With so many differing opinions out there, we decided to find out on our own which chemicals make the best electrolyte solutions. I write this with the assumption that you have already done some basic research concerning electrolysis, and you have a basic knowledge what I am talking about.
Electrolysis can be defined as the passage of an electric current through an ionic substance resulting in chemical reactions at the electrodes and/or separation of materials.
As you may already know, pure water (H2O) is not a conductor of electricity. At least not within the scope of this process. There just aren't enough dissolved ions to allow electrons to flow freely through the solution. In order for us to initiate the electrolytic process, we must make the water conductive, and we do this by introducing ions into the solution. In order to do that, we add a chemical to the water to introduce dissolved ions.
Once we have enough dissolved ions, and the water has become conductive, we can apply electrical current and begin electrolysis, right? If it were that simple, I wouldn't have taken the time to write all this information down. I would just say dump whatever chemical you want into the water and add the electricity. But it just isn't that simple. Keep in mind, that our goal is to split the water molecule into it's separate components, Hydrogen and Oxygen. This is the fuel we wish to generate. Nothing more.
You see, by adding ions to the water, and applying electrical current we can cause the dissolved ions to participate in various chemical reactions. Those chemical reactions are directly related to the conditions of the cell (voltage, amperage, electrolyte, plate material and temperature). These factors can sometimes allow the formation of entirely different compounds within the cell. Compounds that we don't want. For example, if we dissolve salt (NaCl) into the water and apply electricity to the cell, sure, we'll get hydrogen. Unfortunately, we also get aqueous Sodium hypochlorite (NaOCl), which is BLEACH. Not to mention the Chlorine gas that escapes with the Hydrogen, WHICH IS POISONOUS! Remember the Nazi gas chambers? No, No, No, we want to be careful to introduce ions that do not participate in the process, but only allow the water to be conductive.
If your electrolyte contains certain chemicals that can be reduced at the cathode or oxidized at the anode, this means chemical change. That being said, voltage and amperage directly determine what forms in your cell (if anything). In order to avoid this, we must choose an appropriate electrolyte.
Keep in mind that in order to maintain the health of your cell, you must also limit the amperage you apply to it. Higher current (amperage) means that you are passing more electrons through the cell at any given time. Too much current can cause the conditions of the cell to change by altering the equilibrium of chemicals by simple mass action. This can cause even the electrolytes listed below to react, which we wish to avoid. Also, the more power you apply, the more likely your cell will generate excess heat. This means wasted energy.
Here are a few appropriate electrolytes for you to consider. Some may not be appropriate for you, depending on your experience level. We have color coded them based on their level of danger.