The ion conductivity of two series of porous ceramic diaphragms impregnated with caustic potash was investigated by electrochemical impedance spectroscopy. To understand the impact of the pore structure on ion conductivity, the threedimensional (3-D) pore geometry of the diaphragms was characterized with synchrotron x-ray absorption tomography. Ion migration was calculated based on an extended pore structure model, which includes the electrolyte conductivity and geometric pore parameters, for example, tortuosity (s) and constriction factor (b), but no fitting parameters. The calculated ion conductivities are in agreement with the data obtained from electrochemical measurements on the Correspondence concerning this article should be addressed to D. Wiedenmann at daniel.wiedenmann@gmail.com.Published in " " which should be cited to refer to this work.http://doc.rero.ch diaphragms. The geometric tortuosity was found to be nearly independent of porosity. Pore path constrictions diminish with increasing porosity. The lower constrictivity provides more pore space that can effectively be used for mass transport. Direct measurements from tomographs of tortuosity and constrictivity opens new possibilities to study pore structures and transport properties of porous materials.

Hydrogen produced by water electrolysis with renewable electricity is a reliable, affordable and environmental friendly energy carrier for future energy supply and storage. Alkaline water electrolysis is a well matured technique and proved to be suitable for large-scale applications. Materials development for alkaline water electrolyzers is still of interest for academia and industry to address the issues of low compatibility to renewable power sources. A lab-scale system for alkaline water electrolysis was developed, aiming to advance materials development and to bridge the intrinsic properties of materials with their performance under realistic operating conditions. As the smallest pressure-type electrolyzer, it is capable of working at 30 bar and 80 °C with continuous liquid electrolyte circulation. Experimental studies investigate the influence of temperature, pressure, and intrinsic properties of materials on voltage efficiency and hydrogen purity. With appropriate analysis, links between material specifications and overall performance can be established, encouraging new designs and material innovations for alkaline water electrolysis.

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In sorption heat storage, one of the sources of discrepancy between theoretical material based energy storage potential and resulting system performance is the choice of process type. In this paper, in order to understand this performance deviation, a sorption heat storage process categorisation is proposed. This is followed by a review of reported sorption systems categorised according to the proposed process classification. An analysis of the reported systems is then undertaken focusing on the ratio of resulting temperature gain in sorption (ad-or absorption) compared to required temperature lift in desorption. This measure is termed temperature effectiveness and enables a form of system performance evaluation in the broad landscape of sorption thermal energy storage demonstrators. It is argued that other performance parameters such as volumetric energy storage density and volumetric charge and discharge power density are not adequate for comparison due to the highly varying testing conditions applied. From the system evaluation, it is seen that best temperature effectiveness is generally found in a closed, transported process with the ability of single sorbent pass and true counter flow heat exchange. Highlights • There are four basic sorption thermal energy storage processes, open fixed, open transported, closed fixed and closed transported.• Temperature effectiveness, the ratio of resulting sorption temperature lift to required desorption temperature lift, is a universal means for sorption heat storage system performance comparison.• Closed transported sorption thermal energy storage systems show the best performance in respect to temperature effectiveness.

This paper presents a practical study towards the development of a heat and mass exchanger fitting to liquid absorption heat storage for building application. Results of a lab scale setup are shown. To reach high heat capacity in absorption storage, a maximum temperature gain and concentration difference is mandatory. A conventional spiral fined tube heat exchanger is employed as heat and mass exchanger, whereby the tube is installed vertically and the absorbent flows slowly along the fin from top to bottom due to gravitational force. Sufficient time is given for absorption and heat release. Operating with sodium hydroxide as absorbent, a temperature lift of 35 K measured between maximum absorbent temperature and absorbate temperature as well as dilution from 50 wt% to 27 wt% in one continuous process step is attained in absorption. During desorption, a concentration lift from 25%wt to 53% wt at a temperature spread of 44K between desorber and condenser is reached.In relation to the concentration difference, a theoretical energy density of 435 kWh/m3 in respect to the discharged absorbent is reached. This development enables compact, lossless, long term heat storage suitable for space heating and domestic hot water. Nomenclature a Coefficients in equation 2 b Coefficients in equation 1 ρ Density [g/m 3 ] k Constant in equation 1 and 2 l Constant in equation 1 and 2 m Constant in equation 1 and 2 ṁ Mass flow [g/min] p Pressure [kPa] ϑ Temperature [°C] X Mass fraction [kg/kg] This document is the accepted manuscript version of the following article: Fumey, B., Weber, R., & Baldini, L. (2017). Liquid sorption heat storage -a proof of concept based on lab measurements with a novel spiral fined heat and mass exchanger design.