Photoelectrolysis
Encyclopedia
Photoelectrolysis occurs in a photoelectrochemical cell
when light
is used for electrolysis
. In other words, photoelectrolysis is the conversion of light into a current, and then the division of a molecule
using that current.
Photoelectrolysis' main attractiveness to many engineers
and technologists
is its potential to divide water
into hydrogen
and oxygen
. (In this case, the process is sometimes known as water splitting
or splitting water.) According to Crabtree, et al., achieving a hydrogen economy
requires deriving hydrogen efficiently and inexpensively from natural sources without using fossil fuel
s. Photoelectrolysis is often seen as having the potential to fulfill that need. (In contrast, steam reforming
usually or always uses a fossil fuel to obtain hydrogen.) Photoelectrolysis is sometimes known colloquially as the hydrogen holy grail for its potential to yield a viable alternative to petroleum
as a source of energy
; such an energy source would supposedly come without the sociopolitically undesirable effects of extracting and using petroleum.
Some researchers have practiced photoelectrolysis by means of a nanoscale process. In fact, Crabtree, et al. claimed that with suitable semiconductor
s, nanoscale photoelectrolysis of water could someday reach greater efficiency than that of "traditional" photoelectrolysis. Semiconductors with bandgaps smaller than 1.7 electronvolt
s would ostensibly be required for efficient nanoscale photoelectrolysis using light from the Sun
.
Photoelectrochemical cell
Photoelectrochemical cells or PECs are solar cells which generate electrical energy from light, including visible light. Some photoelectrochemical cells simply produce electrical energy, while others produce hydrogen in a process similar to the electrolysis of water.-Photogeneration cell:In this...
when light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
is used for electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
. In other words, photoelectrolysis is the conversion of light into a current, and then the division of a molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
using that current.
Photoelectrolysis' main attractiveness to many engineers
Engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...
and technologists
Engineering technologist
An engineering technologist, is a specialist devoted to the implementation of existing technology within a field of engineering. Technologists often work with engineers in a wide variety of projects by applying basic engineering principles and technical skills...
is its potential to divide 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...
. (In this case, the process is sometimes known as 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...
or splitting water.) According to Crabtree, et al., achieving a hydrogen economy
Hydrogen economy
The hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors Technical Center....
requires deriving hydrogen efficiently and inexpensively from natural sources without using fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
s. Photoelectrolysis is often seen as having the potential to fulfill that need. (In contrast, steam reforming
Steam reforming
Fossil fuel reforming is a method of producing hydrogen or other useful products from fossil fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to...
usually or always uses a fossil fuel to obtain hydrogen.) Photoelectrolysis is sometimes known colloquially as the hydrogen holy grail for its potential to yield a viable alternative to petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
as a source of energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
; such an energy source would supposedly come without the sociopolitically undesirable effects of extracting and using petroleum.
Some researchers have practiced photoelectrolysis by means of a nanoscale process. In fact, Crabtree, et al. claimed that with suitable semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s, nanoscale photoelectrolysis of water could someday reach greater efficiency than that of "traditional" photoelectrolysis. Semiconductors with bandgaps smaller than 1.7 electronvolt
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
s would ostensibly be required for efficient nanoscale photoelectrolysis using light from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
.
See also
- Artificial photosynthesisArtificial photosynthesisArtificial photosynthesis is a chemical process that replicates the natural process of photosynthesis, a process that converts sunlight, water, and carbon dioxide into carbohydrates and oxygen. The term is commonly used to refer to any scheme for capturing and storing the energy from sunlight in...
- ElectrochemiluminescenceElectrochemiluminescenceElectrochemiluminescence or electrogenerated chemiluminescence is a kind of luminescence produced during electrochemical reactions in solutions. In electrogenerated chemiluminescence, electrochemically generated intermediates undergo a highly exergonic reaction to produce an electronically excited...
- PhotoelectrochemistryPhotoelectrochemistryPhotoelectrochemistry is a subfield of study within physical chemistry concerned with the interaction of light with electrochemical systems. It is active domain of investigation. One of the pioneers of this field of electrochemistry was the german electrochemist Heinz Gerischer...