discharge of the electrical double layer. The introduction of pulses has decreased the hydrogen production rate and efficiency. The lower the pulse width, the lower the production rate and efficiency. The effect of electrolyte flow was also observed. An increase in flow has increased mass transfer, promoting an increase in current, production rate, and efficiency. Finally, a mathematical model was proposed to predict pulse behavior.