Oxygen-rich graphene support could lead to durable fuel cell catalysts more resistant to CO poisoning
|TEM image of Pt/RGO1. Click to enlarge.
Scientists at the University of Ulster’s Nanotechnology Institute and collaborators from Peking University and University of Oxford have developed reduced graphene oxide/platinum supported electrocatalysts (Pt/RGO) that could make fuel cells more efficient and more resistant to carbon monoxide poisoning.
The new electrocatalyst design could be a promising alternative for improving durability of fuel cells and eliminating the use of costly bimetallic or ternary metal systems, thereby contributing to expedited realization of fuel cell vehicles, they suggest. A paper on their work appears in ACS’ The Journal of Physical Chemistry C.
This system was tested for potential use as an anode material through the electrooxidation of methanol. Compared to the commercial carbon-supported Pt electrocatalysts, the Pt/RGO showed an unprecedented CO poisoning tolerance, high electrochemical active surface area, and high catalytic mass activity for methanol oxidation reaction, demonstrated by increases of 110, 134, and 60%, respectively.—Sharma et al.
Fuel cells that convert chemical energy directly into electrical energy by electrochemically decomposing a fuel such as hydrogen or methanol are considered a promising new way of powering cars and portable devices. One major hurdle to the commercial use of fuel cells is the CO poisoning of the active platinum catalyst sites, which renders them ineffective and prevents fuel oxidation. The CO poisoning problem is especially severe in direct methanol fuel cells (DMFCs) because CO is always present in critical amounts as an intermediate in methanol oxidation reaction.
So far, the major approach for reducing the poisoning is to alloy platinum with other expensive metals such as Ru, Pd or Au.
The researchers found a less expensive solution. To create a catalyst system that can tolerate more carbon monoxide, they deposited platinum nanocrystals on a support material of graphene oxide and reduced it slightly to increase its electrical conductivity.
They used a simple, scalable and fast microwave approach that has the advantage of reducing graphene oxide (RGO) and forming platinum nanoparticles simultaneously. To test the activity of the Pt/RGO the team looked at the oxidation of methanol. Their research shows that the new material displays an unprecedented CO poisoning tolerance, a much better long term stability and a higher electrocatalytic activity than those exhibited by commercially available carbon-supported Pt (Pt/C) electrocatalysts.
Structural and electronic properties of the electrocatalysts were determined using high resolution X ray photoelectron spectroscopy at the National Centre for Electron Spectroscopy and Surface Analysis (NCESS) at Daresbury, combined with transmission electron microscopy analysis at the EPSRC funded TEM facility at Oxford university.
Our studies of the structure and activity of this catalyst—and comparisons with commercial Pt/C catalysts currently in use—illustrate that the lightly reduced graphene oxide support “protects” the fine platinum nanocrystals from CO poisoning, enabling them to exhibit long term operation stability.—Pagona Papakonstantinou, Professor of Advanced Materials, Ulster University
The abundance of residual oxygen groups on lightly reduced graphene oxide (RGO) plays a major role on the removal of carbonaceous species. When an electrochemical potential is applied to the electrode, water molecules on the RGO support dissociate to form -(OH) groups, which readily oxidize the CO adsorbed groups on the adjacent Pt sites.
This new hybrid electrocatalyst can be considered as a promising alternative for improving durability of DMFCs and eliminate the use of costly bimetallic or ternary metal systems. Furthermore, our one-pot approach can provide an easy, fast, and eco-friendly way to explore the synthesis of other NPs on RGO, which can be exploited for use in fuel-cell technologies and sensing applications.—Sharma et al.
The research was supported by a Leverhulme Trust visiting Fellowship (Dr A. Ganguly) and a VCRS PhD studentship (S. Sharma).
Surbhi Sharma, Abhijit Ganguly, Pagona Papakonstantinou, Xiaopei Miao, Meixian Li, John L. Hutchison, Michael Delichatsios, Sebastian Ukleja (2010) Rapid Microwave Synthesis of CO Tolerant Reduced Graphene Oxide-Supported Platinum Electrocatalysts for Oxidation of Methanol. The Journal of Physical Chemistry C 114 (45), 19459-19466 doi: 10.1021/jp107872z