Photocatalytic membrane reactors for hydrogen production from water

Hydrogen is considered today a promising environmental friendly energy carrier for the next future, since it produces no air pollutants or greenhouse gases when it burns in air, and it possesses high energy capacity. In the last decades great attention has been devoted to hydrogen production from water splitting by photocatalysis. This technology appears very attractive thanks to the possibility to work under mild conditions producing no harmful by-products with the possibility to use renewable solar energy. Besides, it can be combined with the technology of membrane separations making the so-called photocatalytic membrane reactors (PMRs) where the chemical reaction, the recovery of the photocatalyst and the separation of products and/or intermediates simultaneously occur. In this work the basic principles of photocatalytic hydrogen generation from water splitting are reported, giving particular attention on the use of modified photocatalysts able to work under visible light irradiation. Several devices to achieve the photocatalytic hydrogen generation are presented focusing on the possibility to obtain pure hydrogen employing membrane systems and visible light irradiation. Although many efforts are still necessary to improve the performance of the process, membrane photoreactors seem to be promising for hydrogen production by overall water splitting in a cost-effective and environmentally sustainable way.