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D2.6 Optimum Transparent Bipolar Membrane - Executive Summary

This report retraces the approaches and the steps leading to the optimisation of the transparent bipolar membrane (TBM) to be applied in the SunCoChem tandem photoelectrocatalytic reactor (TPER). The selected TBM architecture includes the use of Aquivion® for the proton exchange layer (PEL), of FAA-3 in the bicarbonate form for the anion exchange layer (AEL) and a 3D interface layer based on anion/cation exchange polymer fibres prepared by dual electrospinning. The membrane was asymmetrical with lower thickness of the AEL, representing the limiting component in terms of ion conductivity and thermal/electrochemical stability.

The work performed in task 2.5 aimed first of all at optimising the thickness of the different components of the membrane and of the overall membrane to avoid ions/ species crossover. Furthermore, to reduce its resistance and enhance its performance, different types of water dissociation catalysts (WDC) were incorporated at the fibrous interface.

The selection of the optimal TBM was made based on the results of the physico-chemical and electrochemical characterisation. In particular morphology, ion conductivity, UV-vis transparency, (electro)chemical/thermal stability, mechanical and electrochemical properties were evaluated and compared with the targeted KPIs.

The first-generation membrane, with a 10 μm thick AEL led to ion crossover issues. The second-generation membrane had a greater thickness, with a thicker AEL. The last generation membrane also included WDC nanoparticles (IrO2, Al(OH)3) to reduce the resistance and increase the water dissociation at the TBM interface. A range of characterisation techniques, and in particular electrochemical H-cell measurements, demonstrated that the thick membrane (2nd generation like) with the fibrous interface layer loaded with 0.1 mg/cm2 Al(OH)3 particles possess the adapted properties in terms of conductivity, transparency, stability and performance for application in the project TPER.

Despite the end of the task, further investigation of stability of the performance overtime and optimisation of the WDC loading and deposition technique will be relevant for the project.