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

Abstract

A newly synthesized series of bimetallic CPM-37(Ni,Fe) metal-organic frameworks with different iron content (Ni/Fe ≈ 2, 1, 0.5, named CPM-37(Ni₂Fe), CPM-37(NiFe) and CPM-37(NiFe₂)) demonstrated high N₂-based specific <i>S</i>_BET 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 α,β-Ni(OH)₂, γ-NiO(OH), and, plausibly, γ-FeO(OH) phases obtained <i>via</i> decomposition in the alkaline medium demonstrated a potent electrocatalytic activity in the oxygen evolution reaction (OER). The ratio Ni : Fe ≈ 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.