David Aili
Technical University of Denmark
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Featured researches published by David Aili.
Energy and Environmental Science | 2015
Jiangshui Luo; Annemette Hindhede Jensen; Neil R. Brooks; Jeroen Sniekers; Martin Knipper; David Aili; Qingfeng Li; Bram Vanroy; Michael Wübbenhorst; Feng Yan; Luc Van Meervelt; Zhigang Shao; Jianhua Fang; Zheng-Hong Luo; Dirk E. De Vos; Koen Binnemans; Jan Fransaer
1,2,4-Triazolium perfluorobutanesulfonate (1), a novel, pure protic organic ionic plastic crystal (POIPC) with a wide plastic crystalline phase, has been explored as a proof-of-principle anhydrous proton conductor for all-solid-state high temperature hydrogen/air fuel cells. Its physicochemical properties, including thermal, mechanical, structural, morphological, crystallographic, spectral, and ion-conducting properties, as well as fuel cell performances, have been studied comprehensively in both fundamental and device-oriented aspects. With superior thermal stability, 1 exhibits crystal (phase III), plastic crystalline (phase II and I) and melt phases successively from −173 °C to 200 °C. Differential scanning calorimetry and temperature-dependent powder X-ray diffraction (XRD) measurements together with polarized optical microscopy and thermomechanical analysis reveal the two solid–solid phase transitions of 1 at 76.8 °C and 87.2 °C prior to the melting transition at 180.9 °C, showing a wide plastic phase (87–181 °C). Scanning electron microscopy displays the morphology of different phases, indicating the plasticity in phase I. Single-crystal XRD studies reveal the molecular structure of 1 and its three-dimensional N–H⋯O hydrogen bonding network. The influence of the three-dimensional hydrogen bonding network on the physicochemical properties of 1 has been highlighted. The temperature dependence of hydrogen bonding is investigated by variable-temperature infrared spectroscopy. The sudden weakening of hydrogen bonds at 82 °C seems to be coupled with the onset of orientational or rotational disorder of the ions. The temperature dependence of ionic conductivity in the solid and molten states is measured via impedance spectroscopy and current interruption technique, respectively. The Arrhenius plot of the ionic conductivity assumes a lower plateau region (phase I, 100–155 °C) with a low activation energy of ∼36.7 kJ mol−1 (i.e. ∼0.38 eV), suggesting likely a Grotthuss mechanism for the proton conduction. Variable-temperature infrared analysis, optical morphological observations, and powder XRD patterns further illustrate the structural changes. Electrochemical hydrogen pumping tests confirm the protonic nature of the ionic conduction observed in the lower plateau region. Finally, measurements of the open circuit voltages (OCVs) and the polarization curves of a dry hydrogen/air fuel cell prove the long-range proton conduction. At 150 °C, a high OCV of 1.05 V is achieved, approaching the theoretical maximum (1.11 V).
Energy and Environmental Science | 2014
Junyuan Xu; David Aili; Qingfeng Li; Erik Christensen; Jens Oluf Jensen; Wei Zhang; Martin Kalmar Hansen; Gaoyang Liu; Xindong Wang; Niels J. Bjerrum
Proton exchange membrane steam electrolyzers suffer from insufficient catalyst activity and durability due to the slow reaction kinetics for oxygen evolution reaction (OER) and poor durability under harsh operating environments. Aiming at enhancement of oxygen electrode kinetics and durability, composite support materials for iridium oxide are synthesized via in situ phosphorization reaction on tin doped indium oxide and possess functionalities of high electronic and intrinsic proton conductivity. At 130 °C under a water vapor atmosphere an overall conductivity of 0.72 S cm−1 is achieved with a contribution of around 10−2 S cm−1 proton conductivity. The support structure of three-dimensionally ordered hexagonal arrays displays a high specific surface area of 180 m2 g−1. Benefiting from the mixed conductivities and porous structure in the composite support materials, the supported IrO2 catalysts exhibit about five times enhancement of the OER activity in acidic electrolytes. The improved catalytic performance for the OER was further confirmed by PEM electrolyzer tests at 130 °C. A test of such a steam electrolyzer cell at 350 mA cm−2 shows good durability within a period of up to 1150 hours.
Archive | 2016
Qingfeng Li; David Aili; Hans Aage Hjuler; Jens Oluf Jensen
perspectives DTU Orbit (08/11/2019) High temperature polymer electrolyte membrane fuel cells: Approaches, status, and perspectives This book is a comprehensive review of high-temperature polymer electrolyte membrane fuel cells (PEMFCs). PEMFCs are the preferred fuel cells for a variety of applications such as automobiles, cogeneration of heat and power units, emergency power and portable electronics. The first 5 chapters of the book describe rationalization and illustration of approaches to high temperature PEM systems. Chapters 6 13 are devoted to fabrication, optimization and characterization of phosphoric acid-doped polybenzimidazole membranes, the very first electrolyte system that has demonstrated the concept of and motivated extensive research activity in the field. The last 11 chapters summarize the state-of-the-art of technological development of high temperature-PEMFCs based on acid doped PBI membranes including catalysts, electrodes, MEAs, bipolar plates, modelling, stacking, diagnostics and applications.
Journal of Materials Chemistry | 2017
David Aili; Andrew G. Wright; Mikkel Rykær Kraglund; Katja Jankova; Steven Holdcroft; Jens Oluf Jensen
Advanced alkaline water electrolysis using ion-solvating polymer membranes as electrolytes represents a new direction in the field of electrochemical hydrogen production. Polybenzimidazole membranes equilibrated in aqueous KOH combine the mechanical robustness and gas-tightness of a polymer with the conductive properties of an aqueous alkaline salt solution, and are thus of particular interest in this field of research. This work presents a comprehensive study of ternary alkaline polymer electrolyte systems developed around a polybenzimidazole derivative that is structurally tailored towards improved stability in alkaline environments. The novel electrolytes are extensively characterized with respect to physicochemical and electrochemical properties and the chemical stability is assessed in 0–50 wt% aqueous KOH for more than 6 months at 88 °C. In water electrolysis tests using porous 3-dimensional electrodes completely free from noble metals, they show polarization characteristics comparable to those of commercially available separators and good performance stability over several days.
Archive | 2016
David Aili; Jens Oluf Jensen; Qingfeng Li
Casting of polybenzimidazole membranes by solvent evaporation from homogeneous solution followed by phosphoric acid doping is a widely used procedure for the preparation of proton conducting membranes for high-temperature polymer electrolyte membrane fuel cells. This contribution covers the membrane fabrication process from casting to acid doping and extends to a review of membrane characteristics and modifications. Furthermore, it briefly addresses membrane aspects in connection to fuel cell performance and durability.
Archive | 2016
Qingfeng Li; David Aili; Robert F. Savinell; Jens Oluf Jensen
Acid–base chemistry deals with proton transfer from an acid to a base and represents an effective approach to the development of proton conducting materials. The acidity difference (ΔpKa) of the two components dictates the extent of proton transfer and therefore the ionicity and other properties of an acid–base system. Only an appropriate acidity matching allows for formation of extensive hydrogen bond networks which in turn promotes the proton dynamics and Grotthuss mechanism of the proton conductivity. To frame the hypothesis initial effort is made to compile information of acid–base systems including aqueous solutions, ionic liquids, solid crystals, acid-doped basic polymers, base-doped acidic polymers as well as inorganic solid acids. Upon further validation, the insight might open vision to avenues of material sciences in the field of proton conducting materials.
Archive | 2016
Jingshuai Yang; Ronghuan He; David Aili
Recent progress in the synthesis of polybenzimidazole (PBI) derivatives is summarized for application as high temperature polymer electrolyte membrane in fuel cells. Various designs in the polymer structure are described aiming at improvement of the membrane performance. The ways to produce PBI derivatives containing different functional groups, segments, or blocks of other macromolecules are classified as main-chain modification, copolymerization, and side-chain grafting. The synthetic routes and associated characterization methods particularly with respect to the polymer structures are also addressed.
ACS Applied Materials & Interfaces | 2017
Jin Zhang; Jian Liu; Shanfu Lu; Haijin Zhu; David Aili; Roland De Marco; Yan Xiang; Maria Forsyth; Qingfeng Li; San Ping Jiang
As differentiated from conventional synthetic processes, amino-functionalized hollow mesoporous silica (NH2-HMS) has been synthesized using a new and facile strategy of ion-exchange-induced selective etching of amino-functionalized mesoporous silica (NH2-meso-silica) by an alkaline solution. Nuclear magnetic resonance (NMR) spectroscopy and in situ time-resolved small-angle X-ray scattering (SAXS) reveal that ion-exchange-induced selective etching arises from the gradient distribution of OH- in the NH2-meso-silica nanospheres. Moreover, the ion-exchange-induced selective etching mechanism is verified through a successful synthesis of hollow mesoporous silica. After infiltration with phosphotungstic acid (PWA), PWA-NH2-HMS nanoparticles are dispersed in the poly(ether sulfone)-polyvinylpyrrolidone (PES-PVP) matrix, forming a hybrid PWA-NH2-HMS/PES-PVP nanocomposite membrane. The resultant nanocomposite membrane with an optimum loading of 10 wt % of PWA-NH2-HMS showed an enhanced proton conductivity of 0.175 S cm-1 and peak power density of 420 mW cm-2 at 180 °C under anhydrous conditions. Excellent durability of the hybrid composite membrane fuel cell has been demonstrated at 200 °C. The results of this study demonstrated the potential of the facile synthetic strategy in the fabrication of NH2-HMS with controlled mesoporous structure for application in nanocomposite membranes as a technology platform for elevated-temperature proton exchange membrane fuel cells.
International Journal of Hydrogen Energy | 2011
David Aili; Martin Kalmar Hansen; Chao Pan; Qingfeng Li; Erik Damgaard Christensen; Jens Oluf Jensen; Niels J. Bjerrum
Journal of Materials Chemistry | 2012
David Aili; Lars Nilausen Cleemann; Qingfeng Li; Jens Oluf Jensen; Erik Christensen; Niels J. Bjerrum