Blue Nano (formerly Filigree Nanotech, Inc) (Huntersville, NC) received U.S. Patent 7,632,779 for its method of preparing a catalyst for direct formic acid fuel cells (DFAFC). According to inventors Yi Ding (Shandong, CN) and Rongyue Wang (Shandong, CN) the nanocatalyst results in direct formic acid fuel cells with low noble metal loading, strong toxic resistance and long service life.
Two key issues inhibit the commercialization of DFAFC: the first being low efficiency and the second being the poor stability of its catalysts. Platinum (Pt) is major fuel cell catalyst component. However, carbon monoxide (CO) from the oxidation of formic acid can easily poison (contaminate) the platinum and cause it to lose its catalytic function. Therefore, palladium (Pd) based compounds are often used as an anodic catalyst in DFAFC. Unfortunately, a Pd-based composite catalyst may also display poor stability if it suffers "the poisoning effect" from the carbonaceous intermediates generated during the reaction.
The formic acid on the surface of platinum is oxidized to CO2 via a dual-path mechanism. A direct dehydrogenation path generates CO2 which is not harmful to the catalyst, while an indirect dehydration path generates CO which is toxic to the catalyst. One solution is to incorporate some atoms of bismuth or lead onto the surface of the platinum to improve its effectiveness in formic acid oxidation and to guide the oxidation toward the more desirable direct dehydrogenation path. However, absorbed atoms are very unstable on the surface of platinum. Hence, this type of surface modification to improve the catalyst has little value in practical applications.
In order to increase the utilization of platinum, amorphous carbon (carbon black or carbon fiber) may be used in the catalysts for fuel cells as an inexpensive means of support. However, carbon support is unstable during the electro-oxidation reaction and so the utilization of platinum is still not high enough to satisfy commercial applications.
The formic acid on the surface of platinum is oxidized to CO2 via a dual-path mechanism. A direct dehydrogenation path generates CO2 which is not harmful to the catalyst, while an indirect dehydration path generates CO which is toxic to the catalyst. One solution is to incorporate some atoms of bismuth or lead onto the surface of the platinum to improve its effectiveness in formic acid oxidation and to guide the oxidation toward the more desirable direct dehydrogenation path. However, absorbed atoms are very unstable on the surface of platinum. Hence, this type of surface modification to improve the catalyst has little value in practical applications.
In order to increase the utilization of platinum, amorphous carbon (carbon black or carbon fiber) may be used in the catalysts for fuel cells as an inexpensive means of support. However, carbon support is unstable during the electro-oxidation reaction and so the utilization of platinum is still not high enough to satisfy commercial applications.
According to the inventors, the durability of a platinum catalyst may be significantly improved by depositing gold nanoparticles on platinum particles via the Under Potential Deposition (UPD) method. Gold nanoparticles are very stable on a platinum surface due to the metal similarities of gold and platinum. Depositing a particular amount gold particles onto platinum particles will not only enhance the anti-poisoning properties of a platinum catalyst by decreasing the amount of CO generated during the reaction, but also prolong the life of the platinum catalyst by preventing the platinum from undergoing an oxidation reaction. Recently, they have discovered that gold nanoparticle catalysts are particularly effective in CO oxidation at ambient conditions. Inspired by the potential that adatoms may block certain reaction sites and effectively tune the reaction pathways, the present invention designs and fabricates a layer-structured nanoporous gold-platinum-gold (NPG-Pt--Au) membrane catalyst on which the catalytic activity toward formic acid electro-oxidation is greatly enhanced via alteration of the reaction pathways by top layer gold clusters. An adatom is an atom that lies on a crystal surface, and can be thought of as the opposite of a surface vacancy.
Ding and Wang successfully fabricated a new type of nanostructured electro-catalysts that simultaneously fulfills the three key requirements for a good practical catalyst: 1) ultra-low Pt loading, 2) great tolerance to poisoning, and 3) high stability. In one particular embodiment, a layer-structured, high surface area membrane catalyst was designed and constructed by depositing sub-monolayer Au onto a nanoporous gold (NPG) supported Pt monolayer, which demonstrated dramatically improved catalytic performance in formic acid oxidation. While it is possible to tailor the respective structures and compositions within each structure unit, the present invention represents a general design strategy to functional nanocatalysts which would find applications in clean energy conversion technologies such as fuel cells.
Ding and Wang successfully fabricated a new type of nanostructured electro-catalysts that simultaneously fulfills the three key requirements for a good practical catalyst: 1) ultra-low Pt loading, 2) great tolerance to poisoning, and 3) high stability. In one particular embodiment, a layer-structured, high surface area membrane catalyst was designed and constructed by depositing sub-monolayer Au onto a nanoporous gold (NPG) supported Pt monolayer, which demonstrated dramatically improved catalytic performance in formic acid oxidation. While it is possible to tailor the respective structures and compositions within each structure unit, the present invention represents a general design strategy to functional nanocatalysts which would find applications in clean energy conversion technologies such as fuel cells.
Ding’s and Wang’s method for preparing a catalyst includes the steps of: providing a gold-silver alloy article, removing the silver from the article by immersing the article in a de-alloying solution to form a nanoporous gold (NPG) article with a plurality of nanopores followed by cleaning the surface of the NPG article and removing the de-alloying solution from the nanopores with deionized water.
An electrode is attached to the NPG article and a monoatomic layer/lower layer of copper, silver, or lead, is deposited onto the surface of and within the nanopores of the NPG article by immersing the NPG article in an ion solution to form an M-NPG article. The M-NPG article is removed from the ion solution and the monoatomic/lower layer is replaced with platinum ions by immersing the M-NPG article into a platinum ion solution followed by cleaning the electrode and the NPG-Pt article with deionized water.
A monoatomic layer/lower layer of copper, silver, or lead, is then deposited onto the surface of and within the nanopores of the NPG-Pt article by immersing the NPG-Pt article in an ion solution to form an M-NPG-Pt article. The M-NPG-Pt article is removed from the ion solution and the monoatomic/lower layer of copper, silver, or lead is replaced with gold ions by immersing the M-NPG-Pt article into a gold ion solution to form an NPG-Pt--Au article followed by cleaning the electrode and the NPG-Pt--Au article with deionized water.
