Jun
19
Getting The Platinum Out Of Fuel Cells
June 19, 2013 | Leave a Comment
Scientists from Jülich and Berlin have developed a material for converting hydrogen and oxygen to water in a fuel cell using one tenth of the typical amount of platinum that has been previously required. The fuel cell is pretty much stuck looking for economically viable, efficient and robust units to make commercial scale mass-market units.
The German researchers discovered with the aid of state-of-the-art electron microscopy that the function of the nanometer-scale catalyst particles is decisively determined by their geometric shape and atomic structure. This discovery opens up new paths for further improving catalysts for energy conversion and storage.
The team’s results have been published in the current issue of the journal Nature Materials.
Electron micrograph and atomistic model of oxygen-activating platinum-nickel catalyst particle. Click image for more info.
Hydrogen-powered fuel cells are idealized as a clean alternative to conventional combustion engines because aside from electrical energy power output, the only substance produced during operation is water. Presently the implementation of hydrogen fuel cells is being held up by the high price of platinum. Large quantities of the expensive noble metal are still required for the electrodes in the fuel cells where the chemical conversion processes take place. So far, without the catalytic effect of the platinum, it is not currently possible to achieve the necessary conversion rates with units currently in production.
We know catalysis takes place only at the surface of the platinum so material can be saved. At the same time the efficiency of the electrodes is being improved by using platinum nanoparticles, thus increasing the ratio of platinum surface to material required. Although the tiny particles are around ten thousand times smaller than the diameter of a human hair, the surface area of a kilogram of such particles is equivalent to that of several football fields. There is still a lot of platinum involved.
More platinum could be saved by mixing it with other, less valuable metals, such as nickel or copper. Scientists from Forschungszentrum Jülich and Technische Universität Berlin have proven the point by succeeding in developing efficient metallic catalyst particles for converting hydrogen and oxygen to water using only a tenth of the typical amount of platinum that was previously required.
The new catalyst consists not of the round nanoparticles that are previously in widespread use, but of octrahedral-shaped nanoparticles of a platinum-nickel alloy. The researchers discovered that the unique manner in which the platinum and nickel atoms arrange themselves on the surfaces of these particles serves to optimally accelerate the chemical reaction between hydrogen and oxygen to form water. Round or cubic particles, on the other hand, have different atomic arrangements at the surface and are therefore less effective catalysts for the chemical reaction, something which would have to be compensated for by using increased amounts of noble metal.
The way in which the life-cycle of the catalysts operates and can be optimized by their atomic composition was the subject of the research team’s investigation, which made use of ultrahigh-resolution electron microscopy at the Ernst Ruska-Centre (ER-C), a facility of the Jülich Aachen Research Alliance.
Dr. Marc Heggen from ER-C and the Peter Grünberg Institute at Forschungszentrum Jülich explains, “A decisive factor for understanding the life-cycle of the catalysts was the observation that nickel and platinum atoms prefer not to be evenly distributed at the surface of the nano-octahedra. Although this is advantageous for reactivity, it limits lifetime.”
To identify the location of each element with atomic precision, the researchers used a method in which the electron beam of one of the world’s leading ultrahigh-resolution electron microscopes is finely focused, sent through the specimen and, by interactions with the specimen, loses part of its energy. Each element in the specimen can thus be identified like a fingerprint. Conventional electron microscopes haven’t the capability of detecting such chemical signatures with atomic resolution.
Prof. Peter Strasser from Technische Universität Berlin said, “This pioneering experimental work provides direct evidence for the fact that the choice of the correct geometric shape for the catalyst particles is as important for optimizing their function as the choice of their composition and size. This provides researchers with new possibilities for further improving functional materials, especially catalysts, for energy storage.”
The latest experiments from Strasser’s research group indicate that substantial increases in efficiency may also be possible for the reaction splitting water to produce oxygen in electrolysers, in which the even more expensive noble metal iridium is used.
This is quite an innovative way to look at solving the problem that platinum presents. There are many efforts underway worldwide to get a solution that can scale up to commercial mass-market at pricing which will trigger huge growth. The one it will be isn’t known yet, but as these ideas pile up, one is surely going to make it over the top. When that happens and the market takes off, even more research will get done driving fuel cell and water splitting pricing to ever-lower costs.
Let it come, it can’t happen soon enough.
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