Sustainable calcium-based heterostructure MOFs derived from waste for photocatalytic and electrocatalytic hydrogen production

The pursuit of a hydrogen evolution reaction (HER) catalyst that is both efficient and cost-effective remains a critical challenge in sustainable energy research. The use of waste-derived precursors such as PET bottles and eggshells provides a sustainable route for the synthesis of calcium-based MOFs, aligning with green chemistry and circular economy principles. Metal–organic frameworks (MOFs) are promising catalytic materials due to their tunable structures and flexible coordination environments. In this study, a novel calcium-based heterostructured MOF, Ca-BDC-Mel, was synthesized and compared with its individual counterparts, Ca-BDC and Ca-Mel. In photocatalytic hydrogen evolution, Ca-Mel exhibited the highest activity (1925 μmol g⁻¹ h⁻¹), followed by Ca-BDC-Mel (1055 μmol g⁻¹ h⁻¹), and Ca-BDC (937.0 μmol g⁻¹ h⁻¹). In electrocatalytic measurements, Ca-BDC showed higher chronoamperometric hydrogen generation compared to the other materials. Electrochemical impedance spectroscopy revealed that Ca-BDC-Mel exhibits a low charge transfer resistance (Rct = 12.16 Ω) and the highest electrical double-layer capacitance (Cdl = 276.2 μF cm⁻²), indicating improved interfacial charge-transfer characteristics. Additionally, it delivers an overpotential of 104.5 mV at 10 mA cm⁻², reflecting balanced electrochemical performance among the synthesized materials.