No abstract

The present work suggests two concepts for producing hydrogen by reverse electrodialysis. Reverse electrodialysis is a technology that uses concentration differences to create electrical energy. In this work, the energy is utilised as direct hydrogen production within a closed-loop system. For both system alternatives, waste heat is used to set up the mentioned concentration differences. The first concept is evaporation, where heat is added to boil off excess water from a concentrated solution and thereby increase its concentration. The second concept removes heat to precipitate excess salt. For the precipitation concept to work, a salt where the solubility is highly dependent on temperature must be used. KNO 3 fulfils this requirement. As part of a proof of concept, the conductivity of membranes soaked in KNO 3 was investigated. The conductivity of the salt in two commercialised membranes, Fumatech FKE-50 and FAS-30, was measured and compared to NaCl in the same membranes. The conductivity of K + in FKE-50 was found to be 4.5 and 6.6 mS cm −1 at 25 • C and 40 • C respectively. The conductivity of NO − 3 in FAS-30 was found to be 4.3 mS cm −1 and 6.5 mS cm −1 at 25 • C and 40 • C respectively. Neither of the membranes change conductivity with soaking concentrations. The conductivity at 40 • C compared to 25 • C is significantly better in the FKE membrane, and seemingly better in the FAS membrane. Potential peak power densities for a This is the accepted version of an article published in ECS Transactions.

In this study, six flexible pipe steel armor wires used in oil and gas transportation are characterized, and their hydrogen diffusion coefficients and hydrogen uptakes are measured using an electrochemical hydrogen permeation technique. The wires have ferritic-pearlitic microstructures with round, lamellar, or partially lamellar carbides and the shape and orientation of the grains indicate that the microstructures were plastically deformed to different degrees. It was assumed that hydrogen was transported through the ferrite, so the presence of cementite in the steel armor wires leads to longer hydrogen diffusion paths through the ferrite, which was quantified with a tortuosity factor. After compensating for tortuosity, the normalized steady-state flux shows a tendency to increase as the grain size decreases. The effective diffusion coefficients increase with a decrease of the ferrite-cementite interface area, suggesting trapping on the ferrite-cementite interfaces.The uptake of diffusible hydrogen was lowest for the least plastically deformed materials and about twice as high for the more plastically deformed materials.