Figure 7. a) Schematic illustration, SEM image and OCP test results of a TiO 2-BiVO 4 -CdS heterojunction photoanode. Reproduced with permission. [36] Copyright 2022, Elsevier; b) Schematic illustration, SEM image and OCP test results of a COF(TpBD)-TiO 2 photoanode. Reproduced with permission. [33] Copyright 2020, Elsevier; c) Schematic illustration, SEM image and OCP test results of a SnO 2 /TiO 2 nanorods photoanode. Reproduced with permission. [37] Copyright 2020, Elsevier.