water electrolysis itself:
2 H2O(l) → 2 H2(g) + O2(g)
For other (unwanted) possible reactions, we also have the carbon in the graphite, NaHCO3 (baking soda) which is disolved in the water (so aqueous form I guess?), H2O, and the hydrogen and oxygen from the water's electrolysis
I know the products from other possible reactions are probably not dangerous, but I am afraid they will dilute my hydrogen! I'm really bad at chemistry (just never took the time to learn it well), more of a engineering/physics/math guy, so I can't go much further on my own than what I have above. Thanks for your help !