This study investigates the use of platinum-based catalysts for the hydrogen evolution reaction (HER) in water splitting, a critical process for renewable energy production. Platinum is considered the most effective electrocatalyst for HER, but its high cost and scarcity limit its commercial viability. To address these issues, the authors developed a method to synthesize isolated single platinum atoms and clusters on nitrogen-doped graphene nanosheets (NGNs) using atomic layer deposition (ALD). The ALD technique allows for precise control over the size and density of the platinum catalysts, which are then evaluated for HER activity. The single platinum atoms and clusters exhibit significantly enhanced catalytic activity (up to 37 times) and high stability compared to commercial platinum/carbon (Pt/C) catalysts. X-ray absorption spectroscopy and density functional theory (DFT) analyses reveal that the partially unoccupied density of states of the platinum atoms' 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance. The study demonstrates the potential of single-atom and cluster catalysts in reducing the cost and improving the efficiency of hydrogen production from water electrolysis.This study investigates the use of platinum-based catalysts for the hydrogen evolution reaction (HER) in water splitting, a critical process for renewable energy production. Platinum is considered the most effective electrocatalyst for HER, but its high cost and scarcity limit its commercial viability. To address these issues, the authors developed a method to synthesize isolated single platinum atoms and clusters on nitrogen-doped graphene nanosheets (NGNs) using atomic layer deposition (ALD). The ALD technique allows for precise control over the size and density of the platinum catalysts, which are then evaluated for HER activity. The single platinum atoms and clusters exhibit significantly enhanced catalytic activity (up to 37 times) and high stability compared to commercial platinum/carbon (Pt/C) catalysts. X-ray absorption spectroscopy and density functional theory (DFT) analyses reveal that the partially unoccupied density of states of the platinum atoms' 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance. The study demonstrates the potential of single-atom and cluster catalysts in reducing the cost and improving the efficiency of hydrogen production from water electrolysis.