DRY HYDROGEN PRODUCTION IN A CRITICAL RAW MATERIAL-FREE TANDEM PHOTOELECTROCHEMICAL CELL

The According to the European Strategy Energy Technology plan, by 2050 at least 65% of electric energy should derive from renewable energy sources and, furthermore, CO2 emissions related to the energy production should be reduced by 50%. From this perspective, a drastic reduction in the dependence from fossil fuels could be realized by exploiting all abundant renewable sources that nature reserves: sun, wind, water, and geothermic. These technologies have recently experienced large-scale commercialization, and generate electric energy by directly converting the energy of renewable sources. Photoelectrochemical water splitting is recognised as a promising strategy and it attracts particular interest for storing solar energy into the chemical bonds of hydrogen as fuel, which can be further utilised in fuel cells, internal combustion engines and to progressively decarbonize industrial processes. To achieve high solar to hydrogen conversion efficiencies in practical photoelectrochemical cells, the choice of photoelectrodes and the cell configuration (one or two photoelectrodes) are of great importance.Since overall water splitting consists of two half-reactions, i.e., water oxidation to oxygen and reduction to hydrogen, it is natural to use a two-photoelectrode configuration to maximize both processes with the cell illuminated from the higher energy gap semiconductor. The longer wavelength photons that are not absorbed by the top large band gap absorber are transmitted to and harvested by the bottom low band gap absorber. Owing to band bending, the photogenerated electrons in p-type photocathodes and holes in n-type photoanodes migrate toward the semiconductor-electrolyte interface to reduce and oxidize water, respectively. In parallel, photogenerated holes in the photocathode and electrons in the photoanode are transferred to the external circuit and recombine at the Ohmic back-contact that connects both photoelectrodes.In the context of a Horizon 2020 project (FotoH2), a critical raw material-free tandem photoelectrochemical cell, that is directly capable of producing dry hydrogen, was developed. This work addresses for the first time the use of a porous hydrophobic backing layer in a photoelectrochemical cell to allow direct production of dry hydrogen.