1. Can you briefly describe what you achieved in this article? 

In this study we applied the sol-gel strategy to synthesise and characterise an organic/inorganic hybrid electrolyte system composed of a di-urea cross-linked poly(oxyethylene) (POE)/siloxane (di-ureasil) matrix and a wide concentration range of potassium triflate (KCF₃O₃). The sample with n = 20 (n is the number of oxyethylene units per K⁺ ion) is transparent, flexible, amorphous and thermally stable up to about 220 ºC, has excellent electrochemical stability and exhibits the highest room temperature ionic conductivity (1.1 x 10^-5 Scm^-1 at 22 ºC). This encouraging set of properties induced us to use this material as electrolyte in the assembly of a prototype electrochromic device (ECD) based on two transparent electronically-conducting oxide films of gallium-doped zinc oxide (ZnO-Ga) coated on glass substrates and an electrochromic layer of tungsten trioxide (WO₃). This ECD, with interest for application in "smart windows", exhibits good electrochemical stability and demonstrates a memory effect. Its average transmittance in the visible region is ca. 90% in the coloured state and 85-95 % in the bleached state. The bleaching/colouring time was approximately 60 seconds. The reversible colour change was quantified on the basis of the Commission Internationale d'Eclairage (CIE) colour coordinates system. 

2. Could you explain the significance of your article to the non-specialist? 

Liquid and liquid-like electrolytes may be used in low surface area ECDs without significant electrolyte loss. However, in large area ECDs electrolyte leakage may damage the other components of the device, leading to early failure. This drawback may be elegantly overcome with solid polymer electrolytes (SPEs) prepared by the low-cost, versatile sol-gel method. At present the number of sol-gel derived SPEs that have been investigated in the literature is, however, low. The KCF₃SO₃-doped hybrid electrolyte with n = 20 fulfils the prerequisites of an electrolyte for ECDs (room temperature ionic conductivity of at least 1 x 10^-5 Scm^-1, high transparency and good mechanical, thermal, chemical and electrochemical stability). The encouraging performance of the prototype ECD provides motivation for future studies. 

3. What has motivated you to conduct this work? 

For more than a decade the groups from University of Trás-os-Montes e Alto Douro (Vila Real, Portugal), University of Minho (Braga, Portugal), Chalmers University of Technology (Göteborg, Sweden) and University of Aveiro (Aveiro, Portugal) have been involved in the study of the morphology, structure, thermal and electrochemical behaviour, luminescence and magnetic properties of di-ureasil-based systems, particularly of those incorporating mono-, di- and trivalent triflate salts. We have demonstrated that these hybrids are promising materials with foreseeable applications in the fields of solid state electrochemistry, optics and magnetism/biomimetism, being clearly one of the world team leaders on this subject. The present paper is part of a systematic investigation carried out during the doctoral studies of 1st author Sílvia C. Nunes. The unique properties of the KCF₃SO₃-doped di-ureasil with n = 20 allowed us to pass from the study of fundamental properties to the assembly of prototypes. 

4. Where do you see this work developing in the future? 

Sol-gel derived di-ureasil-based hybrid materials open good perspectives for the development of electrolytes in the context of ECD technology. We intend to continue our work in this fascinating and stimulating field of research. We have recently submitted another paper to the Journal of Materials Chemistry describing an analogous di-ureasil system in which we demonstrate that the room temperature ionic conductivity, one of the factors that limit the practical performance of SPEs in ECDs, may be further improved through the choice of the cation and particularly with the use of a so-called 3rd generation anion. We believe the future of ECDs incorporating hybrid electrolytes is indeed promising. 

5. Are there any particular challenges facing future research in this area? 

The goal of any researcher in the domain of materials science is to pass from the fundamental research stage to the application of new materials in prototype devices and ultimately to see the material reach commercialisation. Although the present work represents a proof of concept, it is clear that the performance of the ECD reported in the present study needs more complete characterisation. For instance, long-term device durability under a wide range of conditions (e.g., variable temperature and humidity) must be confirmed if architectural window applications are envisaged. 

Sílvia Cristina Claúdio Nunes (born in 1979) graduated in Industrial Chemistry at the University of Beira Interior (Portugal). In 2002, she moved to Universidade de Trás-os-Montes e Alto Douro (Vila Real, Portugal) and started work as a Science Research Grant holder in the investigation of gels with optical, magnetic and electrochemical properties. She is currently completing her PhD under the supervision of Professor Verónica de Zea Bermudez. Her research interests in the synthesis of organic-inorganic hybrid materials with multifunctional properties, self-assembly and infrared and Raman characterization, thermal analysis, structural studies and solid state chemistry. 

Verónica Cortés de Zea Bermudez (born in 1962) received her PhD in Electrochemistry from the Institut Polytechnique de Grenoble (Grenoble, France) in 1992. In 1993 she joined the University of Trás-os-Montes e Alto Douro (Vila Real, Portugal) as Assistant Professor where she assumed responsibility for the Chair of Materials Science in the Department of Chemistry. In 1998 she was promoted to Associate Professor. She has been co-director of the Chemistry Center of Vila Real (CQ-VR) since 2003. Her scientific interests have concerned the synthesis via sol-gel chemistry of organic/inorganic hybrids with applications in the domains of solid state electrochemistry, optics and magnetism. Her work has been specifically devoted to the analysis of the thermal, structural, electrochemical and infrared/Raman spectroscopic features of sol-gel derived poly(oxyethylene)/siloxane hybrids incorporating guest salts or lanthanide complexes. Recently she has begun research on the development of hierarchically structured alkyl/siloxane hybrid materials prepared by a combination of sol-gel chemistry and self-assembly routes. She published (or has in press) ca. 98 SCI papers (over 868 citations) and 1 patent application. 

Maria Manuela Silva obtained a Research Assistant position in the Department of Chemistry of the University of Minho (Braga, Portugal) in 1991. She received her PhD in Chemistry from the University of Minho in 1999 and was promoted to Assistant Professor at the same University. Her research activities focus on the synthesis and characterisation of solid polymer electrolytes (SPE) and their application in the domains of solid state electrochemistry (solid state batteries and electrochromic devices). She is also interested in the chemistry (synthesis via sol-gel) of silica-based organic-inorganic hybrid materials. 

Michael John Smith received his PhD in Solid State Electrochemistry from the University of St. Andrews (Scotland) in 1982. After completing post-doctoral fellowships sponsored by the Ministry of Defence (UK) and the Royal Society, he entered the Department of Chemistry of the University of Minho (Braga, Portugal) as Assistant Professor in 1984. Promotion to Associate Professor and Professor of Chemistry took place in 1995 and 2005 respectively. Since 1984 his scientific activity has evolved through vitreous solid electrolytes, solid solution electrodes and SPE. In recent years particular emphasis has been given to the electrochemical and thermal characterisation of SPE systems based on various guest salts and several polymeric matrices. Current interests are directed to the optimization of electrochemical and mechanical properties of SPEs for applications in batteries and electrochromic devices. 

Denis Ostrovskii received his PhD in Solid State Physics from the Institute of Semiconductors Physics (Kiev, Ukraine) in 1996. Between 1995 and 2007 he worked in the Material Physics group of Chalmers University of Technology (Gothenburg, Sweden). In 2007 he joined Solid State Spectroscopy group of Kyoto University (Japan). His main field of activity is vibrational spectroscopy (infrared and Raman). His main research interests are molecular level characterization of complex polymer-based systems ranging from irradiationally modified polymer membranes to low-concentration polymer solutions. Especial emphasis has been placed on ion and proton conducting materials for various electrochemical applications. An important aspect of this activity has been the development of advanced experimental arrangements/devices for materials characterization, such as the in situ spectroscopic study of a Li-ion battery or a fuel cell assembly under operating conditions, etc. Currently his research is directed towards the investigation of fundamental properties of coordination compounds, particularly the role of cooperative effects and elastic properties on the spin crossover phenomena in solids. 

Maria Rute de Amorim e Sá Ferreira André (born in 1974) was awarded her Ph.D. in Physics by the University of Aveiro (Aveiro, Portugal) in 2002 for her thesis on local structure and photoluminescence features of organic-inorganic hybrids modified by lanthanide ions. Since 2003 she has been working at the CICECO Associated Laboratory at University of Aveiro as Assistant Researcher. Her current scientific interests include local structure, photoluminescence features of sol-gel derived organic/inorganic hybrids and silicate materials incorporated lanthanide ions, lanthanide complexes and the modelling of the respective emission recombination mechanisms. Her interests are also related with wave guiding properties, photonics and integrated optical applications of organic-inorganic hybrids. She is co-author of over 80 papers. 

Luís António Ferreira Martins Dias Carlos (born in 1964) received his Ph.D. in Physics from the University of Évora (Évora, Portugal) in 1995 for his work on photoluminescence of polymer electrolytes incorporating lanthanide salts. In 1996 he joined the Department of Physics at the University of Aveiro (Aveiro, Portugal) as Professor Auxiliar. In 1998 was promoted to Professor Associado and in 2004 he completed "Provas de Agregação" in Physics. Currently, he is Full Professor. His current scientific interests include photoluminescence of (i) sol-gel derived organic/inorganic hybrids incorporated lanthanide ions, (ii) lanthanide-based micro and mesoporous silicate materials, (iii) lanthanide coordination complexes, and small-angle X-ray scattering of organic/inorganic nanostructured multifunctional materials. In 2004 he was awarded the Portuguese Science Foundation (FCT) prize for Scientific Excellence. He published (or has in press) over 190 SCI papers, with more than 1350 citations, and supervised(es) 11 post-docs and 13 Ph.D. students. He is a member of the Evaluation board for Materials Science Projects of FCT and on the editorial board of The Open Physical Chemistry Journal. 

João Carlos Matias Celestino Gomes da Rocha (born in 1962) is Full Professor of Inorganic and Materials Chemistry at the University of Aveiro (Aveiro, Portugal), correspondent member of the Lisbon Academy of Sciences and Director of the Centre for Research in Ceramics and Composite Materials-CICECO. He was awarded his Ph.D. in 1990 from the Department of Chemistry of Cambridge University, (Cambridge, UK) and did a one year post-doc in the same group. He is interested in: microporous, layered and dense silicates of transition metals and lanthanides (Ln) and their application in catalysis, gas sorption and separation, photoluminescence and magnetism; crystalline (MOFs) and amorphous organic-inorganic hybrids; solid-state NMR and X-ray diffraction. He published (or has in press) ca. 290 SCI papers, with ca. 3300 citations, and 2 patent applications. He is on the editorial board of Eur. J. Inorg. Chem. and Solid State NMR and is member of the Commission on Inorganic and Mineral Structures of the International Union of Crystallography, Portuguese and American Chemical Societies and Materials Research Society. In 2004 he received the Portuguese Science Foundation prize for Scientific Excellence. 

Alexandra Maria Ferreira Goncalves graduated in materials science at New University of Lisbon (NUL, Lisbon, Portugal) and has been researcher of Materials Researh Centre (CENIMAT) since 2001. She is currently completing her master of Food Technology under the supervision of Professor Elvira Fortunato. Currently interests are directed to the optimization of properties of inorganic solid electrolyte and electrochromic materials for applications in smart labels and electrochromic devices. 

Elvira Maria Correia Fortunato is Associate Professor in the Materials Science Department of the New University of Lisbon (Lisbon, Portugal) and has been director of the Materials Research Centre (CENIMAT) since 1998. A licenciate graduate in materials science (NUL), she received her PhD degree in 1995 (NUL) and her Aggregation (teaching certificate) in 2004 (NUL). Fortunato pioneered European research on thin-film transistors based on oxide semiconductors, demonstrating that oxide materials may be used as true semiconductors. Her recent accomplishments include the first ZnO-based transparent thin-film transistor (TTFT) deposited at room temperature by rf magnetron sputtering with high field-effect mobility. Fortunato's current interests are in the design, fabrication, conduction transport mechanisms and characterization of amorphous multicomponent oxide-based TTFTs. She is also interested in the development of novel electrochromic devices.