The cost is about half that of making hydrogen by electrolysis of water.

Scientists at NASA's Jet Propulsion Laboratory are developing apparatuses for electrolysis of methanol to produce pure hydrogen for use at industrial sites, in scientific laboratories, and in fuel cells. The state-of-the-art onsite hydrogen generators now in use are based on electrolysis of water to produce hydrogen, with oxygen as a byproduct that has no commercial value in this context. The developmental methanol electrolyzers consume less than half the electrical energy of water electrolyzers in producing a given amount of hydrogen. Even when the cost of methanol is included, the cost of producing hydrogen by electrolysis of methanol is still only about half that of producing hydrogen by electrolysis of water.

Figure 1. Methanol Is Electrolyzed to hydrogen (the main product) and carbon dioxide (the byproduct). The carbon dioxide is vented, while the hydrogen is purified with a molecular sieve to remove traces of water and methanol before use.

An aqueous solution of methanol is circulated past the anode, where methanol and water undergo the reaction

CH₃OH + H₂O → CO₂ + 6H⁺ + 6e^–

The hydrogen ions pass through the membrane to the cathode, where they are reduced to hydrogen molecules in the reaction

6H⁺ + 6e^– → 3H₂

Thus, the net reaction in the cell is

CH₃OH → CO₂ + 3H₂

with carbon dioxide liberated on the anode side and hydrogen liberated on the cathode side. Because the membrane is not totally impermeable by water and methanol, traces of these substances pass through along with the protons. However, the water and methanol can easily be removed from the hydrogen stream by use of a molecular sieve, as is routinely done to remove traces of water and oxygen from hydrogen streams produced in water electrolyzers.

If the solid-electrolyte membrane in the cell is made of Nafion™ (or equivalent) perfluorosulfonic acid-based proton-conducting polymer, then the cell can be operated in the temperature range from 5 to 120 °C. The concentration of methanol in the aqueous solution can range from 0.1 to 8 molar. The membrane is the electrolyte, and it is not necessary to acidify the solution to make it electrically conductive.

Figure 2. Less Voltage is needed to electrolyze methanol than to electrolyze water at the same current density, as indicated by these plots of data from an experiment with a prototype methanol electrolyzer and a commercial water electrolyzer.

Refer to NPO-19948, volume and number of this NASA Tech Briefs issue, and the page number.

This Brief includes a Technical Support Package (TSP).

Making Hydrogen by Electrolysis of Methanol (reference NPO-19948) is currently available for download from the TSP library.

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