Introduction to Solar Photon Conversion
The efficient and cost-effective direct conversion of solar photons into solar electricity and solar fuels is one of the most important scientific and technological challenges of this century. It is estimated that at least 20 terawatts of carbon-free energy (1 and 1/2 times the total amount of all forms of energy consumed today globally), in the form of electricity and liquid and gaseous fuels, will be required by 2050 in order to avoid the most serious consequences of global climate change and to ensure adequate global energy supply that will avoid economic chaos. But in order for solar energy to contribute a major fraction of future carbon-free energy supplies, it must be priced competitively with, or perhaps even be less costly than, energy from fossil fuels and nuclear power as well as other renewable energy resources. The challenge of delivering very low-cost solar fuels and electricity will require groundbreaking advances in both fundamental and applied science. This Thematic Issue on Solar Photon Conversion will provide a review by leading researchers on the present status and prognosis of the science and technology of direct solar photoconversion to electricity and fuels. The topics covered include advanced and novel concepts for low-cost photovoltaic (PV) energy based on chemistry (dye-sensitized photoelectrodes, organic and molecular PV, multiple exciton generation in quantum dots, singlet fission), solar water splitting, redox catalysis for water oxidation and reduction, the role of nanoscience and nanocrystals in solar photoconversion, photoelectrochemical energy conversion, and photoinduced electron transfer. The direct conversion of solar photons to electricity via photovoltaic (PV) cells is a vital present-day commercial industry, with PV module production growing at about 75%/year over the past 3 years. However, the total installed yearly averaged energy capacity at the end of 2009 was about 7 GW-year (0.2% of global electricity usage). Thus, there is potential for the PV industry to grow enormously in the future (by factors of 100-300) in order for it to provide a significant fraction of total global electricity needs (currently about 3.5 TW). Such growth will be greatly facilitated by, and probably even require, major advances in the conversion efficiency and cost reduction for PV cells and modules; such advances will depend upon advances in PV science and technology, and these approaches are discussed in this Thematic Issue. Industrial and domestic electricity utilization accounts for only about 30% of the total energy consumed globally. Most ({approx}70%) of our energy consumption is in the form of liquid and gaseous fuels. Presently, solar-derived fuels are produced from biomass (labeled as biofuels) and are generated through biological photosynthesis. The global production of liquid biofuels in 2009 was about 1.6 million barrels/day, equivalent to a yearly output of about 2.5 EJ (about 1.3% of global liquid fuel utilization). The direct conversion of solar photons to fuels produces high-energy chemical products that are labeled as solar fuels; these can be produced through nonbiological approaches, generally called artificial photosynthesis. The feedstocks for artificial photosynthesis are H{sub 2}O and CO{sub 2}, either reacting as coupled oxidation-reduction reactions, as in biological photosynthesis, or by first splitting H{sub 2}O into H{sub 2} and O{sub 2} and then reacting the solar H{sub 2} with CO{sub 2} (or CO produced from CO2) in a second step to produce fuels through various well-known chemical routes involving syngas, water gas shift, and alcohol synthesis; in some applications, the generated solar H{sub 2} itself can be used as an excellent gaseous fuel, for example, in fuel cells. But at the present time, there is no solar fuels industry. Much research and development are required to create a solar fuels industry, and this Thematic Issue presents several reviews on the relevant solar fuels science and technology. The first three manuscripts relate to the daunting problem of producing solar fuels. Lewis and colleagues present a comprehensive review of solar water splitting based on semiconductor electrodes. The semiconductor electrodes are either in direct contact with an aqueous electrolyte, creating a semiconductor-liquid junction, in which case this defines a true photoelectrochemical (PEC) configuration, or the semiconductors can form buried p-n junctions connected to metal anodes and/or cathodes, in which case various combination of PV and PEC cell configurations are possible. The issues of cell energetics, cell efficiency, photocorrosion, and electrocatalysis are discussed in detail. Nocera et al. first discuss the global energy problem and review the issues and technologies for solar energy storage. Then they focus on solar fuels as the best option for solar energy storage at sufficient scale to solve the looming energy crisis.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- DOE - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1004142
- Report Number(s):
- BNL-94578-2011-JA; ISSN 1520-6890; CHREAY; R&D Project: CO-004; KC0301010; TRN: US201103%%367
- Journal Information:
- Chemical Reviews, Vol. 110, Issue 11; ISSN 0009-2665
- Country of Publication:
- United States
- Language:
- English
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30 DIRECT ENERGY CONVERSION
CLIMATIC CHANGE
ELECTRICITY
ELECTRON TRANSFER
ENERGY CONSUMPTION
ENERGY CONVERSION
ENERGY SUPPLIES
FOSSIL FUELS
FUEL CELLS
LIQUID FUELS
NUCLEAR POWER
PHOTONS
PHOTOSYNTHESIS
P-N JUNCTIONS
QUANTUM DOTS
SOLAR ENERGY
WATER
WATER GAS
solar energy
nanoparticles
conjugated polymers