Abstract
The focus of this study is evaluating the status of the most promising methods for water splitting to H-2 and O-2 with their implementation in mind. These are thermochemical water splitting, photocatalytic (PC) and photo-electrocatalytic (PEC) water splitting, and water electrolysis. In addition to evaluating their coherence, potential, and cost, some misconceptions in the PC H-2 production from water over suspended powder catalysts are highlighted. A few needed research directions at the fundamental level together with the main hurdles to cross for large-scale production are presented and in some cases discussed. Although an increasing level of activity has taken place in the last few years for large-scale hydrogen production from water, this is still marginal (at the megawatt scale). A considerable investment in different technologies is needed for a noticeable impact on the environment to occur with an objective to decrease the world dependence on fossil fuels (the terrawatt scale).