The photochemical deposition of Pt on both WSe 2 and ATM/WSe 2 photoelectrodes significantly reduces overvoltage similar to a platinized single crystalline n-type WSe 2 and MoS 2 nanosheets. This behavior can be explained by Fermi level pinning (FLP), caused by gap-states (defects) at the catalyst/semiconductor interface provided by Pt. Here, the W d-band dis- The ATM catalyst on top of the WSe 2 film is more efficient than the photodeposited Pt catalyst, since it activates not only the grain boundaries as Pt, but also the vdW planes of WSe 2 due to the formation of a homogeneous heterojunction. For WSe 2 films of the same thickness (120 nm), coated with Pt or ATM, respectively, photocurrent densities of 1.4 mA cm -2 25 and 2.7 mA cm -2 at 0 V vs. RHE were obtained, i.e. the charge transfer for the ATM catalyst is 2 times higher compared to that of the Pt catalyst (see Supplementary Fig. ). However, taking into account the surface coverage (4 % coverage by Pt islands; 25 100 % coverage of the ATM layer), the charge transfer efficiency of the Pt catalyst is higher by a factor of more than ten compared to that of the ATM catalyst (see Supplementary Fig. ). The ATM/WSe 2 shows a higher photocurrent density at lower voltages starting from 0.1 V than that of the Pt/WSe 2 . However, the latter exhibits higher activity at higher voltages, which is important with respect to the efficiency of the photocathode. Consequently, a Pt-photodeposition on top of the ATM/WSe 2 leads to an enhancement of the photocurrent density at higher voltages, since the Pt catalyst on top of ATM additionally improves the charge transfer for HER.