Tetra-carboxylic acid based metal-organic framework as a high-performance bifunctional electrocatalyst for HER and OER

Tetra-carboxylic acid based 3D porous MOFs 1 and 2, named {[Co2.5(L)]·5H2O}n and 0.5{[Cu(L)]·2H2O}n (L = 4,4′-di(ethoxy)biphenyl-3,3′,5,5′-tetra-(phenyl-4-carboxylic acid)), bearing metal clusters have been facilely constructed by hydrothermal synthesis. Structural studies indicate that 1 presents a 3-nodal (4, 4, 8)-connected topology with the point notation of {44.62}2{48.67.813}, while 2 shows a uninodal (4, 4)-connected network with point symbol of {44.62}. The pristine MOFs are directly utilized for electrocatalysis and poor HER activities are obtained in alkaline solution, which promote the further design and fabrication of a mixed-metal Co/Cu-MOF (3). As expected, 3 shows significantly improved performances for HER with overpotential of 391 mV (10 mA cm−2 current density), low Tafel slope of 94 mV dec−1 and long-term operation stability (14 h). More importantly, the direct utilization of 3 for accelerating OER also presents a fascinating performance in overpotential at 10 mA cm−2 current and durability. The above electrocatalytic performance of pristine 3 can be ascribed to the result of hybridizing strategy for constructing MOFs under hydrothermal procedure, which may favorably produces synergistic effect and more open metal sites. This work provides in-depth understanding of hybrid pristine MOFs for electrocatalysis.