Dual‐Function PCN‐777/WSe ₂ @g‐C ₃ N ₄ Heterostructures for Energy Storage and Hydrogen Evolution

The hybrid supercapattery combines the rapid charge–discharge capability of supercapacitors with the elevated energy storage capacity of batteries. In this study, PCN‐777/WSe 2 @g‐C 3 N 4 heterostructures are synthesized by a hydrothermal method and are evaluated for energy retention and hydrogen evolution reaction (HER) systems. PCN‐777 provides a porous framework for ion transport and structural stability, while WSe 2 enhances electrical conductivity and mechanical strength. The g‐C 3 N 4 promotes interfacial coupling to improve pseudocapacitive storage. Scanning electron microscope and X‐ray diffraction confirm uniform distribution and phase purity. Electrochemical analysis shows a specific capacity ( Q S ) of 1700 C g −1 at 2.0 A g −1 in a three‐electrode system. A hybrid device using PCN‐777/WSe2@g–C3N4 as the anode and activated carbon as the cathode achieves 63.21 Wh kg −1 at 800 W kg −1 and retains 89.3% capacity after 1000 cycles. Kinetic analysis gives slope values of 0.60–0.79, confirming combined surface‐controlled and diffusion‐limited contributions. For HER, the composite requires an overpotential of 69.43 mV at 10 m A cm −2 with a Tafel slope of 77.62 m V/dec, confirming efficient catalytic activity and electron transfer.