Introduction
Electrochemical water-splitting processes have arisen as an alternative for fighting energy source shortages through H2 generation. However, this process requires the usage of catalysts in order to reduce the energy input. Metal organic frameworks (MOFs) are novel materials which may act as water-splitting catalysts due to their stability, crystal structure and high conductivity.
Methods
MOF NH2-MIL-101(Fe) was synthetized through a solvothermal method (20 h, 110°C) using FeCl3∙6H2O, 2-aminoterephthalic acid and dimethylformamide. For the electrochemical water-splitting process assessment, different dosages of MOF-Fe were placed on the working electrode by different means (dropwise, dip-coating, ultrasonic dispersion), with Ni foam for alkaline and neutral pHs or carbon paper for acid pH (1 cm2), using graphite sticks and HgCl2 electrodes as counter and reference electrodes, respectively. This three-electrode cell was connected to a PGSTAT302N potentiostat (Methrom).
Results
MOF-Fe was tested for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at neutral, acid, and alkaline pHs. MOF-Fe showed a high performance in the alkaline OER. Moreover, 0.25 mg/cm2 was found to be the optimal MOF-Fe dosage. Thus, 10, 50 and 100 mA/cm2 were obtained by applying low overpotentials of 300, 347 and 372 mV. This catalyst also exhibited high stability for 90 h at such current densities, defeating the benchmark catalyst (IrO2) in both activity and stability. Characterization analysis showed that MOF-Fe's performance could be explained by its high crystallinity, elevated functional group presence, and great surface area.
Conclusions
The noble metal-free MOF-Fe was a suitable alternative for applying electrochemical water-splitting processes in a more environmentally friendly and economic approach, opening a path for the future application of these processes.
Acknowledgments
This work was supported by Project H2-ZeroWaste (AXA Research Fund). Aida Díez is grateful to Ramon y Cajal (RYC2023-044934-I)'s financial support (MICIU).
