We measured the non-Faradaic double-layer capacitance (C dl ) using cyclic voltammetry (CV) at various scan rates (Figure ) to provide a semi-quantitative estimate of the electrochemical surface area (ECSA). Figure shows the calculated C dl values for MoS 2 @NiFeCo-Mo(doped)-LDH, MoS 2 @NiFeCo-LDH, NiFeCo-Mo(doped)-LDH, and NiFeCo-LDH are 14, 13.4, 12.5, and 7.6 mF cm -2 , respectively. These results suggest that the incorporation of MoS 2 QDs on and Mo in NiFeCo-LDH increases the ECSA and the number of accessible active sites within the hierar-chical heterostructure. Remarkably, the deposition of MoS 2 QDs onto NiFeCo-Mo(doped)-LDH and NiFeCo-LDH significantly increases the effective ECSA to 24.3 and 21.5 mF cm -2 under light irradiation, respectively. The increase in the effective ECSA indicates that the deposition of MoS 2 QDs increases the (effective) active surface area or improves the light absorption, both of which are crucial for the (photo)electrocatalytic HER.