SOLID ACID

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SOLID ACID FUEL CELLS – THE HOLY GRAIL?
BY DANIEL C. SWEENEY, PhD

In this blog we have had frequent occasion to comment upon the inflated expectations fostered among the public by many individuals within the fuel cell industry. At the beginning of this decade fuel cell proponents were confidently predicting that the rollout of fuel cell vehicles would be well underway by mid decade and that a hydrogen transition would be beginning. Obviously such predictions were false.

Introducing any radically new technology is difficult, but fuel cells present special problems which have not proven amenable to easy solutions. Five years ago, the PEM (polymer electrolyte) type of fuel cell, generally seen as the most promising technology, was about an order of magnitude too expensive to sell in designated markets and suffered from serious problems of manufacturability, useful lifespan, and reliability. Since then pricing has not descended significantly and technical limitations have at best been ameliorated.

Fuel cell manufacturers still offer the same assurances that solutions are in the offing and that the technology is essentially good to go, but investors are beginning to have second thoughts, and without a great deal of further investment there is little chance of technical hurdles being overcome.

We have long believed that the best chance for the fuel cell industry would be the development of some entirely new chemistry. We felt that existing designs were probably approaching their design limits and that further investment might well be misguided. Now just such a fundamentally new design has appeared, the solid acid fuel cell.

Solid acids are a recently described class of chemicals intermediate between salts and acids in their characteristics. At somewhat elevated temperatures in the 300 to 400 Centrigade range such substances become “superprotonic” permitting single protons representing hydrogen ions to migrate to an anode or positively charged terminal while blocking oxygen and other atoms.

Nafion, used in PEM fuel cells, has similar properties, but Nafion tends to degrade at temperatures over 80 C, and must be used in conjunction with a costly platinum catalyst. Nafion is also vulnerable to carbon monoxide poisoning and requires ultra high purity hydrogen gas. Furthermore, Nafion must be continually hydrated with distilled water in precise amounts. Finally, Nafion itself is extremely costly.

Nafion is used in almost all PEM fuel cells sold today. For all its limitations, it is considered the best available material by most manufacturers. But if Superprotonic Inc., a Southern California based startup founded by refugees from Cal Tech, is correct, Nafion may now have a real challenger.

According to Calum Chisolm, the president of the firm, Superprotonic’s solid acid membrane possesses all of the desirable characteristics long sought in a fuel cell electrolyte. It operates at medium temperatures, and cannot only tolerate low purity hydrogen but can directly reform methanol and ethanol. It doesn’t require rare earth catalysts, it is cheap to manufacture and form, it is impervious to carbon monoxide, and it doesn’t need hydrdation. Furthermore, it appears to be robust.

We are very used to hyperbole and inflated claims in this business, and so we will reserve judgment on the strength of Superprotonic’s assertions until they are proven or disproven in the marketplace. We did, however, find Dr. Chisolm, refreshingly unassuming when we interviewed him. He admitted that unforeseen obstacles to commercialization could arise and that his company was at a relatively early stage in the development cycle of the solid acid fuel cell.

It should be noted here that other manufacturers such as ITM in Britain, Pemeas in Germany, and PolyFuel here in the U.S. have introduced other alternatives to Nafion without achieving singular success. Nafion has been around since the nineteen sixties and extensive research in Nafion based PEM cells goes back almost twenty years. For all its problems, Nafion has a track record, and Nafion PEM cells are in the marketplace now.

Chisolm informs us that several Japanese electronics majors are also pursuing research in solid acid membranes, so evidently the technology has momentum. We would expect that if its promise is fulfilled we might be seeing some productization early in the next decade. And as for fuel cell vehicles based on solid acid? If it works, and that’s a big if, don’t count on seeing anything until the twenties of this century and that is likely to be limited production. Clearly the fuel cell future we’ve all been hearing about is a good ways off even best case.