The study reports a novel strategy for synthesizing highly active graphitic carbon nitride (g-C₃N₄) from a low-cost precursor, urea, to efficiently produce hydrogen from water using solar energy. The synthesized g-C₃N₄ exhibits an extraordinary hydrogen-evolution rate of approximately 20,000 μmol h⁻¹ g⁻¹ under full arc conditions, leading to a high turnover number (TON) of over 641 after 6 hours. The catalyst shows an internal quantum yield of 26.5% under visible light, which is nearly an order of magnitude higher than that of any other existing g-C₃N₄ photocatalysts. The enhanced activity is attributed to the lower protonation status and the degree of polymerization, as determined by experimental analysis and density functional theory (DFT) calculations. The study also highlights the importance of both protonation and polymerization in controlling the hydrogen-evolution rate, with a lower proton concentration and higher polymerization degree leading to increased activity. The optimized g-C₃N₄ photocatalyst is highly stable, maintaining its activity for over 30 hours without significant loss. This work demonstrates a significant improvement in the efficiency and stability of g-C₃N₄ for hydrogen production from water, making it a promising candidate for practical applications.The study reports a novel strategy for synthesizing highly active graphitic carbon nitride (g-C₃N₄) from a low-cost precursor, urea, to efficiently produce hydrogen from water using solar energy. The synthesized g-C₃N₄ exhibits an extraordinary hydrogen-evolution rate of approximately 20,000 μmol h⁻¹ g⁻¹ under full arc conditions, leading to a high turnover number (TON) of over 641 after 6 hours. The catalyst shows an internal quantum yield of 26.5% under visible light, which is nearly an order of magnitude higher than that of any other existing g-C₃N₄ photocatalysts. The enhanced activity is attributed to the lower protonation status and the degree of polymerization, as determined by experimental analysis and density functional theory (DFT) calculations. The study also highlights the importance of both protonation and polymerization in controlling the hydrogen-evolution rate, with a lower proton concentration and higher polymerization degree leading to increased activity. The optimized g-C₃N₄ photocatalyst is highly stable, maintaining its activity for over 30 hours without significant loss. This work demonstrates a significant improvement in the efficiency and stability of g-C₃N₄ for hydrogen production from water, making it a promising candidate for practical applications.