Revealing the Structural Transformation between the Activity and Stability of 2D and 3D Co-Mo Metal-Organic Frameworks for a Highly Active Oxygen Evolution Reaction

The development of highly active and cost-effective metal-organic frameworks (MOFs) with large surface areas, abundant active sites, and distinct structures resulted in reduced kinetic barriers involving a four-electron transfer path for the oxygen evolution reaction (OER). In this work, the OER activity of cobalt- molybdenum metal-organic framework (Co-Mo-MOF)-based materials was significantly improved by controlling 3D and 2D framework structures, namely, Co-Mo-3D and Co-Mo-2D, respectively. When Co-Mo-3D was reacted in an alkaline electrolyte, a highly porous gyroid morphology with a large surface area was formed and designated as KOH-treated Co-Mo-3D. The KOH-treated Co-Mo-3D demonstrated superior OER electrocatalytic activity with a low overpotential of 210 mV at a current density of 10 mA cm-2 and small Tafel slope of 50 mV dec-1 in alkaline solution. In addition, KOH-treated Co-Mo-3D exhibited excellent long-term durability at different voltages. The detailed structure transformation of Co-Mo-MOFs during the reaction was also provided by in situ X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and ex situ X-ray absorption spectroscopy (XAS). Moreover, density functional theory (DFT) calculations revealed that the hydrogen-bonding network system formed in Co-Mo-3D plays an important role in assisting proton transfer and enhancing the catalytic activity of the OER. This work opens up a new prospect for the design and development of catalytically active pillar-layered MOF catalysts for OERs.