Self-transforming ultrathin α-Co(OH)₂ nanosheet arrays from metal-organic framework modified graphene oxide with sandwich-like structure for efficient electrocatalytic oxygen evolution

Developing efficient and low-cost electrocatalysts for oxygen evolution reaction (OER) with high electrochemical activity and durability for diverse renewable and sustainable energy technologies remains challenging. Herein, an ultrasonic-assisted and coordination modulation strategy is developed to construct sandwich-like metal-organic framework (MOF) derived hydroxide nanosheet (NS) arrays/graphene oxide (GO) composite via one-step self-transformation route. Inducing from unsteady state, the dodecahedral ZIF-67 with Co²⁺ in tetrahedral coordination auto-converts into defect-rich ultrathin layered hydroxides with the interlayered ion NO₃^-. The self-transforming α-Co(OH)₂/GO nanosheet arrays from ZIF-67 (Co(OH)₂-GNS) change the coordination mode of Co²⁺ and bring about the exposure of more metal active sites, thereby enhancing the spatial utilization ratio within the framework. As monometal-based electrocatalyst, the optimized Co(OH)₂-GNS exhibits remarkable OER catalytic performance evidenced by a low overpotential of 259 mV to achieve a current density of 10 mA·cm^-2 in alkaline medium, even exceeding commercial RuO₂. During the oxygen evolution process, electron migration can be accelerated by the interfacial/in-plane charge polarization and local electric field, corroborated by the off-axis electron holography. Density functional theory (DFT) calculations further studied the collaboration between ultrathin Co(OH)₂ NS and GO, which leads to lower energy barriers of intermediate products and greatly promotes electrocatalytic property.