11-08-03 Platinum: Friend or Foe?

Platinum: Friend or Foe?

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03 Aug 2011PDF (507 kb)

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11-08-03 Platinum: Friend or Foe?Platinum is the key catalytically-active component in three of the six main fuel cell types (PEMFC, DMFC and PAFC) currently finding commercial successes in portable, stationary and transport applications. There are good reasons for this success, but significant research effort is focused on removing platinum from these systems. Headlines in the media stating platinum is "a show stopper" and is associated with "prohibitive cost" seem to contradict the current commercial sales, so what is the true picture, and how much spin or hype is generated by these headlines?

It is true that platinum is rare and is mined in a limited number of countries worldwide, with >75% mined in South Africa. This has the knock-on effect of making it relatively expensive, with the price at $1,790 per troy ounce at the time I write this, higher than gold ($1,626/oz), therefore if it were possible to use a cheaper material, people would do so. In a wide variety of catalytic uses, platinum offers benefits in terms of activity and selectivity which cannot be achieved using alternative materials. This is the case in fuel cells, where for both the oxygen reduction reaction and the hydrogen oxidation reaction, the activity and selectivity of platinum exceeds that of all other metals.

The automotive industry is a major user of platinum, particularly for diesel engines, and it has always striven to reduce or remove it from catalytic converters. The legislation governing automotive emissions sets progressively lower limits for emissions than previous iterations. To meet these tightening limits more platinum is generally required, but advances in catalyst technology which allows thrifting have consistently offset the need for more metal; the net effect maintains platinum loadings at fairly consistent levels. In contrast, the fuel cell industry has the freedom to reduce platinum loadings unhindered due to fuel cells already being emission-free and not constrained by similar legislation. This is best illustrated using published work from the US Department of Energy demonstrating that platinum loadings on PEM fuel cells have reduced by more than 80% since 2005.

Further advances are bound to occur with current research focusing on alloy materials, multilayer systems and the incorporation of nano-structured carbon in the catalysts. These advances all still plan to utilise platinum as the active catalytic component, but simply allow for better distribution, greater stability or optimise utilisation of the metal. This means improved activity and longer lifetimes can be achieved without increasing costs.

The potential to remove platinum altogether lies in the discovery of a new material, alloy or compound which outperforms the incumbent. So far this has not been successful, and while many potential materials show promise, they all fail due to shortness of life, corrosion issues, stability and so on. The testing of all fuel cell materials (platinum and otherwise) begins in a controlled environment under relatively benign conditions. It is at this stage that many of the headlines claiming high activity and stability are reported. Once these platinum-free alternatives are exposed to true fuel cell operating conditions, including acidic electrolytes, potential cycling and the presence of oxygen, their degradation pathways become apparent. The truth behind the headlines should therefore be considered carefully and only then can we determine which of the many platinum-free alternatives being researched around the world might succeed in this most aggressive of environments.

I wouldn’t like to say that platinum will never be eliminated from these fuel cell catalysts, but I believe the best roadmap for decreasing its contribution to fuel cell cost has to be the one taken by all other industrial users of the metal by continually reducing loadings and optimising the catalysts. If a further 80% reduction can be achieved over the next five years, then this whole argument becomes redundant.

So is platinum a friend or foe? I would say it is undoubtedly a friend and without it PEM, phosphoric acid and methanol fuel cells would not be as successful as they are. But like all friendships it takes work to make them succeed and we must work with platinum to enable the advancements necessary to guarantee the future of fuel cells.

Dan Carter     Manager

dancarter@fuelcelltoday.com

 

Image: Platinum Gundam (Source: Bandai)

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