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Publications (9 of 9) Show all publications
Goswami, S., Rath, S. P., Thompson, D., Hedström, S., Annamalai, M., Pramanick, R., . . . Venkatesan, T. (2020). Charge disproportionate molecular redox for discrete memristive and memcapacitive switching. Nature Nanotechnology, 15(5), 380-389
Open this publication in new window or tab >>Charge disproportionate molecular redox for discrete memristive and memcapacitive switching
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2020 (English)In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 15, no 5, p. 380-389Article in journal (Refereed) Published
Abstract [en]

Electronic symmetry breaking by charge disproportionation results in multifaceted changes in the electronic, magnetic and optical properties of a material, triggering ferroelectricity, metal/insulator transition and colossal magnetoresistance. Yet, charge disproportionation lacks technological relevance because it occurs only under specific physical conditions of high or low temperature or high pressure. Here we demonstrate a voltage-triggered charge disproportionation in thin molecular films of a metal-organic complex occurring in ambient conditions. This provides a technologically relevant molecular route for simultaneous realization of a ternary memristor and a binary memcapacitor, scalable down to a device area of 60 nm(2). Supported by mathematical modelling, our results establish that multiple memristive states can be functionally non-volatile, yet discrete-a combination perceived as theoretically prohibited. Our device could be used as a binary or ternary memristor, a binary memcapacitor or both concomitantly, and unlike the existing 'continuous state' memristors, its discrete states are optimal for high-density, ultra-low-energy digital computing. Charge disproportionation in thin molecular films of a metal-organic complex enables the realization of a ternary memristor and binary memcapacitor.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-181140 (URN)10.1038/s41565-020-0653-1 (DOI)000521528700001 ()32203436 (PubMedID)2-s2.0-85083361792 (Scopus ID)
Note

For correction, see: Nat. Nanotechnol. 18, 1116 (2023). DOI: 10.1038/s41565-023-01461-9

Available from: 2020-05-19 Created: 2020-05-19 Last updated: 2024-10-23Bibliographically approved
Hedström, S., Halldin Stenlid, J., Liu, C. & Pettersson, L. G. M. (2020). Photodriven CO dimerization on Cu2O from an electronic-structure perspective. Sustainable Energy & Fuels, 4(2), 670-677
Open this publication in new window or tab >>Photodriven CO dimerization on Cu2O from an electronic-structure perspective
2020 (English)In: Sustainable Energy & Fuels, E-ISSN 2398-4902, Vol. 4, no 2, p. 670-677Article in journal (Refereed) Published
Abstract [en]

Electrochemically driven CO2 reduction into alcohols and hydrocarbons is a topic of intense study. Photocatalytic approaches, which instead are powered by light, are also reported, but these generally rely on two-component catalysts and yield only moderately reduced products with a single carbon atom. In this report, we use density functional theory, including its linear-response time-dependent implementation, to investigate the feasibility of photocatalytically driving the dimerization of CO chemisorbed on Cu2O, a crucial step in the chemical conversion of CO2 into C-2 products, such as ethanol and ethylene. We find that CO dimerization into OCCO is greatly aided by the photoinduced population of a low-lying LUMO that is bonding with respect to the C-C bond of two adjacently chemisorbed CO molecules.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-181982 (URN)10.1039/c9se00753a (DOI)000528920000016 ()2-s2.0-85079085202 (Scopus ID)
Available from: 2020-05-28 Created: 2020-05-28 Last updated: 2022-11-08Bibliographically approved
Liu, C., Hedström, S., Stenlid, J. H. & Pettersson, L. G. M. (2019). Amorphous, Periodic Model of a Copper Electrocatalyst with Subsurface Oxygen for Enhanced CO Coverage and Dimerization. The Journal of Physical Chemistry C, 123(8), 4961-4968
Open this publication in new window or tab >>Amorphous, Periodic Model of a Copper Electrocatalyst with Subsurface Oxygen for Enhanced CO Coverage and Dimerization
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 8, p. 4961-4968Article in journal (Refereed) Published
Abstract [en]

Oxide-derived copper electrocatalysts have been found to possess excellent selectivity toward the production of multicarbon products from CO,. The presence of subsurface oxygen in these catalysts has been confirmed experimentally, but the resulting amorphous structure has yet to be captured by theoretical models. In this study, the role of subsurface oxygen atoms is investigated with density functional theory, using a disordered oxide-derived Cu surface model (d-ODCu). The presence of subsurface oxygen atoms increases the maximum adsorption coverage of the important CO intermediate but decreases that of H atoms because of electronic and geometric effects. However, this has no significant influence on the free-energy activation barrier or endothermicity of the CO-dimerization reaction step, allegedly the key to multicarbon product formation.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-167653 (URN)10.1021/acs.jpcc.8b12214 (DOI)000460365200033 ()2-s2.0-85062389011 (Scopus ID)
Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2022-11-02Bibliographically approved
Gedefaw, D., Hedström, S., Xia, Y., Persson, P. & Andersson, M. R. (2018). Design, Synthesis and Computational Study of Fluorinated Quinoxaline-Oligothiophene-based Conjugated Polymers with Broad Spectral Coverage. ChemPhysChem, 19(24), 3393-3400
Open this publication in new window or tab >>Design, Synthesis and Computational Study of Fluorinated Quinoxaline-Oligothiophene-based Conjugated Polymers with Broad Spectral Coverage
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2018 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 19, no 24, p. 3393-3400Article in journal (Refereed) Published
Abstract [en]

Donor-acceptor (D-A) copolymers typically show two absorption peaks in the visible region, flanking a valley region of limited absorptivity. One strategy for more panchromatic light harvesting is to incorporate side-groups orthogonal to the polymer backbone, which enable 2D pi conjugation and can give rise to additional absorption peaks. Here we design and synthesize two D-A polymers which both carry a fluorinated quinoxaline acceptor unit, but while P1 includes a benzodithiophene donor moiety with thiophene side-groups (2D-BDT), the P2 polymer lacks 2D conjugation in its simpler pentathiophene donor segment. The P1 polymer consequently shows an atypical absorption profile with more panchromatic absorption with no apparent valley in the spectrum. In order to understand the structure-electronic relations, the optical and electrochemical properties were predicted using a previously developed computational approach. The predicted optical properties show very good agreement with the experimental results. Solar cells made from P1 show a short-circuit current more than twice as large as P2, attributed to its enhanced spectral coverage. However, poor fill factors limit the preliminary power conversion efficiencies to 3.3 % for P1 and 1.0 % for P2 as blended with PCBM[70] in a 1 : 1.5 (w/w) ratio.

Keywords
computational chemistry, cross-coupling, semiconductors, structure-activity relationships, UV/Vis spectroscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-163670 (URN)10.1002/cphc.201800814 (DOI)000453765300011 ()30381883 (PubMedID)2-s2.0-85057558479 (Scopus ID)
Available from: 2019-01-18 Created: 2019-01-18 Last updated: 2022-10-21Bibliographically approved
La Porte, N. T., Martinez, J. F., Chaudhuri, S., Hedström, S., Batista, V. S. & Wasielewski, M. R. (2018). Photoexcited radical anion super-reductants for solar fuels catalysis. Coordination chemistry reviews, 361, 98-119
Open this publication in new window or tab >>Photoexcited radical anion super-reductants for solar fuels catalysis
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2018 (English)In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 361, p. 98-119Article, review/survey (Refereed) Published
Abstract [en]

The catalytic transformation of carbon dioxide into fuels is one of the most important reactions for creating a sustainable, carbon-neutral energy economy. Given that the sun is the only plausible energy source that can accommodate the increased global energy demand without contributing to catastrophic climate change, it makes sense to use solar energy to drive this reaction, ideally using the largest possible portion of the solar spectrum. Over the past several years, we have explored the use of reduced rylenediimide chromophores, which absorb wavelengths ranging into the near-infrared, as strongly reducing photosensitizers capable of photosensitizing Re(diimine)(CO)(3)L metal centers towards the binding and reduction of CO2. We have explored the effects of varying the binding geometry, donor-acceptor redox potentials, and excitation wavelength on the kinetics of electron transfer from the reduced rylenediimide to the metal center. So far, we have achieved charge-separated lifetimes in electrocatalytically active complexes of 25 ns when illuminated with near-infrared light, and >250 ns when illuminated with blue light.

Keywords
Photoinduced electron transfer, Solar fuels, Ultrafast spectroscopy, Transient absorption, Artificial photosynthesis, Radical anions, CO2 reduction
National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:su:diva-155900 (URN)10.1016/j.ccr.2018.01.018 (DOI)000429761100003 ()2-s2.0-85044597120 (Scopus ID)
Available from: 2018-04-30 Created: 2018-04-30 Last updated: 2022-10-25Bibliographically approved
Hedström, S., Campos dos Santos, E., Liu, C., Chan, K., Abild-Pedersen, F. & Pettersson, L. G. M. (2018). Spin Uncoupling in Chemisorbed OCCO and CO2: Two High-Energy Intermediates in Catalytic CO2 Reduction. The Journal of Physical Chemistry C, 122(23), 12251-12258
Open this publication in new window or tab >>Spin Uncoupling in Chemisorbed OCCO and CO2: Two High-Energy Intermediates in Catalytic CO2 Reduction
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 23, p. 12251-12258Article in journal (Refereed) Published
Abstract [en]

The production of useful compounds via the electrochemical carbon dioxide reduction reaction (CO2RR) is a matter of intense research. Although the thermodynamics and kinetic barriers of CO2RR are reported in previous computational studies, the electronic structure details are often overlooked. We study two important CO2RR intermediates: ethylenedione (OCCO) and CO, covalently bound to cluster and slab models of the Cu(100) surface. Both molecules exhibit a near-unity negative charge as chemisorbed, but otherwise they behave quite differently, as explained by a spin uncoupling perspective. OCCO adopts a high-spin, quartetlike geometry, allowing two covalent bonds to the surface with an average gross interaction energy of -1.82 eV/bond. The energy cost for electronically exciting OCCO- to the quartet state is 1.5 eV which is readily repaid via the formation of its two surface bonds. CO2, conversely, retains a low-spin, doubletlike structure upon chemisorption, and its single unpaired electron forms a single covalent surface bond of -2.07 eV. The 5.0 eV excitation energy to the CO2- quartet state is prohibitively costly and cannot be compensated for by an additional surface bond.

National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:su:diva-158263 (URN)10.1021/acs.jpcc.8b02165 (DOI)000435611900015 ()2-s2.0-85047099777 (Scopus ID)
Available from: 2018-08-06 Created: 2018-08-06 Last updated: 2022-10-26Bibliographically approved
Chaudhuri, S., Hedström, S., Mendez-Hernandez, D. D., Hendrickson, H. P., Jung, K. A., Ho, J. & Batista, V. S. (2017). Electron Transfer Assisted by Vibronic Coupling from Multiple Modes. Journal of Chemical Theory and Computation, 13(12), 6000-6009
Open this publication in new window or tab >>Electron Transfer Assisted by Vibronic Coupling from Multiple Modes
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2017 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 13, no 12, p. 6000-6009Article in journal (Refereed) Published
Abstract [en]

Understanding the effect of vibronic coupling on electron transfer (ET) rates is a challenge common to a wide range of applications, from electrochemical synthesis and catalysis to biochemical reactions and solar energy conversion. The Marcus-Jortner-Levich (MJL) theory offers a model of ET rates based on a simple analytic expression with a few adjustable parameters. However, the MJL equation in conjunction with density functional theory (DFT) has yet to be established as a predictive first-principles methodology. A framework is presented for calculating transfer rates modulated by molecular vibrations, that circumvents the steep computational cost which has previously necessitated approximations such as condensing the vibrational manifold into a single empirical frequency. Our DFT MJL approach provides robust and accurate predictions of ET rates spanning over 4 orders of magnitude in the 10(6)-10(10) s(-1) range. We evaluate the full MJL equation with a Monte Carlo sampling of the entire active space of thermally accessible vibrational modes, while using no empirical parameters. The contribution to the rate of individual modes is illustrated, providing insight into the interplay between vibrational degrees of freedom and changes in electronic state. The reported findings are valuable for understanding ET rates modulated by multiple vibrational modes, relevant to a broad range of systems within the chemical sciences.

National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:su:diva-152652 (URN)10.1021/acs.jctc.7b00513 (DOI)000418205100016 ()29095611 (PubMedID)2-s2.0-85038217503 (Scopus ID)
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2022-10-19Bibliographically approved
Liu, C., Lourenco, M. P., Hedström, S., Cavalca, F., Diaz-Morales, O., Duarte, H. A., . . . Pettersson, L. G. M. (2017). Stability and Effects of Subsurface Oxygen in Oxide-Derived Cu Catalyst for CO2 Reduction. The Journal of Physical Chemistry C, 121(45), 25010-25017
Open this publication in new window or tab >>Stability and Effects of Subsurface Oxygen in Oxide-Derived Cu Catalyst for CO2 Reduction
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2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 45, p. 25010-25017Article in journal (Refereed) Published
Abstract [en]

Oxide-derived copper (OD-Cu) catalysts are promising candidates for the electrochemical CO2 reduction reaction (CO2RR) due to the enhanced selectivity toward ethylene over methane evolution, which has been linked to the presence of subsurface oxygen (O-sb). In this work, O-sb is investigated with theoretical methods. Although O-sb is unstable in slab models, it becomes stabilized within a manually reduced OD-Cu nanocube model which was calculated by self-consistent charge density functional tight binding (SCC-DFTB). The results obtained with SCC-DFTB for the full nanocube were confirmed with subcluster models extracted from the nanocube, calculated with both density functional theory (DFT) and SCC-DFTB. The. higher stability of O-sb in the nanocube is attributed to the disordered structure and greater flexibility. The adsorption strength of CO on Cu(100) is enhanced by O-sb withdrawing electron density from the Cu atom, resulting in reduction of the sigma-repulsion. Hence, the coverage of CO may be increased, facilitating its dimerization.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-149798 (URN)10.1021/acs.jpcc.7b08269 (DOI)000416202900014 ()2-s2.0-85032653868 (Scopus ID)
Available from: 2017-12-19 Created: 2017-12-19 Last updated: 2022-10-20Bibliographically approved
Hedström, S., Chaudhuri, S., La Porte, N. T., Rudshteyn, B., Martinez, J. F., Wasielewski, M. R. & Batista, V. S. (2017). Thousandfold Enhancement of Photoreduction Lifetime in Re(bpy)(CO)(3) via Spin-Dependent Electron Transfer from a Perylenediimide Radical Anion Donor. Journal of the American Chemical Society, 139(46), 16466-16469
Open this publication in new window or tab >>Thousandfold Enhancement of Photoreduction Lifetime in Re(bpy)(CO)(3) via Spin-Dependent Electron Transfer from a Perylenediimide Radical Anion Donor
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2017 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 46, p. 16466-16469Article in journal (Refereed) Published
Abstract [en]

Spin-dependent intramolecular electron transfer is revealed in the Re-I(CO)(3)(py)(bpy-Ph)perylenediimide radical anion (Re-I-bpy-PDI-(.)) dyad, a prototype model system for artificial photosynthesis. Quantum chemical calculations and ultrafast transient absorption spectroscopy experiments demonstrate that selective photoexcitation of Re-I-bpy results in electron transfer from PD-(.) to Re-I-bpy, forming two distinct charge-shifted states. One is an overall doublet whose return to the ground state is spin-allowed. The other, high spin quartet state, persists for 67 ns due to spin-forbidden back-electron transfer, constituting a more than thousandfold lifetime improvement compared to the low-spin state. Exploiting this spin dependency holds promise for artificial photosynthetic systems requiring long-lived reduced states to perform multi-electron chemistry.

National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:su:diva-150899 (URN)10.1021/jacs.7b09438 (DOI)000416496400010 ()29083146 (PubMedID)2-s2.0-85034854187 (Scopus ID)
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2022-10-20Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6496-6865

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