Oxidized Carbons for Storing Electrolyzed Hydrogen

A project log for Monolithic Cotton Supercapacitors

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MECHANICUSMECHANICUS 03/26/2016 at 00:310 Comments

The main problem with aqueous electrolytes especially basic or acidic ones is that they are limited to around .8 volts full cell potential due to electrolysis of the water and evolution of oxygen at the cathode and hydrogen at the anode.

Yes your multimeter may read 1.2 volts potential open circuit but the cell will quickly self discharge to .8volts in a few minutes.

In order to fix this pH neutral electrolytes need to be used and an oxygen scavenger must be present. Cathodic corrosion inhibitors such as potassium nitrite or sodium molybdate are great candidates.

For the anode, oxygen groups present on the carbons can easily store the hydrogen evolved from electrolysis in faradaic redox reactions.

At the cathode when we have KI present iodate- or I2- forms and can be reduced. This produces even more faradaic redox reactions.

These reactions happening at both the anode and cathode defy conventional wisdom on how psuedocapacitors work and things start to look like a battery.

At this point the discharge curves no longer act like capacitors and we can no longer consider them as such. Consequently we also approach energy storage densities of lithium ion batteries. Expressed in farads it would be around 600 farads per gram of active material but as I said that is not an intelligent way to describe these systems. It is best to being using watt hours per gram this also gives us a great comparison between lithium ion and our ultra-capacitors.