Electrolysis of water and
In the classical electrolysis of water, water is decomposed into hydrogen gas and oxygen gas using an electric current passed between two electrodes that are immersed in the water. Hydrogen gas is produced at the cathode and oxygen gas is produced at the anode.
The decomposition of water into hydrogen and oxygen gases by electrolysis at standard temperature and pressure is not favourable thermodynamically. Energy in the form of electricity or heat must be supplied. The reaction occurring at the anode can be represented by:
2H₂OO₂ + 4H+ + 4e-
The reaction occurring at the cathode can be represented by:
4H+ + 4e-
Pure water conducts electricity poorly. If an appropriate electrolyte at an appropriate concentration is added to water, the electrical conductivity of water increases considerably and water is more able to be decomposed into its constituent gases. However, care must be exercised in the choosing of electrolytes so that competition does not occur between the electrolyte and water to gain electrons at the cathode (reduction of cation) and to give up electrons at the anode (oxidation of anion).
In the electrolysis of water, pollutants eventually arise at the anode due to oxidation of electrolyte and this results in the formation of anode mud, etc. Some pollutants may occur also at the cathode from reactions with protons and electrons and substances present in water (carbon compounds for example). In addition, either damage to, or dissolution of, electrodes may occur and the constant cleaning, repair or replacement of electrodes results in substantial financial costs.
At present, the cost of producing hydrogen in practical quantities from the electrolysis of water is many times the cost of producing hydrogen from other sources such as methane. This high cost occurs because electrolysis in practice does not meet efficiencies that are possible in theory. Overpotentials are needed to overcome interactions at the electrode surface. Competing side reactions at the electrodes result in various products and pollutants and less than ideal Faradaic efficiency. In addition, much energy is lost as heat because of the difficulty in finding suitable electrodes – particularly anodes. The cost of hydrogen production from electrolysis of water is a linear function of the costs of electricity and electrode maintenance.
For hydrogen derived from water to be a relevant source of stored energy, there is a need to decrease the power utilized for hydrogen production. There is a need also to identify catalysts or other moieties that can facilitate the production of hydrogen without producing side reactions at the electrodes and without causing damage to, or dissolution of, the electrodes.
A decrease in the power needed for the production of hydrogen, and the utilization of moieties that facilitate hydrogen production without damaging or dissolving electrodes, would enable electricity that is generated from renewable energy sources such as solar, wind, hydro, etc. to be used efficiently and economically in the production of hydrogen. In other words, hydrogen could be a relevant, economic source of stored energy.
Unique Global Possibilities has developed a process to utilize carbon dioxide emissions from fossil fuel combustion to efficiently produce energy, in the form of hydrogen, which can be stored.