So I tried a simple water electrolysis experiment at home, with NaCl as electrolyte, and a 12 v battery. My wires were made of copper and H2 bubbles were only forming at negative terminal(cathode) on the positive side(anode) nothing was happening. after 3-4 minutes water starting to change into a greenish-blue color and I realized that it must be copper reacting with Chloride ions, after 15 minutes my solution was light blue with exceed NaCl at the bottom, after taking the wires out the solution started to turn into a yellow color in about 10 minutes. So my question is what was the yellow solution and why didn't cathode produce any oxygen?
I'm also worried that the yellow solution might chlorine because I later boiled the solution.