Multifunctional electrocatalyst based on MoCoFe LDH nanoarrays for the coupling of high efficiency Electro-Fenton and water splitting process

Abstract

Novel MoCoFe layered double hydroxide (LDH) nanoarray catalysts were prepared by a one-step solvothermal method. These catalysts served as multifunctional catalysts for the coupling of overall water splitting with the Electro-Fenton process. MoCoFe LDH displayed different array structures evolving with Mo content, which results in different catalytic activities in the Oxygen Reduction Reaction (ORR), Oxygen Evolution Reaction (OER), and Hydrogen Evolution Reaction (HER) processes. Among them, Mo2CoFe LDH exhibited about 90% H2O2 selectivity over a wide voltage range and almost 100% degradation efficiency of sulfonamide antibiotics within 45 min. This was due to more open nanowire array structures and bond expansion resulting from the Mo introduction. Density Functional Theory (DFT) calculations showed that the addition of Mo atoms significantly reduced the energy barrier of H2O2 generation at the active site of Co. Meanwhile, Mo0.5CoFe LDH displayed competitive OER performance with an overpotential of 190 mV (vs. RHE) and HER activity with an overpotential of 78 mV@10 mA cm−2. The water splitting cell consisting of Mo0.5CoFe LDH electrodes only required a voltage of 1.53 V to achieve a current density of 10 mA cm−2. This was due to the generation of the crystal-amorphous interface structure via the substitution of Mo for the metal sites in LDH, which contributed to the internal active site exposure. The crystallization-amorphous structure promotes an increase in the number of active sites in terms of unit area by accelerating the M−OH to M−OOH reconfiguration, in addition to that, corrosion resistance and self-healing properties of this structure also helps to improve the stability and durability of the material during the OER process. Noteworthy, the Electro-Fenton/water-splitting coupling device was constructed, benefiting from the excellent Electro-Fenton and water electrolysis performance in alkaline solutions. The complete decolorization of 20 mg L-1 methyl blue could be achieved within 80 min at pH = 14 (Iwater-splitting = 37 mA cm−2, IEF = 8 mA cm−2), and Faraday efficiency of water splitting still remains above 95% after coupling EF. This novel coupling device may help to improve the energy utilization in the electrocatalytic process.