Photochemical hydrogen generation with porphyrin-based systems

• Photocatalytic hydrogen production.
• Porphyrin rings as photosensitizers and as catalysts.
• Complexity, performance and mechanistic insight.

While its main current use is that of a feedstock in the chemical and petrochemical industry, molecular hydrogen can also be considered, in perspective, as an interesting energy carrier to be used in place of conventional fuels, e.g., in devices such as fuel cells. From this viewpoint, of particular interest would be the possibility to generate hydrogen from water splitting using a source of renewable energy such as solar light. This could represent, in principle, an inexhaustible, environmentally friendly energy source. In this review we summarize recent work on photochemical hydrogen evolution carried out with systems based on porphyrins or metalloporphyrins, either as photosensitizers or as catalysts. The systems discussed are varied including different levels of complexity, performance, and mechanistic insight. In general porphyrin molecules appear as a very promising class of photosensitizers for photocatalytic hydrogen production.