Electrical conductivity measurements of aqueous and immobilized potassium hydroxide

Abstract

It is important to know the conductivity of the electrolyte from a alkaline electrolysis cell at a given temperature and concentration to reduce the polarization loss during electrolysis through optimal cell and system design. The conductivity of aqueous KOH at elevated temperatures and high concentrations was investigated using the van der Pauw method in combination with electrochemical impedance spectroscopy (EIS). Conductivity values as high as 2.7 S·cm -1 for 35 wt%, 2.8 S·cm -1 for 45wt%, and 2.8 S·cm -1 for 55 wt% concentrated aqueous solutions were measured at 200 °C. Micro-and nano-porous solid pellets were produced and used to immobilize aqueous KOH solutions. These are intended to operate as ion-conductive diaphragms (electrolytes) in alkaline electrolysis cells, offering high conductivity and corrosion resistance. The conductivity of immobilized KOH has been determined by the same method in the same temperature and concentration range. Conductivity values as high as 0.67 S·cm -1 for 35 wt%, 0.84 S·cm -1 for 45 wt%, and 0.73 S·cm -1 for 55 wt% concentrated immobilized aqueous solutions were determined at 200 °C. Furthermore, phase transition lines between the aqueous and aqueous + gaseous phase of aqueous KOH were calculated as a function of temperature, concentration and pressure in the temperature range of 100-300 °C, for concentrations of 0-80 wt% and at pressures between 1 and 100 bar.

Porous poly(perfluorosulfonic acid) membranes for alkaline water electrolysis

“…Since the ohmic losses predominate at high gas production rates, the systems are generally operated at low current densities [18]. The ohmic resistance can, however, be reduced by increasing the operating temperature [19], which is advantageous from kinetic and thermodynamic points of view but very challenging when it comes to the stability of key materials. Operating temperatures as high 250°C have been reported for pressurized cells with KOH immobilized in a ceramic matrix, showing performance comparable to that of PEM cells [20].…”

Membrane electrolysis—History, current status and perspective

“…The traditional method, using a phosphoric acid-doped polybenzimidazole (PBI) membrane, has not proven to be viable due to the insufficient oxidative stability of this material under water electrolysis conditions [96,97]. An alternative, based on a porous separator containing immobilized KOH/H2O melt operating at 240 °C, has recently been reported [98,99]. Water acts both as a reactant and flux in the system.…”

Metallic muscles and beyond: nanofoams at work

“…It is emphasized that low sweep rates are required during actuation in nanoporous metals via an electrolyte; in fact dimensional changes in nanoporous metal/electrolyte composite actuators vanish at sweep rates beyond a few tens of mV/s. That behavior has two origins: (i) the low room-temperature ionic conductivity of electrolytes [100] does not favor a rapid transport of ions to the nanoporous metal/electrolyte interface; (ii) the equilibration of redox reactions involved in charged transferred at the nanoporous metal/electrolyte interface is not satisfied during fast sweep rates as highlighted in Ref. [93].…”