What Is SPE/PEM in a Hydrogen Water Bottle?

SPE/PEM is the membrane inside a hydrogen water bottle that keeps the hydrogen in your water and sends everything else out. SPE stands for solid polymer electrolyte and PEM for proton exchange membrane. In a hydrogen water bottle the two names describe the same part: a thin sheet that sits between two electrodes and splits them into separate chambers.

To see why that sheet matters, start with what the bottle is doing when you press the button.

How a hydrogen water bottle makes hydrogen

Rechargeable hydrogen water bottles use electrolysis. A small electric current passes through water and splits some of the water molecules apart:

• hydrogen gas forms at the negative electrode (the cathode);
• oxygen gas forms at the positive electrode (the anode).

The hydrogen dissolves into the water, and that dissolved hydrogen is what makes it hydrogen water. The question every design has to answer is what happens to the oxygen, and to anything else the current produces at the anode.

The problem with a bottle that has no membrane

In the simplest bottles, both electrodes sit in the same water. Hydrogen and oxygen form side by side, and both end up in the water you drink. Drinking water also carries dissolved salts. Tap water in particular contains chloride, and electrolysis can turn chloride into chlorine at the anode. With both electrodes in one chamber, any chlorine formed there has nowhere to go but your water.

What the SPE/PEM membrane changes

An SPE/PEM bottle puts the membrane between the electrodes, so each one works in its own chamber:

1. In most bottles the anode sits below the membrane, in a separate lower chamber. Oxygen and any by-products form there.
2. The membrane lets hydrogen ions (protons) pass through it, and very little else.
3. On the drinking side, those protons become hydrogen gas at the cathode and dissolve into your water.
4. The gases from the lower chamber leave through a vent instead of entering your drink.

The membrane is usually paired with platinum-coated electrodes. Platinum is a catalyst: it speeds up the reaction at the electrodes.

What to check when you compare bottles

• Is it SPE/PEM? If the listing does not say so, assume both electrodes share one chamber.
• Is there a vent for the lower chamber? The membrane separates the gases, and the vent is where the unwanted ones leave.
• How is the hydrogen level stated? Figures are given in ppm (parts per million) or ppb (parts per billion), and "up to" means a maximum, not the level in every cycle.
• What touches the water? Look at the bottle material and the lid, since you will drink from it every day.
• What do you have to keep buying? Some systems need filters or replacement parts.

How the HDRO Bottle 4.0 does it

The HDRO Bottle 4.0 is an SPE/PEM hydrogen water bottle. It uses a platinum-coated proton exchange membrane, and a dual chamber exhaust vent expels the oxygen and chlorine gases, so only hydrogen is infused into your drinking water. It produces up to 6.0 ppm (6,000 ppb) of dissolved hydrogen.

The bottle itself is 9.1 oz (270 ml) of polycarbonate, shatter-proof body and lid. There are no filters and no replacement parts to buy.

For more on using it, see our hydrogen water bottle FAQ.