Supply risk considerations for photoelectrochemical water splitting materials

Abstract

Hydrogen is a key enabler of a carbon neutral economy. The main production route of renewable hydrogen is via renewable wind and solar power and water splitting via electrolyzers. Photoelectrochemical water splitting is an alternative production route using incoming solar radiation to produce hydrogen and oxygen via a photoabsorber material with suitable band gaps and positions. Various absorber materials are being discussed in research and further developed at the lab scale. However, these materials need to be scalable in production, with low supply risk, because of the scale of hydrogen production needed to satisfy the global need for green hydrogen. Here, we semi-quantitatively assess the short-term and long-term supply risks due to potential supply reduction, demand increase, concentration risks, and political risks of eight chemical elements contained in nine promising absorber materials for photoelectrochemical water splitting. On an element level, supply risks are lowest for iron, copper, and tantalum in the present scenario and tin in the future scenario. The supply risks are highest for bismuth in the present scenario and future scenario. On a material level, present supply risks are lowest for hematite and highest for bismuth vanadate. Bismuth vanadate has the highest future supply risks, but tin tungsten oxide achieves the lowest supply risk score in the future scenario. The results show that some frequently discussed photoelectrochemical absorber materials have higher supply risks than typically perceived. In contrast, other materials should be more intensively studied because of their promising low long-term supply risk evaluation. Our method provides a separate assessment of present and future supply risks, which was previously unavailable for the criticality assessments.