Session ThOF. There are 6 abstracts in this session.



Session: Materials 2, time: 4:00-4:20

Ligands on Nanocrystals: From Molecular Picture to Macroscopic Solubility


Xueqian Kong
Zhejiang University, Hangzhou, China
For nanocrystals of semiconductor (often called quantum dots), the surface ligands play an important role in controlling their morphology, stability and many physicochemical properties. From solid-state NMR (SSNMR), not only did we understand static pictures such as the coordination structures and the partitioning of different ligands, but also we precisely determined the dynamics of individual chain segments. From the SSNMR investigations, the fundamental connection between microscopic molecular interaction and macroscopic thermodynamic parameters has been revealed.
 

Session: Materials 2, time: 4:20-4:40

Atomistic Description of Active Surface Sites by 195Pt DNP SENS
 


Alicia Lund1; Christopher P. Gordon3; Keith Searles3; Ribal Jabbour1; Pierrick Berruyer2; David Gajan1; Lyndon Emsley2; Christophe Copéret3; Anne Lesage1
1High Field NMR Center of Lyon, Villeurbanne, France; 2EPFL, Lausanne, Switzerland; 3ETH Zurich, Zurich, N/A
We have recently shown that by leveraging the tremendous increase of the NMR sensitivity induced by DNP, the 3D structure of surface sites could be fully resolved. We demonstrated this approach on an organometallic Pt-NHC complex anchored on an amorphous silica surface. Here, we show that the presence of stabilizing noncovalent interactions between Pt and surface oxygen atoms is confirmed by DNP surface enhanced ultrawideline 195Pt NMR spectroscopy. The experimental 195Pt CSA tensor parameters were then confronted with DFT calculated values obtained on model structures in order to get new insight into the environment of the Pt atom. For the surface complex, the calculations show clear evidence for the presence of an oxygen atom in the coordination sphere of platinum.

Session: Materials 2, time: 4:40-5:00

De Novo Photovoltaic Paramagnetic Copper-doped Double Perovskite:   Deducing Atomic Structure with Ultrahigh Field Solid-state NMR and EPR


Vladimir K. Michaelis1; Abhoy Karmakar1; Mya Dodd1; Enrico Ravera2; Satyam Agnihotri1
1University of Alberta, Edmonton, Canada; 2CERM, University of Florence, Sesto Fiorentino (FI), Italy
Since 2016, lead-free halide double perovskite materials have been explored as potential alternatives to highly-toxic and less-environmentally stable lead-halide perovskite materials for solar cell applications. However, the larger bandgap (> 2 eV) for most of the double perovskites reported to date makes them less efficient materials for solar cells. Here, we present a new heterovalent Cu(II) doped double perovskite material, Cs2SbAgCl6, with a bandgap of ca. 1 eV and with long-term thermal and moisture stability. The complex structure and location of the Cu(II) cation are decoded using multinuclear (Cs-131 and Sb-121) solid-state NMR at 11.7 and 21.1 T and EPR spectroscopy.

Session: Materials 2, time: 5:00-5:20

Dynamic Nuclear Polarization with Transition Metal Centers: A step towards Hyperfine DNP Spectroscopy


Sheetal Kumar Jain
UC Santa Barbara, Goleta,
Use of transition metal centers as polarizing agents for DNP is an essential step towards endogenous DNP to study systems, like metalloproteins and battery compounds. Such experiments can improve the NMR sensitivity and at the same time can provide local structural information. In this work, we performed DNP using transition metal centers (V4+) with wide EPR lines, spanning 3-5GHz, as polarizing agents to achieve 1H NMR signal enhancements of up to 33 at 6.9T field and 4K temperature. This study opens the possibility for the characterization of a broad range of paramagnetic materials archetypes with intrinsic transition metal centers that were not accessible to DNP before, but of relevance to battery applications, heterogeneous catalysis to biological function.

Session: Materials 2, time: 5:20-5:40

Real-time monitoring of calcium phosphate pre-nucleation clusters formation by dissolution dynamic nuclear polarization   


Dennis Kurzbach1; Emmanuelle Weber1; Thomas Kress2; Geoffrey Bodenhausen3; Daniel Abergel1; Steffi Sewsurn4; Thierry Azaïs4
1ENS Paris, Paris, France; 2Ecole Normale Supérieure, Paris, France; 3École Normale Supérieure, Paris, France; 4Sorbonne Universités, Paris, France
The precipitation of calcium phosphate (CaP) is an important process of academic and industrial interest ranging from crystallographic studies via fundamental biomineralization processes to bone repair. Yet, the mechanisms of the initial stages of CaP formation remain to a large extent unclear since the pre-nucleation clusters (PNC) that appear at the beginning of CaP precipitation are elusive, metastable and difficult to characterize. We develop dissolution dynamic nuclear polarization (D-DNP) into a real-time biomineralization toolbox to probe the PNC charcteristic. We find that CaP PNCs form after preparation of a hyperpolarized calcium phosphate solution with a rate constant of 1.5 s-1. These early-stage PNCs display a diameter of Rh » 0.9 nm and accommodate 3 phosphate units.
 

Session: Materials 2, time: 5:40-6:00

Discovery of New Capacity Fade Mechanism in LixSn Batteries with Derivative Operando (dOp) NMR Spectroscopy.


Philip Grandinetti; Anne Co; Jose Lorie-Lopez
The Ohio State University, Columbus, OH
Using derivative operando Li-7 NMR to follow the charge and discharge of LixSn nanoparticle electrodes, we have determined that capacity fade in these electrodes arises from particles losing contact with the carbon/PVDF binder during delithiation.  Our results reveal, however, a peculiar mechanism where disconnected particles are pushed back into contact with the circuit by the remaining connected particles during lithiation; thus allowing the cell to reach full capacity during every lithiation cycle.  Our Li-7 NMR results have further identified the disconnecting LixSn phases as those undergoing the largest decreases in diameters on delithiation, i.e., Sn, Li2Sn5, LiSn, and Li7Sn3.  These results suggest a number of strategies for reducing capacity fade in a range of nano-structured intermetallic electrodes.