The ohmic resistances of the anion and cation ion-exchange membranes (IEMs) that constitute a reverse electrodialysis system (RED) are of crucial importance for its performance. In this work, we study the influence of concentration (0.1 M, 0.5 M, 1 M and 2 M) of ammonium bicarbonate solutions on the ohmic resistances of ten commercial IEMs. We also studied the ohmic resistance at elevated temperature 313 K. Measurements have been performed with a direct two-electrode electrochemical impedance spectroscopy (EIS) method. As the ohmic resistance of the IEMs depends linearly on the membrane thickness, we measured the impedance for three different layered thicknesses, and the results were normalised. To gauge the role of the membrane resistances in the use of RED for production of hydrogen by use of waste heat, we used a thermodynamic and an economic model to study the impact of the ohmic resistance of the IEMs on hydrogen production rate, waste heat required, thermochemical conversion efficiency and the levelised cost of hydrogen. The highest performance was achieved with a stack made of FAS30 and CSO Type IEMs, producing hydrogen at 8.48× 10${}^{-7}$ kg m${}_{mem}^{-2}$s${}^{-1}$ with a waste heat requirement of 344 kWh kg${}^{-1}$ hydrogen. This yielded an operating efficiency of 9.7% and a levelised cost of 7.80 € kg${}_{H_2}^{-1}$.

This work presents an integrated hydrogen production system using reverse electrodialysis (RED) and waste heat, termed Heat to H ${}_2$ . The driving potential in RED is a concentration difference over alternating anion and cation exchange membranes, where the electrode potential can be used directly for water splitting at the RED electrodes. Low-grade waste heat is used to restore the concentration difference in RED. In this study we investigate two approaches: one water removal process by evaporation and one salt removal process. Salt is precipitated in the thermally driven salt removal, thus introducing the need for a substantial change in solubility with temperature, which KNO ${}_3$ fulfils. Experimental data of ion conductivity of K ${}^{+}$ and NO ${}_3^{-}$ in ion-exchange membranes is obtained. The ion conductivity of KNO ${}_3$ in the membranes was compared to NaCl and found to be equal in cation exchange membranes, but significantly lower in anion exchange membranes. The membrane resistance constitutes 98% of the total ohmic resistance using concentrations relevant for the precipitation process, while for the evaporation process, the membrane resistance constitutes over 70% of the total ohmic resistance at 40 ${}^{\circ }$ C. The modelled hydrogen production per cross-section area from RED using concentrations relevant for the precipitation process is 0.014 ± 0.009 m ${}^3$ h ${}^{-1}$ (1.1 ± 0.7 g h ${}^{-1}$ ) at 40 ${}^{\circ }$ C, while with concentrations relevant for evaporation, the hydrogen production per cross-section area was 0.034 ± 0.016 m ${}^3$ h ${}^{-1}$ (2.6 ± 1.3 g h ${}^{-1}$ ). The modelled energy needed per cubic meter of hydrogen produced is 55 ± 22 kWh (700 ± 300 kWh kg ${}^{-1}$ ) for the evaporation process and 8.22 ± 0.05 kWh (104.8 ± 0.6 kWh kg ${}^{-1}$ ) for the precipitation process. Using RED together with the precipitation process has similar energy consumption per volume hydrogen produced compared to proton exchange membrane water electrolysis and alkaline water electrolysis, where the energy input to the Heat to H ${}_2$ -process comes from low-grade waste heat.

The electrolyte is one of the three essential constituents of a Lithium-Ion battery (LiB) in addition to the anode and cathode. During increasingly high power and high current charging and discharging, the requirement for the electrolyte becomes more strict. Solid State Electrolyte (SSE) sees its niche for high power applications due to its ability to suppress concentration polarization and otherwise stable properties also related to safety. During high power and high current cycling, heat management becomes more important and thermal conductivity measurements are needed. In this work, thermal conductivity was measured for three types of solid state electrolytes: Li ${}_7$ La ${}_3$ Zr ${}_2$ O ${}_{12}$ (LLZO), Li ${}_{1.5}$ Al ${}_{0.5}$ Ge ${}_{1.5}$ (PO ${}_4$ ) ${}_3$ (LAGP), and Li ${}_{1.3}$ Al ${}_{0.3}$ Ti ${}_{1.7}$ (PO ${}_4$ ) ${}_3$ (LATP) at different compaction pressures. LAGP and LATP were measured after sintering, and LLZO was measured before and after sintering the sample material. Thermal conductivity for the sintered electrolytes was measured to 0.470 ± 0.009 WK ${}^{-1}$ m ${}^{-1}$ , 0.5 ± 0.2 WK ${}^{-1}$ m ${}^{-1}$ and 0.49 ± 0.02 WK ${}^{-1}$ m ${}^{-1}$ for LLZO, LAGP, and LATP respectively. Before sintering, LLZO showed a thermal conductivity of 0.22 ± 0.02 WK ${}^{-1}$ m ${}^{-1}$ . An analytical temperature distribution model for a battery stack of 24 cells shows temperature differences between battery center and edge of 1–2 K for standard liquid electrolytes and 7–9 K for solid state electrolytes, both at the same C-rate of four.