Dalhousie-led team develops single-atom platinum-gold catalyst; nearly 100-fold increases in efficiency
A Dalhousie University-led team has developed a longer-lasting, higher-efficiency platinum catalyst. The new catalyst combines gold and platinum to form what’s known as a single-atom catalyst, resulting in nearly 100-fold increases in efficiency over market platinum catalysts, says Peng Zhang, the Dalhousie professor who led this research. A paper on their work is published in the journal Nature Materials.
Here we report a facile colloidal method to prepare a series of platinum–gold (PtAu) nanoparticles with tailored surface structures and particle diameters on the order of 7 nm. Samples with low Pt content, particularly Pt4Au96, exhibited unprecedented electrocatalytic activity for the oxidation of formic acid. A high forward current density of 3.77 A mgPt−1 was observed for Pt4Au96, a value two orders of magnitude greater than those observed for core–shell structured Pt78Au22 and a commercial Pt nanocatalyst.
Extensive structural characterization and theoretical density functional theory simulations of the best-performing catalysts revealed densely packed single-atom Pt surface sites surrounded by Au atoms, which suggests that their superior catalytic activity and selectivity could be attributed to the unique structural and alloy-bonding properties of these single-atomic-site catalysts.—Duchesne et al.
Platinum catalysts help deactivate exhaust gases from combustion engines. Platinum is also used to help drive the chemical reactions that make zero-emissions hydrogen fuel cells possible.
Single-atom platinum (blue ball) coated gold (yellow ball) nanoparticles can serve as a highly efficient catalyst for a fuel cell chemical reaction (i.e. formic acid oxidation).
Not only is efficiency improved at the outset, but it is maintained through the catalyst’s lifetime. Usually, a platinum catalyst works less well over time as carbon monoxide molecules tightly bond to and block platinum from helping reactions along.
Improvements come from two properties: the single atom structure, which maximizes platinum’s active surface area, and the unique electronic properties that adding gold to create an alloy helps to achieve.
The magic happens because of the alloy. Think about iron: it very easily gets rusty in the air, but if you have an iron alloy, like stainless steel, its properties are totally different.—Peng Zhang
For example, making a gold-platinum alloy stops the platinum catalyst from losing efficiency and “poisoning” over time. Catalyst poisoning is one of the major challenges. This is because if two platinum atoms are side-by-side, then carbon monoxide from the chemical reaction binds tightly to them, poisoning the catalyst and gradually degrading its efficiency. When researchers ensure that there are no platinum clusters within a larger gold lattice, the poisoning effect disappears.
Zhang’s team worked with three Canadian Light Source facilities at the University of Saskatchewan to understand and test their alloyed catalysts, as they tried various combinations and structures of platinum and gold.
Synchrotrons are one of the most powerful tools to study. Alloys are super hard to study with regular tools, since it’s hard to distinguish the two metals from each other. With a synchrotron, you can easily tune the energy to take only the platinum, and then the gold.—Peng Zhang
As the researchers reduced the platinum content of their catalyst, they found great improvements in its function, until eventually they hit upon the single-atom model that maximized platinum’s surface area and minimized poisoning.
Further, the team found that the simple chemical technique they used to prepare the alloy resulted in a higher overall concentration of platinum atoms than typical alloys by nearly 10 times. Alloys normally contain very low concentrations of single atoms, below 1%. Zhang’s team created an alloy with 7% single-platinum atoms.
Like platinum, gold is expensive. The researchers used gold as a first step to show the concept, but will now look at other, less expensive metals, to make this more usable for industry, said Zhang.
Duchesne, Paul, Z. Y. Li, Christopher Deming, Victor Fung, Xiaojing Zhao, Jun Yuan, Tom Regier et al. (2018) “Golden Single-atomic-site Platinum Electrocatalysts.” Nature Materials doi: 10.1038/s41563-018-0167-5