2D Ni-Naphthalene-2,6-Dicarboxylic Acid Metal-Organic Framework as Electrocatalysts for Efficient Overall Water Splitting

Two-dimensional metal-organic frameworks (MOFs) are regarded as promising electrocatalysts because of their high surface area and tunable compositions. Herein, a novel nickel-based 2D MOF for efficient oxygen evolution reaction (OER) has been developed. Ni-NDC MOF nanosheets (NDC = naphthalene-2,6-dicarboxylic acid) are successfully synthesized on a nickel foam (NF) through a surfactant-assisted one-step hydrothermal method. The resulting Ni-NDC@NF possessing a high electrochemically active surface area of 3.06 mF cm⁻² exhibits excellent OER performance with a low overpotential of 249 mV at 10 mA cm⁻², a small Tafel slope of 74 mV dec⁻¹, 100% faradaic efficiency, and long-term stability of 24 h at least. For the application of a bifunctional catalyst, NiMo alloy is electrodeposited on the Ni-NDC@NF to enhance hydrogen evolution reaction activity. The overall water splitting in a two-electrode configuration of NiMo/Ni-NDC@NF electrodes as both anode and cathode require only a 1.56 V for 20 mA cm⁻². The photovoltaic-electrocatalysis system powered by the tandem solar cell represents a high solar-to-hydrogen efficiency of ≈22%. This work will contribute to inspiring the design of novel MOF composite catalysts using vertically aligned 2D MOF nanosheet architecture, thereby enlarging the potential of MOFs on next-generation electrocatalysts and energy devices.