By Abe Danaher | September 10, 2020

Five years ago, before University of South Carolina Professor William Mustain’s record-breaking advances, the fate of anion exchange membrane (AEM) fuel cells seemed set in irrelevancy. They were the third horse in a two-horse race – lagging far behind batteries and proton exchange membrane (PEM) fuel cells as the world began wondering what would power the green energy future it envisioned.

At the time, lithium ion batteries posed a viable, clean alternative to combustion engines, while PEM fuel cells – though cost-prohibitive – also produced zero emissions and offered faster refueling times than batteries. Both were being tested in cars and gaining interest from the utility industry.

It's very rare in your life that you know that you are the best in the world at something. And even if this is just a brief period in time where we are the best in the world at this, I am very proud of our team for the accomplishing it.

- William Mustain, Chemical Engineering

All the while, AEM fuel cells fell by the wayside. Their advantages – zero emissions, fast refueling rates and much lower production costs than PEM fuel cells – were overshadowed by their poor performance and lack of durability. The field had stagnated, as the few researchers left in it were solely focused on one thing: the development of a new membrane that they hoped would miraculously change the course of the field. Though new and better membranes were being successfully developed, the performance and durability of AEM fuel cells were not improving.

“Nobody, and I mean nobody at the time, could make a fuel cell that operated reasonably well at all,” says Mustain, openly admitting that this included his own team as well.

Then, in an early 2016 meeting with former Ph.D. student Travis Omasta, he had an epiphany.  If every material that was put into an AEM fuel cell failed, he thought, then it couldn’t be the materials that were limiting cell behavior – it had to be that the field didn’t understand how these cells worked from a fundamental perspective. So, he pulled together his team and declared a new path going forward.

“I told everyone in my group that we would no longer be making materials,” he says. “We are done doing what everyone else is doing – making fancy new membranes or catalysts. It is clearly not working. We are going to take off-the-shelf materials, and the first thing we're going to do is really understand how these cells actually work.”

In the world of AEM fuel cells at the time, choosing to pursue a route outside of materials discovery was a death sentence to receiving funding. For years after this, Mustain did not receive a dollar of national funding for his fuel cell work and was forced to self-fund his own graduate students. The entire time, he was confident that his novel approach would work. But, others in his field were not quite so confident.

“Most of the community wouldn't have thought that the approach would work,” says Bryan Pivovar, a senior research fellow at NREL who has worked in the field of AEM fuel cells for over 15 years.

But it did. By taking an engineering approach to the AEM fuel cell problem, Mustain made the largest advances in the field’s history, and in the process, became internationally recognized for his work.

“He's really well respected and he's been really important to the field,” Pivovar says. “And the truth is, the field wouldn't be where it is today without those contributions.”

Instead of focusing on the membrane, Mustain considered all of the physical and operating parameters within the cell’s design, such as temperature, dew point, compression and flow rate, and he slowly worked to optimize each of them. Once successful, he paired up with John Varcoe from the University of Surrey and Paul Kohl from Georgia Tech, both of whom are leading membrane researchers, and employed his own optimization techniques on cells using their top-performing materials. The results may have single-handedly saved AEM fuel cells.

Mustain’s recent paper, published in Nature Communications, showed a five times increase in AEM fuel cell performance compared to where the field was in 2016. Then, his work published in Advanced Energy Materials improved the cell’s lifetime durability to 2,000 hours, blowing away previous studies which typically struggled to achieve 100 hours.

“This feels great,” Mustain says. “We spend a lot of time, effort, sweat and tears in pursuing these things that we believe in. And to have one of those things pay off – it's amazing. It's very rare in your life that you know that you are the best in the world at something. And even if this is just a brief period in time where we are the best in the world at this, I am very proud of our team for the accomplishing it. It has also been very fulfilling to work hard and to have it recognized by the broader community.”

Now, the two biggest questions surrounding the field – performance and durability – have been answered, putting AEM fuel cell performance on par with the PEM fuel cells that have long been viewed as superior. Mustain is actively pursuing solutions to the next hurdles – managing their tolerance to carbon dioxide from the air and improving the start/stop performance of the cell –  through funding from the Department of Energy and the National Science Foundation.

He thinks it could be as soon as five years before AEM fuel cells are powering trucks or cars.

“Now, as you transition from high performance into practical applications with these devices, you have to start asking yourself, what do we have to think about? What do we have to do that’s different to enable that to happen? What is the next stage in AEM fuel cell engineering that needs to be done to make this transition possible? And that’s exactly what our group is doing right now,” he says.

AEM fuel cells may still have a way to go before they are powering cars or attached to the national energy grid. But, because of the work by Professor Bill Mustain and his team, there’s once again hope that, one day, they will.