Using ALD for photoelectrolysis of water

In one hour, the Earth receives more energy from the sun than the entire human race consumes in a year. However, the intermittent nature of this resource has limited its share of the energy mix. One promising approach is to store this renewable but discontinuous energy in the form of fuels. As these compounds are produced from solar energy, they are known as solar fuels. In 1972, it was demonstrated that it was possible to produce dihydrogen and dioxygen by photodissociation of water on a titanium oxide electrode under solar illumination. This discovery has opened up promising prospects for the sustainable production of dihydrogen. As this process shares many similarities with photosynthesis, it is sometimes referred to as artificial photosynthesis. There are other molecules that can be used as solar fuels (for example, methanol, formic acid or formaldehyde) but we're going to focus this article on dihydrogen as it is the most promising and therefore the most studied at present along with its oxidizer, dioxygen. H ₂ has a high energy density (33 kWh·kg- ¹ ), is non-toxic and does not contribute to global warming, since its combustion does not generate CO ₂ . It is still little used as it is mostly extracted from fossil resources. However, when produced by the photoelectrochemical dissociation of water, it is pure enough to be used directly in fuel cells. In order to make water photodissociation processes commercially viable, it is necessary to optimize the yield of photoelectrochemical cells, increase their stability and lower the overall production cost of dihydrogen (between $2 and $4 per kg of H ₂ ).

Today, the efficiency of photoelectrochemical cells varies between 12% and 18%, depending on the type of material used for the photoelectrode and the cell architecture (single or multi-junction), whereas the theoretical limit values are 24.4% and 30% for tandem and multi-junction cells respectively. High-efficiency, high-cost devices were already implemented in the 2000s, but since then the improvements needed to manufacture efficient systems compatible with market constraints have not been achieved. It is therefore essential to significantly reduce costs, increase photoconversion efficiency and ensure the longevity of the devices. To meet this challenge, it is of course necessary to select an efficient, low-cost photosensitive material, but it is also possible to optimize the geometry of the photoelectrode. Recent studies have shown that structuring electrodes at micro and nano scales, as well as functionalizing them, can lead to a significant increase in cell performance.

Among the many...