Nanostructured Molybdenum (IV) disulfide (MoS2) Electrodes

Description of Technology
Quantum dot sensitized solar cells (QDSSCs) are a widely studied system for harvesting light and converting it to electrical energy.  QDs are an attractive photoabsorber because their energy of absorption in the visible region can be tuned based on their size and because they have large absorption coefficients. Great strides are being made into developing new, more efficient absorber layers on the photoanode; however, instability of the cathode material prevents these cells from working effectively for more than a few seconds. Platinum, the most common counter electrode used for the study of QDSSCs, as well as gold and glassy carbon quickly become poisoned by the sulfide, resulting in significant current drops. Thus, these materials require large overpotentials to operate, lowering solar cell efficiencies and making them unsuitable for long-term use in a device. Also, platinum is rare and expensive, so replacing it with an inexpensive, earth-abundant material is a desirable goal in the long run. 

Molybdenum (IV) disulfide (MoS2) is a naturally occurring semiconductor found in nature as the mineral molybdenite and can be synthesized from inexpensive, earth-abundant materials. It has been found that edge sites where Mo is exposed -- not the faces -- of nano-MoS2 are the catalytic sites for electrochemical H2 evolution, so maximizing the relative number of edge sites to facial sites will improve electrochemical activity in a cell.  Existing techniques can be employed to produce flower-like MoS2 microspheres with uniformly sized spheres with distinct petal shapes.  Producing a uniform layer of these nano-flowers on a substrate would create an ideal counter electrode for QDSSCs, but previous attempts to deposit such structures on a substrate have largely been unsuccessful.

The present invention uses a Mo foil to produce the desired uniform growth of MoS2 petals from the Mo foil, making the foil both the source of Mo as well as the substrate.  This petaled MoS2 electrode shows a vastly improved polysulfide reduction compared to Glassy Carbon, ordinary Mo foil, Pt and Au.  The petaled MoS2 electrode lost only 0.63% of its initial current density at -1 V whereas Pt lost 13.58% after only five scans, indicating the petaled MoS2 films are highly stable as cathodes.

The technology was tested in a solar device setting, using standard photoanodes to test the efficiency of a device employing petaled MoS2 as its cathode. Devices in which a petaled MoS2 cathode was used achieved nearly fivefold improvement in efficiency over those employing a Pt cathode.

Intellectual Property Status
A U.S. Provisional Patent Application has been filed.

Inventors: 
Janet MacdonaldShane Finn
Licensing manager: 
Chris Harris

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