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Introducing the PLOS ONE Energy Materials Collection – Author Perspectives, Part 1

It is difficult to overestimate the importance of the role that advances within the science of energy materials may play in our lives over the next few decades. As the world grapples with the challenges of increasing energy demand and dynamic usage patterns, the community of scientists developing materials for future energy production, usage and storage are a vital part of building a sustainable future. In August of 2021, PLOS ONE published a new collection of Energy Materials papers, showcasing state-of-the-art research in this exciting field. We interviewed some of the authors whose research is part of this collection, in order to shed further light on the discoveries they have made and the challenges they continue to tackle.

Rosa Mondragón

I have a PhD in Chemical Engineering from Universitat Jaume I in Castelló (Spain). I defended my PhD thesis about spray drying of nanofluids in 2013 and that was my first experience with the amazing field of nanofluids. I am currently Associate Professor in the Fluid Mechanics area of the Department of Mechanical Engineering and Construction in Universitat Jaume I and I belong to the Multiphase Fluids research group. My research is focused on the synthesis and characterization of nanofluids for heat transfer, thermal energy storage and solar radiation absorption applications. I have been participant member of the COST Action “Overcoming Barriers to Nanofluids Market Uptake – NANOUPTAKE” (2016-2020) whose objectives were the development of a common understanding about nanofluids preparation and characterization and the acceleration of the transfer of knowledge from fundamental research to industrial applications.

Rosa Mondragon’s paper in this collection: Mondragón R, Sánchez D, Cabello R, Llopis R, Juliá JE (2019) Flat plate solar collector performance using alumina nanofluids: Experimental characterization and efficiency tests. PLoS ONE 14(2): e0212260. https://doi.org/10.1371/journal.pone.0212260

Can you tell us a bit about the beginning of this project that led to your PLOS ONE paper? If you weren’t involved in the study from the start, what was your first impression of the study?

RM: I began my research on nanofluids for heat transfer applications in 2010 but after some years doing experimental characterization of thermophysical properties at the lab scale (thermal conductivity, viscosity, specific heat, etc.) we needed to move towards the analysis of its use in real applications. The only difficulty was to find any research group having the suitable facilities to start a joint collaboration. Besides, most of the facilities required quite a big volume of fluids making also a challenge sending the nanofluid to a different research centre. Fortunately, we found out that the Thermal Engineering research group of our department had recently acquired a flat plate solar collector that could be used. That was the beginning of the project that led to the paper published and some lessons learnt.

What is it about nanofluids that make them such a good candidate for use in solar collectors?

RM: The term nanofluid was coined to refer to the mixture of nanoparticles dispersed in a base fluid with improved thermal properties, specifically thermal conductivity. This thermal conductivity enhancement achieved due to the higher thermal conductivity of the solid nanoparticles leads to an increase in the heat transfer capacity of the fluid and the efficiency of the solar collector. However, there are more variables involved in the process such as the decrease in the specific heat capacity or the increase in the viscosity. As a result, a combined experimental analysis of all the nanofluid thermophysical properties is necessary to ensure a better performance of the nanofluid in transferring the thermal energy obtained from the absorbed solar energy, compared to the base fluid. It is also worth mentioning that there exist a wide variety of nanoparticles with good thermal properties, inexpensive and non-toxic that can be selected.

Was there anything that surprised you during this study, or did everything go exactly according to plan?

RM: Of course not everything went exactly according to the plan but it comes with the experimental research. We had a previous experience using the nanofluid in a thermohydraulic loop and we knew that the compatibility with the materials in pipes and pumps was very important to avoid oxidation and corrosion. If the solar collector was made to transport water, the addition of the nanoparticles should not have caused any problem. However, the acidic conditions needed to stabilize the nanoparticles in water promoted the oxidation of the materials and the corrosion of the copper tubes. Moreover, the contact of the concentrated nanofluid with the hot surface of the tubes caused a deposition layer as is shown in the paper. As a result, the enhancement theoretically predicted for the solar collector efficiency was not achieved due to the thermal resistance caused by the nanoparticle layer. The nanofluid initially white became orangish after the tests which confirmed that is highly recommended to check the compatibility of the nanofluid with the materials of the experimental facilities to ensure a good performance and to achieve the best results.

Bernhard Springer

Bernhard Springer, M. Sc. is currently a research associate at University of Applied Sciences Landshut (UAS Landshut) and a PhD student at Technical University Munich (TUM). He studied physics at the TUM from 2011 and finished his Bachelor’s degree in 2015. From 2015 till 2017 he studied Applied and engineering physics at the TUM and finished with a Master’s degree. Since 2017 he is working as a research associate at the Technology Centre Energy affiliated to the UAS Landshut. In 2018 he started with his PhD studies at the chemistry department of the TUM. Since 2019 he is working with his colleagues on the Project “SpinnAP”. His fields of research include Electrospinning, Lithium-Ion-Batteries  and solid-state electrolytes.

Bernhard Springer’s paper in this collection: Springer BC, Frankenberger M, Pettinger K-H (2020) Lamination of Separators to Electrodes using Electrospinning. PLoS ONE 15(1): e0227903. https://doi.org/10.1371/journal.pone.0227903

Can you tell us a bit about the beginning of this project that led to your PLOS ONE paper? If you weren’t involved in the study from the start, what was your first impression of the study?

BS: The project leading to my publication is “Spinning Technologies for Advanced Battery Production” (SpinnAP) and is funded by the Bavarian Research Foundation. The project aims to improve lithium ion batteries, both liquid and solid electrolyte systems, using electrospinning. An example for such an improvement is to enable lamination on different separators using electrospinning, like described in my paper. In addition, suitable production processes as well as an improved nanofiber output for industrial applications are part of our development focus. To achieve this, we also develop our own high-output electrospinning machine within the frame of the project. We are supported by our project partners 3M Dyneon GmbH, AKE Technologies GmbH and Brückner GmbH with their respective expertise.

Electrospinning seems like a very promising method for the future of lithium ion batteries. What do you think are the main advantages this can bring to the consumer or user of lithium ion batteries?

BS: For lithium ion batteries using a liquid electrolyte, lamination can achieve two main advantages: First, lamination is able to improve the charge and discharge capability, as shown by Frankenberger et al (https://doi.org/10.1016/j.jelechem.2019.02.030). Unfortunately, not all separators are capable for lamination. Using electrospinning we want to enable lamination for all types of separators to combine the advantages of lamination with the advantages of the respective separators, e.g. lower production costs or safety enhancement. Second, lamination creates a firm connection between the electrodes and the separator. This can be positive for the production speed of the cells, since the individual layers can not be displaced during the following production steps. This can lead to an increased production output and more inexpensive battery cells.

As an early career scientist, how did you prepare yourself for the review process when submitting your first few papers? Is there anything you know now that you wish you’d known before that first submission?

BS: In preparation to my first submission, I intensely discussed with my colleagues from the Technology Center Energy, a research facility of the University of Applied Sciences Landshut, about their previous experiences. In addition, I read the guidelines provided by PLOS regarding the submission process carefully.

What hopes do you have for the future of research into sustainable energy solutions? Do you have a clear sense at this point where you would like to go in your career?

BS: I do not have a clear sense where I would like to go in my career yet, but I do intend to pursue an industrial career path. At the moment I strongly focus on my dissertation.

David López Durán

David is Professor in the Department of Physics of the University of Córdoba (Spain). He obtained the MSc degree in the Complutense University of Madrid (Spain), and his PhD in the Fundamental Physics Institute (FPI) of the Spanish National Research Council (SNRC) in Madrid. He has developed his work in La Sapienza, University of Rome (Italy), Argonne National Laboratory, IL (USA), and CIC Nanogune, San Sebastián (Spain), among others. His research topics are: weakly bound molecular clusters, collisions of molecules at low and ultralow temperatures, and potential energy surfaces of small molecular aggregates. Some recent scientific contributions are: (1) “The CECAM electronic structure library and the modular software development paradigm”, J. Chem. Phys. 153, 024117-1/024117-23 (2020) article promoted as part of the “Chemical Physics Software Collection” of the Journal of Chemical Physics (September 2021), and (2) interview in TV (May 2021): https://www.youtube.com/watch?v=HJ71JPVdhtw

David López Durán’s paper in this collection: López-Durán D, Plésiat E, Krompiec M, Artacho E (2020) Gap variability upon packing in organic photovoltaics. PLoS ONE 15(6): e0234115. https://doi.org/10.1371/journal.pone.0234115

Can you tell us a bit about the beginning of this project that led to your PLOS ONE paper? If you weren’t involved in the study from the start, what was your first impression of the study?

DL: This article came up as part of the work supported by the “Centre Européen de Calcul Atomique et Moléculaire” (CECAM), which is formed by several institutions in Europe and funds multiple activities, one of them a partnership between some of these institutions, network called “E-CAM”, and to which I belonged. One of the targets of E-CAM was to bring closer the academic and the industrial worlds through several initiatives, for instance a collaboration between two nodes with different profiles. This manuscript came up due to the work developed in my former institutions, CIC Nanogune (San Sebastián, Spain) and University of Barcelona (Barcelona, Spain), and the industrial partner Merck Chemicals Ltd. (Southampton, United Kingdom). The climate change and global warming are, unfortunately, a hot topic in science and we tried to contribute to its solution studying organic photovoltaics. Specifically, we addressed the problem of the arrangement of the molecules in order to maximize the electric current.

How do you think that the results you obtained in this study will impact the development of organovoltaics in the future?

DL: The design of a device to generate energy based in any kind of photovoltaic molecules must include the analysis of several factors in order to obtain the maximum performance. One of them is the HOMO-LUMO band gap of the constituent molecules, which are usually a donor-acceptor pair, magnitude which dramatically depends on the geometry arrangement of these pairs. As this gap becomes smaller, the electronic transference is easier and, therefore, the generation of electric current. But to be small this gap is necessary that the molecules were arranged in a convenient way one with respect to the others, i. e. with their active electronic areas clearly accessible. In this work we study a great number of configurations of an organic donor-acceptor pair in gas phase, as previous step before moving to the solid phase of a real device. Our study will impact the subsequent research because now there are available some hints about the optimal geometry configuration of the molecules.   

Was there anything that surprised you during this study, or did everything go exactly according to plan?

DL: The donor-acceptor pair that we studied is 4modBT-4TIC, molecules which are based on others extensively employed in the organic photovoltaics field. We found several surprises, the first one being that the variation of the gap in all the studied configurations was around 0.3 eV, which is significant considering that the gaps in this context are not larger than 1 eV. The second surprise was the lack of correlation between the binding energy of the pair and the HOMO-LUMO band gap: the arrangement with the maximum binding energy was not that with the maximum gap and, in turn, the configuration with the maximum gap was not that with the maximum binding energy. A third surprise was that the arrangement with the maximum binding energy were much more bound that the rest. All these findings pose new questions and, therefore, further research is needed.

What’s the most unusual or unexpected collaboration you’ve been a part of during your research?

DL: I have never had an unusual or unexpected collaboration during my scientific career. However, I would like to mention that I feel very lucky because I have known people from all over the world. These experiences enrich you and make you think in a more broad and comprehensive way.

Disclaimer: Views expressed by contributors are solely those of individual contributors, and not necessarily those of PLOS.

Featured image: https://doi.org/10.1371/journal.pone.0243296

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