Is electrolyte chemical consumed during alkaline water electrolysis?

[Stormer]

In alkaline water electrolysis you add Potassium hydroxide, or Sodium hydroxide to the water you want to turn into hydrogen and oksygen. But is the Potassium hydroxide, or Sodium hydroxide consumed during electrolysis and needs to be replaced? Or do you just have to keep adding water as it is turned into hydrogen and oxygen?

 

[Baluncore]

I expect for a DC current cell, collecting the gasses separately, the potassium metal or sodium metal would be electro-plated onto the electrode. That may depend on the cell voltage.
For an an AC current cell, collecting mixed gasses, the metals would not be consumed as they are cyclically plated onto, and then stripped off the electrodes.

 

[Bystander]

potassium metal or sodium metal would be electro-plated onto the electrode

Are you certain? We're talking about an aqueous system

 

[Baluncore]

I expect

Are you certain?

No.
But reaction of the metal and water may be prevented by the voltage gradient at the polarised electrode surface.
Do you have a better answer?

 

[Bystander]

https://en.wikipedia.org/wiki/Sodium#Commercial_production

 

[Stormer]

I expect for a DC current cell, collecting the gasses separately, the potassium metal or sodium metal would be electro-plated onto the electrode. That may depend on the cell voltage.
For an an AC current cell, collecting mixed gasses, the metals would not be consumed as they are cyclically plated onto, and then stripped off the electrodes.

In that case alkaline water electrolysis would come out pretty bad compared to PEM electrolysis even with the higher cost of the materials in the PEM membranes.
Or maybe you can switch a DC alkaline elektrolyser polarity at regular intervals making a kind of low frequency switched AC and at the same time switching a valve to keep the oxygen and hydrogen in their separate output pipes? Just to avoid the electroplating of the electrodes, and the consumption of the electrolyte chemistry.

 

[Baluncore]

Just to avoid the electroplating of the electrodes, and the consumption of the electrolyte chemistry.

I think it is only necessary to momentarily remove the potential to recover the plated material. That suggests a pulsed, or a full-wave rectified AC supply will continuously recycle the metal hydroxide while keeping the gasses separate.