Fig. 9. Theoretical maximum efficiency ranges (color bar for quantification of STH efficiency is located on the extreme right and applies to all three types) as a function of band gap(s) of the involved semiconductor particle(s) for the three conceptual reactor design types (for ideal, no-overpotential case; or for non-ideal case that includes overpotentials). The best theoretical case for each type as ideal and non-ideal cases are indicated with stars. The most efficient laboratory-scale demonstration with their material combinations (located at their respective band gaps) are also indicated with a star (termed “best experiment”). The colored contour plot in type 2 and 3 indicate the non-ideal case and black iso-lines indicate the ideal case. For the theoretical predictions in type 2 and 3, the redox mediator potential is optimized for the particular band gap combination (see details in Fig. 4 and 5). Typical material types (oxysulphide, oxynitride, non-oxides and metal oxides) used in experiments and their band gap ranges are indicated by colored bars.