Adjusting organic ligands to construct four 3D metal-organic frameworks with Co2N2O8 SBUs as efficient bifunctional electrocatalysts for OER and HER.

• MOFs 1 − 4 showed multinuclear special 3D pillar-layered structures through adjusting ligands strategy. • MOFs 1 − 4 can promote the electrocatalytic decomposition of water in alkaline media. • MOF 3 obtained lower overpotentials of 180 and 196 mV (10 mA·cm−2) in OER and HER, respectively. • MOFs 1 − 4 exhibit excellent stability during electrolysis over 10 h. Multidentate ligands can be used to construct structurally adjustable metal-organic framework materials due to their abundant coordination sites. MOFs 1 − 4 with different configurations are synthesized by solvothermal method based on the symmetrical tetracarboxylic acid H 4 L main ligand (H 4 L = 5′-(4-carboxyphenyl)-[1,1′:2′,1′'-terphenyl]-4,4′,4′'-tricarboxylic), named [Co 2 (L)(bimb)] n (MOF 1, bimb =(1,1′-(1,4-butanediyl) bis (imidazole)), [Co 2 (L)(bix)] n , (MOF 2, bix =1,4-bis(imidazol-1-ylmethyl) benzene), [Co 4 (L) 2 (bidpe) 2 ] n (MOF 3, bidpe =4,4′-bis(imidazolyl)diphenyl ether) and {[Co 4 (L)(bibdp) 2 (C 3 H 7 NO)]·2(C 3 H 7 NO)} n (MOF 4, bibdp =4,4′-bis(1-imidazolyl) biphenyl), respectively. The rich coordination sites of H 4 L carboxylic acid ligands bring diverse coordination modes, forming Co 2 N 2 O 8 secondary construction units. Based on it, MOFs 1 − 4 exhibits pillar-layered 3D porous supramolecular structure. Electrochemical measurements support that MOFs 1 − 4 exhibits excellent OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) activities, especially MOF 3 , which only requires overpotentials of 180 and 196 mV to reach the current density of 10 mA·cm−2. Remarkable catalytic performance of MOF 3 is attributed to the abundant and dispersed reactive active sites brought by the 3D interpenetrated structure assembled based on tetranuclear metal clusters. The HER occurs through Volmer-Heyrovsky mechanism, meanwhile, possible mechanisms of OER have been predicted. This investigation provides inspiration for exploring multi-core structured MOF materials as efficient HER/OER bifunctional catalysts for electrolytic overall water splitting. [Display omitted] [ABSTRACT FROM AUTHOR]