Tuesday, 9 January 2018

N8 Materials Modelling Meeting - York

The Annual N8 HPC/CCP5/UKCP, "New Horizons in Atomistic Simulations", one day network meeting, at York brought together experts in quantum and atomistic simulations of materials.

Predicted TEM diffraction pattern for Methylammonium Lead Iodide
Robyn Ward, presented her recent work, in collaboration with Christopher Handley, Colin Freeman, and John Harding, on the prediction of rare earth element dynamics within perovskite materials, and the prediction of transition electron spectra, and the determination of the magnitude and phase of the octahedral tilts in these simulations. This work is significant as it now allows us to connect simulation to experimental spectra, and offer insight into the atomic scale dynamics of these materials which is not seen by the experimental analysis techniques. 

Keynote presentations included:

Andrew Morris, from the Department of Metallurgy and Materials at the University of Birmingham presented his work on Ex nihilo Discovery and Design of Energy Materials. In particular Andrew focused on the use of computers to design new battery materials, and the use of quantum mechanical simulations to predict materials for the task rapidly. The challenge he presented is how to rapidly screen material structures and determine by simulation their battery properties (voltages and energy density). In particular Andrew makes use of AIRSS, ab initio random structure searching, which allows him to find the optimal crystal structure for a given stoichiometry for a novel material.

Steve Parker, from the University of Bath, presented his work on the atomistic simulation of interfaces. His main focus was on the role and composition of the interfaces in energy materials, and the mechanisms of thermal and atom transport. His simulations utilised both force fields and quantum mechanics to perform multiscale modelling. Using these methods he demonstrated the ability of simulations to predict the morphology of surfaces and in turn nano-particles. One important issue was the influence of impurities upon oxygen diffusion across grain boundaries. This is relevant to improving the lifetime of the nuclear fuel uranium dioxide. A future challenge is to investigate the heterointerfaces which are significant when we consider capacitor materials that form a core-shell structure.

Dominik Jochym, from the STFC Rutherford Appleton Laboratory presented some exciting work on computational Muon-Spin simulation by Density Functional Theory. Muons allow for the probing of the electron density and spin states, and for probing the magnetic fields of novel materials. The capability of predicting from ab initio such spectra opens up new avenues for understanding the local chemistry of materials and how we might design materials for future technological challenges.










Thursday, 21 December 2017

Cold Sintering Processing - What is it?




PhD Student Sinan Faouri briefly gives us an overview of Cold Sintering Processing, a novel technique for the processing of functional materials that addresses the energy cost of manufacturing these materials.

Sintering is a thermal treatment process of forming a dense bulk solid material by heat or pressure before reaching its melting point [1,3]. The conventional sintering process is a high temperature sintering method where powders are heated between 50-75% of melting temperature to > 95% theoretical density [2]. Heating the starting materials to high temperatures facilitates the motion of atoms, enabling the homogenisation of the bulk solid [5].

Cold sintering processing (CSP) is a novel technique developed recently to achieve dense ceramic solids at extremely low temperatures ( < 180 ℃ ). across a vast variety of elements and composites [3]. The process includes using aqueous-based solutions (eg: water) as transient solvents to aid densification by a non-equilibrium mediated dissolution–precipitation process [4].

In order to provide a good environment and conditions for precipitation and recrystallization in hydrothermal reactions, a convenient aqueous solution should be chosen carefully which will be also significant in reducing sintering temperature [5].

To achieve densified bulk materials, some additional characteristics to the pre-dominance diagrams are used when studying CSP effective factors as shown in figure (1) [5].






    


Figure 1: Flowchart summary of CSP stages



Figure (1) shows a flowchart for the possible roots of CSP from particle rearrangement to densification. The internal characteristics that affect CSP are the material’s composition, crystal structure, particle size and solubility in water [5]. Some of the physical variables determining the kinetic processes for mass transport are the hot press pressure, sintering temperature, time of sintering, the rate of heating, and the atmosphere pressure [5]. Preparing a convenient aqueous solution is also critical as some other significant factors to CSP include the nature of the solute, the concentration of the solute and pH value. The latter can be studied via pre-dominance diagrams [5].

The dissolution nature plays a significant role in determining whether densification will eventually occur or not. If the materials dissolve equally with ease, a direct and simple CSP is possible, since the surface of material can be easily dissolved in water with a homogenous chemical stoichiometry [5]. However, no densification will occur if one material dissolves more easily that the other. This is because one material will form a passive surface [5]. Negligible dissolution can work well in CSP if a saturated solution is added that targets the chemical compounds of the material to be densified [5].

The next steps in CSP are evaporation of the liquid, the hydrothermal crystal growth (in the case of water as a solvent) or formation of a glass/intermediate phase, and eventually grain growth and densification or recrystallization of a glass where it gets ejected as shown in CSP flowchart in figure (1) [5].





References

2.      Dr. Jing Guo, Dr. Hanzheng Guo, Amanda L. Baker, Prof. Michael T. Lanagan, Dr. Elizabeth R. Kupp, Prof. Gary L. Messing, Prof. Clive A. Randall. Cold Sintering: A Paradigm Shift for Processing and Integration of Ceramics. Volume 55, Issue 38 September 12, 2016. Pages 11457–11461
3.      Hanzheng Guo, Jing Guo,  Amanda Baker, and Clive A. Randall. Hydrothermal-Assisted Cold Sintering Process: A New Guidance for Low-Temperature Ceramic Sintering. ACS Appl. Mater. Interfaces 2016, 8, 20909−20915
4.      Jing Guo, Amanda L. Baker, Hanzheng Guo, Michael Lanagan, and Clive A. Randall. Cold Sintering Process: A New Era for Ceramic Packaging and Microwave Device Development.  J. Am. Ceram. Soc., 1–7 (2016)
5.      Hanzheng Guo, Amanda Baker, Jing Guo, and Clive A. Randall. Cold Sintering Process: A Novel Technique for Low-Temperature Ceramic Processing of Ferroelectrics. J. Am. Ceram. Soc., 1–19 (2016)

Friday, 3 November 2017

Energy of the Future - Solid Oxide Fuel Cells

FMD PhD student, Julia Ramirez Gonzalez gives us an overview of how Solid Oxide Fuel Cells operate and the importance of such materials in meeting future energy production challenges.

Can you imagine our daily life without electricity? Maybe we can deal with it for a couple of hours, but this commodity has become one of the engines of our generation [1]. Nevertheless, the environmental implications of producing energy by fossil fuel combustion, is the driving force to look for more efficient and environmentally friendly alternatives of electricity generation.

Fuel cells are one of the alternatives. These devices generate electricity by an electrochemical reaction of gaseous reactants. One of the reactants is the oxygen in the air, and the other is hydrogen or a hydrocarbon [2]. The configuration of this devices resembles a sandwich. It has two electrodes, one in contact with fuel (anode), and the other in contact with oxygen (cathode): These two interfaces are separated by and electrolyte. There are many types of fuel cells, which are classified by its type of electrolyte, such as polymer electrolyte membrane (PEM), alkaline (AFC), phosphoric acid (PAFC), molten carbonate (MCFC), and solid oxide (SOFC) [3]. Each type differs in its operation temperatures, useful fuel, efficiency and therefore its applications.

Research on SOFC showed that these materials can work with higher hydrocarbons, giving them the advantage of fuel flexibility. And the most important feature is that all of its components are solid, which avoids the risk of spillages, gives it the freedom for stacking configuration, and it is a quiet system as it does not have any moving parts [2][4] . 

But how does it work? On one side of the cell there is a high concentration of oxygen and on the other side there is none. An electrical potential gradient across the electrolyte is built up. However, the electrolyte does not allow electrons or gas to flow through, but its crystal structure has oxygen vacancies, which allows the migration of oxygen ions. Therefore, at the three-phase boundary, cathode-electrolyte-air, oxygen will be reduced, by obtaining electrons from the cathode [2], Equation 1. 




Eq. 1
Thus, oxygen ions can hop through the electrolyte and can reach the anode-electrolyte-fuel boundary, where the fuel oxidizes; where the products will be steam and electrons, Equation 2 [2].




Eq. 2


If the anode and cathode are connected by an external circuit, the cycle is repeat again as long as the two gases are present, and this is how electricity can be harvested through the external circuit. As shown in the video. 







These devices operate in the temperature range between 500-1000°C, which adds challenges to the material requirements. The materials need to have chemical stability, to avoid reaction with the reactants, a similar thermal expansion coefficient, to reduce the possibility of cracks during cycling; strength and toughness, no one likes a broken device; but also, it has to be easy to fabricate and have a low cost [4].

As you can see there are many requirements, but material scientists like these challenges and have come up with several options.

Yttria-stabilised zirconia is the most widely used as an electrolyte, which is zirconia doped with yttria (Zr1-xYxO2-x/2; x: 0.08). It can also be doped with calcium oxide, magnesium oxide, scandium oxide, neodymium oxide and ytterbium oxide. In addition, cerium oxide doped with samarium (SDC), gadolinium (GDC), and calcium (CDC); lanthanum gallate; bismuth yttrium oxide; barium cerate and strontium cerate, can be also used. The reason of the high operation temperatures of these devices is to promote the oxide ion conduction within the electrolyte [4].

Both electrodes have to be able to distribute the hydrogen and oxygen respectively, serve as catalysts and allow the flow of electrons. Therefore, the anode is a porous ceramic-metallic composite. The metal provides the electronic conduction pathway for the electrons, the ceramic made from the same material as the electrolyte assures a similar thermal expansion coefficient and good compatibility. The popular choice is Ni-YSZ, but there is also Ni-SDC and Ni-GDC [4]. 

For the cathode also a porous structure to allow the flow of gas usually made from a perovskite-type lanthanum strontium manganite (LSM), and lanthanum calcium manganite (LCM); also provides a similar thermal expansion. It is been discovered that by making a composite of perovskite and electrolyte increases the active sites for the electrochemical reactions [4]. 

These electricity generation systems have many possibilities and applications. It can be used as a combined heat and power plant, distributed generation, but also used in remote areas as the generation can be at the point of consumption, reducing the transmission costs. It has an efficiency of ~60% [3]. From an environmental point of view the CO2 emissions will be considerable reduced, Mike Manson an expert in SOFC from Manchester said to The Guardian that a 35% reduction in CO2 emission could be possible using this technology, comparing it with consuming electricity from gas power plant and hot water from a boiler [5]. There is also the idea of a hybrid/gas turbine cycle, to take advantage of the high temperatures of the existing power plants [3]. There are many companies that see the potential of this technology and have and R&D area dedicated to it, as Rolls-Royce and Bloomenergy [6][7]. 

In summary, SOFC are a great alternative for the generation of electricity, further research needs to be done to reduce its operations temperatures, but it represents a step closer to a greener electricity technology era.

[1]          “Key world energy statistics,” Int. Energy Agency, 2017.
[2]          R. J. Kee, H. Zhu, and D. G. Goodwin, “Solid-oxide fuel cells with hydrocarbon fuels,” Proc. Combust. Inst., vol. 30, pp. 2379–2404, 2005.
[3]          D. of Energy, “Comparison of Fuel Cell Technologies | Department of Energy.” [Online]. Available: https://energy.gov/eere/fuelcells/comparison-fuel-cell-technologies. [Accessed: 01-Nov-2017].
[4]          A. B. Stambouli and E. Traversa, “Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy,” Renew. Sustain. Energy Rev., vol. 6, pp. 433–455, 2002.
[5]          D. Clark, “Manchester Report: Ceramic fuel cells | Environment | The Guardian,” The Guardian, 2009. [Online]. Available: https://www.theguardian.com/environment/2009/jul/13/manchester-report-fuel-cells. [Accessed: 30-Oct-2017].
[6]          Rolls-Royce, “Rolls-Royce grows global fuel cells capability with US acquisition – Rolls-Royce.” [Online]. Available: http://www.rolls-royce.com/media/press-releases/yr-2007/rr-grows-global-fuel-cells.aspx. [Accessed: 02-Nov-2017].
[7]          Bloomenergy, “Fuel Cell Energy - Solid Oxide Fuel Cells SOFC | Bloom Energy.” [Online]. Available: http://www.bloomenergy.com/fuel-cell/solid-oxide/. [Accessed: 02-Nov-2017].



Friday, 6 October 2017

Sustainability of Operation Research and Management

Lucy receiving her award from the Conference Chairs,
Prof. Ying Fan and Prof. Ernesto DR Santibanez.
The Second Global Conference on The Applications of Operations Research and Operations Management for Sustainability (GCTAOS) was held from the 6th to the 8th September at Beihang University in Beijing, China.

Lucy Smith was able to attend after receiving the Research Student’s Travel Grant from the Worshipful Company of Armourers and Brasiers and present research on the life cycle assessments of high and intermediate temperature Solid Oxide Fuel Cell material structures. In addition to this, the Advance Resource Efficiency Centre, led by Prof. Lenny Koh, were able to showcase the SCEnATi (Supply Chain Environment Analysis Tool) to an international audience.

A wide range of key note speakers gave their thoughts on issues such as smart systems, relief chain management, energy investment and technology evaluation. This paved the way for an interesting collection of presentations on similar topics from other academics.

The conference was attended by academics, student and industry representatives allowing for interesting discussion and future collaboration opportunities.

Lucy was awarded the Best Paper Award, in recognition of the professional excellence of the paper for ‘Life cycle assessments and environmental profile evaluations of high and intermediate solid oxide fuel cells’ by L. Smith, F. Yang, T. Ibn. Mohammed, I. M. Reaney, D. C. Sinclair and S. C. L. Koh.


Monday, 11 September 2017

11th EUCO-TCC - Barcelona

11th European Conference on Theoretical and Computational Chemistry 3rd-7th of September, Barcelona, Spain

The central courtyard of the institute bathed in the glorious Barcelona sun.
Hosted at the Institute for Catalan Studies (IEC), in Barcelona, a majestic building built in the 17th century, the IEC, along with EuCheMS (European Chemical Services), hosted the 11th European Conference on Theoretical and Computational Chemistry.

As a computational chemist working in material science this was the perfect opportunity to network with a diverse group of researchers, who all share the same interest in simulating chemistry at the atomic level. Topics included solvation, catalysis, biochemical reactions, and material science. Given the nature of the conference there was also a focus on the techniques being developed to simulate these systems, such as density functional theory, molecular dynamics, and machine learning.

Highlights for myself included the work by Matti Hellstroem, from Georg-August-Universitat Goettingen, who works for Jorg Behler. Matti presented recent work on simulations of water and sodium hydroxide using the Behler type neural network potentials. The simulations represent how mature these methods are, though also demonstrate that there are still some hurdles to overcome. Mattis’ demonstration of the process of proton transfer through the system, and the importance of the types of clusters that form locally about sodium to enable the making and breaking of bonds.

The SnIP double helix structure
Tom Nilges from the Technical University of Munich, presented his work on the curious inorganic double helix SnIP semiconductor that have potential as a functional material. The double helices consist of  twisted chains of tin iodide (SnI+) intertwined phosphide (P–) chain. The band gap of the material, and mechanical strength, lends itself well to potential solar cell applications, and the next steps are exploring the analogues of the material.

The keynote lecture, and EuChemMS award winner, Ursula Roethlisberger, from Ecole Polytechnique Federale de Lausannae, Institut des Sciences det Ingenierie Chimiques, presented her novel work combining machine learning and computational chemistry. Primarily her work utilises DFT calculations to generate high quality, and well sampled training data, that can then lead to quick hits for discovering molecules with ideal properties. I also took the time to chat to her regarding her work on simulating MALI and related photovoltaic materials, and how she is using machine learning to search the structure space of these materials.

Overall the conference was an excellent opportunity to connect with fellow computational chemists, some who are familiar faces, and to present the research from the SUbST group to a wider audience.

Tuesday, 1 August 2017

Next Generation Force Fields - Designing force fields in an age of cheap computing - Perspective


This past week at Halifax Hall, the University of Sheffield was host to a workshop of experts and world leaders on computational chemical simulations. The aim of the workshop was to present the advances in this field, for the atomistic simulation of bulk materials, surfaces, interfaces, solutions, biomolecules, and more. It was also a chance for the delegates to discuss the next challenges facing the discipline given the increasing power of computers.

Chaired by Dr Colin Freeman, Dr Chris Handley, and Prof. John Harding, the invited speakers included Prof. Nohad Gresh, Prof. Jorg Behler, Prof. Bernd Hartke, Prof. Stefan Goedecker, Dr Peter Brommer, Prof. Paul Popelier, Dr Paul Richmond, and Dr David Mobley.

From the talks and contributions it was clear there are common challenges that all researchers face in the coming years. In terms of the technologies available, the push to GPU computing, driven by machine learning, means that the software used for chemical simulations must be reassessed if they are going to exploit the potential computer power on offer.

Another key issue is how machine learning is used to design new chemical simulations. Machine learning, such as neural networks, or Gaussian process regression, can be trained to extract the underlying non-linear relationship between atomic positions and some property of the system (we are often looking for the relative energy differences for a given configuration of atoms, and the associated forces as these are used to drive the molecular dynamics simulation). The machine learning methods use for training data quantum mechanical simulations. The danger however, is that while the non-linear model is discovered, we retain no information about the true physics at play, which is critical if we wish to have a deeper understanding of the interactions at play within a simulation.

Physics driven models are the alternative, but these models rely on knowing the proper functional forms for describing the interactions between atoms. Classical force fields often use functional forms that have been used over the decades that were initially chosen for computational convenience. Going forward our choice of functional forms used should be reassessed given that computational power is no longer an issue.
The effect of d-electrons on atomic configurations is an
electronic orbital effect and one that is not captured in
traditional force fields.


Related to the two previous points, is one of transferability. Force fields are often fitted, and thus simulate well, a particular chemical system in certain conditions. Knowing the limits of a particular model, and also how badly it will perform when if such conditions are met, is knowledge not often provided when a force field is published. Care must be taken that a model is capable of representing all the relevant physics that describes the system. There may be underlying physics not accounted for by the model explicitly, which hinders the transferability of the model when applied to similar chemical systems.

Transferability, data driven models, and physical driven models, ultimately are tied to how we partition the energy of a force field. By this we mean, how do we cut up the force field into different interactions, and how we even define these interactions. How do we define bonds? Can we accommodate reactivity into our models? What of electrostatic interactions? Should we use multipolar descriptions of charge?

Fitting and automation can be reliant on "wizardry". By that we mean, "to use a force field, and to design derivatives of it, how much highly specific expertise do we require - is the force field only really usable by those who designed it?" This is not ideal, as this slows the development of new models, and also hinders insight into why models work and fail for particular simulations.

Finally there is the topic of the reference data. More often than not, force fields are fitted to quantum mechanically generated reference data. We assume that this data is the "truth". Though, while many of the programs that perform quantum mechanical calculations have over time become closer in agreement with each other, they all share the same issue of accuracy. The fitting of force fields is thus a cyclic issue, where a reassessment of the training should be performed periodically.

Going forward the issues raised during the workshop will help inform CECAM and EU funding on future force field development and how it plays a critical role in computational chemistry, even in an age of high performance computing.

As organisers of the workshop, Colin, Chris and John would like to thank CECAM and CCP5 for the generous funding for the event, the invited speakers for their informative presentations, and the attendees whom we hope will have taken away new ideas and new future collaborations.



Conference Attendees

Wednesday, 12 July 2017

Advanced Resource Efficiency Centre (AREC) Showcase in the European Parliament




On 27th June 2017, the AREC team, led by Professor Lenny Koh, showcased its research and impact at the ‘Pathways to Global Policy, Industry and Societal Impact on Resource Efficiency and Sustainability’ event at the European Parliament, Brussels.

The event was hosted by John Procter, MEP for Yorkshire and Humber, through the White Rose Brussels group (https://brussels.whiterose.ac.uk/) and attended by policy makers, industry representatives and academics. The main aims of the event were to present the impact of AREC’s research and develop potential future connections to further extend AREC’s impact reach.


The event included a panel discussion from Professor Lenny Koh, Professor Panos Ketikidis (Vice Principal: Research and Innovation, International Faculty of the University of Sheffield in Thessaloniki, Greece), Jay Sterling Gregg (European Energy Research Alliance, representing “e3s”, Brussels, Belgium), Philippe Micheaux Naudet (Association of Cities and Regions for Sustainable Resource Management – ACR, Brussels, Belgium) and Maria Rincon-Lievana (Policy Officer – Circular Economy Action Plan, DG Environment, Brussels Belgium).

Professor Koh presented the SCEnATi (Supply Chain Environmental Analysis) tool to the group of industry specialists and academics. The SCEnATi tool is used within the FMD group to produce comparative hybrid life cycle assessments of functional materials and devices.

Professor Koh commented “Being resource efficient and sustainable should be embedded as a new norm in every supply chain, every business and every organisation whether these are public, private or third sectors. Policies that support this goal, industry practices that promote such implementation, technologies/tools that enable this achievement, and research and innovation that underpin the delivery of this new norm would lead to positive societal, economic and environmental impact”.


For further information on the SCEnATi tool please contact: Lucy Smith, lsmith17@sheffield.ac.uk