Profiles

Photograph of Andrew J. Pell

Andrew Pell

Associate Professor

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Works at Department of Materials and Environmental Chemistry
Telephone 08-16 23 76
Email andrew.pell@mmk.su.se
Visiting address Svante Arrhenius väg 16 C
Room C520
Postal address Institutionen för material- och miljökemi 106 91 Stockholm

About me

I graduated in 2005 with an MSci from the University of Cambridge in Natural Sciences, specializing in chemistry.  I stayed at Cambridge to complete a PhD in solution NMR under the supervision of James Keeler in 2009, where I worked on the development of new methods in what is now known as pure-shift NMR. Afterwards I moved to the Centre de RMN à Très Hauts Champs at the Ecole Normale Supérieure de Lyon to perform postdoctoral work in paramagnetic solid-state NMR on materials and metalloproteins with Guido Pintacuda and Lyndon Emsley.  I returned to Cambridge in 2014 for a second postdoctoral position with Clare P. Grey on paramagnetic solid-state NMR of lithium-ion battery materials.

I have been employed at the Department of Material and Environmental Chemistry at Stockholm University since April 2016 firstly as assistant professor, and then as associate professor from April 2020.

Research

Solid-state NMR spectroscopy of materials

My research interests concern the development and application of solid-state nuclear magnetic resonance (NMR) spectroscopy to materials.

Solid-state NMR is an efficient tool for the characterization of micro-crystalline, poorly crystalline, or materials with structural or compositional disorder including organometallic complexes, inorganic frameworks, battery materials, and biological systems. In combination with other techniques, NMR can provide unique insights into the analysis of processes such as the reaction mechanisms of catalysts, the description of surface reactions/binding, ion conductivity, and many more.

Z Ma, A Jaworski, J George, A Rokicinska, T Thersleff, TM Budnyak, G Hautier, AJ Pell, R Dronskowski, P Kustrowski, A Slabon, Exploring the origins of improved photocurrent by acidic treatment for quaternary tantalum-based oxynitride photoanodes on the example of CaTaO2N, J Phys Chem C124, 152–160 (2020). https://doi.org/10.1021/acs.jpcc.9b09838

WR Brant, R Mogensen, S Colbin, DO Ojwang, S Schmid, L Häggström, T Ericsson, A Jaworski, AJ Pell, R Younesi, Selective control of composition in Prussian white for enhanced material properties, Chem Mater31, 7203–7211 (2019).https://doi.org/10.1021/acs.chemmater.9b01494

P Rzepka, Z Bacsik, AJ Pell, N Hedin, A Jaworski, Nature of chemisorbed CO2in zeolite A, J Phys Chem C123, 21497–21503 (2019). https://doi.org/10.1021/acs.jpcc.9b04142

NC George, J Brgoch, AJ Pell, C Cozzan, A Jaffe, G Dantelle, A Llobet, G Pintacuda, R Seshadri, BF Chmelka, Correlating local compositions and structures with the macroscopic optical properties of Ce3+-doped CaSc2O4, an efficient green-emitting phosphor, Chem Mater29, 3538–3546 (2017). https://doi.org/10.1021/acs.chemmater.6b05394

J Xu, DH Lee, RJ Clément, X Yu, M Leskes, AJ Pell, G Pintacuda, X-Q Yang, CP Grey, YS Meng, Identifying the critical role of Li substitution in P2-Nax[LiyNizMn1-y-z]O2(0 < xy,z< 1) intercalation cathode materials for high-energy Na-ion batteries, Chem Mater26, 1260–1269 (2014). https://doi.org/10.1021/cm403855t– in top 1% most cited in the field of materials science

Paramagnetic NMR

Paramagnetic metal ions are present at the active sites of many catalytic and electrochemical processes that are at the core of modern chemistry, and are the key constituents of many new versatile materials. As such they have a tremendous impact on industry, energy, and the environment. The key to being able to understand and explain the function and macroscopic bulk properties of these materials is to obtain a picture of their local three-dimensional structure.

The aim of our research in this area is to provide a robust tool for characterizing systems containing paramagnetic metal ions down to the molecular or atomic level, and therefore to provide a link between the structure and the bulk properties of such paramagnetic systems. To achieve this aim we develop new solid-state NMR techniques in combination with novel theoretical and computational methods.

However paramagnetic systems have resisted NMR characterization since paramagnetic centres with large magnetic moments result in signals with extremely large shifts, large shift anisotropies, and very short relaxation times.  On the one hand these effects provide a direct probe of the electronic structure in these compounds. On the other hand these same effects present a problem for spectroscopy, and mask the information that can usually be extracted from a diamagnetic molecule.

This field has experienced a real revolution in recent years, due to a combination of improved radiofrequency (RF) probe technology and better RF irradiation schemes.  These developments have opened the door to measuring and exploiting paramagnetic effects as a source of structural and electronic information.

However, despite this recent progress, many issues remain to be addressed before paramagnetic NMR can become a routine tool for the studying systems of increasing complexity that are increasingly playing a part in chemistry and biology. We aim to address the barriers that currently oppose the acquisition and interpretation of the NMR spectra, and to extend the fields of application, attacking relevant chemical and biological problems, with novel techniques to determine structure.

JP Carvalho, A Jaworski, MJ Brady, AJ Pell, Separation of quadrupolar and paramagnetic shift interactions with TOP-STMAS/MQMAS in solid-state lighting phosphors, Magn Reson Chem, in press (2020). https://doi.org/10.1002/mrc.5004– invited article for “Solid-State NMR for Materials Sciences” Special Issue

R Pigliapochi, L O’Brien, AJ Pell, MW Gaultois, Y Janssen, PG Khalifah, CP Grey, When do anisotropic magnetic susceptibilities lead to large NMR shifts?  Exploring particle shape effects in the battery electrode material LiFePO4, J Am Chem Soc141, 13089–13100 (2019).https://doi.org/10.1021/jacs.9b04674

R Aleksis, JP Carvalho, A Jaworski, AJ Pell, Artefact-free broadband 2D NMR for separation of quadrupolar and paramagnetic shift interactions, Solid State Nucl Magn Reson,101, 51–62 (2019). https://doi.org/10.1016/j.ssnmr.2019.05.001– invited article for “pNMR” Special Issue, cover article

AJ Pell, G Pintacuda, CP Grey, Paramagnetic NMR in solution and the solid state, Prog Nucl Magn Reson Spectrosc111, 1–271 (2019). https://doi.org/10.1016/j.pnmrs.2018.05.001– in top 1% most cited in the field of chemistry

AJ Pell, G Pintacuda, Broadband solid-state MAS NMR of paramagnetic systems, Prog Nucl Magn Reson Spectrosc84–85, 33–72 (2015). https://doi.org/10.1016/j.pnmrs.2014.12.002

Oxyhydrides for energy conversion and hydrogen storage

Perovskite-type oxyhydrides have interesting potential applications in electrochemistry, energy conversion, and hydrogen storage.  Some of these materials exhibit ion and electron conductivity  We use solid-state NMR in combination with DFT to answer fundamental questions as to how much hydride is present, where it is, how it moves throughout the lattice, and the nature of the electronic structure.

C Eklöf-Österberg, L Mazzei, EJ Granhed, G Wahnström, R Nedumkandathil, U Häussermann, A Jaworski, AJ Pell, SF Parker, NH Jalarvo, L Börjesson, M Karlsson, The role of oxygen vacancies on the vibrational motions of hydride ions in the oxyhydride of barium titanate, J Mater Chem A8, 6360–6371 (2020).https://doi.org/10.1039/c9ta11912d

R Aleksis, JP Carvalho, A Jaworski, AJ Pell, Artefact-free broadband 2D NMR for separation of quadrupolar and paramagnetic shift interactions, Solid State Nucl Magn Reson,101, 51–62 (2019). https://doi.org/10.1016/j.ssnmr.2019.05.001– invited article for “pNMR” Special Issue, cover article

C Eklöf-Österberg, R Nedumkandathil, U Häussermann, A Jaworski, AJ Pell, M Tyagi, NH Jalarvo, B Frick, A Faraone, M Karlsson, Dynamics of hydride ions in metal hydride-reduced BaTiO3samples investigated with quasielastic neutron scattering, J Phys Chem C123, 2019–2030 (2019). https://doi.org/10.1021/acs.jpcc.8b08451– cover article

R Nedumkandathil, A Jaworski, J Grins, D Bernin, M Karlsson, C Eklöf-Österberg, A Neagu, C-W Tai, AJ Pell, U Häussermann, Hydride reduction of BaTiO3– Oxyhydride versus O vacancy formation, ACS Omega3, 11426–11438 (2018).https://doi.org/10.1021/acsomega.8b01368

Topological insulators

Topological insulators are materials which act as electronic insulators in the ‘interior’ of the particles, but have conducting electronic states (Dirac electrons) on the surfaces.  As such, they possess a number of fascinating properties that are relevant both physics and materials chemistry.  From the point of view of fundamental physics, detecting these Dirac electronic states is critical for the study of important surface quantum properties, such as Majorana zero modes, where simultaneous probing of the bulk and edge electron states is required.  We do this using state-of-the-art solid-state NMR in combination with DFT calculations. Once these questions have been addressed, there is still a huge area of applications to explore, including electrochemical applications and catalysis.

W Papawassiliou, A Jaworski, AJ Pell, JH Jang, Y Kim, S-C Lee, HJ Kim, Y Alwahedi, S Alhassan, A Subrati, M Fardis, M Karagianni, N Panopoulos, J Dolinšek, G Papavassiliou, Resolving Dirac electrons with broadband high-resolution NMR, Nat Commun11, 1285 (2020). https://doi.org/10.1038/s41467-020-14838-4

New methods in broadband, high-resolution 14N NMR

Nitrogen is one of the most important elements found in chemistry, materials science, and biology.  It is found in many diverse systems including pharmaceutical molecules, polymers, supramolecular assemblies, and biological macromolecules where it often plays a crucial role in providing structural stability, and information coding, via hydrogen bonding.  However whilst solid-state NMR should be the method of choice to probe both the atomic-level structure and dynamic processes, it has yet to emerge as a widely-used tool for probing this broad variety of nitrogen environments.  This is because although the most abundant isotope 14N has a high natural abundance of 99.6%, the combination of the integer spin of I=1, typical quadrupolar interaction strengths of a few MHz, and a low gyromagnetic ratio result in very broad NMR signals of very low sensitivity.  Whilst these effects in principle provide a direct probe of the local nitrogen structure and dynamics in these systems, they also present a substantial problem for spectroscopy, resulting in very poor sensitivity and resolution, which make it difficult to extract useful information.

Here we aim to design, optimize, and implement new experimental NMR schemes to observe 14N atomic environments.  Recently we have proposed a new pulse scheme for broadband 14N double-quantum NMR using a combination of fast MAS >50 kHz and low RF field strengths that are capable of excitation with high sensitivity, using ideas that we have previously developed for paramagnetic systems. This initial breakthrough has yielded some very promising results there is still considerable scope for optimization.  This development of the arsenal of techniques for 14N solid-state NMR is the key to making progress in the structural characterization of the wide variety of systems described above.

AJ Pell, KJ Sanders, S Wegner, G Pintacuda, CP Grey, Low-power broadband solid-state MAS NMR of 14N, J Chem Phys146, 194202 (2017). https://doi.org/10.1063/1.4983220

Group members

Postdoctoral researchers

Dr Jinqin Yang (co-supervisor with Prof. Niklas Hedin and Prof. Alexander Lyubartsev)

PhD research students

Wassilios Papawassiliou

Rihards Aleksis

José Pedro Albuquerque de Carvalho

Former group members

Aleksander Jaworski (postdoc 2020)

Lucia Corti (masters 2020)

Min Lin (visiting PhD 2020)

Elodie Guillard (intern 2018)

Diana Bernin (postdoc 2016)

Positions

We are always looking for masters students, PhD students, and postdocs. Interested candidates should send a cover letter and CV by email. Masters and PhD candidates should have a background in chemistry, physics, or materials science.  Postdoctoral candidates should have a strong background in experimental or theoretical NMR spectroscopy.

Files

Last updated: February 25, 2021

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