The hybrid sulfur cycle (HyS) is a two-step water-splitting process intended to be used for

hydrogen production Hydrogen production is the family of industrial methods for generating hydrogen gas. As of 2020, the majority of hydrogen (∼95%) is produced from fossil fuels by steam reforming of natural gas and other light hydrocarbons, partial oxidation of ...

. Based on

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

oxidation and reduction, it is classified as a hybrid

thermochemical cycle Thermochemical cycles combine solely heat sources (''thermo'') with ''chemical'' reactions to split water into its hydrogen and oxygen components. The term ''cycle'' is used because aside of water, hydrogen and oxygen, the chemical compounds used in ...

because it uses an

electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outc ...

(instead of a thermochemical) reaction for one of the two steps. The remaining thermochemical step is shared with the sulfur-iodine cycle. The Hybrid sulphur cycle (HyS)was initially proposed and developed by Westinghouse Electric Corp. in the 1970s, so it is also known as the "Westinghouse" cycle. Current development efforts in the United States are being led by the

Savannah River National Laboratory The Savannah River National Laboratory (SRNL) is a multi-program national laboratory for the U.S. Department of Energy’s (DOE) Office of Environmental Management. SRNL is located at the Savannah River Site (SRS) near Jackson, South Carolina. I ...

Process description

The two reactions in the HyS cycle are as follows: # H₂SO₄ → H₂O + SO₂ + ½ O₂ (thermochemical, ''T'' > 800 °C) # SO₂ + 2 H₂O → H₂SO₄ + H₂ (electrochemical, ''T'' = 80-120 °C) : : Net reaction: H₂O → H₂ + ½ O₂ Sulfur dioxide acts to depolarize the

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

of the

electrolyzer In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from na ...

. This results in a significant decrease in the reversible cell potential (and, therefore, the electric power requirement) for reaction (2). The

standard cell potential In electrochemistry, standard electrode potential E^\ominus, or E^\ominus_, is a measure of the reducing power of any element or compound. The IUPAC "Gold Book" defines it as: ''"the value of the standard emf (electromotive force) of a cell in wh ...

for reaction (2) is -0.158 V at 298.15 K, compared to -1.229 V for the electrolysis of water (with oxygen evolution as the anodic reaction).

References

Chemical reactions Inorganic reactions Hydrogen production {{reaction-stub

Process description

See also

References