Northeastern University

What it takes to be fossil-free

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One of my first conversations here at Northeastern was with Chemistry professor Sanjeev Mukerjee who has one ultimate goal for his research: “to replace all combustion related power sources with an electrochemical energy conversion storage system, which are cleaner, more efficient, and very silent.” Mukerjee’s team at the Center for Renewable Energy Technology(NUCRET) explores how electrochemical reactions can be used to meet this goal from both an energy conversion and storage perspective.

Energy stored in the chemical bonds of both fossil- and biofuels can be cleanly and efficiently converted into a useable form without running into certain limitations of the standard combustion process. This is especially important since there isn’t a limitless supply of fossil fuels out there.

Only there are a couple of problems that we’re all pretty familiar with these days: First, combustion has a lot of byproducts (amorphous carbon molecules) that are not good for the lungs or the environment. Second, there isn’t a limitless supply of fossil fuels out there.

Mukerjee is exploring better ways to break those bonds using fuel cells and better ways to store the released energy using lithium air batteries.

“There’s this misconception out there that we can somehow magically create super-batteries that will power a car for a 300 mile range. Right now the best you can do is between 60 and 100 miles.” Conventional autos, he says, can only drive for 60-70 miles on the most advanced lithium ion battery before needing to be recharged. 100 mile ranges are possible when you use the lightest (and most expensive) composite materials for the body. Reaching 300 miles isn’t a question of better technology, it’s a question of chemistry.

The lithium air battery, which was invented and patented by NUCRET’s K. M. Abraham in 1997, can work in aqueous and non-aqueous systems, meaning it could be put to use in a variety of energy conversion and storage settings. The oxygen reduction reaction in Lithium Air batteries works on oxygen in, well, the air (go figure). Traditional lithium-ion batteries works on the oxygen in a metal-oxide electrode, often cobalt, which is pretty expensive.

Platinum, as my engaged friends know, is another expensive metal typically used as that catalyst in current low temperature fuel cell technologies for the oxygen reduction reaction. Mukerjee’s team is developing new catalysts that do not rely on noble metals. “We’re looking at iron nitrogen based systems – trying to understand how the oxygen reduction works in them and how you can reliably make it. We know it does happen, now we’re investigating how and why it happens.” While these systems are still low-performing, the cost is orders of magnitude less than the platinum based system.

Initially, fuel cells could be used as a stand-in for the combustion engine but still use fossil fuels as a source of hydrogen, natural gas being the most exciting to Mukerjee. “Between Canada and the US, there’s enough Natural gas to last us a couple hundred years. But then there is a vast resource, which is still being looked at — gas hydrates in the ocean floor near geological vent sites. This resource is so vast in terms of its potential capacity that we’d possibly never run out in 400 to 500 years.”

Still, it’s not good enough. While no renewable energy can completely replace fossil fuels right now, Mukerjee says, we need to begin developing technologies and business models that can eventually allow for a smooth transition when the chemistry and engineering problems have been worked out.

Here you can watch Mukerjee speak for himself:


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