Q & A
June 30, 2008

Penn State's Craig Grimes

Energy Research News Editor Eric Smalley carried out an email conversation with Craig Grimes, a Professor of electrical engineering at Pennsylvania State University.

Grime's research is in hydrogen generation, solar cells, materials for controlling electromagnetic energy, and environmental sensors. His lab has developed a method of producing dense arrays of titanium dioxide nanotubes of the optimal sizes and shapes for turning light into electricity. His team has used the nanotubes to extract hydrogen from water, generate useful amounts of electricity, and study fundamental aspects of light harvesting, charge separation and charge transport.

Grimes has written more than 250 journal articles, a dozen book chapters, and twenty patents. He is founder or co-founder of four companies. He is co-author of The Electromagnetic Origin of Quantum Theory and Light, editor of The Encyclopedia of Sensors, and co-author of Light, Water, Hydrogen: The Solar Generation of Hydrogen by Water Photoelectrolysis.

Grimes was born and raised in Ann Arbor Michigan. He received B.S. degrees in electrical engineering and physics from Pennsylvania State University in 1984, and a Ph.D. degree in electrical and computer engineering from the University of Texas at Austin in 1990. In 1990 he joined the Lockheed Palo Alto Research Laboratories where he worked on artificial dielectric structures. From 1994 to 2001 Grimes was a faculty member of the Electrical and Computer Engineering Department at the University of Kentucky.

ERN: What are the important or significant trends you see in energy research?

CG: The trends I see are: (1) People are becoming aware that we have a problem. (2) Much effort and resources expended in the wrong direction, i.e. food into SUV fuel. (3) The beginnings of significant (larger scale) solar energy conversion research, but unfortunately not in the United States.

ERN: What would you like to see happen? Is this different from today's national and global energy research priorities?

CG: A clear look at the numbers indicates that beyond a miracle, e.g. nuclear fusion somehow made to work, the only way out of the energy/global warming end game are means of economically (i.e. using earth-plentiful resources) converting sunlight into electricity and/or chemical fuel.

ERN: What is the general focus of your research, and how does it relate to energy?

CG: My research group is working towards material architectures for efficiently converting sunlight into electricity or chemical energy -- notably hydrogen by water splitting, using materials that are still relatively plentiful in the earth's crust. The 'plentiful in the earth's crust' is a key point. The world population is so huge that we are rapidly burning through many of the known reserves of certain elements. So if you come up with a great solar cell but it requires indium or platinum, you have a problem.

ERN: Your work with titanium dioxide nanotubes has applications in both hydrogen generation and photovoltaics. How is nanotechnology significant for energy research?

CG: Conversion of sunlight into photogenerated charge, and then useful collection of that charge, is an interface problem. That is to say, we need to understand and be able to control material properties at their interface, i.e. boundaries with other materials.

Our work on the nanotube arrays is one approach to that. It's a controlled interface of specific, large surface area geometry. The ordered array gives rise to facile charge transport. The nanoscale features of the geometry facilitates charge separation.

ERN: Solar water splitting -- using the sun's energy and a catalyst to break the bonds in water molecules -- promises to be a very clean method of generating hydrogen for fuel. What's the state of solar water splitting research, and what are the hurdles and milestones ahead?

CG: It's a tough problem. One needs materials of the correct bandgap (like iron oxide) so they capture a large fraction of the incident solar spectrum energy. The materials need to have excellent charge transport properties, like TiO2 [titanium dioxide], so the photogenerated charge can be collected to do useful work (as opposed to having the photogenerated charge not separate and hence simply recombine). Then you need material to be resistant to photocorrosion, like SrTiO3 [strontium titanate].

The desired properties can work against each other in a circular manner. For example photogenerated holes, rather than oxidize water, which is what we would like them to do, tend to attack materials having 'low' bandgaps (i.e. the very same materials that are suitable for capturing a significant fraction of the solar spectrum energy). Materials having 'large' band gaps, e.g. TiO2, are almost impervious to photocorrosion but capture only a small fraction of the incident solar spectrum light (about 4%).

ERN: What are some of the strategies you and other researchers are investigating?

CG: Well, basically tricking materials with suitable band gaps into behaving, with respect to photocorrosion, like they have a large bandgap. Different geometries to minimize unwanted recombination, e.g. the nanotube arrays with wall thickness less than the minority carrier diffusion length. And, like mother nature's photosynthesis, coming up with device architectures where two low energy photons are coupled together to split water.

ERN: What is the best-case scenario in terms of cost and capacity for generating hydrogen by solar water splitting?

CG: Someone comes upon the right material architecture to provide us something that doesn't cost much (plentiful), is impervious to photocorrosion, and converts sunlight to hydrogen (or alternative chemical fuel) with a photoconversion rate of about 30%. I think this is possible, but its a very hard problem and not one likely to be solved without application of considerable resources.

ERN: Will solar water splitting ever be able to provide hydrogen on demand, or will we have to separately solve the hydrogen storage problem to take advantage of sun-generated hydrogen?

CG: Depends upon the application. A few photoconversion panels on the roof of a SUV won't get you very far. However, one-third of the earth is desert. It would be nice to use these lands for something, maybe something like generating energy.

Yes, there are problems with hydrogen storage. Nothing compares with finding a huge lake of oil, free for the pumping! Too bad these lakes of oil are finite and burning the oil has rather negative consequences. It's hard to beat something that is more or less free, relatively safe to use, and provides 121.8 megajoules per gallon. 121.8 megajoules per gallon! An average person can generate about 80 watts over a sustained period, run the math per people equivalents.

ERN: What is the math?

CG: 121.8 megajoules = 17.5 80-watt people working for 24 hours per the equivalency of a gallon of gas. If you think how far your car can go on a gallon of gas, and how long it would take a cluster of people to push it that far, the numbers come out about the same.

ERN: This brings up the question of liquid hydrogen versus gas hydrogen. How much energy does it take to liquefy hydrogen, and is storing hydrogen in liquid form worth it?

CG: Depends, we'll have to work it out. I think we may all use propane-tank like cylinders and go with that. Fuel cells might work, so we might be able to put the H2 into fuel cells (but we have a long ways to go for this vision to become reality).

ERN: Is the hydrogen economy feasible, and if not, what place will hydrogen have in the energy mix of the future?

CG: It's feasible, but not free. While we are used to spending vast fortunes on this war or the other, we are not used to spending money on energy since it has been more or less free since 1900 or so. Still, for all the hoopla of $4/gallon gas the amount of annual federal spending on developing new solar energy technologies is equal to about what a professional baseball player makes.

And there you have it. We have built a society predicated upon, in essence, free energy. We don't need slaves or farm animals anymore since we have petroleum. However since nothing that we know of is so energy dense and stable, and more or less free, as petroleum, what replaces it will most likely be a mixture of this and that chosen for the specific application.

ERN: What is the actual amount of federal spending on new solar energy technologies?

CG: Let me put it this way, an elevated local highway interchange (I99 and US322) was built here a few years ago for $160 million dollars, an amount that significantly exceeded NREL's [National Renewable Energy Laboratory] annual budget -- at least then, and may still although the food-to-fuel dollars might have changed the dollar totals. [Ed. note: NREL's budget is about $235 million.]

ERN: Photovoltaics research is proceeding along several avenues: dye-sensitized, organic semiconductor, thin-film, multijunction and variations of these involving nanotechnology. What is the state of photovoltaics research, and where would you place your bets?

CG: Today the PV market is almost entirely silicon. Can we do better in terms of cost and efficiciencies? I certainly hope so, but here it becomes a multi-variable drama and what comes out is anyone's guess.

ERN: Concentrated solar power systems, which focus sunlight to generate heat to drive mechanical electricity generators, are emerging as a relatively cost-effective method of producing electricity from sunlight. What role will these systems play in large-scale power generation?

CG: It's a great idea and approach. One just needs cost effective materials able to withstand high temperatures without degradation. Buying expensive ceramic materials for fighter jets engines is fine with DoD [Department of Defense] budgets, but may be challenging per a production scale commercial product.

ERN: Is the government's goal of achieving grid parity -- making solar electricity price-competitive with traditional sources of electricity like coal-fired power plants -- by 2015 realistic?

CG: It's not going to happen unless we do something besides talk, and it's not going to happen without government intervention, e.g. a tax on CO2 emissions and $ incentives to develop, sell and buy solar cell technology. Japan and the European Union have active financial support systems in place to encourage use of solar energy. They are the leaders.

ERN: What are the important social questions related to energy?

CG: It's a finite earth, with finite resources. The world has some 9 billion people on it now, racing to ten billion. Push will come to shove when the resources start to run out. If you read much history you'll know everyone gets along fine when supply of a precious resource, e.g. food, water, energy, exceeds demand, but not so when demand exceeds supply.

ERN: What are your thoughts on the state of public understanding of energy and energy research?

CG: I would like to think that the average person understands the issues associated with fossil fuels, and the issues associated thereof. We've lived in a golden age of good times, where all the public marketing of research has gone towards finding a cure for afflictions largely brought on by our wealth.

The public should but probably doesn't understand how little basic energy science research goes on in our country -- in fact up until two years ago solar energy was, at least in government circles, largely ridiculed and written off. Almost 30 years ago Ronald Reagan was our visionary who tore the solar panels off the White House roof Jimmy Carter had installed, and slashed to almost zero funding for solar energy research.

It would have been really helpful to us all to have spent the past 30 years working on new solar energy technologies.

ERN: What could be done to improve the pursuit of energy research in terms of business trends, politics, and/or social trends?

CG: The best thing to do would simply be to realize basic energy research is important, and dedicate significant resources to the science and engineering that will lead to new solar energy technologies. What do I mean by 'significant resources'? Something comparable to what we have spent on the invasion of Iraq.

ERN: In terms of energy and anything affected by energy, what will be different about our world in five years? In 10? In 20?

CG: I think our future is one of inelastic demand. Imagine what happens when supplies of food, water, and energy are not sufficient to meet demand. There is a reason we keep a vast military presence around the middle east.

ERN: What do you imagine you will be working on in five years? 10 years?

CG: Improved materials for solar energy conversion.

ERN: What got you interested in science and technology?

CG: Curiosity of the world around us..... or maybe random chance.


CG: "Isn't that interesting? And, by knowing X we can hopefully figure out Y and then do Z!"


CG: I tell them to work hard, it's a tough world out there.


CG: I'm a great fan of Evan S. Connell, e.g. The White Lantern, and some of the earlier work of Diane Ackerman, e.g. A Natural History of the Senses -- well-written discourses on various aspects on the world about us, and our part in it.

ERN: What are your interests outside of work, and how do they inform how you understand and think about energy, and science and technology in general?

CG: My kids. Without them I'd probably punt the slog and go surfing, let the world sort itself without me.

ERN: What question would you like to be asked in an interview like this? What's the answer to that question?

CG: Question: What would you tell the President of the United States if you had a brief audience with him or her?

Answer: Unless we come up with a means of providing cheap solar fuel it's game over for modern civilization. We need to be spending something like DoD's ~$1,000,000,000,000/year budget on solar energy. Doing so will avoid the collapse of modern civilization while providing us with a safer, cleaner, and healthier world.

ERN: Is there anything else you'd like to say?

CG: I wish I saw more reasons to be optimistic about this topic. But as it is mankind seems to have bet on a faith-based energy policy: So let's hope for a miracle!

Think of it this way. You have a cabin in the woods that you have surrounded with latent heat in the form of dried wood. Now you could carefully and slowly burn some of this latent heat, logs, in the fireplace and all would be well. Or you could go crazy and decide to burn all the wood in a comparative instant because you're really (really really) cold.

That's effectively what we are doing on a global scale -- burning many millions of years of stored latent heat, in the form of fossil fuels, in a comparative instant. Since we are not actually, as a society, really doing anything about this we are in essence betting our future that somehow, someway, something will save us. A faith based energy policy.

Back to ERN June 30, 2008



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