10 February 2011

Better Fuel Cell Material Discovered

A new material to be used in fuel cell catalyst assemblies, looks promising.

A fuel cell is a battery based on electrolysis. It separates water into hydrogen and oxygen when you charge it, and the used the pure hydrogen as fuel when you want electricity. This works more efficient when the chemical reactions are mediated by a catalyst. Your typical fuel cell today uses platinum on a bed of graphite, the same kind of carbon used in pencils.

A new material would use graphine, which is a sheet of interconnected hexagons of carbon, instead of graphite, that is treated with "crystallized nanoparticles of the metal oxide known as indium tin oxide -- or ITO" before adding platinum nanoparticles. The crux of why it works better is that it prevents the platinum from clumping, so it maximizes the amount of platinum that is carrying out a catalyst function, and prevents the platinum from being carried away from the rest of the material.

Initial efforts to determine its properties have been encouraging. The new material breaks down 40% more oxygen for the same amount of platinum than a comparable conventional catalyst assembly and is about twice as durable.

Does it make economic sense?

In a conventional fuel cell, the graphite substrate is virtually free relative to the very high cost of the platinum (a few dollars per kilogram or less). It isn't clear how much it costs to produce the graphene-ITO substrate. But, given the anticipated greater durability and efficiency, the break even point for the new substrate ought to be roughly two-thirds of the cost of the platinum it supports. The threshold price with platinum prices at $1830 per ounce (about $61 per gram) is about $40 for the amount of substrate necessary to combine with one gram of platinum.

Graphene sheets cost about $100 per square centimeter (by weight on the order of $50 per gram), but the raw materials are cheap and the costs are falling as it enters mass production and are expected to be cut in half in a decade.

Indium tin oxide prices are largely driven by the cost of indium, and cost several times as much as aluminum zinc oxide which is a substitute in many applications. Indium prices are highly volatile (dropping 70% in a recent year from a peak price) and are on the order of $0.60 per gram (i.e. about $18 per ounce, which is on the same order of magnitude as silver). Tin costs about $0.03 per gram ($14 per pound), so indium prices is the main drive of ITO prices.

Realistically, the graphene, and not the ITO, would be the main driver of the proposed new fuel cell substrate, and the price looks likely to make economic sense in the medium term future as graphene prices fall.

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