Developing Battery and Fuel Cell Materials with Raman Microscopy

Interview conducted by Will SoutterJun 27 2018

Professor Sanjeev Mukerjee, college of science at Northeastern University, talks to AZoM about his research into electric catalysis for developing battery and fuel cell materials with raman microscopy.

Can you tell us then a bit about your background, and how you came to work in the field of electrochemistry?

Well, I'm a professor in the college of science at Northeastern University. I’ve been here for 20 years and rose through the ranks from an assistant professor to now distinguished professor.

I did my undergraduate and master's degree in India and came to the United States to do a PhD at Texas A&M University one of the best places to do fuel cell research in world. While doing my undergraduate, I was fascinated by catalysis, and I started my career researching hydrogen's catalysis.

It was when I got into electrocatalysis I really started to enjoy it. That's the most elegant form of catalysis where you have control over the density of states of your catalytic materials.

Can you describe some of your current or recent research projects in electric catalysis?

We have multiple research projects. One of the most recent projects is to bring down the cost of hydrogen by making sustainable catalyst materials to work in an alkaline environment to do hydrogen evolution reaction at voltages which will enable hydrogen production at below $2 a kilogram. This project is funded by Department of Energy, and we hope that will revolutionize both energy storage and transportation through fuel cell cars.

Another project is looking at lithium-air batteries where we're trying to make the oxygen reaction reversible in a nonaqueous electrolyte environment.

We are also running a third project that’s trying to replace platinum in a conventional fuel cell, low temperature and medium temperature fuel cell, such as proton exchange membrane fuel cells as well as the phosphoric acid temperature, and that will revolutionize fuel cell transportation as used in a car or a light-duty truck.

Then there are esoteric projects such as the new one from NASA where we're trying to enable CO₂ mitigation in a closed, confined environment as a part of the plasma pyrolysis project to enable hydrogen pumping in that overall setup.

What impact are broad changes such as electrification in the automotive industry and increased energy storage demand having on the battery industry?

Well, this is a quiet revolution. The cost of renewable electrons have really gone down dramatically. Compared to what we had rejected 10 years ago, both solar and wind cost of electricity is at par or below what a super thermal power station unit of electricity costs.

The main thing is we need energy storage, and energy storage has to be both reliable, and it has to be scalable and affordable. This is where electrochemistry can offer really good solutions. There are solutions right now, but they're very expensive, and that's what we are working towards changing.

The other big area, of course, is the battery-powered electric vehicles which will revolutionize our transportation. That combined with autonomous driver mode will enable people to question whether you need to own a car or not. The whole sharing economy and the fact that you can get transportation via an app on your smart phone, on demand, to go anywhere, plus the fact that it will be battery-powered. You don't need to worry about recharging your battery, because that's the prerogative of whoever is running the transportation service.

The way we live, the way we move ourselves, everything is going to change slowly. It's just like how computation, and then the internet took over our lives. Now, someone like my daughter cannot imagine a life without Wi-Fi. It's almost like oxygen. For the young people, it's just like that.

We'll slowly move away from the internal combustion engine, or the whole idea of burning things, to move people, to energize our environment. The whole thing is going to be replaced.

Image Credits: buffaloboy/shutterstock.com

A couple years ago, even when we had no lithium-ion batteries, we had nickel-metal hydride batteries, the analog cell phones would last a week, because basically what you did was talk on it. Now, with lithium-ion batteries which are almost an order of magnitude higher in energy density and even power density now, my smart phone just lasts a day if at all. It depends on how I use it.

Yes, we are demanding more and more out of our devices, and, especially, this remarkable device which we call a smart phone. It does everything. Have you ever imagined that ... We used to have music which was stored in first vinyl records and then in CDs. A person like me, I had hundreds of them. There were shelves full of CDs. Now, everything basically fits into this. It's a remarkable device.

As graduate students, we used to go and buy a stereo. Now, none of my graduate students here in the lab have a car, have a stereo system, or own a TV. This is remarkable. Now, of course, the virtual reality headphones, that's amazing. Who will want a TV? But you need a battery for this.

What will be interesting is if your cars start to dominate, obviously, the amount of charge they need to store is huge.

A typical electric vehicle needs 75 kilowatt hour battery. That's a big, huge battery pack. Safety is paramount, because if you don't treat the lithium-ion battery nicely, it will blow up. It's a huge energy density packed in a relatively small volume. That's where most of the electric vehicle manufacturers are concentrating their efforts on.

How are these industrial trends changing the demands for more advanced electrochemical technologies? How has this impacted your own work?

Well, when you are at a university our job is to look at fundamental science which will impact technology 10 to 20 years down the line. That's how I look at lithium-air batteries. We have a lot of problems, and we are just at the beginning point of trying to understand them.

But in terms of being able to look at an electrochemical couple with the highest energy density, lithium-oxygen couple is the main thing. If you look at the standard reduction potentials, you will see both are pretty much at opposite ends of the spectrum.

It's very natural that as an electrochemist and as a person who likes to work on battery-related technology, this will be a natural progression towards ... Where I would aspire to go. That's how I'm involved in it. I don't see that happening any time soon. It's going to be a very long-term research mission.

But in the meantime, we have short-term goals as well. Trying to improve the safety of current lithium-ion batteries is one of those noble goals to aspire for. Those are also within our range of things we are working on.

How do you use Raman and FT-IR techniques in battery development, and how important are they in the suite of analytical tools you use?

These are vibrational spectroscopy. They typically look at things which are absorbed on an electrode surface, and they are complementary to each other.

Most of the time, FTIR has too many interfering peaks in the range of materials which we use, so Raman is actually much more useful for us. We use it for a whole variety of things. If we are trying to look at transition metal oxides and oxidation state change as lithium-ion is intercalated into a structure, we can look at the charge composition from the point of view of the different transition metal oxides.

We can also look at it from the point of view of what we call SEI layer formation, that's the solid electrolyte interface. The solid electrolyte interface is a very important aspect related to safety of a lithium-ion battery, because they are the passivation layer which forms on an electrode surface preventing it from going haywire.

When I talk of transition metal oxides, for example, there are unstable oxidation states which we don't want it to go towards. That's another safety-related issue.

All of these things, trying to understand how the electrolyte degrades as a function of cycling, all of that can be studied by Raman spectroscopy. That's what we are trying to enable here.

Have you got any specific examples from the recent projects you've been talking about of findings or studies that you're doing that are relying heavily on Raman microscopy or Raman spectroscopy?

Yes, for lithium-air batteries we are using Raman to understand how different electrolytes in a nonaqueous case interact with the catalyst material when we do oxygen reduction. Similarly, for hydrogen evolution reaction, we are looking at the interaction of the catalyst material in the alkaline-rich environment, especially when we consider the anion exchange polymer-based ionomers, because some of them specifically absorb to the various transition metals which are in the catalyst material.

All of those are typical examples of how we are using it at the moment. Of course, it will change as we evolve in our different projects.

How important is the actual instrumentation that you're using and the partnership that you have with manufacturers?

Partnership with the manufacturer is very critical because most of the time we are at the cutting edge of an analytical tool. Being able to talk to the application folks and those who design these instruments is a very critical aspect of what we are trying to achieve here.

Of course, it's a matter of competition with our peers. If we can get an advantage by having a good relationship with a manufacturer of an instrument and a high-end instrument at that, we certainly would like to enable that.

That's why our partnership with Thermo Fisher is so critical, because we talk to the people who have designed the Raman microscope. As we move along, we are trying to do the spectroscopy under in situ operating conditions, so when we do it under operando conditions there are certain aspects of how that instrument interacts with our cells which is very critical. That's where our partnership is so effective.

What battery challenges can FTIR and Raman data help you solve with reagrd to distance on charge?

These are all related to the choice of materials and how that material interacts with the blend of electrolytes you're using, and, of course, the potential range to which you charge and discharge the battery. This is a materials-related issue, and it's totally dependent on all these parameters which I just mentioned.

Using a spectrometer like Raman is very effective. As I mentioned before, it looks at how the charge compensation is happening within the lattice of an intercalating host. It looks at what type of passivation layer you're forming on that electrode surface. It looks at how the electrolyte is degrading over the range of potentials you're cycling the battery at.

It also looks at what happens as a functional rate capability, or how quickly you charge and discharge that battery. There's all this concern about how much time you need to charge or recharge your battery, especially in the context of a car. Everybody wants it to be done as quickly as possible. That is a materials-related issue. That's a design-related issue also.

All of that can be looked at ... One of the main techniques to look at that is through the Raman microscope, and, especially, if it can be done under in situ conditions.

What other techniques would you recommend for tackling these challenges as well, and how does Raman fit into that?

Raman is a spectroscopy technique. It always has to be tied with the electrochemical techniques. We have a whole host of electrochemical techniques which we use ranging from the simple charge, discharge to very complicated routines including impedance, electrochemical impedance techniques. All of that is then tied into the spectroscopy, and that close correlation between the two is what we use to glean materials properties.

Do you use other surface analysis techniques as well like XPS?

Yes. We certainly use XPS, but XPS is very difficult to do under in situ conditions. There are quasi ambient condition XPS, but that has a limited range of things you can do compared to what Raman does, because Raman can be done completely under in situ conditions.

The other technique which we use a lot is synchrotron X-ray techniques. That's very complementary, because that is actually looking at the coordination environment around the transition metal. Between the two, we have a complete mapping of materials properties.

How do you see the results of your work, and of others in the field, impacting industrial battery technology in the coming years?

My mission in life is to render the internal combustion engine to a museum, just like steam engines. When I was kid, steam engines were pretty much a part of a railway network. Now only if you have the novelty of going to some kind of a special train ride, you see a steam engine. The same thing is going to happen to the internal combustion engines, to these coal-based super thermal power stations, though many people don't like me saying that. There will be some gas turbines still in existence, but most of us will be living with much more renewable energy.

We will have autonomous cars. We'll have electric cars. Then, eventually, if you want to drive a long distance, we'll have fuel cell cars with hydrogen filling stations. Although that is still pretty far off, especially as far as United States is concerned. I do see other places which are smaller in geographical size like, for example, Japan and Germany and the rest of Europe adopting this very quickly. That will change the shape of our future.

The shape of our future is this, which quietly happened. We don't question it, but you cannot imagine a life without it now. It does everything. It plays your music. It navigates you. It communicates for you. There are apps, thousands of apps which you can use. You can cook with it. You can do social networking with it. It's amazing. It reads the news for me in the morning. It's amazing. That's how a quiet revolution happens. That's what it looks like.

Do you think that maybe something like methane would be easier to store and transport and have the infrastructure for, as hydrogen is just going to be too much of a challenge?

Yes, absolutely. We are not talking of hydrogen transportation. We are talking of making hydrogen on demand from methane, from natural gas, and that is an off-the-shelf technology. There's no research required. It's a reformer technology which has been there for 20 years. We have tweaked it. We have refined it.

What we are trying to do is make hydrogen not from methane but from electrolysis of water using solar or wind, so renewable electrons. That's our mission, because that's where we want to go eventually, not to a fossil source.

But in the meantime, you can make hydrogen quite cheaply between $2 to $4 a kilogram from methane. There is no excuse not to have a hydrogen network. This is somewhere which I don't understand completely that there is a lag. But people are doing it. California is one state which is heavily invested in the hydrogen network. Other states are making the right noises. It's going to happen. It's a very big country, and so it will take some time in the United States.

In other countries it can be done very fast. Germany is one of them and, of course, Japan. They are large economies. China is making all the right noises. They recognize the fact that having gas-based internal combustion engines with the numbers they have is unsustainable. When China and India make the switch, that's it. It's done.

About Dr. Sanjeev Mukerjee

Dr. Sanjeev Mukerjee is a Professor in the Department of Chemistry and Chemical Biology (Northeastern University), where he has been since September of 1998. He also heads the Northeastern University Center for Renewable Energy Technology (NUCRET) and its subset the Laboratory for Electrochemical Advanced Power (LEAP). Dr. Mukerjee holds an M. Tech from the Indian Institute of Technology in Kharagpur, India, and a Ph.D. from Texas A&M University in College Station, Texas.