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Alkaline electrolyzer, where am I doing wrong?

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Junior Member level 2
Mar 22, 2022
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According to wiki the cell voltage is (say) 2.4 V and the current density is 0.3A/cm2 Electrolyzer cell resistance = anode resistance + cathode resistance + electrolyte resistance Assume that the electrodes are made of stainless steel 316L with a thickness of 0.3 mm and the electrolyte layer between them is 2 mm. The operating temperature is 60C and the electrolyte is 25% KOH.

Resistivity of steel 316L for 60C = 7,67232E-06 Ohm*mm
Specific electrical resistance 25% KOH for 60C = 9,657298288 Ohm*mm

Assume square electrodes 100x100mm, 30% of the area is for bubbles and free space for gas removal, i.e. the area of the electrodes is 7000mm2.

R electrodes = 2 * (7,67232E-06*0,3/7000) = 6,57627E-10 Ohm
R electrolyte= 9,657298288*2/7000= 2,759228E-03 Ohm
R cell= 5,51846E-03 Ohm

Where is the problem ?
if ohms law applies I=U/R = 2.4/ 5.51846E-3 = 435A for an area of 70cm2 ie, current density 6.2 A/cm2
Where am I making mistake?

You are omitting 1.23 V potential difference from your calculation. Electrolysis cell is no pure resistor.

if only it were that simple.
For alkaline (KOH, NaOH) elektolyser paid,

Vcell = Vrev + (Ra + Rc + Rele ) * Iel + hact,a + hact,c

Vrev reversible potential (voltage) for 20C and pressure 1 bar is 1.23 V it changes with temperature and pressure
Ra Rc ohmic resistances of anode and catode electrodes
Rele represents the ohmic loss of elektrolytes
Iel current over cell
hact,a hact,c activation overvoltage at the anode and the cathode. depends on temperature and current density. Anode activation overvoltage will typical 0,2 - 0,45 V

Thank you for your help.
Why am I asking this?
I am thinking of building an electrolyzer as a source of HHO gas for the welder and brazing.
Thanks to the EU bullshit, it is increasingly difficult and expensive to have pressure cylinders with oxygen and acetylene.
And so I'm considering HHO+PB

Due to the price and simplicity, I am thinking of connecting directly to the rectified 230V
This gives the basic parameters of DC 310V 16A.
Electrode material stainless steel 316L 0.3mm, sold in sheets 1x2m

I am able to get from sheet metal

9x9x2= 162
electrode with an internal surface 98x98 mm , active surface for examaple 73%
Active surface 70cm2 , electrode distance 2mm.
cell resistance at 10C and 25% KOH 12,224 mOhm for 60C 5,518 mOhm, current density for 16A 0.23A/cm2

8x8x2=128 electrode with an internal surface 110x110 mm , active surface 88cm2
cell resistance at 10C and 25% KOH 9,743 mOhm for 60C 4,484 mOhm, current density for 16A 0.182A/cm2

etc. in short, I'm trying to figure out what number of electrodes and what size will be optimal

There's been a lot of folks trying HHO and you should look at construction that works and that doesn't. I believe math will let you down in the face of unknowns. Even simple stuff like making bubbles leave quick and correct, and of course suppressing internal combustion (not that bad an event at low pressure, but a sure-fire (heh) efficiency killer).

I have looked at several commercially available electrolyzer welders and several commercially supplied cells
An example of this is a welding machine using HHO + vapors from acetone, toluene or technical benzine, which was produced by us more than 30 years ago


this is what a commercially produced electrolyzer cell looks like today, this one is for 12V


The common denominator is , the designers were interested in the highest possible performance with the lowest possible production costs, not efficiency, and so the cells work with a voltage over 3V to achieve higher performance per area with lower efficiency.

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