Electrolyte-less design of PEC cells for solar fuels: Prospects and open issues in the development of cells and related catalytic electrodes

The possibilities and prospects offered from a new electrolyte-less (EL) cell design for photoelectrocat-alytic (PEC) cells to produce solar fuels, particularly by reduction of CO2, are discussed in this perspectivecontribution. The concept of EL configuration is presented evidencing the several potential advantages,but also the need to develop novel specific nanostructured electrodes. Some aspects of the preparationof photoanode and electrocatalysts for EL-PEC solar cells are discussed, with focus on thin films based onarrays of vertically aligned TiO2nanotubes and nanocarbon-based gas diffusion catalytic electrodes forCO2reduction, respectively. New possibilities for design of cells, particularly suitable for medium-hightemperature of operations (150–200◦C), necessary for process intensification and reduction of the costs,are also presented. These new type of cells require the development of new types of semiconductors,which are briefly outlined.