Around 1900 Tesla talked about running electricity generated at Niagara Falls through HHO cells to produce free gas. Whether it was actually done then I'm not sure.
HHO gas water electrolysis can be free in series from direct current consumed in a load outside of a cell.
I have since increased the length of carbon vs. aluminum and down to 0.07 amps, 1.25 watt, consumed at 17.85v.
I believe zero power consumption is possible within an HHO cell.