Volkswagen and Stanford University develop modified ALD process to increase Pt/C fuel cell catalyst efficiency, improve durability
Volkswagen and Stanford University have developed in partnership a new catalyst production process to reduce the comparatively high cost of automotive fuel cell technology.
One of the biggest cost drivers for fuel cells is the use of the precious metal platinum as a catalyst to operate the fuel cell. The material is conventionally distributed as particles on carbon powder. However, the desired catalytic process only takes place on the surface of the platinum particles, which wastes large quantities of the cost-intensive material.
In the new process developed by Volkswagen and Stanford, platinum atoms are specifically placed on a carbon surface using a modified atomic layer deposition (ALD) technique in order to produce extremely thin particles. This can reduce the amount of platinum currently required to a fraction of the usual amount.
The researchers published a paper in the journal Nature Catalysis earlier this year, describing the process.
Here, we show that carbon monoxide can be used as a passivation gas during atomic layer deposition to modify the surface energy of already deposited Pt nanoparticles to assist direct deposition onto a carbon catalyst support. The passivation process promotes two-dimensional growth leading to Pt nanoparticles with suppressed thicknesses and a more than 40% improvement in Pt surface-to-volume ratio.
This approach to synthesizing nanoparticulate Pt/C catalysts achieved high Pt mass activities for the oxygen reduction reaction, along with excellent stability likely facilitated by strong catalyst–support interactions afforded by this synthetic technique.—Xu et al.
The researchers use carbon monoxide as a growth inhibitor during ALD; CO strongly adsorbs on the deposited Pt surface, passivating it from subsequent Pt precursor adsorption. As a result, two-dimensional growth of Pt nanoparticles can be realized.
The researchers reported that the passivation-gas-incorporated ALD (PALD) technique enabled the direct deposition of thinner Pt nanoparticles onto carbon-based catalyst supports, which enabled greater Pt utilization due to a more suitable nanoparticle morphology. A combination of effects allowed for the PALD Pt/C catalysts to achieve a twofold increase in the mass activity for ORR compared to a commercial Pt/C catalyst.
This technology opens up enormous possibilities for cost reduction, as the amount of precious metal used is minimised. At the same time, service life and catalyst performance are increased. In addition to the fuel cell, atomic layer deposition also offers a whole range of other applications requiring high-performance materials, such as next-generation lithium-ion batteries.—Friedrich Prinz, the Finmeccanica Professor in the School of Engineering at Stanford University, Professor of Materials Science and Engineering, Professor of Mechanical Engineering and Senior Fellow at the Precourt Institute for Energy
Professor Prinz is also Director of the Nanoscale Prototyping Laboratory and Co-director of Stanford Energy 3.0. In his lab, a wide range of nano-fabrication technologies are employed to build prototype fuel cells, capacitors and batteries that are used to test new concepts and novel material structures through atomic layer deposition, scanning tunneling microscopy, impedance spectroscopy and other technologies.
Conventional batteries can also benefit from the researchers’ new findings.
This is of course also interesting for other automotive applications, such as batteries. However, the modified variant of ALD (atomic layer deposition), which was developed here, takes the whole thing to a whole new level.—Dr. Thomas Schladt from Volkswagen Group Research
The task of the researchers is now to transfer the results obtained in the laboratory to industrial large-scale production.
Shicheng Xu, Yongmin Kim, Joonsuk Park, Drew Higgins, Shih-Jia Shen, Peter Schindler, Dickson Thian, J. Provine, Jan Torgersen, Tanja Graf, Thomas D. Schladt, Marat Orazov, Bernard Haochih Liu, Thomas F. Jaramillo & Fritz B. Prinz (2018) “Extending the limits of Pt/C catalysts with passivation-gas-incorporated atomic layer deposition” Nature Catalysis volume 1, pages 624–630 doi: 10.1038/s41929-018-0118-1