The Platinum Problem in Electrocatalysis

The sourcing and storage of renewable energy is a key piece in the pursuit to reverse the effects of man-made climate change. By finding new, abundant, renewable sources of energy, we lessen our dependence on fuels and processes that cause harm to our environment. But even among some of the leading solutions to our emerging energy crisis, there remain inefficiencies and potential points of failure.

Joshua Snyder, Ph.D., associate professor of chemical and biological engineering, is using his expertise in electrocatalysis to help minimize these problems.

One of Snyder’s active areas of research is in nanostructured electrocatalysts. Many commonly used catalysts are composed of platinum-based materials, because the precious metal is efficient in the catalytic conversion of fuels — such as the oxidation of hydrogen in fuel cells to extract electricity and water — and is stable under harsh device conditions. But platinum is expensive and limited so Snyder is developing strategies to make the most out of what we have.

“Typically, fuel cell catalysts are composed of solid, spherical nanoparticles of platinum,” Snyder explains. “The issues plaguing fuel cell commercialization are their high loadings of expensive platinum and their limited operational longevity. Solid spherical nanoparticles contain a significant fraction of inactive platinum within the core of the particles and are susceptible to corrosion under operational conditions. The loss of active material over time yields a decay in power density, to the point that the device is no longer useful.”

A potential fix, Snyder says, is to make the platinum particles porous. This increases the available surface area for the reaction to happen on, decreasing the amount of platinum needed in the device. But the most stable configuration of a surface is a sphere, so within a short window, the platinum particles will try to rearrange themselves into a solid sphere and the benefit of the porous configuration will be lost. This process is called coarsening. Snyder’s goal is to develop a better understanding of the underlying atomic scale processes that govern coarsening, and devise mitigation strategies to increase the longevity of porous catalyst materials.

“One strategy is to dope the surface of the platinum with a metal atom that moves very slowly,” Snyder says. “We have used iridium as a test case, and that's been successful at preventing the area loss in these materials for a longer period. While the cost of iridium precludes its use in a commercial device, this is a promising strategy that could be made viable with a suitable cheaper surface dopant.”

Over the last few years, Snyder’s research group discovered that ionic liquids — chemical salts that are liquid at room temperature — could be applied to the surface of a platinum catalyst and almost instantly triple its electrochemical activity, allowing you to use a third the amount of platinum mass and still have the same power output.

“It was a unique discovery in the lab, but in practice, it turned out to be a lot more difficult to implement in a real device,” Snyder admits. “We’ve been working with Texas A&M and the National Renewable Energy Laboratory (NREL) to develop an ionic liquid-based polymer that we can put into fuel cell catalyst layers. This work is funded by the Department of Energy. And we’re finding that we’re getting the same kind of results as we did in the lab scale: a two-to-three-times improvement in the performance of these devices.”

An important part of Snyder’s work with the Department of Energy is to stretch the idea into something that can be applied to a real-world device, which is why the work he’s doing with NREL and Texas A&M is so important. It’s also the kind of thinking that Snyder pushes his graduate students to do.

“I want my students to go beyond the fundamental science and take their ideas and make them actually work in something that’s relevant,” he says. “This project is kind of doing that for me. NREL is partnering with General Motors to test our new material in commercial fuel cell devices, and it’s working pretty well.”

If platinum is so finicky, why use it? Snyder explains that, while there has been a push for non-platinum group metal catalysts, there are tradeoffs in terms of how active the materials are versus how long they can be used.

“Once you start looking at both options, you see that activity and durability are sort of inversely related,” he says. “The catalysts that are most active aren’t durable and the catalysts that are most durable aren’t as active. You need to find a middle ground, and in a way, that’s the best description of engineering.”

Regardless of the methods, Snyder believes it’s important to continue to innovate new ways to produce and consume renewable energy.

“It’s clear that we're coming to a point, even in our lifetimes, where fossil derived fuels are going to be too expensive. We're going to reach peak oil production within the next 10 to 20 years and after that, prices are going to continue to trend upward at continually increasing rates,” he explains. “So even if you refuse to accept the detrimental environmental impact of burning fossil fuels as a viable reason for removing them from our energy portfolio, renewables are quickly approaching cost competitiveness.”

Because of the limited availability of platinum and other catalysts, Snyder knows that fuel cells can’t be the single solution to our energy storage needs. But he sees great potential in the technology if the progress that he and other researchers have made can continue, and especially if different renewable energy technologies can be combined.

“I can imagine a future where, in your home, you have a solar cell on the roof and a water electrolyzer in the basement,” he says. “You take the solar energy and you run the electrolyzer to make hydrogen from water, and then the fuel cells take that hydrogen and produce energy. That could easily happen within our lifetimes. You just need the people with the creativity to do it.”