Targeting Histamine Receptors in Irritable Bowel Syndrome: A Critical Appraisal

Irritable bowel syndrome is a group of functional gastrointestinal disorders with not yet fully clarified etiology. Recent evidence suggesting that mast cells may play a central role in the pathogenesis of irritable bowel syndrome paves the way for agents targeting histamine receptors as a potential therapeutic option in clinical treatment. In this review, the role of histamine and histamine receptors is debated. Moreover, the clinical evidence of anti-histamine therapeutics in irritable bowel syndrome is discussed

Improvement of safe bromine electrolytes and their cell performance in H2_{2}/Br2_{2} flow batteries caused by tuning the bromine complexation equilibrium

Hydrogen bromine redox flow batteries utilize bromine electrolytes in their positive half cell, offering capacities larger than 100 Ah L$^{-1}$. Addition of quaternary ammonium compounds, so-called bromine complexing agents (BCA), may increase safety as they reduce the vapour pressure of bromine in the posolyte. However, they have not been applied so far. They (a) interact with perfluorosulfonic acid membranes leading to significant reduction of membrane conductivity and (b) they form a low conductive ionic liquid with polybromides, leading to high overvoltage if the formation happens at the electrode. In this work a solution to this problem is proposed by an excess addition of Br$_{2}$ to these electrolytes. The excess bromine leads to a permanent bromine fused salt phase in the tank. Bromine formed in the cell stays in the aqueous phase and bromine transfer between the two phases happens in the tank. Transfer of Br2 without the transfer of [BCA]$^{+}$ cations exists between the phases, while [C2Py]$^{+}$ cations remain in the fused salt and do not influence cell performance. For the first time a posolyte capacity of 179.6 Ah L$^{-1}$ based on 7.7 M hydrobromic acid with BCA is achieved compared to previous investigations with e.g. 53.9 Ah L$^{-1}$

Reactive transport in porous electrodes : from pore-scale to macroscale descriptions

Macroscopic homogenized descriptions of reactive electrolyte transport through porous electrodes capture important sub-scale effects by the use of effective parameters, such as the dispersion tensor or the effective reaction rate. We apply the volume averaging method (VAM) to upscale the transport of electrolyte through periodic unit cells and evaluate the dependency and sensitivity of macroscopic effective parameters on pore-scale properties. The effective parameters can be applied in macroscopic cell models of redox flow batteries to study the effect of different pore-scale geometries within porous electrodes on the mass transfer rate or homogeneity of the electric current density

Mass transport limitations in concentrated aqueous electrolyte solutions : theoretical and experimental study of the hydrogen-bromine flow battery electrolyte

Modelling and simulation is a powerful tool to support the development of novel flow cells such as electrolysers and flow batteries. Electrolytes employed in such cells often consist of aqueous solutions of highly concentrated solutes at elevated temperatures. Such conditions pose numerous challenges in conventional model parametrisation because of non-ideal behaviour of the electrolytes. The aim of this work is to study mass transport of electroactive species in highly-concentrated media. We selected the hydrogen-bromine flow battery posolyte, HBr (aq) and Br2, as an exemplary flow battery electrolyte and we leveraged chronoamperometric techniques involving ultramicroelectrodes to study diffusion and migration of bromide and bromine at high concentration and temperature. We successfully simulated the current densities of HBr/Br2 redox reactions in solutions up to 8 mol L–1 using advanced mass transport theory which agreed well with the results obtained with ultramicroelectrodes. While uncharged species transport (Br2) can be credibly modelled using conventional theories such as Fick’s law, charged species (Br–) require special treatment as the diffusion coefficient vary with concentration up to 50 % with respect to the limiting value at infinite dilution. The transport of charged species without added supporting electrolyte occurs via both migration and diffusion and the contribution of migration current may be up to 50 % of the total current. At HBr concentration  0.6 mol L–1 migration appears to be suppressed due to the “self-screening” effect of the electrolyte. Proper experimental electrolyte characterisation under operating conditions similar to the actual flow cell applications is indispensable to establish predictive models and digital twins of electrochemical devices. Straightforward transfer of concepts known in electro-analytical chemistry to flow cells modelling may lead to erroneous simulations or model overfitting

Improvement of safe bromine electrolytes and their cell performance in H2/Br2 flow batteries caused by tuning the bromine complexation equilibrium

Hydrogen bromine redox flow batteries utilize bromine electrolytes in their positive half cell, offering capacities larger than 100 Ah/L. Addition of quaternary ammonium compounds, so-called bromine complexing agents (BCA), may increase safety as they reduce the vapour pressure of bromine in the posolyte. However, they have not been applied so far. They (a) interact with perfluorosulfonic acid membranes leading to significant reduction of membrane conductivity and (b) they form a low conductive ionic liquid with polybromides, leading to high overvoltage if the formation happens at the electrode. In this work a solution to this problem is proposed by an excess addition of Br2 to these electrolytes. The excess bromine leads to a permanent bromine fused salt phase in the tank. Bromine formed in the cell stays in the aqueous phase and bromine transfer between the two phases happens in the tank. Transfer of Br2 without the transfer of [BCA]+ cations exists between the phases, while [C2Py]+ cations remain in the fused salt and do not influence cell performance. For the first time a posolyte capacity of 179.6 Ah/L based on 7.7 M hydrobromic acid with BCA is achieved compared to previous investigations with e.g. 53.9 Ah/L

An enhanced 1-D model of a hydrogen-bromine flow battery

Acknowledgements: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement no. 765289. *Project website: www.flowcamp-project.euOne of the flow battery systems which utilizes abundantly available chemicals for electrolytes, characterized by high power density, is the hydrogen-bromine flow battery. First proposed in 1969 [1], it has recently received new attention and has been undergoing development, in which numerical simulations play an important role. To date, a few papers devoted to modeling and simulation of this particular new-generation flow battery chemistry were published. In the present work, a one-dimensional (1D), steady-state, macrohomogeneous, mathematical model of a single-cell hydrogen-bromine flow battery (HBFB) is developed, described and solved. It comprises of the most relevant transport through-plane processes and electrochemical phenomena for the operation of the HBFB, namely: charge transport, water, gaseous hydrogen, proton, bromine and (tri)bromide mass transport. Furthermore, the model is enhanced with supplementary phenomena to better approximate the physics described in the simulation such as: bromine-tribromide ionic equilibria, Nernstian losses due to reactant local surface concentration variations, Donnan potential on the HBr/Br2 solution-membrane interface, and gas adsorption in the ionomer on the gaseous hydrogen side according to Henry’s law. The model description emphasizes the importance of electrochemical and flux sign conventions, and the meaning of appropriate boundary conditions, which was seldom the case in the published modeling approaches. A complete set of plots of each dependent variable and the associated fluxes are provided. A system of nonlinear second-order partial differential equations describing the problem is solved using COMSOL Multiphysics software with the General PDE Form module for a better control over the actual governing equations (conservation laws) as well as auxiliary algebraic field equations. The 1D approach allows for solving the problem within seconds on a laptop-class computer and permits running multiple case studies within short time. Moreover, a parametric study is performed (Fig. 1) to examine the impact of selected parameters on the overall performance of a single cell. The validity of the model is verified based on results from a set of experiments carried out at Fraunhofer ICT (internal, multidisciplinary cooperation within the Flowcamp* project) using an isothermal single test cell

Exploring the thermodynamics of the bromine electrode in concentrated solutions for improved parametrisation of hydrogen–bromine flow battery models

Thermodynamic properties of the bromine electrode in an exemplary hydrogen–bromine flow battery (HBFB) are investigated in detail. Open-circuit potential (OCP) measurements of HBRB electrolytes in a liquid junctionfree setup and electrolyte Raman spectra are employed to estimate polybromides speciation. An improved mathematical description of the bromine electrode OCP versus state of charge is provided. This paper addresses the phenomenon of polybromides formation at concentrations up to 7.7 mol L-1 HBr and 3.85 mol L-1 Br2 and their significant impact on the OCP. The model takes into account tri-, penta- and heptabromides formation, precisely modelled electrolyte activity coefficients (up to 11-molal HBr), electrolyte density, and temperature. It is elucidated that the polybromide formation constants found in literature treating dilute electrolytes are substantially too low. Newly determined equilibrium constants, applicable over a wider concentration range are provided for 25 and 43 ◦C together with their standard enthalpy changes. The model is successfully validated in an independent experiment using a real, pilot-scale HBFB. It is concluded that the usage of a simple Nernst-like equation to calculate the OCP of flow battery electrodes containing concentrated electrolytes leads to erroneous results

Exploring the thermodynamics of the bromine electrode in concentrated solutions for improved parametrisation of hydrogen-bromine flow battery models

Thermodynamic properties of the bromine electrode in an exemplary hydrogen–bromine flow battery (HBFB) are investigated in detail. Open-circuit potential (OCP) measurements of HBRB electrolytes in a liquid junction-free setup and electrolyte Raman spectra are employed to estimate polybromides speciation. An improved mathematical description of the bromine electrode OCP versus state of charge is provided. This paper addresses the phenomenon of polybromides formation at concentrations up to 7.7 mol L-1 HBr and 3.85 mol L-1 Br2 and their significant impact on the OCP. The model takes into account tri-, penta- and heptabromides formation, precisely modelled electrolyte activity coefficients (up to 11-molal HBr), electrolyte density, and temperature. It is elucidated that the polybromide formation constants found in literature treating dilute electrolytes are substantially too low. Newly determined equilibrium constants, applicable over a wider concentration range are provided for 25 and 43 °C together with their standard enthalpy changes. The model is successfully validated in an independent experiment using a real, pilot-scale HBFB. It is concluded that the usage of a simple Nernst-like equation to calculate the OCP of flow battery electrodes containing concentrated electrolytes leads to erroneous results