Bimetallic CPM-37(Ni,Fe) metal-organic framework: enhanced porosity, stability and tunable composition

A newly synthesized series of bimetallic CPM-37(Ni,Fe) metal-organic frameworks with different iron content (Ni/Fe approximate to 2, 1, 0.5, named CPM-37(Ni2Fe), CPM-37(NiFe) and CPM-37(NiFe2)) demonstrated high N2-based specific SBET surface areas of 2039, 1955, and 2378 m2 g-1 for CPM-37(Ni2Fe), CPM-37(NiFe), and CPM-37(NiFe2), having much higher values compared to the monometallic CPM-37(Ni) and CPM-37(Fe) with 87 and 368 m2 g-1 only. It is rationalized that the mixed-metal nature of the materials increases the structural robustness due to the better charge balance at the coordination bonded cluster, which opens interesting application-oriented possibilities for mixed-metal CPM-37 and other less-stable MOFs. In this work, the CPM-37-derived alpha,beta-Ni(OH)2, gamma-NiO(OH), and, plausibly, gamma-FeO(OH) phases obtained via decomposition in the alkaline medium demonstrated a potent electrocatalytic activity in the oxygen evolution reaction (OER). The ratio Ni : Fe approximate to 2 from CPM-37(Ni2Fe) showed the best OER activity with a small overpotential of 290 mV at 50 mA cm-2, low Tafel slope of 39 mV dec-1, and more stable OER performance compared to RuO2 after 20 h chronopotentiometry at 50 mA cm-2. CPM-37 MOFs demonstrate enhanced stability for mixed metal variants, which ensure favorable local charge distribution/balance. The decomposition of these MOFs leads to mixed metal oxides with lower Tafel slope in the OER than for the RuO2 benchmark.