Guanidinium nonaflate as a solid-state proton conductor

Guanidinium nonaflate, a novel pure protic organic ionic plastic crystal (POIPC) with an elegant symmetrical cation, is discovered to be a new solid-state proton conductor.</p

A universal strategy for metal oxide anchored and binder-free carbon matrix electrode : a supercapacitor case with superior rate performance and high mass loading

Financial support from China Fund KU Leuven (ISP/13/02SJT) is acknowledged. J. Luo acknowledges the Research Foundation - Flanders (FWO) for FWO Postdoctoral Fellowship (12F5514N), a Research Grant (Project number: 1529816N) and a travel grant (V410316N) for a Visiting Professorship in Technical University of Denmark. X. Zhang is grateful to the China Scholarship Council. We thank Prof. Dirk De Vos (KU Leuven) for technical discussions, Prof. Lei Li (Shanghai Jiao Tong University) for providing nickel foams and Prof. Qingfeng Li (Technical University of Denmark) for assistance in TEM measurements. Appendix ADespite the significant advances in preparing carbon-metal oxide composite electrodes, strategies for seamless interconnecting of these two materials without using binders are still scarce. Herein we design a novel method for in situ synthesis of porous 2D-layered carbon-metal oxide composite electrode. Firstly, 2D-layered Ni-Co mixed metal-organic frameworks (MOFs) are deposited directly on nickel foam by anodic electrodeposition. Subsequent pyrolysis and activation procedure lead to the formation of carbon-metal oxides composite electrodes. Even with an ultrahigh mass loading of 13.4 mg cm, the as-prepared electrodes exhibit a superior rate performance of 93% (from 1 to 20 mA cm), high capacitance (2098 mF cm at a current density of 1 mA cm), low resistance and excellent cycling stability, making them promising candidates for practical supercapacitor application. As a proof of concept, several MOF derived electrodes with different metal sources have also been prepared successfully via the same route, demonstrating the versatility of the proposed method for the preparation of binder-free carbon-metal oxide composite electrodes for electrochemical devices

Ultrasensitive binder-free glucose sensors based on the pyrolysis of in situ grown Cu MOF

A non-enzymatic glucose sensor based on carbon/Cu composite materials was developed by the in-situ growth and subsequent pyrolysis of metal-organic frameworks (MOFs) on Cu foam. After pyrolysis, SEM, HRTEM and STEM-EELS were employed to clarify the hierarchical Cu@porous carbon electrode. It is found that the Cu nanoparticles are uniformly embedded in the carbon matrix, carbon matrix in close contact with the pyrolized carbon sheets. The electrocatalytic activity of the Cu@porous carbon matrix electrode for glucose sensing was explored by cyclic voltammetry (CV) and chronoamperometry. The resulting Cu@porous carbon matrix electrode displays ultrahigh sensitivity (10.1 mA cm⁻² mM⁻¹), low detection limit (0.6 μM), short response time (less than 2 s) and good stability, indicating that the developed electrode is a promising glucose sensor

Critical Role of Phosphorus in Hollow Structures Cobalt-Based Phosphides as Bifunctional Catalysts for Water Splitting

Cobalt phosphides electrocatalysts have great potential for water splitting, but the unclear active sides hinder the further development of cobalt phosphides. Wherein, three different cobalt phosphides with the same hollow structure morphology (CoP-HS, CoP-HS, CoP-HS) based on the same sacrificial template of ZIF-67 are prepared. Surprisingly, these cobalt phosphides exhibit similar OER performances but quite different HER performances. The identical OER performance of these CoP-HS in alkaline solution is attributed to the similar surface reconstruction to CoOOH. CoP-HS exhibits the best catalytic activity for HER among these CoP-HS in both acidic and alkaline media, originating from the adjusted electronic density of phosphorus to affect absorption–desorption process on H. Moreover, the calculated ΔG based on P-sites of CoP-HS follows a quite similar trend with the normalized overpotential and Tafel slope, indicating the important role of P-sites for the HER process. Moreover, CoP-HS displays good performance (cell voltage of 1.67 V at a current density of 50 mA cm) and high stability in 1 M KOH. For the first time, this work detailly presents the critical role of phosphorus in cobalt-based phosphides for water splitting, which provides the guidance for future investigations on transition metal phosphides from material design to mechanism understanding.W.Z. and N.H. contributed equally to this work. X.Z. and J.F. are grateful for the Research Foundation-Flanders (FWO) project (12ZV320N). Funding from National Natural Science Foundation of China (project No.: 22005250, 21776120, and 51901161) is appreciated. M.X. is grateful to the National Natural Science Foundation of China (project No.: 22179109). W.Z. is grateful to the China Scholarship Council (NO. 201808310068). W.G. is grateful to the China Scholarship Council (NO. 201806030189). S.X. is grateful to the China Scholarship Council. K.W. is grateful to the Oversea Study Program of Guangzhou Elite Project. Funding from the Research Foundation–Flanders (FWO) (project No.: G0B3218N) and Natural Science Foundation of Fujian Province, China (No.: 2018J01433) is acknowledged. ICN2 acknowledges funding from Generalitat de Catalunya 2017 SGR 327 and the Spanish MINECO project ECOCAT and subproject NANOGEN. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science Ph.D. program. This work has received funding from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement No. 654360 NFFA-Europe. X.H. thanks China Scholarship Council for scholarship support (201804910551)

Protic salts as electrolytes for high temperature polymer electrolyte membrane fuel cells

Polymer electrolyte membrane fuel cells (PEMFCs) using proton-conducting membranes have been extensively studied as an environmentally friendly electricity generation technology. In particular, high temperature PEMFCs operating in the temperature range of 100-200 oC are suitable for application in co-generation stationary power plants and electric vehicles. However, the state-of-the-art Nafion-based and other sulfonated membranes for low temperature (typically 100 oC). As a result, suitable anhydrous proton conductors are urgently needed as the key component for the development of high temperature PEMFCs. On the one hand, protic ionic liquids (PILs), formed by proton transfer between a Bronsted acid and a Bronsted base, have advantages for electrochemical applications due to their superior advantages of low vapour pressure, non-flammability, good thermal and electrochemical stability, and high ionic conductivity as well as intrinsic proton conductivity. Compared with aprotic ionic liquids (AILs), PILs have received far less attention. Although the past decade has witnessed a growing body of research work related to PILs in various fields, the practical application of PILs as electrolytes for high temperature PEMFCs is still in its infancy. On the other hand, organic ionic plastic crystals (OIPCs) have recently emerged as novel electrolytes for solid-state electrochemical devices. As unique materials, they exhibit intrinsic ionic conductivity, non-flammability, negligible vapor pressure, high electrochemical and thermal stability, and a better electrode/electrolyte interfacial contact with the elimination of leakage problems compared with liquid electrolytes including AILs and PILs. Intuitively, protic OIPCs with high intrinsic proton conductivity and good mechanical flexibility are expected to be desirable electrolytes for the realization of all-solid-state high temperature PEMFCs. However, there have been very limited reports about the application of protic OIPCs as electrolytes for PEMFCs. Therefore, this thesis explores PILs and protic OIPCs as electrolytes for high temperature PEMFCs. It contains the following four parts: Firstly, the system consisting of a Bronsted acid (methanesulfonic acid, CH3SO3H) and a Bronsted base (1H-1,2,4-triazole, C2H3N3) has been investigated in detail as a model Bronsted acid-base system for a deeper understanding of the chemical essence of Bronsted acid-base interactions and a subsequent rational design of PIL-based membranes. The thermal properties, crystalline structure, acid-base interactions, ionic conductivity, proton conduction behavior and electrochemical stability of the system were explored. It was found that the proton conduction in the base-rich region of the system follows a combination of Grotthuss-type and vehicle-type mechanisms. The relatively high ionic conductivity, wide electrochemical window and good thermal stability demonstratedtheC2H3N3-CH3SO3H system as promising electrolytes for high temperature PEMFCs. Secondly, as the reported PILs and protic molten salts often have relatively high melting points, a practical and generalized approach has been developed for utilizing them in devising anhydrous proton conductors through the investigation of the solvation effect of 1H-1,2,4-triazole towards imidazolium methanesulfonate. The addition of 1H-1,2,4-triazole lowered the high melting point of imidazolium methanesulfonate (188 oC) to less than 100 oC, while maintaining the high ionic conductivity over a wide composition range of the blend. It was found that suitable blends of a PIL (or a protic molten salt) and a Bronsted base may serve as electrolytes with a wider liquid temperature range for high temperature PEMFCs operating under non-humidifying conditions. Thirdly, novel phosphonium-based PILs have been developed. They exhibited higher thermal stability and ionic conductivity than the corresponding ammonium-based PILs, no matter whether the P and N center atoms are bonded to the electron-donating octyl groups or the electron-withdrawing phenyl groups, indicating phosphonium-based PILs are highly promising non-aqueous electrolytes. Finally, imidazolium methanesulfonate was studied as a model anhydrous proton conductor for high temperature PEMFCs, with particular attention to its plastic crystalline property. It is found that imidazolium methanesulfonate undergoes transformation from crystalline to plastic crystalline at 174 oC and then molten states at 188 oC successively from ambient temperature to 200 oC. At the melting point of 188 oC, a low entropy of fusion of around 24 J mol-1 K-1 was observed. In particular, a high ionic conductivity of 1.0 × 10-2 S cm-1 is reached at 185 oC in the plastic phase. In the molten state, the contribution of protons to the ionic conductivity of imidazolium methanesulfonate was demonstrated. A Nafion membrane has been successfully doped with imidazolium methanesulfonate. To the best of our knowledge, this may be the first report on a protic OIPC consisting of protonated imidazole (C3H5N2+) and an organic anion. The good thermal stability, high ionic conductivity, wide electrochemical window, favorable plastic crystal behavior and simple synthesis make imidazolium methanesulfonate a highly interesting model proton conductor for high temperature PEMFCs. In conclusion, PILs and protic OIPCs are unique and highly promising electrolytes for high temperature PEMFCs. Their physicochemical properties have been revealed in detail. The PILs, protic OIPCs and related approaches developed in this work enable further rational research of high temperature anhydrous proton conductors.Acknowledgements Abstract Samenvatting List of abbreviations and symbols Table of contents 1. Introduction 1.1. Polymer electrolyte membrane fuel cells (PEMFCs) 1.2. Protic salts 1.2.1. Protic ionic liquids (PILs) and protic molten salts 1.2.1.1 PIL formation through proton transfer 1.2.1.2 PIL types 1.2.1.3 Basic physicochemical properties 1.2.1.3.1 Phase transitions 1.2.1.3.2 Thermal stability and volatility 1.2.1.3.3 Ionic conductivity and proton-conducting mechanisms 1.2.1.4 Fuel cell performances 1.2.2. Protic organic ionic plastic crystals (protic OIPCs) 1.3. PhD dissertation overview References 2. Protic ionic liquid and ionic melts prepared from methanesulfonic acid and 1H-1,2,4-triazole as high temperature PEMFC electrolytes 2.1. Introduction 2.2. Experimental 2.2.1. Materials 2.2.2. Water content and anion impurities 2.2.3. Thermal analysis 2.2.4. X-ray diffraction 2.2.5. Fourier transform infrared (FT-IR) spectra 2.2.6. Ionic conductivity 2.2.7. Linear sweep voltammograms 2.3. Results and discussion 2.3.1. Water content and anion concentrations 2.3.2. Crystal structure 2.3.3. Thermal properties 2.3.4. Infrared studies 2.3.5. Ionic conduction behavior 2.3.6. Electrochemical stability 2.4. Conclusions Acknowledgements Supplementary information References 3. 1H-1,2,4-Triazole as solvent for imidazolium methanesulfonate 3.1. Introduction 3.2. Experimental 3.2.1. Chemicals 3.2.2. Anion concentrations 3.2.3. X-ray diffraction (XRD) 3.2.4. Thermal analysis 3.2.5. Fourier transform infrared (FT-IR) spectra 3.2.6. Ionic conductivity 3.2.7. Electrochemical polarization 3.3. Results and discussion 3.3.1. Anion concentrations 3.3.2. Thermal, FT-IR and structural analysis 3.3.3. Computational studies 3.3.4. Electrochemical behavior 3.4. Conclusions Acknowledgements References 4. Physicochemical properties of phosphonium-based and ammonium-based protic ionic liquids 4.1. Introduction 4.2. Experimental 4.2.1. Chemicals 4.2.2. Thermal analysis 4.2.3. Fourier transform infrared (FT-IR) spectra 4.2.4. Ionic conductivity 4.2.5. Ion volume calculation 4.3. Results and discussion 4.3.1. Thermal analysis 4.3.2. FT-IR analysis 4.3.3. Ion conduction behavior 4.4. Conclusions Acknowledgements Supplementary information References 5. Imidazolium methanesulfonate as a high temperature proton conductor 5.1. Introduction 5.2. Experimental 5.2.1. Chemicals 5.2.2. X-ray diffraction (XRD) studies 5.2.3. Thermal analysis 5.2.4. pH titration 5.2.5. Fourier transform infrared (FT-IR) spectra 5.2.6. Ionic conductivity 5.2.7. Electrochemical polarization 5.3. Results and discussion 5.3.1. Thermal and structural analysis 5.3.2. Ionic conductivity 5.3.3. Interfacial electrochemical properties 5.3.4. Characterizations of the membranes 5.4. Conclusions Acknowledgements Supplementary information References 6. Conclusions and outlook 6.1. General conclusions 6.2. Outlook List of publicationsnrpages: 128status: publishe

Physicochemical properties of phosphonium-based and ammonium-based protic ionic liquids

Trioctylphosphonium triflate, trioctylammonium triflate, triphenylphosphonium triflate and triphenylammonium triflate were synthesized and characterized. It was found that phosphonium-based protic ionic liquids (PILs) exhibit higher thermal stability and ionic conductivity than the corresponding ammonium-based PILs, no matter whether the P and N center atoms are bonded to the electron-donating octyl groups or the electron-withdrawing phenyl groups. The ion conduction behavior of the PILs can be adequately described by the Vogel–Fulcher–Tamman (VFT) equation. The higher ionic conductivity of phosphonium-based PILs may be attributed to their weaker hydrogen bond and Coulombic interactions as well as higher carrier ion concentrations, indicated by infrared analysis, lattice potential energy estimation and VFT fitting results. Interestingly, the stronger hydrogen bonds inside trioctylammonium triflate may lead to a much decreased melting point. Furthermore, compared with electron-withdrawing phenyl, electron-donating octyl enhanced the thermal stability of the PILs.status: publishe

Imidazolium methanesulfonate as a high temperature proton conductor

Imidazolium methanesulfonate (1) has been studied as a model proton conductor for high temperature polymer electrolyte membrane fuel cells (PEMFCs). It is found that 1 undergoes transformation from crystalline to plastic crystalline and then molten states successively from ambient temperature to 200 °C. The solid–solid phase transition of 1 at 174 °C has been preliminarily verified by differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). At the melting point of 188 °C, 1 displays a low entropy of fusion of around 24 J mol−1 K−1. In particular, a high ionic conductivity of 1.0 × 10−2 S cm−1 is reached at 185 °C in the plastic phase. The activation energy for ionic conduction decreases as 1 is heated from the crystal phase to the melt phase. In the molten state, the contribution of protons to the ionic conductivity of 1 was corroborated electrochemically. In addition, 1 is electrochemically active for H2 oxidation and O2 reduction at a Pt electrode while it shows a high electrochemical window of 2.0 V. Furthermore, a Nafion® membrane has been successfully doped with 1, as identified by infrared spectroscopy, powder XRD, grazing incidence XRD and thermogravimetric analysis. To the best of our knowledge, this may be the first report on a protic organic ionic plastic crystal (OIPC) consisting of protonated imidazole (C3H5N2+) and an organic anion. The good thermal stability, high ionic conductivity, wide electrochemical window, favorable plastic crystal behavior and simple synthesis make 1 a highly interesting model proton conductor for high temperature PEMFCs.status: publishe

Poly(ionic liquid)s-based nanocomposite polyelectrolytes with tunable ionic conductivity prepared via SI-ATRP

In this study, a novel kind of organic–inorganic core–shell SiO2-poly(p-vinylbenzyl) trimethylammonium tetrafluoroborate (SiO2–P[VBTMA][BF4]) nanoparticle was well designed and successfully synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP). Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and scanning electron microscopy (SEM) were used to confirm the formation of the core–shell nanoparticles and the surface modification. In order to overcome the challenge of the characterization of the number average molecular weight of poly(ionic liquid)s, “sacrificial initiator” method was used here employing a trimethylsilyl (TMS)-labeled initiator as the NMR marker for integration. In addition, good thermal stability of the new hybrid polyelectrolyte was proved by thermogravimetric analysis. The electrochemical impedance measurements revealed that the room temperature conductivity reached 10−4 S cm−1, which is much higher than that of the pure poly(ionic liquid)s and varies with the amount of the grafted polymer and the test temperature. The X-ray diffraction (XRD) tests further investigated the crystal structure of the nanocomposite and pure P[VBTMA][BF4]. The temperature dependence of ionic conductivity conforms to Arrhenius behavior for both of the nanocomposites and the pure polymer. The results indicated that the SI-ATRP approach provided a simple and versatile route to tune the ionic conductivity of the hybrid nanoparticles by changing the chain length of the grafted polymer, which can be potentially used in a variety of electrochemical devices.status: publishe