Nuclear energy continues to be an important energy source. It is responsible for 27% of the European Union’s (EU) electricity and it is expected that the demand for nuclear power will remain constant in the coming decades. To improve the safety and energy efficiency of nuclear energy, we perform computational materials research on innovative reactor technologies, new nuclear fuel materials, as well as on long-term environmental-safe storage of radioactive nuclear waste.

Nuclear energy continues to be an important energy source. It is responsible for 27% of the European Union’s (EU) electricity and it is expected that the demand for nuclear power will remain constant in the coming decades. To improve the safety and energy efficiency of nuclear energy, we perform computational materials research on innovative reactor technologies, new nuclear fuel materials, as well as on long-term environmental-safe storage of radioactive nuclear waste. To achieve a safe and efficient usage of nuclear energy, scientific research on various topics is required, such as for example, the thermonuclear properties of current and next-generation nuclear fuel materials, the stability and durability of both fuel and reactor vessel materials under extreme conditions, and last but not least, the corrosion and dissolution of spent nuclear fuel. Through our computational materials’ modeling we provide an important knowledge based expertise, which is essential to obtain a scientifically founded understanding of nuclear energy materials and to be able to predict their long-term behavior.

Materials Research for Nuclear Fuel Materials

Name of Mattias’ project [Link to Mattias’ page]

Materials Research for Nuclear Fuels

The 2011-Fukushima Daiichi accident emphasized how essential it is to have a thorough understanding of the reaction of nuclear fuel materials with water. It is unlikely that a similar, earthquake related accident would occur in Sweden. Yet the reaction of nuclear fuel with water is important from a different perspective: spent nuclear fuel from Swedish reactors will be stored in deep underground repositories, which appears as a promising solution [1] to the problem: what to do with nuclear waste?

The repository’s implementation requires a comprehensive understanding of fuel corrosion processes in order to present a safety case based on scientifically sound estimations of possible environmental impacts. After a long time, the spent nuclear fuel – composed primarily of uranium dioxide with other actinides (Np, Pu) and fission products – will react with ground water. In collaboration with Svensk kärnbränslehantering (SKB) the group of Peter Oppeneer performs materials modeling simulations to investigate the dissolution of the nuclear fuel through reaction with water. We use ab initio molecular dynamics and atomistic thermodynamics to simulate the reactivity of UO₂ surfaces with water, which furnish the conclusion that UO₂ surfaces will always react with water under equilibrium conditions (atmospheric pressure and room temperature) leading to its dissolution in water [2], see figure 1.

People and contact

Prof. Rajeev Ahuja, Dr. Sudip Chakraborty, Dr. Anton Grigoriev, Dr. C. Moyses Araujo, Dr. Wei Luo, Amitava Banerjee, Rafael Barros Neves de Araujo, Thanayut Kaewmaraya, Vivekanand Shukla, Teeraphat Watcharatharapong, John Wärnå

Office Å13106
Telephone +46 18 471 3626

Email rajeev.ahuja@physics.uu.se

Research

2D Catalytic-Materials

In particular, we predict the enhanced water splitting activity of recently synthesized two dimensional (2D) semiconducting materials MX₂ (where M=Ti, Hf, Zr and X=S, Se, Te), hydrogenated silicene, stanene and phosphorene from the band edge alignment concept. The real catalytic mechanism of water dissociation is hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) which are needed to be envisaged together with the band edge alignment. A fundamental understanding of how to improve solar hydrogen production with such 2D materials is of great technological importance. We have performed a theoretical investigation [1, 2] in order to find the optimum photocatalytic activity of ultra-thin silicane and germanane with a series of functionalizing adatoms. HER and OER activity are determined from the surface-adsorbate interaction. This study can be an intuitive way to theoretically rationalize HER and OER activity for a series of functionalized different two-dimensional systems before performing the actual experiment in the laboratory. A comparative study of HER mechanism on WS₂ and PtS₂ monolayers has also been performed recently [3]. The lightest 2D catalytic material has been found in the form of Boron monolayer based on our electronic structure calculations [4]. We have also investigated a novel defect engineered g-C₃N₄ nanosheet produced by hydrogen treatment [5]. On the basis of experimental as well as DFT calculations, it has been shown that the formation of two-coordinated nitrogen vacancy in g-C₃N₄ is responsible for the narrowed band gap and the enhancement in solar absorption. With improved optical absorption in the visible range, higher surface area, open pore structure, and lower rate of electron−hole recombination of the defective g-C₃N₄, it leads to higher photocatalytic activity as compared to pristine g-C₃N₄.

1. Theoretical Evidences Behind Bifunctional Catalytic Activity in Pristine and Functionalized Al₂C monolayer, R Almeida, A Banerjee, S Chakraborty, J Almeida, R Ahuja, ChemPhysChem, (2017).
2. Rationalizing Hydrogen and Oxygen Evolution Reaction Activity of Two-dimensional Hydrogenated Silicene and Germanene, C. Rupp, Sudip Chakraborty, J. Anversa, R. Baierle, R. Ahuja, ACS Appl. Mater. Interfaces, 8, 1536 (2016).
3. The effect of impurities in ultra-thin hydrogenated silicene and germanene: A first principles study, C. Rupp, Sudip Chakraborty, R. Ahuja, R. Baierle, PhysChemChemPhys, 17, 22210 (2015).
4. A Comparative Study of Hydrogen Evolution Reaction on WS2 and PtS2 pseudo-monolayer: Insight based on Density Functional Theory, S. H. Mir, Sudip Chakraborty, J. Warna, S. Narayan, P. C. Jha, P. K. Jha, R. Ahuja, Catalysis Science & Technology 7, 687-692 (2017).
5. Two-dimensional Boron: Lightest Catalyst for Hydrogen and Oxygen Evolution Reaction, S. Mir, Sudip Chakraborty, P. K. Jha, J. Warna, H. Soni, P. Jha, R. Ahuja, Applied Physics Letters, 109, 053903 (2016).
6. Defect Engineered g-C3N4 for Efficient Visible Light Photocatalytic Hydrogen Production, Q. Tay, P. Kanhere, C. Ng, S. Chen, Sudip Chakraborty, A. Huan, T. Sum, R. Ahuja, and Z. Chen, Chemistry of Materials, 27, 4930 (2015).

Crystal structure prediction from first-principles: random search and metadynamics simulations

The properties of a material are highly dependent on the crystal structure. We develop ab initio theory capable to predict new structures, utilizing the search tools to explore the configurational space based on genetic algorithm methods, random search methods, data mine approaches, topological modeling methods, and metadynamics. We employ this method to study the structure of the novel complex light metal hydrides as well as to investigate the H₂ dissociation on the metal hydride surfaces. Predicting crystal structures is a computational time-consuming task, therefore we spend a lot of time on optimizing the computational methods.

1. Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2: A High Voltage Organic Cathode for Sodium Rechargeable Batteries, Rafael B Araujo, Amitava Banerjee, Rajeev Ahuja, J. Phys. Chem. C, 2017, 121 (26), pp 14027–14036

Hydrogen storage

Light-metal hydrides and high-surface area materials are considered as promising hydrogen storage systems. We explore both kinds in terms of their electronic structure with the aim of understanding existing hydrogen desorption mechanisms, and possibly predict ways to improve their functionality.

The understanding of H₂ dissociation on metal surfaces is a key point toward the design of suitable hydrogen storage materials. We calculate the H₂-dissociation energy barriers with the Nudged Elastic Band Method and investigate the effect of impurities on these barriers. We aim on catalysts design that fasten the H-sorption reactions in novel hydrogen storage materials.

An extensive review on Hydrogen Storage Materials for stationary and mobile applications has been published recently [3]. We have also shown the hydrogen storage enhancement in 2D materials like silicene and its hydrogenated counterpart [4] and hydrogen desorption from MgH2 [5].

1. Nanostructured materials for solid-state hydrogen storage: A review of the achievement of COST Action MP1103. Callini, E., Aguey-Zinsou, K., Ahuja, R., Ramon Ares, J., Bals, S. et al. International journal of hydrogen energy, 41(32): 14404-14428, 2016.
2. Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art. Lai, Q., Paskevicius, M., Sheppard, D., Buckley, C., Thornton, A. et al. ChemSusChem, 8(17): 2789-2825, 2015.
3. Hydrogen storage materials for mobile and stationary applications: Current state of the art, Q. Lai, A. Thornton, M. Hill, Z. Haung, H.K. Lui, Z. Guo, M. Paskevicius, D. Sheppard, C. Buckely, A. Banerjee, Sudip Chakraborty, R. Ahuja, K.F. Aguey-Zinsou, ChemSusChem (Review), 8, 2789 (2015).
4. Functionalization of hydrogenated silicene with alkali and alkaline earth metals for efficient hydrogen storage, T. Hussain, T. Kaewmaraya, Sudip Chakraborty, R. Ahuja, PhysChemChemPhys, 15, 43, 18900 (2013).
5. Improvement in Hydrogen Desorption from β and γ-MgH2 upon Transition Metal Doping, T. Hussain, T. A. Maark, Sudip Chakraborty, R. Ahuja, ChemPhysChem, 16, 12, 2557 (2015). (Selected Cover Article).

Molecular electronics

Molecular electronics is a rapidly developing research field at the interface of physics, chemistry, and engineering, in which electron transport through molecules is investigated. The project involves design and ab initio simulations of molecular structures, metal and semiconductor surfaces and molecular adsorption applied to molecular electronics, biological and nano-sensors and synthesis of novel materials. Our research is performed within the environment of the Uppsala University UniMolecular Electronics Center (U³MEC) which focuses on molecular electronics based on single or small assemblies of molecules.

Organic batteries

Organic based battery materials can be produced from biomass and are expected to have a significantly lower environmental footprint from raw material extraction and material processing. Current organic matter based alternatives offer capacities comparable to their inorganic counterparts but in most cases they suffer from poor cycling stability, low conductivity or large polarization losses. In this project the combination of a conductive polymer backbone with high capacity redox groups is studied to overcome capacity fading due to dissolution as well as conductivity pathways through the material.

1. Assessing the electrochemical properties of polypyridine and polythiophene for prospective applications in sustainable organic batteries. Rafael B Araujo, Amitava Banerjee, Puspamitra Panigrahi, Li Yang, Martin Sjödin, Maria Strømme, C. Moyses Araujo, Rajeev Ahuja. Physical Chemistry Chemical Physics 19 (4), 3307-3314
2. Designing strategies to tune reduction potential of organic molecules for sustainable high capacity batteries application. Rafael B Araujo, Amitava Banerjee, Puspamitra Panigrahi, Li Yang, Maria Strømme, Martin Sjödin, Carlos Moyses Araujo, Rajeev Ahuja. J. Mater. Chem. A, 2017, 5, 4430-4454

Solar cell

The Organic–Inorganic hybrid perovskites have opened new avenues to develop low cost and high efficiency photovoltaic devices. Perovskites with general formula MAX3 (M=Organic part; A=Pb, Sn; X= Halogens) have attracted significant attention as efficient light harvesters. In particular, CH3NH3PbI3 has been intensely studied over the past couple of years for solar cell applications. Solar cells based on the hybrid perovskites have shown efficiencies of more than 20%, claiming these materials as potential candidates for next generation solar devices. Lead based perovskite solar cells are relatively new devices and modeling of these materials is focused on understanding the materials properties. Additionally, searching Lead free hybrid perovskite is another interesting future challenge of this field. We also focus on stability of Guanidium (GA) based hybrid perovskites GAPbI3 and GAPbBr3 hybrid perovskite along with electronic properties and solar energy conversion efficiency. Further alloying of GAPbI3 will be considered to evaluate formation probability of intermediate alloy. The outcome is planned to be connected with the experimental observations to have a more impact in the scientific community.

1. Bromination Induced Stability Enhancement with Multivalley Optical Response Signature in Guanidinium [C(NH2)3]+ Based Hybrid Perovskite Solar Cells, Amitava Banerjee, Sudip Chakraborty, Rajeev Ahuja, Journal of Materials Chemistry A 5(35):18561-18568 (2017)
2. Substitution induced band structure shape tuning in hybrid perovskites (CH3NH3Pb1-xSnxI3) for efficient solar cell applications, P. Kanhere, Sudip Chakraborty, C. Rupp, R. Ahuja, Z. Chen, RSC Advances, 5, 107497 (2015)
3. Rational Design and Combinatorial Screening Approach for Lead free and Emergent Hybrid Perovskites, Sudip Chakraborty, W. Xie, N. Mathews, M. Sherburne, R. Ahuja, Mark Asta, S. G. Mhaisalkar, ACS Energy Letters 2, 837 (2017)

Solar fuel production (Photoelectrocatalysis)

A promising sustainable solution for solar energy harvesting and utilization is artificial photosynthesis: the sunlight is used to split the water molecules and subsequently reduce the CO₂, producing methane and methanol. We computationally design photoelectrocatalysts suitable for such application.

Topological insulators

Topological insulators attract increasing attention due to the novel quantum state based on quantum spin Hall effect and hence the potential applications in quantum computation and spintronics. We are extensively working on the pressure-induced topological insulating behavior in experimentally synthesized materials based on first principles electronic structure calculations. Ge2Sb2Te5 is one such interesting material where we have found topological insulating behavior under the external pressure and strain. [1, 2] GeTe/Sb2Te3 phase-change superlattice is another interesting material that shows topological insulating behavior. [3] Recently, we have demonstrated how the superconducting critical temperature can be tuned with the external high pressure in Sb2Se3 [4] and Sb2Te3 [5] topological insulators.

1. Pressure-induced topological insulating behavior in the ternary chalcogenide Ge2Sb2Te5, B. Sa, J. Zhou, Z. Song, Z. Sun, R. Ahuja, Physical Review B 84, 085130 (2011).
2. Strain-induced topological insulating behavior in ternary chalcogenide Ge2Sb2Te5. B. Sa, J. Zhou, Z. Sun, R. Ahuja, Europhysics Letters, 97, 27003 (2012).
3. Topological insulating in GeTe/Sb2Te3 phase-change superlattice B. Sa, J. Zhou, Z. Sun, J. Tominaga, R. Ahuja, Physical review letters 109 (9), 096802, 2012.
4. High pressure driven superconducting critical temperature tuning in Sb2Se3 topological insulator, J. Anversa, Sudip Chakraborty, P. Piquini, R. Ahuja, Applied Physics Letters 108, 212601 (2016).
5. Superconductivity in Topological Insulator Sb2Te3 Induced by Pressure, J. Zhu et al. Scientific Reports 3, 2016 (2013).

Full list of publications

Publications up to April 2015

Selected Publications

• Kotmool et al., High pressure-induced distortion in face-centered cubic phase of thallium PNAS, 113, 11143 (2016).
• Jiang et al., Tunable assembly of sp3 cross-linked three dimensional graphene monoliths Adv. Funct. Mater. 23, 5846 (2013).
• Sa et al., Topological insulating in GeTe/Sb2Te3 phase-change superlattice Phys. Rev. Lett. 109, 96802 (2012).
• Mao et al., Electronic dynamics and plasmons of sodium under compression PNAS (2011).
• Århammar et al., Unveiling the complex electronic structure of amorphous metal oxides PNAS (the Proceedings of the National Academy of Sciences, USA) 108, 6355 (2011).
• Krisch et al., Phonon Spectra for a Anomalous Elemental Metal: Cerium PNAS (the Proceedings of the National Academy of Sciences, USA) 108, 9342 (2011).
• Sun et al., Pressure-induced reversible amorphization and an amorphous-amorphous transition in Ge2Sb2Te5 phase-change memory material PNAS (the Proceedings of the National Academy of Sciences, USA) 108, 10410 (2011).
• Li et al., Rhodium dihydride (RhH2) with high volumetric hydrogen density Proc. Natl. Acad. Sci. USA 108, 18618 (2011).
• Kim et al., Predicted formation of superconducting platinum-hydride crystals under pressure in the presence of molecular hydrogen Phys. Rev. Lett. 107, 117002 (2011);
  highlighted in APS Physics, Editor's Suggestion.
• Ahuja et al., Relativity and the Lead-Acid Battery Phys. Rev. Lett. 106, 018301 (2011);
  selected as research highlights in Nature 469, 269 (2011) & The Economist, 398, No. 8716 pp. 75-76 (2011).
• Mattesini et al., Hemispherical anisotropic patterns of the Earth’s inner core Proc. Natl. Acad. Sci. USA 107, 9507 (2010).
• Kim et al., General trend for pressurized superconducting hydrogen-dense materials Proc. Natl. Acad. Sci. USA 107, 2793 (2010).
• Ding et al., The Importance of Strong Carbon-Metal Adhesion for Catalytic Nucleation of Single-Walled Carbon Nanotubes Nano Letters 8, 463 (2008).
• Ahuja et al., A new high-pressure structure in curium linked to magnetism Science 309, 110 (2005).
• Sharma et al., Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO Nature-Materials 2, 673 (2003).
• Schnadt et al., Experimental evidence for sub-3-fs charge transfer from an aromatic adsorbate to a semiconductor Nature 418, 620 (2002).
• Dubrovinsky et al., The Hardest Known Oxide Nature 410, 653 (2001).

Prof. Rajeev Ahuja

Contact Information

Office
Å13106

Telephone
+46 18 471 3626

Email
rajeev.ahuja@physics.uu.se