Devices               Batteries               Electrocatalysis               Material Design

Engineered 2D Transition Metal Dichalcogenides (TMDs) are highly active and affordable electrocatalysts that could significantly contribute to the widespread implementation of green hydrogen and other clean technologies. For instance, redox flow batteries, electrolyzers and fuel cells. Our material discovery methodology relies on finely tuning the structure, composition, and dimensions of different TMDs and composite materials as a viable tool to modulate substrate/catalyst interaction and associated catalytic activity. Among different reactions, we pay emphasis to new materials and testing methods to accelerate reactions including hydrogen evolution and oxidation, oxygen evolution and reduction, CO2 reduction or the electrosynthesis of ammonia via nitrogen activation.

Articles from the Group

Metallic 2D Materials for Electrocatalytic Reduction of CO₂ and N₂

Metallic 2D materials have recently emerged as a class of potentially inexpensive catalysts with enhanced activity and increased stability. However, their overall activity relative to state-of-the-art noble metal catalysts is limited by slower reaction kinetics and high charge transfer resistance. Our group’s seminal work several years ago (Nature Materials 12, 850-855, 2013) revealed that these factors can be mitigated by metallic 2D materials. In subsequent works (Nature Materials 15, 1003 - 1009, 2016), we have shown that increasing the metallic phase concentration and lowering the electrical resistance between the support and catalyst nanoparticles can lead to substantial improvement in catalytic performance.

An example of this is shown in the Figure (Nature Materials, 2019), which shows that with metallic NbS₂ it is possible to achieve very high current densities (several Amps-cm^-2) in proof of concept electrolyzer devices for electrocatalytically generating hydrogen. We expect metallic nanosheets to be exceptionally good catalysts for the HER or CO2RR and other reactions. We are therefore investigating the properties of 2D materials towards CO₂ reduction and the hydrogen evolution reactions to identify the best candidates for both reactions.

Microelectrochemical Cells for Catalysis and Energy Storage

Our group has developed microelectrochemical cells (See Figure and Nature Materials 15, 1003 - 1009, 2016) that allow precise identification of catalytically active sites. We can lithographically pattern devices so that only specific regions of the catalyst material (e.g. edge or basal plane) with well-defined number of atoms are exposed to the electrolyte. Thus, we can accurately quantify the activity of edge sites or the basal plane and because we know the exact area of the patterned electrocatalytically active region, it is possible to precisely extract fundamental parameters such as the exchange current density, the turnover frequency, and Tafel slopes for atomic active sites.

Microelectrochemical cells are also ideally suited for in-situ study of structural changes as well as quantum transport during electrochemical cycling. We fabricate nanodevices to drive intercalation into electrodes from chemically exfoliated and mechanical exfoliated nanosheets. We make vertical heterostructures of different 2D materials to study intercalation dynamics at different interfaces. Multiple metal contacts are deposited to form Hall bars so that electrical properties such as sheet resistance, carrier density from Hall voltage and Hall mobility of the carriers can be measured during electrochemical charging and discharging.