artificial photosynthesis

{{short description|Artificial process that uses sunlight energy to drive chemical synthesis}}

Artificial photosynthesis is a chemical process that biomimics the natural process of photosynthesis. The term artificial photosynthesis is used loosely, referring to any scheme for capturing and then storing energy from sunlight by producing a fuel, specifically a solar fuel.{{cite journal |doi=10.1039/b800489g |title=Heterogeneous photocatalyst materials for water splitting |date=2009 |last1=Kudo |first1=Akihiko |last2=Miseki |first2=Yugo |journal=Chem. Soc. Rev. |volume=38 |issue=1 |pages=253–278 |pmid=19088977 }} An advantage of artificial photosynthesis would be that the solar energy could converted and stored. By contrast, using photovoltaic cells, sunlight is converted into electricity and then converted again into chemical energy for storage, with some necessary losses of energy associated with the second conversion. The byproducts of these reactions are environmentally friendly. Artificially photosynthesized fuel would be a carbon-neutral source of energy, but it has never been demonstrated in any practical sense. The economics of artificial photosynthesis are noncompetitive.

Overview

Numerous schemes have been described as artificial photosynthesis.

Photocatalytic water splitting, the conversion of water into hydrogen and oxygen:

:: {{chem2|2 H2O -> 2 H2 + O2}}

: This scheme is the simplest form of artificial photosynthesis conceptually, but has not been demonstrated in any practicable way.

Light-driven carbon dioxide reduction, the conversion water, carbon dioxide into carbon monoxide or organic compounds and oxygen. In the conceptually simplest manifestation, this process gives CO:{{cite journal

|last=Barton|first=Emily E.|author2=Rampulla, David M.|author3= Bocarsly, Andrew B.

|title=Selective Solar-Driven Reduction of CO₂ to Methanol Using a Catalyzed p-GaP Based Photoelectrochemical Cell

|doi=10.1021/ja0776327|pmid=18439010

}}

:: {{chem2|2 CO2 -> 2 CO + O2}}

: Related processes give formic acid ({{chem|HCO|2|H}}):

:: {{chem2|2 H2O + 2 CO2 -> 2 HCO2H + O2}}

: Variations might produce formaldehyde or, equivalently, carbohydrates:

:: {{chem2|2 H2O + CO2 -> H2CO + O2}}

: These processes replicate natural carbon fixation.

File:Природна наспроти вештачка фотосинтеза.jpg

Because of the socio-economic implications, artificial photosynthesis is topical, despite the many challenges.{{Cite book|last=Navarro|first=R.M.|author2=del Valle, F.|author3= de la Mano, J.A. Villoria|author4= Álvarez-Galván, M.C.|author5= Fierro, J.L.G. |title= Photocatalytic Water Splitting Under Visible Light: Concept and Catalysts Development|year=2009|volume=36|pages=111–143| doi=10.1016/S0065-2377(09)00404-9|series=Advances in Chemical Engineering |isbn=9780123747631}}{{cite journal|last=Styring|first=Stenbjörn|title=Artificial photosynthesis for solar fuels|journal=Faraday Discussions|volume=155|date=21 December 2011|issue=Advance Article|pages=357–376|doi=10.1039/C1FD00113B|pmid=22470985|bibcode=2012FaDi..155..357S}}{{cite news| url= https://www.economist.com/blogs/babbage/2011/02/artificial_photosynthesis| title=The Difference Engine: The sunbeam solution| newspaper=The Economist | date=11 February 2011}}{{cite journal|last=Listorti|first=Andrea|author2=Durrant, James|author3= Barber, Jim|title=Solar to Fuel|journal=Nature Materials|date=December 2009|volume=8|issue=12|pages=929–930|doi=10.1038/nmat2578|pmid=19935695|bibcode = 2009NatMa...8..929L}} Ideally the only inputs to produce such solar fuels would be water, carbon dioxide, and sunlight. The only by-product would be oxygen,{{cite journal|last=Styring|first=Stenbjörn|title=Artificial photosynthesis for solar fuels|journal=Faraday Discussions|volume=155|date=21 December 2011|issue=Advance Article|pages=357–376|doi=10.1039/C1FD00113B|pmid=22470985|bibcode=2012FaDi..155..357S}}{{cite news| url= https://www.economist.com/blogs/babbage/2011/02/artificial_photosynthesis| title=The Difference Engine: The sunbeam solution| newspaper=The Economist | date=11 February 2011}}{{Cite web |title=Artificial Photosynthesis Can Produce Food in Complete Darkness |url=https://scitechdaily.com/artificial-photosynthesis-can-produce-food-in-complete-darkness/amp/ |access-date=2022-06-28 |website=scitechdaily.com |date=25 June 2022 |language=en-US}} by using direct processes.{{cite web|last=Gathman|first=Andrew|title=Energy at the Speed of Light|url=http://www.rps.psu.edu/0009/energy.html|work=Online Research|publisher=PennState|access-date=16 January 2012|archive-date=12 July 2012|archive-url=https://web.archive.org/web/20120712093211/http://www.rps.psu.edu/0009/energy.html|url-status=dead}}{{Cite book|last=Carraro|first=Mauro|author2=Sartorel, Andrea|author3=Toma, Francesca|author4=Puntoriero, Fausto|author5=Scandola, Franco|author6=Campagna, Sebastiano|author7=Prato, Maurizio|author8= Bonchio, Marcella|title=Artificial Photosynthesis Challenges: Water Oxidation at Nanostructured Interfaces|year=2011|volume=303|pages=121–150| doi=10.1007/128_2011_136| pmid=21547686|series=Topics in Current Chemistry|doi-broken-date=1 November 2024 |isbn=978-3-642-22293-1}}{{cite journal |last=Bockris |first=J.O'M. |author2=Dandapani, B. |author3=Cocke, D. |author4= Ghoroghchian, J. |title=On the splitting of water|journal=International Journal of Hydrogen Energy |year=1985 |volume=10|issue=3|pages=179–201|doi=10.1016/0360-3199(85)90025-4|bibcode=1985IJHE...10..179B }}

History

Artificial photosynthesis was first anticipated by the Italian chemist Giacomo Ciamician during 1912.{{cite journal | last1 = Armaroli | first1 = Nicola | author-link = Nicola Armaroli | author-link2 = Vincenzo Balzani | last2 = Balzani | first2 = Vincenzo | year = 2007 | title = The Future of Energy Supply: Challenges and Opportunities | journal = Angewandte Chemie | volume = 46 | issue = 1–2| pages = 52–66 | doi = 10.1002/anie.200602373 | pmid = 17103469 }} In a lecture that was later published in Science,{{cite journal | last1 = Ciamician | first1 = Giacomo | author-link = Giacomo Ciamician | year = 1912| title = The Photochemistry of the Future | url = https://zenodo.org/record/1448090| journal = Science | volume = 36| issue = 926| pages = 385–394| doi = 10.1126/science.36.926.385 | pmid = 17836492 | bibcode = 1912Sci....36..385C }} he proposed a switch from the use of fossil fuels to radiant energy provided by the sun and captured by technical photochemistry devices. In this switch, he saw a possibility to lessen the difference between the rich north of Europe and poor south and ventured a guess that this switch from coal to solar energy would "not be harmful to the progress and to human happiness".{{cite journal | last1 = Balzani | first1 = Vincenzo | display-authors = etal | year = 2008 | title = Photochemical Conversion of Solar Energy | journal = ChemSusChem | volume = 1 | issue = 1–2| pages = 26–58 | doi = 10.1002/cssc.200700087 | pmid = 18605661 | bibcode = 2008ChSCh...1...26B }}

During the late 1960s, Akira Fujishima discovered the photocatalytic properties of titanium dioxide, the so-called Honda-Fujishima effect, which could be used for hydrolysis.{{cite journal |last=Fujishima|first=Akira|author2=Rao, Tata N.|author3=Tryk, Donald A. |title=Titanium dioxide photocatalysis |journal=Journal of Photochemistry and Photobiology C: Photochemistry Reviews|date=29 June 2000|volume=1|issue=1|pages=1–21 |doi=10.1016/S1389-5567(00)00002-2|s2cid=73665845 }}

Visible light water splitting with a one piece multijunction semiconductor device (vs. UV light with titanium dioxide semiconductors) was first demonstrated and patented by William Ayers at Energy Conversion Devices during 1983.William Ayers, {{US Patent|4466869}} "Photolytic Production of Hydrogen"Ayers, W.M. and Cannella, V. (1984) "Tandem Amorphous Silicon Photocathodes", Proc. Int'l. Conf. on Electrodynamics and Quantum Phenomena at Interfaces, Telavi, USSR This group demonstrated water photolysis into hydrogen and oxygen, now referred to as an "artificial leaf" with a low cost, thin film amorphous silicon multijunction sheet immersed directly in water. Hydrogen evolved on the front amorphous silicon surface decorated with various catalysts while oxygen evolved from the back side metal substrate which also eliminated the hazard of mixed hydrogen/oxygen gas evolution. A polymer membrane above the immersed device provided a path for proton transport. The higher photovoltage available from the multijunction thin film device with visible light was a major advance over previous photolysis attempts with UV or other single junction semiconductor photoelectrodes. The group's patent also lists several other semiconductor multijunction compositions in addition to amorphous silicon.

Since the 1990's, much has been learned about catalysts hydrogen evolution reaction{{cite journal |last1=Kärkäs |first1=Markus D. |last2=Verho |first2=Oscar |last3=Johnston |first3=Eric V. |last4=Åkermark |first4=Björn |date=2014 |title=Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation |journal=Chemical Reviews |volume=114 |issue=24 |pages=11863–12001 |doi=10.1021/cr400572f |pmid=25354019}} and oxygen evolution reaction.{{cite journal |doi=10.1021/cr400572f |title=Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation |date=2014 |last1=Kärkäs |first1=Markus D. |last2=Verho |first2=Oscar |last3=Johnston |first3=Eric V. |last4=Åkermark |first4=Björn |journal=Chemical Reviews |volume=114 |issue=24 |pages=11863–12001 |pmid=25354019 }} Unfortunately, no practical system has been demonstrated despite intense efforts.{{cite journal |last1=Ham |first1=Rens |last2=Nielsen |first2=C. Jasslie |last3=Pullen |first3=Sonja |last4=Reek |first4=Joost N. H. |date=2023 |title=Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis |journal=Chemical Reviews |volume=123 |issue=9 |pages=5225–5261 |doi=10.1021/acs.chemrev.2c00759 |pmc=10176487 |pmid=36662702}}{{cite journal |last1=Reyes Cruz |first1=Edgar A. |last2=Nishiori |first2=Daiki |last3=Wadsworth |first3=Brian L. |last4=Nguyen |first4=Nghi P. |last5=Hensleigh |first5=Lillian K. |last6=Khusnutdinova |first6=Diana |last7=Beiler |first7=Anna M. |last8=Moore |first8=G. F. |date=2022 |title=Molecular-Modified Photocathodes for Applications in Artificial Photosynthesis and Solar-to-Fuel Technologies |journal=Chemical Reviews |volume=122 |issue=21 |pages=16051–16109 |doi=10.1021/acs.chemrev.2c00200 |pmid=36173689}}{{cite journal |doi=10.1021/acs.chemrev.2c00759 |title=Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis |date=2023 |last1=Ham |first1=Rens |last2=Nielsen |first2=C. Jasslie |last3=Pullen |first3=Sonja |last4=Reek |first4=Joost N. H. |journal=Chemical Reviews |volume=123 |issue=9 |pages=5225–5261 |pmid=36662702 |pmc=10176487 }}

Catalysis

=Catalytic triad=

File:Triad general scheme.svg

Some concepts for artificial photosynthesis consist of distinct components,{{cite journal |doi=10.1039/d2cp03655j |title=Self-assembled systems for artificial photosynthesis |date=2023 |last1=Campagna |first1=Sebastiano |last2=Nastasi |first2=Francesco |last3=La Ganga |first3=Giuseppina |last4=Serroni |first4=Scolastica |last5=Santoro |first5=Antonio |last6=Arrigo |first6=Antonino |last7=Puntoriero |first7=Fausto |journal=Physical Chemistry Chemical Physics |volume=25 |issue=3 |pages=1504–1512 |pmid=36448376 |bibcode=2023PCCP...25.1504C |doi-access=free }} which are inspired by natural photosynthesis:

Light-harvesting complexes in bacteria and plants capture photons and transduce them into electrons, injecting them into the photosynthetic chain.
Proton-coupled electron transfer along several cofactors of the photosynthetic chain, causing local, spatial charge separation.
Redox catalysis, which uses the aforementioned transferred electrons to oxidize water to dioxygen and protons; these protons can in some species be utilized for dihydrogen production.

These processes could be replicated by a triad assembly, which could oxidize water at one catalyst, reduce protons at another, and have a photosensitizer molecule to power the whole system{{cite journal |doi=10.1021/ar900209b |title=Solar Fuels via Artificial Photosynthesis |date=2009 |last1=Gust |first1=Devens |last2=Moore |first2=Thomas A. |last3=Moore |first3=Ana L. |journal=Accounts of Chemical Research |volume=42 |issue=12 |pages=1890–1898 |pmid=19902921 }}

=Catalysts=

Some catalysts for solar fuel cells are envisioned to produce hydrogen.{{cite journal|last=Andreiadis|first=Eugen S.|author2=Chavarot-Kerlidou, Murielle|author3= Fontecave, Marc|author4= Artero, Vincent|title=Artificial Photosynthesis: From Molecular Catalysts for Light-driven Water Splitting to Photoelectrochemical Cells|journal=Photochemistry and Photobiology|date=September–October 2011|volume=87|issue=5|pages=946–964|doi=10.1111/j.1751-1097.2011.00966.x|pmid=21740444|doi-access=free}}

1) A homogeneous system is one such that catalysts are not compartmentalized, that is, components are present in the same compartment. This means that hydrogen and oxygen are produced in the same location. This can be a drawback, since they compose an explosive mixture, demanding gas product separation. Also, all components must be active in approximately the same conditions (e.g., pH).

2) A heterogeneous system has two separate electrodes, an anode and a cathode, making possible the separation of oxygen and hydrogen production. Furthermore, different components do not necessarily need to work in the same conditions. However, the increased complexity of these systems makes them harder to develop and more expensive.{{Cite journal|last=Wang|first=Qian|date=24 August 2020|title=Molecularly engineered photocatalyst sheet for scalable solar formate production from carbon dioxide and water|url=http://nrl.northumbria.ac.uk/id/eprint/44595/1/Nature%20Energy%20AAM.pdf|journal=Nature Energy|volume=5 |issue=9 |pages=703–710 |doi=10.1038/s41560-020-0678-6|bibcode=2020NatEn...5..703W |s2cid=225203917 }}

=Selected catalysts=

Many catalysts have been evaluated for both the O₂-evolution and the reductive sides of the process. Those listed below, which includes both oxidizer and reducers, are not practical, but illustrative:

{{chem|Cd|1-{{mvar|x}}|Zn|{{mvar|x}}|S}} photocatalysts. {{chem|Cd|1-{{mvar|x}}|Zn|{{mvar|x}}|S}} solid solution catalyze hydrogen production from water splitting under sunlight irradiation.{{cite journal

|title= Influence of Zn concentration in the activity of {{chem|Cd|1-{{mvar|x}}|Zn|{{mvar|x}}|S}} solid solutions for water splitting under visible light

|journal= Catalysis Today |volume= 143 |issue= 1–2 |pages= 51–59

|doi= 10.1016/j.cattod.2008.09.024 }}

Nitrogen-doped and cadmium selenide quantum dots-sensitized titanium dioxide nanoparticles and nanowires, also yielded photoproduced hydrogen.{{cite journal

|title=Synergistic Effect of CdSe Quantum Dot Sensitization and Nitrogen Doping of TiO₂ Nanostructures for Photoelectrochemical Solar Hydrogen Generation

|doi=10.1021/nl903217w|pmid=20102190|bibcode = 2010NanoL..10..478H

}}

Cobalt phosphate.{{cite journal

|last=Kanan|first=Matthew W.|author2=Nocera, Daniel G.

|title=In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co²⁺

|doi=10.1126/science.1162018

|bibcode = 2008Sci...321.1072K|pmid=18669820

|s2cid=206514692}}{{cite journal

|last=Lutterman|first=Daniel A.|author2=Surendranath, Yogesh|author3= Nocera, Daniel G.

|title=A Self-Healing Oxygen-Evolving Catalyst

|doi=10.1021/ja900023k|pmid=19249834

}}{{cite web

|url=http://www.technologyreview.com/Energy/21155/?a=f

|title=Solar-Power Breakthrough: Researchers have found a cheap and easy way to store the energy made by solar power

|publisher=Technologyreview.com |access-date=2011-04-19

}}{{cite web

|last=Kleiner|first=Kurt

|title=Electrode lights the way to artificial photosynthesis

|url=https://www.newscientist.com/article/dn14441|work=NewScientist

|publisher=Reed Business Information Ltd.|access-date=10 January 2012

}}

Inexpensive iron carbonyl complexes catalyze hydrogen evolution.{{cite web

|url=http://www.azonano.com/news.asp?newsID=14936

|title=Light-Driven Hydrogen Generation System Based on Inexpensive Iron Carbonyl Complexes |work=AZoNano.com

|publisher=AZoNetwork |date=2 December 2009 |access-date=2011-04-19

}}{{cite journal

|title=Light-Driven Hydrogen Generation: Efficient Iron-Based Water Reduction Catalysts

|doi=10.1002/anie.200905115|pmid=19937629

}} Gold electrode covered with layers of indium phosphide to which iron carbonyl compounds to achieve photoelectrochemical hydrogen production.{{cite journal

|title=Water Splitting by Visible Light: A Nanophotocathode for Hydrogen Production

|doi=10.1002/anie.200906262|pmid=20140925

|doi-access=free}}

Bismuth vanadate

{{cite journal

|last=Kalyanasundaram|first=K.|author2=Grätzel, M.

|title=Artificial photosynthesis: biomimetic approaches to solar energy conversion and storage

|doi=10.1016/j.copbio.2010.03.021|pmid=20439158

}} Similar to natural photosynthesis, such artificial leaves can use a tandem of light absorbers for overall water splitting or CO₂ reduction. These integrated systems can be assembled on lightweight, flexible substrates, resulting in floating devices resembling lotus leaves.{{Cite journal |last1=Andrei |first1=Virgil |last2=Ucoski |first2=Geani M. |last3=Pornrungroj |first3=Chanon |last4=Uswachoke |first4=Chawit |last5=Wang |first5=Qian |last6=Achilleos |first6=Demetra S. |last7=Kasap |first7=Hatice |last8=Sokol |first8=Katarzyna P. |last9=Jagt |first9=Robert A. |last10=Lu |first10=Haijiao |last11=Lawson |first11=Takashi |last12=Wagner |first12=Andreas |last13=Pike |first13=Sebastian D. |last14=Wright |first14=Dominic S. |last15=Hoye |first15=Robert L. Z. |display-authors=10 |date=2022-08-17 |title=Floating perovskite-BiVO4 devices for scalable solar fuel production |url=https://www.repository.cam.ac.uk/bitstreams/7787036d-4bad-4347-8c8e-7afbc6dbbb88/download |journal=Nature |volume=608 |issue=7923 |pages=518–522 |doi=10.1038/s41586-022-04978-6 |pmid=35978127 |bibcode=2022Natur.608..518A |s2cid=251645379 }}

Metal-Organic Framework (MOF)-based materials have been investigated for water oxidation.{{cite journal

|author= Binod Nepal |author2=Siddhartha Das |year= 2013

| title= Sustained Water Oxidation by a Catalyst Cage-Isolated in a Metal–Organic Framework

| journal= Angew. Chem. Int. Ed. |volume= 52 |issue= 28 |pages= 7224–27

| doi= 10.1002/anie.201301327

|pmid= 23729244

|citeseerx= 10.1.1.359.7383

}}{{cite journal

| author1= Rebecca E. Hansen |author2= Siddhartha Das |year= 2014

| title= Biomimetic Di-manganese Catalyst Cage-isolated in a MOF: Robust Catalyst for Water Oxidation with Ce(IV), a Non-O-Donating Oxidant

| journal= Energy Environ. Sci.|volume= 7 |issue= 1 |pages= 317–322

| doi= 10.1039/C3EE43040E

}} The stability and tunability of this system is projected to be highly beneficial for future development.[http://cen.acs.org/articles/91/i26/Stable-Water-Oxidation-Inside-Cage.html Chemical & Engineering News]

=Catalyst stability=

Catalysts for artificial photosynthesis are expected to effect turn over numbers in the millions. Catalysts often corrode in water, especially when irradiated. Thus, they may be less stable than photovoltaics. Hydrogen oxidation catalysts are very sensitive to oxygen, being inactivated or degraded in its presence; also, photodamage may occur over time.{{cite journal

|last=Krassen|first=Henning|author2=Ott, Sascha|author3= Heberle, Joachim

|title=In vitro hydrogen production—using energy from the sun

|doi=10.1039/C0CP01163K|pmid=21103567

|bibcode = 2011PCCP...13...47K

}}

Research centers

Research centers were established across the globe,{{cite journal |vauthors= Faunce TA, Lubitz W, Rutherford AW, MacFarlane D, Moore GF, Yang P, Nocera DG, Moore TA, Gregory DH, Fukuzumi S, Yoon KB, Armstrong FA, Wasielewski MR, Styring S |s2cid= 97344491 |title= Energy and Environment Policy Case for a Global Project on Artificial Photosynthesis |journal= Energy and Environmental Science |year= 2013 |volume= 6 |issue= 3 |pages= 695–698 |doi= 10.1039/C3EE00063J}} including Sweden,{{cite journal

|last=Hammarström|first=Leif|author2=Styring, Stenbjörn

|title=Coupled electron transfers in artificial photosynthesis

|doi=10.1098/rstb.2007.2225

|pmid=17954432|pmc=2614099}} U.S.,{{cite web

|url=http://solarfuelshub.org/

|title=Home – Joint Center for Artificial Photosynthesis

|publisher=Solarfuelshub.org |access-date=2012-11-07

}} with the aim of finding a cost-effective method to produce fuels using only sunlight, water, and carbon-dioxide as inputs.{{cite web |url=http://media.caltech.edu/press_releases/13365 |title=Caltech-led Team Gets up to $122 Million for Energy Innovation Hub |publisher=Caltech Media Relations |date=21 July 2010 |access-date=2011-04-19 |url-status=dead |archive-url=https://web.archive.org/web/20110809044623/http://media.caltech.edu/press_releases/13365 |archive-date=9 August 2011 }} Japan,{{cite web

|url=http://www.digitalworldtokyo.com/index.php/digital_tokyo/articles/man-made_photosynthesis_looking_to_change_the_world

|title=Man-made photosynthesis looking to change the world

|publisher=Digitalworldtokyo.com |date=14 January 2009 |access-date=2011-04-19

}} This was confirmed with the establishment of the KAITEKI Institute later that year, with carbon dioxide reduction through artificial photosynthesis as one of the main goals.{{cite web

|title=The Establishment of the KAITEKI Institute Inc.

|url=http://www.mitsubishi.com/e/csr/back/environment.html|work=CSR Environment

|publisher=mitsubishi.com|access-date=10 January 2012

}}{{cite web

|title=Research

|url=http://www.kaiteki-institute.com/research/index.html

|publisher=The KAITEKI Institute|access-date=10 January 2012

}} and Australia.[https://web.archive.org/web/20160419232838/http://medicalschool.anu.edu.au/towards-the-sustainocene Global Artificial Photosynthesis- Breakthroughs for the Sustainocene Canberra and Lord Howe island 2016]. medicalschool.anu.edu.au

Various components

= Hydrogen catalysts =

Hydrogen is the simplest solar fuel. Its formation involves only the transference of two electrons to two protons:

:{{chem2|2 e- + 2 H+ -> H2}}

The hydrogenase enzymes effect this conversion{{cite journal

|last=Tard|first=Cédric|author2=Pickett, Christopher J.

|title=Structural and Functional Analogues of the Active Sites of the [Fe]-, [NiFe]-, and [FeFe]-Hydrogenases

|doi=10.1021/cr800542q|pmid=19438209

}}{{cite journal

|title=Synthesis of the H-cluster framework of iron-only hydrogenase

|journal=Nature|date= 2005|volume=433|pages=610–613

|doi=10.1038/nature03298

}}

Dirhodium photocatalyst{{cite journal

|last=Heyduk|first=Alan F.|author2=Nocera

|title=Daniel G.

|doi=10.1126/science.1062965

|bibcode = 2001Sci...293.1639H|pmid=11533485

|s2cid=35989348}} and cobalt catalysts.{{cite journal

|title=Electrocatalytic hydrogen evolution by cobalt difluoroboryl-diglyoximate complexes

|doi=10.1039/B509188H

|pmid=16175305|url=https://authors.library.caltech.edu/4825/3/HUXcc05supp.pdf}}

= Water-oxidizing catalysts =

Water oxidation is a more complex chemical reaction than proton reduction. In nature, the oxygen-evolving complex performs this reaction by accumulating reducing equivalents (electrons) in a manganese-calcium cluster within photosystem II (PS II), then delivering them to water molecules, with the resulting production of molecular oxygen and protons:

:2 H₂O → O₂ + 4 H⁺ + 4e⁻

Without a catalyst (natural or artificial), this reaction is very endothermic, requiring high temperatures (at least 2500 K).

The exact structure of the oxygen-evolving complex has been hard to determine experimentally.{{cite journal

|title=X-ray damage to the Mn₄Ca complex in single crystals of photosystem II: A case study for metalloprotein crystallography

|doi=10.1073/pnas.0505207102

|bibcode = 2005PNAS..10212047Y |pmid=16103362 |pmc=1186027

|doi-access=free }} As of 2011, the most detailed model was from a 1.9 Å resolution crystal structure of photosystem II.{{cite journal

|title=Crystal structure of oxygen-evolving photosystem II at a resolution of 1.9 Å

|doi=10.1038/nature09913|pmid=21499260

|bibcode = 2011Natur.473...55U

|s2cid=205224374|url=http://ousar.lib.okayama-u.ac.jp/files/public/4/47455/20160528084139320094/Nature_473_55–60.pdf}} The complex is a cluster containing four manganese and one calcium ions, but the exact location and mechanism of water oxidation within the cluster is unknown. Nevertheless, bio-inspired manganese and manganese-calcium complexes have been synthesized, such as [Mn₄O₄] cubane-type clusters, some with catalytic activity.{{cite journal

|title=Development of Bioinspired ₄O₄−Cubane Water Oxidation Catalysts: Lessons from Photosynthesis

|doi=10.1021/ar900249x|pmid=19908827

}}

Some ruthenium complexes, such as the dinuclear μ-oxo-bridged "blue dimer" (the first of its kind to be synthesized), are capable of light-driven water oxidation, thanks to being able to form high valence states. In this case, the ruthenium complex acts as both photosensitizer and catalyst. This complexes and other molecular catalysts still attract researchers in the field, having different advantages such as clear structure, active site, and easy to study mechanism. One of the main challenges to overcome is their short-term stability and their effective heterogenization for applications in artificial photosynthesis devices.{{Cite journal|last1=Zhang|first1=Biaobiao|last2=Sun|first2=Licheng|date=2019|title=Artificial photosynthesis: opportunities and challenges of molecular catalysts|journal=Chemical Society Reviews|volume=48|issue=7|pages=2216–2264|doi=10.1039/C8CS00897C|pmid=30895997 |doi-access=free}}

Many metal oxides have been found to have water oxidation catalytic activity, including ruthenium(IV) oxide (RuO₂), iridium(IV) oxide (IrO₂), cobalt oxides (including nickel-doped Co₃O₄), manganese oxide (including layered MnO₂ (birnessite), Mn₂O₃), and a mix of Mn₂O₃ with CaMn₂O₄. Oxides are easier to obtain than molecular catalysts, especially those from relatively abundant transition metals (cobalt and manganese), but suffer from low turnover frequency and slow electron transfer properties, and their mechanism of action is hard to decipher and, therefore, to adjust.

= Photosensitizers =

File:Delta-ruthenium-tris(bipyridine)-cation-3D-balls.png, a broadly used photosensitizer.]]

Nature uses pigments, mainly chlorophylls, to absorb a broad part of the visible spectrum. Artificial systems can use either one type of pigment with a broad absorption range or combine several pigments for the same purpose.

Ruthenium polypyridine complexes, in particular tris(bipyridine)ruthenium(II) and its derivatives, have been extensively used in hydrogen photoproduction due to their efficient visible light absorption and long-lived consequent metal-to-ligand charge transfer excited state, which makes the complexes strong reducing agents. Other noble metal-containing complexes used include ones with platinum, rhodium and iridium.

Metal-free organic complexes have also been successfully employed as photosensitizers. Examples include eosin Y and rose bengal. Pyrrole rings such as porphyrins have also been used in coating nanomaterials or semiconductors for both homogeneous and heterogeneous catalysis.

As part of current research efforts artificial photonic antenna systems are being studied to determine efficient and sustainable ways to collect light for artificial photosynthesis. Gion Calzaferri (2009) describes one such antenna that uses zeolite L as a host for organic dyes, to mimic plant's light collecting systems.{{Cite journal|last1=Calzaferri|first1=Gion|title=Artificial Photosynthesis| journal = Topics in Catalysis |year=2010|volume = 53| issue = 3|pages = 130–140 |doi=10.1007/s11244-009-9424-9|s2cid=195282014|url=https://boris.unibe.ch/5081/1/11244_2009_Article_9424.pdf}} The antenna is fabricated by inserting dye molecules into the channels of zeolite L. The insertion process, which takes place under vacuum and at high temperature conditions, is made possible by the cooperative vibrational motion of the zeolite framework and of the dye molecules.{{cite journal

|author1=Tabacchi, Gloria |author2=Calzaferri, Gion |author3=Fois, Ettore |title=One-dimensional self-assembly of perylene-diimide dyes by unidirectional transit of zeolite channel openings

|doi=10.1039/C6CC05303C |url=http://pubs.rsc.org/en/content/articlepdf/2016/cc/c6cc05303c |pmid=27484884|doi-access=free|hdl=11383/2057444|hdl-access=free}} The resulting material may be interfaced to an external device via a stopcock intermediate.{{cite journal|author1=Calzaferri, Gion |author2=Méallet-Renault, Rachel |author3=Brühwiler, Dominik |author4=Pansu, Robert |author5=Dolamic, Igor |author6=Dienel, Thomas |author7=Adler, Pauline |author8=Li, Huanrong |author9=Kunzmann, Andreas |title=Designing Dye–Nanochannel Antenna Hybrid Materials for Light Harvesting, Transport and Trapping |journal=ChemPhysChem |volume=12 |issue=3| pages=580–594 |year=2011 |doi=10.1002/cphc.201000947 |pmid=21337487 |doi-access=free }}{{cite journal

|author1=Tabacchi, Gloria |author2=Fois, Ettore |author3=Calzaferri, Gion |title=Structure of Nanochannel Entrances in Stopcock-Functionalized Zeolite L

|doi=10.1002/anie.201504745 |url=https://figshare.com/articles/Structure_of_nanochannel_entrances_in_stopcock-functionalized_Zeolite_L/3798654 |pmid=26255642|s2cid=205388715 |hdl=11383/2030753|hdl-access=free}}

= Carbon dioxide reduction catalysts =

In nature, carbon fixation is done by green plants using the enzyme RuBisCO as a part of the Calvin cycle. RuBisCO is a rather slow catalyst compared to the vast majority of other enzymes, incorporating only a few molecules of carbon dioxide into ribulose-1,5-bisphosphate per minute, but does so at atmospheric pressure and in mild, biological conditions.{{cite journal

| s2cid = 205052478 }} The resulting product is further reduced and eventually used in the synthesis of glucose, which in turn is a precursor to more complex carbohydrates, such as cellulose and starch. The process consumes energy in the form of ATP and NADPH.

Artificial CO₂ reduction for fuel production aims mostly at producing reduced carbon compounds from atmospheric CO₂. Some transition metal polyphosphine complexes have been developed for this end; however, they usually require previous concentration of CO₂ before use, and carriers (molecules that would fixate CO₂) that are both stable in aerobic conditions and able to concentrate CO₂ at atmospheric concentrations haven't been yet developed.{{cite journal

|last=Dubois|first=M. Rakowski|author2=Dubois, Daniel L.

|doi=10.1021/ar900110c|pmid=19645445

|title=Development of Molecular Electrocatalysts for CO2Reduction and H2Production/Oxidation

}} The simplest product from CO₂ reduction is carbon monoxide (CO), but for fuel development, further reduction is needed (for example, to multi-carbon products), and a key step also needing further development is the transfer of hydride anions to CO.

= Photobiological production of fuels =

Another area of research within artificial photosynthesis is the selection and manipulation of photosynthetic microorganisms, namely green microalgae and cyanobacteria, for the production of solar fuels. Many strains produce hydrogen naturally.{{cite journal|last=Magnuson|first=Ann |author2=Anderlund, Magnus |author3=Johansson, Olof |author4=Lindblad, Peter |author5=Lomoth, Reiner |author6=Polivka, Tomas |author7=Ott, Sascha |author8=Stensjö, Karin |author9=Styring, Stenbjörn |author10=Sundström, Villy |author11=Hammarström, Leif|title=Biomimetic and Microbial Approaches to Solar Fuel Generation |journal=Accounts of Chemical Research|date=December 2009|volume=42|issue=12| pages=1899–1909 |doi=10.1021/ar900127h|pmid=19757805

|url=https://zenodo.org/record/3424059 }} Algae biofuels such as butanol and methanol have been produced at various scales. This method has benefited from the development of synthetic biology,{{cite web |last=JCVI

|title=Synthetic Biology & Bioenergy – Overview |url=http://www.jcvi.org/cms/research/groups/synthetic-biology-bioenergy/ |publisher=J. Craig Venter Institute|access-date=17 January 2012 }}{{cite web |title=Hydrogen from Water in a Novel Recombinant Cyanobacterial System |url=http://www.jcvi.org/cms/research/projects/hydrogen-from-water-in-a-novel-recombinant-cyanobacterial-system/overview/ |publisher=J. Craig Venter Institute|access-date=17 January 2012 }} Diverse biofuels have been developed, e.g., acetic acid from carbon dioxide using "cyborg bacteria".{{Cite news|url=https://www.bbc.co.uk/news/science-environment-40975719|title='Cyborg' bacteria deliver green fuel source from sunlight |newspaper=BBC News|date=22 August 2017|last1=McGrath |first1=Matt }}

Some solar cells are capable of splitting water into oxygen and hydrogen, approximately ten times more efficient than natural photosynthesis.{{cite web

|title=Debut of the first practical "artificial leaf" |url=http://portal.acs.org/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_ARTICLEMAIN&node_id=222&content_id=CNBP_026944&use_sec=true&sec_url_var=region1&__uuid=fc6e4031-a1f8-4093-9d1a-07bbc67134d0|archive-url=https://archive.today/20130224044911/http://portal.acs.org/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_ARTICLEMAIN&node_id=222&content_id=CNBP_026944&use_sec=true&sec_url_var=region1&__uuid=fc6e4031-a1f8-4093-9d1a-07bbc67134d0|url-status=dead|archive-date=24 February 2013|work=ACS News Releases |publisher=American Chemical Society|access-date=10 January 2012}}{{cite journal

|s2cid=12720266|title=Wireless Solar Water Splitting Using Silicon-Based Semiconductors and Earth-Abundant Catalysts

|doi=10.1126/science.1209816|pmid=21960528

|bibcode = 2011Sci...334..645R

}} Sun Catalytix, the startup based on the artificial leaf, stated that it will not be scaling up the prototype as the device offers few savings over other ways to make hydrogen from sunlight.{{Cite journal

|author=Van Noorden

|first = Richard

|url=http://www.nature.com/news/artificial-leaf-faces-economic-hurdle-1.10703

|title='Artificial leaf' faces economic hurdle

|journal=Nature

|doi=10.1038/nature.2012.10703

|year=2012

|s2cid = 211729746

|doi-access=free}}

Some photoautotrophic microorganisms can, under certain conditions, produce hydrogen. Nitrogen-fixing microorganisms, such as filamentous cyanobacteria, possess the enzyme nitrogenase, responsible for conversion of atmospheric N₂ into ammonia; molecular hydrogen is a byproduct of this reaction, and is many times not released by the microorganism, but rather taken up by a hydrogen-oxidizing (uptake) hydrogenase. One way of forcing these organisms to produce hydrogen is then to annihilate uptake hydrogenase activity. This has been done on a strain of Nostoc punctiforme: one of the structural genes of the NiFe uptake hydrogenase was inactivated by insertional mutagenesis, and the mutant strain showed hydrogen evolution under illumination.{{cite journal

|title=A hydrogen-producing, hydrogenase-free mutant strain of Nostoc punctiforme ATCC 29133

|doi=10.1016/S0360-3199(02)00121-0

|bibcode=2002IJHE...27.1291L }}

Many of these photoautotrophs also have bidirectional hydrogenases, which can produce hydrogen under certain conditions. However, other energy-demanding metabolic pathways can compete with the necessary electrons for proton reduction, decreasing the efficiency of the overall process; also, these hydrogenases are very sensitive to oxygen.

Several carbon-based biofuels have also been produced using cyanobacteria, such as 1-butanol.{{cite journal

|last=Lan|first=Ethan I.|author2=Liao, James C.

|title=Metabolic engineering of cyanobacteria for 1-butanol production from carbon dioxide

|doi=10.1016/j.ymben.2011.04.004|pmid=21569861

}}

Synthetic biology techniques are predicted to be useful for this topic. Microbiological and enzymatic engineering have the potential of improving enzyme efficiency and robustness, as well as constructing new biofuel-producing metabolic pathways in photoautotrophs that previously lack them, or improving on the existing ones. Another topic being developed is the optimization of photobioreactors for commercial application.{{cite journal

|last=Kunjapur|first=Aditya M.|author2=Eldridge, R. Bruce

|title=Photobioreactor Design for Commercial Biofuel Production from Microalgae

|doi=10.1021/ie901459u

}}

= Food production =

Researchers have achieved controlled growth of diverse foods in the dark {{tooltip|2=via a two-step electrocatalytic process that converts carbon dioxide, electricity, and water into acetate, which is then consumed by food-producing organisms to grow|via solar energy and electrocatalysis-based artificial photosynthesis}}. It may become a way to increase energy efficiency of food production and reduce its environmental impacts.{{cite magazine |last1=Reynolds |first1=Matt |title=Scientists Are Trying to Grow Crops in the Dark |url=https://www.wired.com/story/plants-growing-in-darkness/ |access-date=23 July 2022 |magazine=Wired}}{{cite journal |last1=Hann |first1=Elizabeth C. |last2=Overa |first2=Sean |last3=Harland-Dunaway |first3=Marcus |last4=Narvaez |first4=Andrés F. |last5=Le |first5=Dang N. |last6=Orozco-Cárdenas |first6=Martha L. |last7=Jiao |first7=Feng |last8=Jinkerson |first8=Robert E. |title=A hybrid inorganic–biological artificial photosynthesis system for energy-efficient food production |journal=Nature Food |date=June 2022 |volume=3 |issue=6 |pages=461–471 |doi=10.1038/s43016-022-00530-x |pmid=37118051 |s2cid=250004816|doi-access=free }} However, it is unclear if food production mechanisms based on the experimental process are viable and can be scaled.

Some advantages, disadvantages, and efficiency

A concern usually addressed in catalyst design is efficiency, in particular how much of the incident light can be used in a system in practice. This is comparable with photosynthetic efficiency, where light-to-chemical-energy conversion is measured. Photosynthetic organisms are able to collect about 50% of incident solar radiation, however the theoretical limit of photosynthetic efficiency is 4.6 and 6.0% for C3 and C4 plants respectively.{{cite journal|author1-link=Robert E. Blankenship|author9-link=David M. Kramer (biophysicist) |last=Blankenship|first=Robert E. |author2=Tiede, David M. |author3=Barber, James |author4=Brudvig, Gary W. |author5=Fleming, Graham |author6=Ghirardi, Maria |author7=Gunner, M. R. |author8=Junge, Wolfgang |author9=Kramer, David M. |author10=Melis, Anastasios |author11=Moore, Thomas A. |author12=Moser, Christopher C. |author13=Nocera, Daniel G. |author14=Nozik, Arthur J. |author15=Ort, Donald R. |author16=Parson, William W. |author17=Prince, Roger C. |author18=Sayre, Richard T.

|s2cid=22798697 |title=Comparing Photosynthetic and Photovoltaic Efficiencies and Recognizing the Potential for Improvement

|doi=10.1126/science.1200165|pmid=21566184

|bibcode = 2011Sci...332..805B

|url=https://escholarship.org/uc/item/9cf6c2dq }} In reality, the efficiency of photosynthesis is much lower and is usually below 1%, with some exceptions such as sugarcane in tropical climate.{{cite journal | last1 = Armaroli | first1 = Nicola | author-link = Nicola Armaroli | author-link2 = Vincenzo Balzani | last2 = Balzani | first2 = Vincenzo | year = 2016 | title = Solar Electricity and Solar Fuels: Status and Perspectives in the Context of the Energy Transition | journal = Chemistry – A European Journal | volume = 22 | issue = 1| pages = 32–57 | doi = 10.1002/chem.201503580 | pmid = 26584653 }} In contrast, the highest reported efficiency for artificial photosynthesis lab prototypes is 22.4%.{{cite journal | last1 = Bonke | first1 = Shannon A. | s2cid = 94698839 |display-authors=et al | year = 2015 | title = Renewable fuels from concentrated solar power: towards practical artificial photosynthesis | journal = Energy and Environmental Science | volume = 8 | issue = 9| pages = 2791–2796 | doi = 10.1039/c5ee02214b }} However, plants are efficient in using CO₂ at atmospheric concentrations, something that artificial catalysts still cannot perform.{{cite web

|last=Biello|first=David

|title=Plants versus Photovoltaics: Which Are Better to Capture Solar Energy?

|url=http://www.scientificamerican.com/article.cfm?id=plants-versus-photovoltaics-at-capturing-sunlight

|publisher=Scientific American|access-date=17 January 2012

}}

References

External links

[https://web.archive.org/web/20090220174033/http://www.rsbs.anu.edu.au/ResearchGroups/PBE/index.php Engineering light-activated metalloproteins to split water] at Australia National University
[https://web.archive.org/web/20151208093441/http://techtv.mit.edu/videos/633-daniel-nocera-describes-new-process-for-storing-solar-energy Daniel Nocera describes new process for storing solar energy] at Massachusetts Institute of Technology.
[https://www.youtube.com/watch?v=itoWfzlM5vU Paul Alivisatos on Artificial Photosynthesis] at Lawrence Berkeley National Laboratory
[http://www.nanowerk.com/news/newsid=13409.php Nanocapsules for artificial photosynthesis] a Nanowerk News article
[http://web.mit.edu/newsoffice/2008/oxygen-0731.html MIT Solar Revolution Project] {{Webarchive|url=https://web.archive.org/web/20140328205311/http://web.mit.edu/newsoffice/2008/oxygen-0731.html |date=28 March 2014 }}

Category:Hydrogen production

Category:Photochemistry

Category:Renewable energy technology

Category:Fuel production

artificial photosynthesis

Overview

History

Catalysis

=Catalytic triad=

=Catalysts=

=Selected catalysts=

=Catalyst stability=

Research centers

Various components

= Hydrogen catalysts =

= Water-oxidizing catalysts =

= Photosensitizers =

= Carbon dioxide reduction catalysts =

= Photobiological production of fuels =

= Food production =

Some advantages, disadvantages, and efficiency

See also

References

External links