Seminar: Dr Martina Lessio - First-Principles Investigations of Catalysts and Materials for Energy and Electronics Applications

Wednesday, 19 September 2018 - 3:00pm – Wednesday, 19 September 2018 - 4:00pm  |  CHEMSCI M10

Speaker: Scientia Seminar

(Photo)electrochemical CO2 reduction is a promising technology for the sustainable production of liquid fuels but presents some fundamental challenges. Overcoming these challenges requires the development of efficient catalysts, which could be accelerated by the discovery of the chemical mechanism by which existing successful catalysts operate. In the first part of my talk, I will present mechanistic insights gained primarily using density functional theory (DFT) methods for two promising catalytic systems.

The first system uses a p-GaP photoelectrode and a pyridine (Py)-based co-catalyst to reduce CO2 to methanol under illumination. We use accurate models of the electrode/solution interface to compute relevant properties of species at this interface that help us gain mechanistic insights. In particular, our results disprove the long-standing mechanistic hypothesis that the formation of a pyridinyl radical (PyH•) is an essential step to generate the active catalyst in this system. In fact, we show that PyH• is unstable and spontaneously transfers its electron to the photoelectrode surface. At the same time, we identify other intermediates that can form more favorably and may react to generate adsorbed dihydropyridine (DHP), a catalyst proposed in an alternative mechanism. Moreover, we provide strong evidence based on our calculations and experimental observations that the mechanism cannot be fully homogeneous and must involve surface-bound intermediates, thus further supporting the hypothesis of an adsorbed catalyst such as DHP. However, we also find that adsorbed DHP formation is likely kinetically hindered. We therefore propose and investigate an alternative co-catalytic intermediate bound to the surface that we predict to form and react with CO2 more favorably. 

The second system consists of a molecular electrocatalyst based on a rhenium complex with a bipyridine ligand that reduces CO2 to CO. In collaboration with experimental scientists, we perform a systematic study of the effect of changing the substituents of the bipyridine ligand on the stability and activity of the catalyst. We find that while electron-donating substituents improve the catalytic performance, too much electron density on the ligand can lead to catalyst destabilization. Such design principles are necessary for the development of improved catalysts. 

The second part of my talk will focus on a relevant class of materials for electronics applications, namely transition metal dichalcogenides. In particular, I will introduce recent experimental findings by our collaborators showing unexpected magnetism in semiconducting MoTe2. Understanding the origin of the magnetism is key for the development of new magnetic semiconductor materials that can contribute to the field of spintronics. Here, we use DFT calculations to study intrinsic defects in MoTe2 and determine whether they can be the source of the observed magnetism.