Metallic two-dimensional metal-organic framework arrays for ultrafast water splitting

This work reports a universal dissolution-recrystallization method to synthesize two-dimensional (2D) conductive metal-organic framework (MOF) arrays. The MOF arrays have exhibited excellent structural characteristics for electrochemical reactions, including ultrathin architecture, metallic conductivity, and hierarchical macro-/micro-porosity. Particularly, 2D nickel, iron-MOF arrays act as bifunctional electrocatalysts for water splitting, which deliver a current density of 500 mA cm−2 at an overpotential of 305 mV for anodic oxygen evolution reaction (OER), 359 mV for hydrogen evolution reaction (HER), and ~640 mV for overall reactions. The electrode also shows prolonged stability against bulk water splitting (up to 20 h at 500 mA cm−2). In addition, the water splitting system has been further coupled with commercial solar cells to simulate natural water photolysis, demonstrating a high solar-to-hydrogen efficiency of 17.69%. Mechanism study thorough density function theory (DFT) computations shows strong synergistic effect between Ni and Fe active sites that can reduce the Gibbs energy barrier of hydroxyl dissociation step (OH* → O*) during OER and H* desorption step during HER simultaneously. These promising results open up enormous opportunities of designing versatile low-dimensional conductive MOF architectures for renewable energy applications.