Nissan Doubles Power Density with New Fuel Cell Stack

One area of energy storage that appears to be moving towards viability quicker than battery technology at present is the hydrogen fuel cell. Nissan Motor yesterday revealed its next generation Fuel Cell Stack (2011 Model) for Fuel Cell Electric Vehicles (FCEV).

Through improvements to the Membrane Electrode Assembly and the separator flow path, Nissan has improved the power density of the Fuel Cell Stack to 2.5 times greater than its 2005 model, and in so doing has created a world's best 2.5 kW per liter power density.




The cost of the 2011 model Fuel Cell Stack has been reduced to one sixth of the 2005 model. Furthermore, molding the supporting frame of the Membrane Electrode Assembly (MEA) integrally with the MEA's single-row lamination has reduced its size by more than half compared to conventional models.

Compared with the 2005 model, both the usage of platinum and parts variation has been reduced to one quarter, thereby reducing cost of the Next Generation Fuel Cell Stack to one-sixth of the 2005 model. In so doing, Nissan engineers have achieved an important breakthrough with the development of a compact and durable hydrogen fuel-cell stack - capable of delivering ample power - that can be manufactured in volume at competitive cost.

Most importantly, it's not one of those Japanese research lab breakthroughs that's still effectively ten years away. Nissan's fuel-cell team says it can be ready for market as soon as sufficient supplies of hydrogen are available. According to Nissan, taxis, delivery vans and other city-specific fleets could quickly be converted to zero-emission fuel cells.

"We never got discouraged and we never gave up," says Masanari Yanagisawa, a 10-year veteran in the company's fuel-cell R&D efforts. "So we just kept working, patiently and persistently. As a result, we have achieved what we believe is a major breakthrough.

"We have made great strides in two critical areas: power density and cost. Our 2011-model fuel-cell stack delivers power density at 2.5 kilowatts per liter, 2.5 times better than our 2005 model.

"As a result, the new stack is also a lot smaller. We can now pack 85 kilowatts of power in a 34-liter package. Better yet, we have brought the production cost down by 85 percent, close to meeting the U.S. Department of Energy cost target for 2010 - a widely referenced benchmark.

"We slashed the price by reducing the need for platinum by 75 percent," Yanagisawa says. "The Membrane Electrode Assembly [MEA] comprises 80 percent of the stack's cost, and platinum is half the cost of an MEA, so this was a huge step forward."

The other key challenge in developing fuel-cell stacks is to design a structure that delivers high power- density; that's durable and easy to manufacture without flaws. This is very tricky.

Each fuel cell is a carefully built sandwich with layers ultra-thin polymer electrolyte membrane. Each membrane has an anode layer and a cathode layer on both sides. On the outer side of each of each of these anode/cathode layers are separators, which form channels through which hydrogen, air and cooling water flow.

As each fuel cell generates a maximum of one volt, you need to stack lots of sandwiches together to get enough power to run a car. The process is so fiddly that building a model ship in a bottle seems a snap by comparison. No wonder so many teams around the world have given up in frustration.

But with their craft legacy of patient attention to minute detail, this is the kind of work that Japanese tend to excel at. Since 2001, the Nissan team has built a succession of prototype fuel-cell vehicles, first with partners like Ballard Power Systems Inc. and UTC Fuel Cells LLC, then in-house from 2005. Each stack was incrementally better than its predecessor.

The 2005 prototype achieved a range of 500 kilometers, matching a conventional car. A 2008 version achieved an important breakthrough in cold-weather tolerance. But putting enough cells together in a durable stack was a hurdle the team just couldn't get over. After managing to stack more than 400 cells, they would watch in frustration as the brittle contraption fell apart on the lab floor.

Finally, in 2009, the team had a conceptual breakthrough with a technique that involves molding plastic around the MEA to create insulating frames between each of 400+ layers in the stack - thereby ensuring the layers neither short out nor fall apart.

"This breakthrough puts us, no question, in the front rank of fuel-cell developers around the world," Yanagisawa says. "Best of all," he adds with a grin, "it puts us ahead of our competitors."

So can we expect to see a Nissan Fuel Cell Electric Vehicle (FCEV) coming round the corner soon? "We are now ready to go to market at any time," Yanagisawa says. "The only hurdle remaining is hydrogen distribution. Give us the hydrogen and we'll give you an FCEV. We're good to go!".