Efficiency in photocatalytic production of hydrogen: energetic and sustainability implications

Hydrogen generation through a photocatalytic process appears to be a promising technology to produce this energy vector through a novel, efficient, green, and sustainable process. The fruitful use of sunlight as an excitation source and renewable bio-derived reactants as well as the development of highly efficient catalysts are required to achieve this goal. In this perspective article, we focus on describing how to braid energy and sustainability sides of hydrogen photo-generation into a single parameter, allowing quantitative measurement and trustful comparison of different catalytic systems. Starting from the energy-related efficiency parameters defined by the IUPAC, we present novel approaches leading to parameters enclosing energy and sustainability information. The study is completed with the analysis of other, non-IUPAC, parameters of broad use such as the solar-to-hydrogen observable. The set of results available in the literature for the water splitting reaction and the use of bio-derived sacrificial molecules are reviewed to assess the potential of such reactions in the energy-efficient and sustainable production of hydrogen.