Report on First-phase photoelectrolysis cell materials (D 4.1), FOTOH2 H2020-NMBP-2017, R.E. 43/2019, Grant Agreement n° 760930

Deliverable D4.1 deals with photoelectrolysis cell materials developed within Work Package 4 (WP4) of FotoH2 project in the first phase. In particular, the contents regard materials development and optimization of a pho- toelectrochemical cell (PEC) based on tandem architecture. The tandem cell is a device able to capture a significant portion of solar irradiation thanks to an assembling of a solid transparent membrane between an n-type and a p-type metal oxide semiconductors. Specific materials, at the photoanode and photocathode, were benchmarked and investigated in comparison with a standard TiO2 anode semiconductor and a conventional Pt cathode (dark counter-electrode). Several semiconductor materials were prepared and characterised according to the indications obtained from the modelling activity in WP3. The most suitable tandem couple, until now, is based on a n-type P- or Ti-doped Fe2O3 photoanode and p-type CuO photocathode, including protective layers and ionomer coatings. Appropriate deposition technologies include nanocolumnar growth by using cost-effective bath deposition methods, electrodeposition and successive chemical/thermal treatments. The employment of a solid ion exchange polymer electrolyte membrane was investigated for both acidic and alkaline media in order to substitute the corrosive liquid electrolyte and to increase the durability of the PEC. Ionic conductivity and hydrogen-oxygen crossover rate were determined. An anionic membrane electrolyte was selected accordingly to some relevant properties such as good ionic conductivity, corrosion mitigation aspects, proper light transmission for the tandem configuration and electrochemical performance. Furthermore, a porous and highly conducting hydrophobic backing substrate was developed as support for the photocathode to allow both the achievement of pure hydrogen in the output stream and to provide a good ohmic contact with the semiconductor layer. By substituting the transparent conductive glass with the porous Sigracet substrate, a step change improvement in efficiency was observed reaching 1.7 % as enthalpic efficiency at a bias of 0.6 V and about 5% throughput efficiency at the reversible potential for water splitting. Co-catalysts, such as NiFe-oxide nanoparticles, were prepared, implemented at the photoanode and compared with the standard promoters based on critical raw materials, such as perovskite (LSFCO) and IrRuOx. Ni-based nanomaterials were also synthesised and physico-chemically characterised with the aim of using these materials for the promotion of hydrogen evolution at the photocathode. Ionomer dispersions, obtained by dissolving the solid membrane in appropriate solvents, were also employed in order to increase the electrode-electrolyte interface and favour the interaction of the electrode with the solid polymer membrane. Their suitable deposition procedure along the nano-structured electrode surface was properly improved in terms of ionomer loading and use of solvents in the dispersion.