Saltwater Electrolysis - Adding HCl

JohnRC

In the brine electrolysis, the cathode reaction will always give you hydrogen. Addition of acid will assist this reaction, and also provide your electrolyte with better conductivity.

The anode reaction is a fairly fine balance in a 3-way competition between
(i) emission of chlorine gas:

2 Cl^–(aq) --> Cl₂(g) + 2 e^–

(ii) emission of oxygen gas:

2 H₂O --> 4 H⁺ + O₂(g) + 4 e^–

and (iii) erosion of the anode (depending on the anode material)

M(solid) --> Mⁿ⁺(aq) + n e^–

Keeping the chloride ion concentration high, and choosing an anode material that is a good conductor but otherwise unreactive will help promote reaction (i)

Acidification using HCl is a good move for your electrolysis, but completely useless if you are hoping to obtain NaOH as a product.

Glassy carbon or graphite is probably the best anode material. Note that even unreactive metals -- silver, gold, platinum -- tend to react with nascent chlorine.