Basic Research Needs for Solar Energy Utilization

At the PEM system electrodes, this reaction scheme breaks up into two half-reactions:

Cathode PEM Hydrogen Production

2 H+ + 2e− → H 2 (2)

Anode PEM Oxygen Production

H 2 O → ½ O 2 + 2 H+ + 2e− (3)

The alkaline systems differ in the components of the reactions scheme:

Cathode Alkaline Hydrogen Production

2 H 2 O + 2e− → H 2 + 2 OH− (4)

Anode Alkaline Oxygen Production

2 OH−→ ½ O 2 + H 2 O + 2e− (5)

Process Diagram

The overall process for the production of hydrogen gas is depicted in the process diagram shown
in Figure 70, where the input of process water results in an output of compressed hydrogen to a
storage tank.

Not all of the commercial water electrolyzers mentioned above contain all of the elements of this
process. Some units lack water deionizers or reverse osmosis purification units, and others do not
have compressor units that can attain the 6,000 psi pressure required for hydrogen storage. The

Figure 70 Process flow diagram (Source: Ivy 2004)