Bifunctional carbon quantum dot-embedded metal-organic framework nanohybrid as a highly efficient electrocatalyst for water splitting and CO2 reduction

Abstract

Bifunctional carbon quantum dot (CQD)-embedded metal-organic framework (MOF) (CQD@MOF) nanohybrid as an energy-efficient electrocatalyst is fabricated for electrochemical water splitting and CO2 reduction through a simple and environmentally friendly method using natural resources. Key parameters, such as synthesis temperature, deposition temperature and time, pH and type of electrolyte, and scan rate, are optimized to fabricate binder-free CQD@MOF/nickel foam (NF) electrodes. Excellent hydrogen and oxygen evolution reactions occur with a current density of 50 mA/cm2 at lower overpotentials of 48.00 and 135 mV in a 1 M potassium hydroxide (KOH) electrolyte at a scan rate of 5 mV/s, respectively. In a two-electrode system, the CQD@MOF/NF electrode exhibits a low overpotential of 1.36 V to achieve 10 mA/cm2, confirming the practical feasibility of overall water splitting. Furthermore, the electrode exhibits high chemical stability and robustness even after 4000 cycles and more than 17 h. These results are attributed to the effective combination of substantial adsorption sites and the improved conductivity of the MOF induced by the electron-accepting characteristics of the CQDs with high charge transfer rates during water splitting. Finally, electrochemical CO2 reduction of the CQD@MOF/NF electrode is demonstrated by continuously maintaining a specific current density for 12 h, which can extend the technological potential of carbon nanohybrid as an electrocatalyst for green energy applications.