Molybdenum sulfide (MoS2) has attracted considerable attention as one of noble-metal-free co-catalysts of hydrogen evolution reaction (HER) for artificial photosynthetic water splitting. There are well-known challenges in optimizing its catalytic activity to pursue the replacement of platinum (Pt) for HER, owing to the edge-limited active sites and intrinsically poor conductivity. Herein, we prepared metallic MoS2 nanodots (MNDs) with 1T-phase occupation and edge-exposure maximum to achieve the simultaneous optimization of electric conductivity and active sites. When integrated as co-catalysts with graphitic carbon nitride (g-CN) for sunlight-driven HER in alkaline electrolyte, the outstanding photocatalytic activity with hydrogen evolution rate of 5.62 mmol g(-1) h(-1), over 280 times higher than that of pure g-CN, demonstrates the excellent co-catalytic performance of 1T-MoS2 NDs (1T-MNDs) that even comparable to state-of-the-art Pt. The photo-induced charge dynamics describe the role of 1T-MNDs in facilitating charge separation as well as surface catalytic reaction, suggesting a promising potential of 1T-MNDs with more active sites and higher conductivity as Pt-alternative co-catalysts for solar hydrogen production. (C) 2019 Elsevier Inc. All rights reserved.