Copper-chlorine cycle
Encyclopedia
The copper–chlorine cycle (Cu–Cl cycle) is a four-step thermochemical cycle
. It has a maximum temperature requirement of about 530 degrees Celsius. The Cu–Cl cycle is one of the prominent thermochemical cycles under development within the Generation IV International Forum (GIF). Through GIF, over a dozen countries around the world are developing the next generation of nuclear reactors for highly efficient production of both electricity and hydrogen.
The Cu–Cl cycle involves four chemical reaction
s for water splitting
, whose net reaction decomposes water
into hydrogen
and oxygen
. All other chemicals are recycled. The Cu–Cl process can be linked with nuclear plants and/or other heat sources such as solar and industrial waste heat (i.e., incinerators, chemical plants or lost energy from furnaces) to potentially achieve higher efficiencies, lower environmental impact and lower costs of hydrogen production than any other conventional technology.
The Cu–Cl cycle is a hybrid process that employs both thermochemical
and electrolysis steps.
Legend: (g)—gas; (l)—liquid;(aq)—aqueous solution; the balance of the species are in a solid phase. Atomic Energy of Canada Limited has demonstrated experimentally a CuCl electrolyzer in which hydrogen is produced electrolytically at the cathode and Cu(I) is oxidized to Cu(II) at the anode, thereby combining above steps 1 and 4 to eliminate the intermediate production and subsequent transport of solid copper.
s, the ability to use low-grade waste heat to improve energy efficiency, and potentially lower cost materials. In comparison with other thermochemical cycles, the Cu–Cl process requires relatively low temperatures of up to 530 °C (986 °F).
Another significant merit of this cycle is a relatively low voltage (thus low electrical energy expenditure) that is required for the electrochemical step (0.6 to 1.0 V, perhaps even 0.5 if lower current density can be achieved). The overall efficiency of the Cu–Cl cycle has been estimated to be just over 43%, excluding the additional potential gains of utilizing waste heat in the cycle.
Solids handling between processes and corrosive working fluids present unique challenges for the engineering equipment development. Among others, the following materials are being currently used: spray coatings, nickel alloys, glass-lined steel, refractory materials, and other advanced materials.
Thermochemical cycle
Thermochemical cycles combine solely heat sources 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 these processes are continuously recycled.If work is partially used...
. It has a maximum temperature requirement of about 530 degrees Celsius. The Cu–Cl cycle is one of the prominent thermochemical cycles under development within the Generation IV International Forum (GIF). Through GIF, over a dozen countries around the world are developing the next generation of nuclear reactors for highly efficient production of both electricity and hydrogen.
The Cu–Cl cycle involves four chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
s for water splitting
Water splitting
Water splitting is the general term for a chemical reaction in which water is separated into oxygen and hydrogen. Efficient and economical water splitting would be a key technology component of a hydrogen economy. Various techniques for water splitting have been issued in water splitting patents in...
, whose net reaction decomposes water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
into hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. All other chemicals are recycled. The Cu–Cl process can be linked with nuclear plants and/or other heat sources such as solar and industrial waste heat (i.e., incinerators, chemical plants or lost energy from furnaces) to potentially achieve higher efficiencies, lower environmental impact and lower costs of hydrogen production than any other conventional technology.
The Cu–Cl cycle is a hybrid process that employs both thermochemical
Thermochemistry
Thermochemistry is the study of the energy and heat associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase change may do the same, such as in melting and boiling. Thermochemistry focuses on these energy changes, particularly on the...
and electrolysis steps.
Process description
The four reactions in the Cu–Cl cycle are listed as follows:- 2 Cu + 2 HCl(g) → 2 CuCl(l) + H2(g) (430–475 °C)
- 2 Cu2OCl2 → 4 CuCl + O2(g) (500 °C)
- 2 CuCl2 + H2O(g) → Cu2OCl2 + 2 HCl(g) (400 °C)
- 2 CuCl → CuCl2(aq) + Cu (ambient-temperature electrolysis)
- Net reaction: 2 H2O → 2 H2 + O2
Legend: (g)—gas; (l)—liquid;(aq)—aqueous solution; the balance of the species are in a solid phase. Atomic Energy of Canada Limited has demonstrated experimentally a CuCl electrolyzer in which hydrogen is produced electrolytically at the cathode and Cu(I) is oxidized to Cu(II) at the anode, thereby combining above steps 1 and 4 to eliminate the intermediate production and subsequent transport of solid copper.
Advantages and disadvantages
Advantages of the copper–chlorine cycle include lower operating temperatureOperating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
s, the ability to use low-grade waste heat to improve energy efficiency, and potentially lower cost materials. In comparison with other thermochemical cycles, the Cu–Cl process requires relatively low temperatures of up to 530 °C (986 °F).
Another significant merit of this cycle is a relatively low voltage (thus low electrical energy expenditure) that is required for the electrochemical step (0.6 to 1.0 V, perhaps even 0.5 if lower current density can be achieved). The overall efficiency of the Cu–Cl cycle has been estimated to be just over 43%, excluding the additional potential gains of utilizing waste heat in the cycle.
Solids handling between processes and corrosive working fluids present unique challenges for the engineering equipment development. Among others, the following materials are being currently used: spray coatings, nickel alloys, glass-lined steel, refractory materials, and other advanced materials.
See also
- Cerium(IV) oxide–cerium(III) oxide cycle
- Hybrid sulfur cycleHybrid sulfur cycleThe hybrid sulfur cycle is a two-step water-splitting process intended to be used for hydrogen production. Based on sulfur oxidation and reduction, it is classified as a hybrid thermochemical cycle because it uses an electrochemical reaction for one of the two steps...
- Iron oxide cycleIron oxide cycleThe iron oxide cycle is a two-step thermochemical cycle proposed for use for hydrogen production.-Process description:The thermochemical two-step water splitting process uses redox systems...
- Sulfur–iodine cycle
- Zinc–zinc oxide cycle