Metal–Organic Frameworks with Assembled Bifunctional Microreactor for Charge Modulation and Strain Generation toward Enhanced Oxygen Electrocatalysis

• Published in: ACS nano 2022-06, Vol.16 (6), p.9523-9534
• Main Authors: He, Fan, Zhao, Yingjie, Yang, Xiaoxuan, Zheng, Sixing, Yang, Bin, Li, Zhongjian, Kuang, Yongbo, Zhang, Qinghua, Lei, Lecheng, Qiu, Ming, Dai, Liming, Hou, Yang
• Format: Article
• Language: English
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.2c02685

Two-dimensional metal–organic frameworks (MOFs) have served as favorable prototypes for electrocatalytic oxygen evolution reaction (OER). Despite promising catalytic activity, their OER reaction kinetics are still limited by the sluggish four-electron transfer process. Herein, we develop a ferrocene carboxylic acid (FcCA) partially substituted cobalt-terephthalic acid (CoBDC) catalyst with a bifunctional microreactor composed of two species of Co active sites and ligand FcCA (CoBDC FcCA). Benefiting from the ultrathin nanosheet structure, CoBDC FcCA catalyst exhibits an excellent OER performance with a low overpotential of 280 mV to reach 10 mA cm–2 and a small Tafel slope of 53 mV dec–1. Structure characterization together with theoretical calculations directly unravel the coordination for two species of Co active moieties with FcCA forming a microreactor of tensile strain, leading to a conversion of the Co spin from a high spin state (t2g 5eg 2) to an intermediate spin state (t2g 6eg 1) to regulate antibonding states of Co 3d and O 2p orbital. In situ spectroscopic measurements for mechanistic understanding reveal that this CoBDC FcCA catalyst possesses an optimal OH* adsorption energy for propitious formation of O–O bonds in the OOH* intermediate, thus effectively decreasing the thermodynamic Gibbs free energy of the rate-determining step (O* → OOH*) to accelerate reaction kinetics for the whole OER process. When loaded on an integrated BiVO4 photoanode as a cocatalyst, CoBDC FcCA enables highly active solar-driven oxygen production from water splitting.