Microwave-assisted rapid controllable synthesis of hexagonal prismatic CoNi-MOF-74 and its derivative for efficient oxygen evolution reaction

Abstract

Optimizing the composition and structure of metal-organic framework (MOF) materials has been proven effective in enhancing the performance of the oxygen evolution reaction (OER). However, rapid and controllable synthesis of MOF materials still faces challenges. In this work, we employed microwave assistance and surfactant soft templating to achieve rapidly synthesize CoNi-MOF-74 with controllable morphology. By incorporating 4% polyvinyl pyrrolidone (PVP), we successfully synthesized uniform hexagonal PVP4%-CoNi-MOF-74 within a remarkably short time of only 20 min. The PVP4%-CoNi-MOF-74 exhibited a mesoporous structure, displaying an impressive BET surface area of 1321.8 m2/g. PVP4%-CoNi-C alloy was obtained through a direct high-temperature treatment of PVP4%-CoNi-MOF-74 in an N2 environment. The PVP4%-CoNi-C alloy successfully preserved their initial morphology and pore structure, and exhibited excellent OER performance. At a current density of 10 mA/cm2 in a 1.0 M KOH solution, it demonstrated an overpotential of 310 mV, outperforming the commercial precious metal catalyst RuO2 (overpotential of 394 mV). Impressively, even after 3000 cycles, the overpotential of PVP4%-CoNi-C alloy only experienced a minimal positive shift of 0.02 V, showcasing its excellent stability. Through a combination of experimental findings and DFT calculations, it is believed that the superior OER performance of the PVP4%-CoNi-C alloy can be attributed to its morphological dependence induced by the hexagonal prism structure, its large specific surface area facilitating more active sites, as well as the enhanced coordination interactions and faster electron transfer capabilities provided by the unique CoNi active site module.