[AguxOne]

Hi i'm new in the forum, i'd like to help in everything i can.
But now i have a question many people get's confused and i hope someone could give me a nice explanation.

The thing is how to know which reaction is gonna occur into an electrolitic cell from all the posibilities.
For example, i built an electrolitic cell, it has 2 electrodes, one is made of stainless steel, the other is common graphite; and i use sodium bicarbonate as electrolyte.
The cell works nice... and fast too, electrodes are large, and i'm using a printer transformer, a 30V-0,8A lexmark one.
I use it to inflate a balloon, and it works.
The thing is that i thinked at first (in old prototypes), that the reaction that was taking place was always the classic electrolysis separating H2 and O2, but searching some information i find that that's wrong.
I was producing H2 and CO2 that came from the graphite bar (according the internet).
If am not wrong (and please correct me!!), production of O2 needs 1,3V only and i could'nt find the CO2 one (i thinks it's more).
So that's an example of two possible reactions, but only one happens.
Weird answers i got: 1.Both reactions can occur at the same time,  2. Obviously will happen the CO2 one, 3. Both reactions occur in fact, but the O2 is cinetically disadvantaged (wtf, an explanation of this would be REALLY nice); etc of similar answers.
According to my knowledge, ONE reactions occurs (don't know which) until equilibrium is reached, or working conditions change.

Tested other electrolytes, alkalyne ones works always like the recent example.
The other 2 i have are HCl and NaCl, but both works the sames way, i got hydrogen, and clorine oxidizes and got Cl2 and i almost die trying (many times xD).
So i'd like a complete explanation or at least thoughts to discuss, that would be interesting, and if obviously everyone is invited to propose forms to modify my experiment to get O2.
So that's it, greetings
Oh and of course ,can't leave without evidence!

[Borek]

Both reactions occur in fact, but the O2 is cinetically disadvantaged (wtf, an explanation of this would be REALLY nice);

That just means that evolution of O₂ is much slower. To speed up the reaction you can apply higher voltage, but then you are in th erange where other reactions can take place.

As far as I know there is no simple method to predict these things. That is, there is no problem to predict possible reactions using table of standard potentials, but there is no simple way of predicting reaction kinetics, so the reality can differ form predictions.

[AguxOne]

So both reactions occurs then? If there were 100 possible reactions in potential range, they will all happen at the same time (don't matter the rate)? Or they will just happen some random ones that only depends on my working conditions?
If i want to obtain O2 at a reasonable speed, changing the electrode will help? I mean if i use a platinum electrode, i'll get O2 faster? Can other reactions take place with platinum in my conditions?
Can you recomend a cheaper electrode, or at least other ones that can work?
The more little concentracion of carbonates present in water can react at normal voltages to get CO2?
Thanks for the reply!