Caltech’s Nate Lewis on Converting Scalable Sunlight-to-Fuel with Green Hydrogen

Nate Lewis

Nate Lewis, Caltech's George L. Argyros Professor of Chemistry and a leading solar energy researcher, served as director of the Joint Center for Artificial Photosynthesis (JCAP), a US Department of Energy Innovation Hub originally tasked for developing a direct sunlight-to-fuel system—“doing what plants do, but 10x better.” Professor Lewisin this VX News interview, elaborates on what his research team discovered about converting electricity into fuel and green hydrogen’s role as a critical enabling technology for decarbonizing transportation fuels and scaling long-term grid energy storage

Established in 2010, the Joint Center for Artificial Photosynthesis (JCAP) at Caltech has been the United States’ Department of Energy Innovation Hub for researching scalable strategies for the generation of fuels from sunlight. What are the breakthroughs in research and policy that continue to drive your work?

The better way to phrase our mission would be that JCAP was the launching point of what we all hope and have promised success in converting electricity and/or sunlight directly into fuel, which is critical because it provides the now unavailable bridge between the stationary sector and mobility transport sector. Now, fuels and electricity are completely decoupled, and while there are many ways to make decarbonized – even cheap – electricity from wind and solar, there are very few ways to make carbon-neutral fuel. If you can convert electricity into fuel, that would be a critical enabling technology that would solve so many issues for long-term grid storage and for decarbonized transportation fuels within our existing infrastructure. The linchpin is converting electricity to fuels, one way or another.

And what has your research team learned about converting electricity into fuel since your 2014 TPR interview?

We've learned a lot on the science and technology side. When we first started, this was just a concept that was almost magic. We needed two light absorbers, two catalysts, and a piece of plastic to hold it in to make, essentially, a high-performance rain-jacket magic-carpet that could suck in the sunlight and water, and maybe carbon dioxide, and wick out either hydrogen or a liquid fuel. That sounds almost like Fantasyland, but we discovered, out of those five pieces that we needed, four of them, and have an engineering design around the fifth.

By any measure, we made tremendous breakthroughs in replacing expensive catalysts made with platinum and iridium with cheap ones with nickel and cobalt that can be scaled. We found a stable replacement for iridium as a water oxidation catalyst to make oxygen that hasn’t been found in a century of identifying the architecture for how you would build this, modeling it, and identifying light absorbers that can be coupled to get both the red and the blue parts of the rainbow.

So, we needed those five pieces, and we had no idea what they were going to be or how they were going to piece together.  It's, as I like to say, like drawing to a straight, you need all the numbers aligned too, or you don't have much of a hand. So, we did that. We could, really, have made the first demonstration system that does what nature does but 10x better; 10x more efficiently.

That means, if you want to make fuel, we could do it with 10x less land than a biomass harvesting refinery needs. That would be fantastic if we had the opportunity to demonstrate. We could do the engineering and scale up, while improving the generations of the technology. It's at the point where, if there's a will there's a way, and humans are very good at innovation once the invention has been made that shows that it's possible.

So, we were very close to making that final, possibly major, leap, and then the Department of Energy refocused the JCAP effort toward, not splitting water into hydrogen, but also directly making a liquid transportation fuel from carbon dioxide. That's much harder, and much less progress was made on doing that. So, we have a job undone, which is to finish the deal on the first goalpost that we were really remarkably close to doing, and I would hope that we would find a way to do that, which is what my research group continues to focus on.

However, the catalysts we discovered to replace expensive elements turned out to have a dual use; not only to be, potentially, missing puzzle pieces in a direct sunlight-to-fuel system, but also as enablers for an indirect system that's more well-known and proven to commercialization: electrolysis, when you apply electricity to water to produce hydrogen and oxygen. That process is expensive now, primarily because the catalysts are expensive.

So, we have a path, in principle, for a two-step process that takes advantage of really cheap solar and wind electricity and converts it into fuel as a second step connected to the grid. That would produce central station hydrogen that would be used for transportation and storage. It's just a question of which way is the most cost effective to skin that cat, and we're really interested in that. Also, it’s a shorter-term commercialization effort.

What from this important research should a new federal administration prioritize? 

I have a whole talk about this: “Top 10 things That We Don't Know How to Do That We Need To Do to Get to a Fully Decarbonized, Cost Effective Energy Economy.”

When I first gave that talk it was about how we need to lower the cost of solar and figure out how to really harness wind, biofuels, and things that are now mostly mainstream.  That was 10 years ago. You can argue that ball’s rolling, but our work is not done. There are 10 new things that we don't know how to do that we need to do.

The reason being that you have to be careful what you wish for or you might get it. You might get really cheap, intermittent, variable solar and wind, but you don't want blackouts every hour or every week, no matter how cheap it is. So, you've got to find a way to store it at grid scale cost effectively.

Batteries are obviously high on everybody's radar. But the sun has this little problem; not only does it go out every night, but in California for instance the sun didn't shine brightly over the whole state for four consecutive days in January. To get through the rare weather-related events, you need to have lots of mostly idle energy storage, and that's very expensive. So, we have to figure out other ways. Hydrogen is one way to do that load balancing to avoid blackouts during rare weather events or in the summer when the wind just goes into the doldrums for three weeks at a time over the whole country. You just can't shut off the whole country. Because of that, even if you know it's coming, demand management is not going to get you there; we need grid-scale long-duration storage.

We need, for example, to find ways to make cement that doesn't emit carbon dioxide. Most people aren't aware that the inherent manufacture of concrete and cement— by its chemical formula from calcium carbonate lime to make calcium oxide—emits carbon dioxide, and it's 8 percent of global emissions. Unless we find a way to build all of our buildings and bridges out of a different structural material, we're going to have residual emissions that simply aren't compatible with stabilizing the climate.  The same goes for steel. How do we build our cities and infrastructure of the future in a deeply decarbonized way? People haven't come to grips with that because we've done the easy stuff first, but the hard stuff’s still there.

We're going to need a way to do climate monitoring, for instance. Even if we say we're on a path to cut emissions, how would anybody know that we were? We need technology to understand how to verify even well-intended nation's carbon emissions reductions. We don't have any of that right now. There are a couple more on the list, but long-duration storage and grid balancing, cement and steel manufacturing for buildings, transportation fuels (there’s no such thing as a plugin hybrid airplane, so we’ve got to find a way to decarbonize them), and climate emissions monitoring so we know we're being good stewards and doing what we're supposed to do to take care of the one planet we have as home. Sounds good to me.

Continuing with that theme, the fall we had rolling brownouts executed by our utilities in California because of the extensive heat, which was also affecting air quality. Do events like the latter signal the globe already has crossed a climate threshold?  How should research centers like Caltech and your lab, now meet this existential challenge?

That's in the eye of the beholder. The data and the trends are unequivocal and show that we have more extreme weather events, that the Earth is warming at an unprecedented rate, that melting glaciers events are credibly and plausibly linked to human activities (anthropogenic sources, as it's called technically.) There's no question about that. To the question about tipping points and nonlinearities, it's not what we know, it's what we know we don't know that are the big issues. We know that the average climate model says the Earth will warm by a couple degrees. We know that the average path, predicted by the average of all these climate models, is almost certainly not the path that the Earth is on. We just don't know which one it is. And so, there's a spectrum of possible outcomes.

The alarm bells are certainly there, and the question is whether we really want to take the risk of going to a place that we can’t come back from, that we second guess ourselves and then wonder didn't we do something about it when we had the chance? This is all about risk management, and your perception of whether you're willing to take the risk. People also don't generally realize the lifetime of carbon dioxide impacts and emissions. What we do now will impact our atmosphere for, in the absence of ways to remove and undo Humpty Dumpty here, some 3000 years. Some people say 10,000 years. By any measure, we're changing the planet on which we live for a timescale comparable to modern human history, with no easy way out.

As we're seeing in a different arena, in the arena of infectious disease and biochemistry, nature doesn't call itself red or blue. It's got its own rules and it doesn't listen to anything other than what it wants to do. It's batting last in this game and has all of the heavy hitters on its side. The same thing is true with climate change. It's going to do what it's going to do, and whether or not we choose to respond to the alarm bells, is our decision. Because the laws of physics can't be repealed, like the laws of economics or politics.

In this moment of time in 2020, when there's no universal acclaim for science, address the policy environment in which you work at Caltech, and what the investigative opportunities are and what new resources are needed?

 It's actually an exciting time still. The pace of innovation is still accelerating. People are still very, very interested and excited about innovation and discovery that would enable sustainability. We have come to realize pretty broadly that this is our problem, and we can fix it if we really put our minds to it. We're going to need science and technology; it's not all policy. We’ve got to invent our way to figuring out how to do some of these things. How to bring everybody in this century out of poverty while giving them the energy services they need, but also not emitting so much carbon dioxide that we mess it up for future generations? This is a science and technology problem.

 If you look at the heartbeat and the pulse of the coworkers and students, they're plowing straight ahead with whatever resources they have to try to make an impact and do something about it in a very positive way. That wasn't there 10 years ago when I was one of the few people trying to motivate people to work on this problem. So, that's very gratifying. I think there's a lot of momentum, and we can do a lot of great things if we keep going.

But during the pandemic, with shelter-in-place and social distancing, you're obviously not having many conversations at the Faculty Club or down at the ‘water cooler.’ Give us a sense of how collaborative research is being conducted.

I haven’t been on a live campus since March 1, so I don't know what those conversations are. The only people I contact are through Zoom and when it's scheduled in advance. There are no faculty conversations that I've been a part of over lunch at the Athenaeum and no informal get togethers or seminars. My graduate students are now back socially distanced, mostly working in shifts or at low density in our labs. We have to find mechanisms, which have been less than satisfying, to get them out of individual caves, basically. They can't really talk to anybody else when they're working. We can't recruit new graduate students to come into the program in person. They're all gone, and they're going to be gone for the fall term too. And I don't know what to do.

People are still in their labs and doing science, but there's a missing context and dimension to how that evolves. It's much more structured, and by necessity, not many surprises can occur. We're mostly in autopilot mode, self-driving here for a while. We were going in a good direction, but if there were course changes needed, we can't figure them out fast, if at all. I think everybody hopes we get back to a little bit more normal old school operation soon.

For context, Caltech/JPL remains involved, for example, with NASA’s Mars mission and is staffing up and building a new, well-endowed Resnick Sustainability Institute. Elaborate on the status of Caltech’s 2021 commitment to scientific & technological innovation on campus—and what is awaiting a new national commitment to science.

There are all sorts of activities that are impacted. JPL is kind of crippled; only mission-essential personnel can come in. A lot of their technology development and external outreach activities and all of their innovations with small businesses are pretty slowed down, if existent, in terms of real activities, other than monitoring contracts. It almost seems impossible now to stand up a new mission because you wouldn't have the planners. You couldn't have anybody building anything because the density has to stay low. My wife works there, so I know this intimately. So, that's really slowed, and would come back to the normal brisk excitement of interplanetary exploration of who we are, where we came from, and what else is around us, just waiting. That's all pent up.

 At campus, from the sustainability side, there's a lot of excitement over the opportunity given by that remarkable Resnick gift. There are some plans to start putting that to great use on sustainability for water, sunlight-to-fuels, and a few other targeted areas and more. But I don't see how we can really initiate and launch a new vibrant effort until some of the shackles are taken off. Nothing probably can really happen until we do that.

Turning to California’s goal of decarbonizing our energy economy, address the role of natural gas as a bridge fuel and promise of hydrogen from the vantage point of your research work.

They're very similar questions. I don't see a technically credible method of decarbonizing and meeting the state's goals—of meeting 15 states’ goals for decarbonization and net zero emissions by 2045 or 2050—that doesn't involve a significant amount of using fuel to provide energy services. It doesn’t have to be fossil fuel, but you've got to have fuel somewhere.

You can't load balance the system by pumping rocks uphill every summer and dumping them down every winter . It's just not scalable to the levels that you would need even if it were cost effective on the margins. You need fuel. You need decarbonized fuel to make high temperature heat to make our steel. You need fuel to run an airplane. So, we need fuel.

Whether that fuel is natural gas made from hydrogen and carbon dioxide, or it's just hydrogen itself, the technology in the marketplace should figure this out. If you can really make cheap hydrogen and you can capture CO2, we already know how to make natural gas. It's called methanation; that's the easy part. The hard part is getting the CO2 out of the air and the hydrogen out of water and doing that cheaply. Then we could be done, and we could have basically unlimited renewable natural gas.

How does this fit into whether natural gas is a bridge? It's inevitable that it's a bridge. The question is whether it’s a bridge to somewhere. We need it to load balance right now. We wouldn't have cheap wind and solar if we had to build enough wind and solar, by itself, to avoid the variability that we now fill by burning natural gas in power plants. There's no other way to do that cost effectively now. So, gas is here, and we need it, or we would have unaffordable renewable electricity because of all of the extra idle power we'd need to get through the lulls.

If you want to phase out fossil natural gas, do you replace that essential grid service function with hydrogen or with renewable natural gas? Then, it's a bridge. If you don't replace it, because we don't have the technology and cost feasibility to do that, then you need to have negative emissions, and whether or not those are affordable is a whole other story. They're like the Joker in the deck that optimists say we'll pull out just when we need them, but pessimists say you can't count on it, and so we better keep our options open for other systems. Hydrogen would be one.

Lastly,  now, that the national election is over, what keeps you up at night?

I'm in a pretty good spot now. I've got a lot of things on my plate, but I'm seeing a lot of positive progress. Ten years ago, my answer to that question would have been different. You may have asked me before, but the thing that kept me up at night then was whether we would ever actually figure out that this is our one chance and do something about it. That we would not just try to wave a magic wand, say we have all the technology we need, and be done. It's more like, we can only get halfway there with what we now know, and we need to innovate and invent the other half. People realize that, and we're on our way to trying solve that. It's not a forlorn “are we ever going to wake up” existential threat. It's more of an optimistic tone, more exciting. More, ‘let's go get it done,’ rather than being scared we won't even pull our heads out of the sand to even try. I'm much more optimistic that we're trying and that we'll get it done.

“We have a path, in principle, for a two-step process that takes advantage of really cheap solar and wind electricity and converts it into (carbon-neutral ) fuel.”
"(T)here are very few ways to make carbon-neutral fuel. If you can convert electricity into fuel, that would be a critical enabling technology that would solve so many issues for long-term grid storage and for decarbonized transportation fuels within our existing infrastructure. The linchpin is converting electricity to fuels, one way or another."
“Hydrogen is one way to do that load balancing to avoid blackouts during rare weather events or in the summer when the wind just goes into the doldrums for three weeks at a time over the whole country.”