Low-crystalline mixed Fe-Co-MOFs for efficient oxygen evolution electrocatalysis

Metal-organic frameworks (MOFs), as an state-of-the-art electrocatalyst, have been shown an efficient alternative to precious metals. Herein, we have synthesized a series of mixed Fe-Co-MOFs (MFC-MOFs) with low crystallinity by a simple one-step solvothermal method, which can be applied as direct electrocatalysts for oxygen evolution reaction. The broadening and weakened XRD diffraction peaks and the diffused ring in SAED reveal the low-crystalline characteristic of MFC-MOFs. The shifted Co 2p3/2 and Fe 2p3/2 peaks in XPS confirm the redistribution of local electrons in MFC-MOFs. The formation of more favorable Co in higher valence state is confirmed in XPS, which is more beneficial to be transformed into active OOH-like intermediates for OER. The optimal MFC-MOFs exhibits a lower overpotential at 10 mA cm−2, which decreases in 212 and 140 mV compared to that of Fe-MOFs and Co-MOFs, respectively. Meanwhile, a remarkably low Tafel slope (37 mV dec−1) and a favorable long-term stability (over 20 h) are obtained on the MFC-MOFs, which are all much superior to those of the as-synthesized RuO2. The enhanced catalytic activity can be mainly attributed to the inter-molecular synergy between Co-MOFs and Fe-MOFs, which affords MFC-MOFs low-crystalline structure and enlarged surface area. The optimized structure in return promotes the exposure of more active sites and remarkably improves the charge transfer capability. Overall, the design strategy based on the inter-molecular synergistic interactions and low-crystalline structure are worthy to be extended to increase the stability, catalytic active sites and electron transfer ability of mixed-node MOF electrocatalysts.