Duke team develops new core-shell copper nanowire catalyst for efficient water oxidation for solar fuels
|A transparent film of copper nanowires was transformed into an electrocatalyst for water oxidation by electrodeposition of Ni or Co onto the surface of the nanowires. Chen et al. Click to enlarge.|
A team led by Benjamin J. Wiley at Duke University has introduced a new electrocatalyst for water oxidation consisting of a conductive network of core-shell nanowires that is just as efficient as conventional metal oxide films on indium tin oxide (ITO) and a great deal more transparent and robust. A paper on their work is published in the journal Angewandte Chemie.
Water oxidation (2H2O → O2 + 4e- + 4H+) is a key step for converting solar energy into chemical fuels. Nickel and cobalt oxides are attractive anode materials for the oxidation of water because they are readily available and demonstrate high catalytic activity. For use in photoelectric synthesis cells, in which chemical conversions are driven by light, the oxides are typically electrodeposited onto ITO substrates. ITO is used because of its high transmittance and low sheet resistance.
However, the high potentials required for the oxidation of water cause the conductivity of ITO surfaces to fall. In addition, indium is expensive and the production of ITO films is costly. Another disadvantage is that the catalytic oxide layers reduce the light transmittance and thus the light captured by the photovoltaic components.
Herein we report a new approach to create transparent catalysts for water oxidation that eliminates the need for ITO. We replaced the ITO electrode with a conducting network of copper nanowires (CuNWs), which have the advantage of being made from an element that is 1000 times more abundant and 100 times less expensive than indium, and can be deposited using fast liquid-phase coating processes.
We then use electrodeposition to create a conformal layer of nickel or cobalt around the NWs to serve as a catalyst. These core–shell NW networks exhibit sustained electrocatalytic water oxidation with activities comparable to thin films of metal oxides, but transmit up to 6.7 times more light.—Chen et al.
The nanowire film can also be deposited onto a flexible sheet of polyethylene terephthalate (PET) plastic instead of glass. Unlike ITO-based electrocatalysts on PET substrates, which suffer from significant loss of conductivity after repeated bending, the film made of nanowires isn’t really affected.
This fabrication method can most likely be extended to create core–shell nanowire networks with a wide variety of compositions for various applications. Core–shell nanowire networks exhibit electrocatalytic performance for water oxidation equivalent to metal oxide films of similar composition, but are several times more transparent. The greater transmittance, mechanical flexibility, and lower materials cost of nanowire network catalysts relative to thin film catalysts deposited on ITO opens up new possibilities to engineer more efficient, mechanically robust, and affordable light-harvesting architectures for scalable production of solar fuels.—Chen et al.
This work was supported in part by the NSF Research Triangle MRSEC (DMR-1121107) and an NSF CAREER award (DMR-1253534). One of the team was supported by a NSF graduate research fellowship.
Zuofeng Chen, Aaron R. Rathmell, Shengrong Ye, Adria R. Wilson, and Benjamin J. Wiley (2013) “Optically transparent water oxidation catalyst made from copper nanowires,” Angewandte Chemie International Edition doi: 10.1002/anie.201306585