Prof Tom Meyer, Energy Frontier Research Centre, University of North Carolina, was in Dublin to participate in a Dublin Region Higher Education Alliance Master Class on Solar Energy. Afterwards, he gave a public lecture on “Our Energy Future: Science, Technology and Policy Challenges for the 21st Century – A US Perspective“. The lecture was held at TCD, and was sponsored by the Royal Society of Chemistry Republic of Ireland Local Section. It considered the various current and future world energy demands, and the role renewable energies have to play in providing this energy. My summary is given below.
Prof Thomas J Meyer has been researching the photochemistry of ruthenium complexes since the late 1960′s. Much of what we know about electron transfer in ruthenium polypyridyl complexes today is due to work conducted by Meyer and others in this period. Meyer worked with Henry Taube, who won the Nobel Prize in 1983 “for his work on the mechanisms of electron transfer reactions, especially in metal complexes”, publishing a paper with him in Inorganic Chemistry (1968) on excited state oxidation potentials of ruthenium-amine complexes. This work was an important pre-cursor to a 1973 paper published by Taube, Meyer and co-workers on the reduction of oxygen by these complexes. In the mid-1970′s, at a time when the oil crisis of the time was reaching a peak, Meyer published a series of important papers in Journal of American Chemical Society on the nature and kinetics of quenching of ruthenium amine complexes (including ruthenium – tris-bipyridyl) which gave great kinetic and mechanistic insight into the electron transfer between the metal complexes and an array of quenchers. Meyer reiterated in an article written in 1975 the importance of understanding electron transfer in the study of energy conversion, especially so with metal complexes as these absorb strongly at wavelengths of solar interest.
A surge of interest in these systems was observed the oil crisis, which faded somewhat in the 80′s and it wasn’t until Gratzel’s work on dye-sensitised solar cells, reported in 1990, that generated efficiencies that would allow for devices to become realistic contributors to energy supply. Since that itme, work has been concentrating on enhancing light absorption capacity, currently champoined by a ruthrnium dy “N3″ (see DSSC post), as well as considering and optimising electron transfer processes in the solar cell devices.
Meyer’s lecture in TCD considered the current and future status of energy demands. It was a message he has delivered to the american political system, across administrations, during his tenure at the Los Alamos National Laboratory. Meyer reported that in the US, energy costs make up 7 – 10% of the cost of living, and 7% of overall world trade. A large demand in energy increase has been observed since 1900′s and this surge is expected to continue until at least 2100. While current stable economies’ energy usage will level off, emerging and transitional ecomomies (China, India, etc) will place major demands on the world’s energy supply. In the six years since 1999, China and India increased their energy usage by 80% and 25%, respectively (Cicerone). (A presentation by Cicerone, Preseident of the National Academy of Sciences is reference below and places thes enegy demands in context). In summation, >100 TW of additional ‘clean’ energy will be required by 2100.
The US currently uses 26% of the world’s oil supply, greater than the next five net using countries combined. 26% of the world’s oil is in the middle-east. Globally, the cost of oil is increasingly expensive to extract, as reserves become more and more difficult to source. Therefore additional energies from alternate sources is required to factor the loss in and increasing expensive of oil production; as well as the surge in energy demand from emerging economies. In addition, this energy supply must be in the context of envrironmental considerations, primarily global warming.
Meyer outlined several strategies to large scale energy production. Principal among these were nuclear, solar, and clean hydrocarbons. These and others are considered below.
Coal currently supplies 27% of the world’s energy demands, including half of US energy needs. It is also responsible for 35% of US carbon dioxide emissions. In principle, it could provide increased energy requirements until 2050, if 1% of GDP was used in dealing with carbon dioxide sequestration. The story of coal usage inclues the story of FutureGen – an initiative announced by the Bush administration in 2003. This was aimed at using coal as a clean fuel, with achieved targets of 275 MW of energy production with 90% carbon dioxide sequestration. However, the project was cancelled by the Bush administration in Jan 2008, due to massive cost overruns ($900M). The Obama adminsitration has restarted this work (June 2009), recognising that clean coal will be a crucial element to supplying energy demands in the forseeable future. Oil shale and tar sands are estimated to contain 2 trillion barrels of oil. However, it expensive (requireing a lot ofwater) and enviornmentally damaging to extract oil from these reserves.
Hyrdogen fuel is obtained from a variety of sources – primarily methane, but also from coal extraction and water electrolysis. In the latter case, electrolysis of water to produce hydrogen (and oxygen) is utililised by photochemical processes. Meyer identified the Idaho National Laboratory hydrogen programme as one which was making good progress in the production of hydrogen as a mass fuel. The advantages of hydrogen were good efficiency, and water and heat as emission products. However, the current costs (for transportation) are ca. $3500/kW, with a target of $35/kW. Another significant problem with the use of hydrogen was storage and transportation, which were expensive because of the nature of the fuel.
Nuclear energy provids ~20% of US energy, and increased usage would result in a significant decrease in greenhouse gases. There are 44 nuclear reactors currently being built internationally, and therefore these will be significnat contributors in to the future. The issues, well know, of nuclear power are what to do with waster, control (political issue), reprocessing and general safety issues.
Renewable energies provide an alternative approach to the solution. It is estimated that wind could provide 20% of US energy requirements. However, solar energy is a real viable option, given that 26,000TW per year of sunclight isiincident on the Earth’s surface (net amount after absorption etc). the technology is on the cusp of mass implementation, with some lingering problems regarding efficiencies. (In the US, there are also problems regardingthe arrangement of the national grid (see Grid 2030 project). Current estimates are that solar generation of 3 TW, assuming 10% efficiency solar cells, would cost approximately $60 Trillion (covering an area of 57k sq – miles). Current and future work will be focussed on reducing this cost.
Meyer reiterated the point in his talk, and again in questions, that there must be a political will to drive this work forward. Solar energy could have emerged as a major player much earlier, if work started after the oil crisis had continued apace. 6% of US energy is currently sourced from renewable sources; with 85% from coal, oil and gas. The hope is that by 2059, these numbers can be reversed!
C. R. Bock, T. J. Meyer, D. G. Whitten, Photochemistry of transition metal complexes. Mechanism and efficiency of energy conversion by electron-transfer quenching, J. Amer. Chem. Soc., 1975, 97, 2909 – 2911.
R. J. Cicerone, National Academy of Sciences, Address to the 145th Annual Meeting, available at: http://www.nationalacademies.org/includes/NASmembers2008.PDF [Oct 2009]
Las Alamos National Lab: National Security Science: http://www.lanl.gov/ [Oct 2009]
T. J. Meyer and H. Taube, Electron transfer reactions of ruthenium ammines, Inorg. Chem., 1968, 7, 2369 – 2371.
J. R. Pladziew, T. J. Meyer, J. A. Broomhea, and H. Taube, Reduction of oxygen by hexamammineruthenium(II) and by tris (ethylenediamine) ruthenium (II), Inorg. Chem., 1973, 12, 639 – 643.
H. Taube, Nobel Prize Lecture Nobel Prize 1983, http://nobelprize.org/nobel_prizes/chemistry/laureates/1983/taube-lecture.html [Oct 09]
R. C. Young, T. J. Meyer and D. G. Whitten, Kinetic relaxation measurement of rapid electron-transfer reactions by flash photlysis – conversion of light energy into chemical energy using Ru(bpy)3(3+)-Ru(bpy)3(2+*) couple, J. Amer. Chem. Soc., 1975, 97, 4781 – 4782.
Flash photolysis revolutionised the science of photochemistry by allowing for rapid (and the definition of that term was era-dependent) monitoring of photochemical intermediates. Since its development in the mid-20th century, flash photolysis has been at the centre of studies of photochemical/physical processes. Developed by Porter, working with Norrish at Cambridge, at the microsecond timescale, the instrumentation has now evolved to the femtosecond timescale – nine orders of magnitude faster over four decades. Porter said in 1975 that he anticipated femtosecond spectroscopy within five years, and it was primarily instrumental issues which delayed his vision. His foresight was eventually realised with the work of Egyptian photophysicist Ahmed Zewail, working at Caltech. This first in a sequence of articles covers the historical development of flash photolysis, we will look in future posts at the progress leading up to Zewail’s development of femtosecond spectroscopy as well as outlining how it is used experimentally to study photochemical intermediates.
1. Development of Early Instrumentation
When Ronald Norrish, Goerge Porter and Manfred Eigen were awarded the Nobel Prize in 1967, for studies of extremely fast chemical reactions, effected by disturbing the equilibrium by means of very short impulses of energy, it was an acknowledgement of their pioneering work in developing apparatus to study microsecond chemical reactions in the microsecond timescale. Eigen’s work inolved using sound waves (a form of pressure) to perturb (or distort) systems, subtly, and Porter, working as a student of Norrish’s at Cambridge, used UV flashes to perturb systems creating electronically excited states. Prior to this development, “fast” reaction kinetics were capable of being studied only on the sub-second time-scale using stopped-flow apparatus, which was developed in the 1920′s. The concept was simple in principle – distort the system at equilibrium using a high-energy flash of light and detect how fast the system restores to equilibrium. The difference here from previous approaches to kinetic analysis was that studies, for example in stopped flow, examined how fast systems approached equilibrium on mixing, and hence were limited by how fast mixing could be effected.
Porter has said that his work for the navy during World War II, as a radar scientist using pulses of electromagnetic radiation was the seed for his ideas at Cambridge when he went to work as Norrish’s graduate student after the war in 1945. Having been sent to get a replacement lamp for a torch for experiments he was conducting to study the CH2 radical (the torch was acting as a continuous light source), Porter saw flash-lamps being manufactured at the Siemen’s factory in Preston, UK and in 1947, introduced the idea of using flash lamps as a pulse of energy to “study transient phenomenon”. The second flash (the true genius of the development), after the burst of light creating the transient state, would essentially photograph the transient phenomenon – so the time scale of the flash was crucial. At the time, millisecond measurement was considered “far beyond direct physical measurement”. Flash photolysis would allow liftetimes 1000 times shorter to be measured by 1950.
The flash lamp used by Porter was a high-intensity pulsed lamp used by the Royal Navy at the time for night-time aerial photography. It was contained in a 1 m long quartz tube (2000 μF charged to 4 kV for those interested in electronics). It could be discharged in 2 ms. The probe flash – a less intense light source which would measure the changes in absorption after the initial flash was 50 microseconds, and both the initial flash (pump) and probe were timed using a timing wheel, which can be seen in the photograph of the original apparatus (to the right of the apparatus) below.
2. Early Experiments
Interestingly, the first experiments the apparatus was used in have direct relevance to modern science – the study of hydroxyl radicals in hydrogen-oxygen-nitrogen dioxide systems and in the study of the ClO radical in chlorine-nitrogen-oxygen systems. These species and intermediates generated are at the heart of stratospheric chemistry research today. Early transient absorption spectroscopy experiments (see Windsor article in same issue, referenced below) were on triplet-triplet absorption in polyaromatic hydrocarbons (PAHs), again environmentally relevant species today. These studies looked at the kinetics of decay of the triplet state, in the microsecond timescale, and how they were affected by solvent viscosity, presence of oxygen, etc. These studies formed the backbone of a wide and ever-growing research into organic compounds (including my own on enone-alkene cycloadditions some 40 years later!).
It’s difficult for us now to comprehend the true genius exhibited by Porter in his development of flash photolysis. I think it demonstrates magnificent scientific flair, taking together his previous experience, observance of available instruments parts and an obviously great understanding of chemistry, and combining to develop flash photolysis. The development of the technique revolutionised the fields of kinetics and photochemistry, with implications across a huge variety of fields, including, as we have seen above, stratospheric chemistry and organic photochemistry. Porter has sown the seeds for fast very fast and ultimately ultrafast reaction kinetics, which essentially required faster and faster laser pulses to achieve. By the late 1960′s, nanosecond spectroscopy was feasible.
In the next article on this topic, which will be linked here, we will look at Zewail’s work in developing femtosecond spectroscopy.
This article is sourced from various articles, as indicated below:
Van Houten, J. A Century of Chemical Dynamics Traced through the Nobel Prizes: 1967: Eigen, Norrish, and Porter, J. Chem. Educ., 2002, 79(5), 548 – 550. Overview of the development of Flash Photolysis in the context of Nobel Prizes in kinetics generally.
Thrush, B. A., The Genesis of Flash Photolysis, Photochem. Photobiol. Sci., 2003, 2, 453 – 454. Short article on the experimental details, as part of a special issue on George Porter’s work and influence in the area. The journal issue generally shows the scope of flash photolysis in photochemistry research today.
Farago, P., Interview with Sir George Porter, J. Chem. Educ., 1975, 52(11), 703 – 705. Great interview with Porter – what comes across so well is his keen interest in science and in promotion of good science communication. Well worth a read.
Windsor, M. W., Flash photolysis and triplet states and free radicals in solution, Photochem. Photobiol. Sci., 2003, 2, 455 – 458. Wonderful personal account of Porter’s first student (as I can gather) and his work on the development of triplet-triplet absorption spectroscopy.