π‐Conjugated Molecule Boosts Metal–Organic Frameworks as Efficient Oxygen Evolution Reaction Catalysts

Abstract

Metal-organic frameworks (MOFs), as a new type of promising materials in electrochemistry, are well investigated by researchers in recent years. [17][18][19][20] Due to the poor conductivity of MOFs, strategies are developed to increase the conductivity and improve the electrochemical performance, such as doping different elements (both metals and nonmetals), [21,22] incorporating conductive materials (such as graphene), [23,24] encapsulating active molecules, [25,26] and even undergoing calcination [27,28] or pyrolysis. [29][30][31] Zeolitic imidazolate frameworks (ZIFs), [32,33] as a new subfamily of MOFs, exhibit not only crystalline multiporosity as MOFs but also high thermal and chemical stability as zeolites. Attributed to the outstanding properties, ZIF derivatives are unique potential candidates in diversified applications such as chemical separation, [34,35] sensors, [36][37][38] energy storage, [39,40] and catalysis. [41,42] π-Conjugated molecules are used to construct planar conductive MOFs in recent years due to the high charge mobility and the corresponding MOFs are explored as good electrocatalysts, [43] electrode materials, [44] sensors, [45] and so on. In our study, a simple MOF architecture, named ZIF-67, was used as the raw material to prepare a high-performance catalyst for OER. The organic molecule HHTP (2,3,6,7,10,11-hexahydroxytriphenylene) was coated on ZIF-67 via a facile one-step hydrothermal method and the obtained composite, denoted as HHTP@ZIF-67, presented higher electrocatalytic efficiency and durability than many reported MOF materials. To the best of our knowledge, this is the first time that a π-conjugated molecule was coated directly on MOFs to ameliorate their electrochemical capabilities. This work will shed light on the further application of MOFs as promising electrocatalysts in energy storage and conversion.ZIF-67 was synthesized according to the previous work by Dong and co-workers [46] and utilized to prepare our porous electrocatalysts. The composite HHTP@ZIF-67 was successfully obtained after combining ZIF-67 together with HHTP under different solvothermal conditions (40, 60, 80, and 100 °C). The synthesis route is presented in Scheme 1.Since the as-prepared sample under 60 °C manifests the most uniform in both size and surface morphology that can be visualized in Figure S1 (Supporting Information), the following characterizations and discussions are focused on HHTP@ZIF-67 obtained under 60 °C when comparing with the pristine ZIF-67.To improve the efficiency of water electrolysis, developing efficient oxygen evolution reaction (OER) electrocatalysis is extremely important due to its four-electron transfer dynamics. In this work, a π-conjugated molecule (2,3,6,7,10,11-hexahydroxytriphenylene, HHTP), which can accelerate the electron transfer, is coated directly on pristine ZIF-67, resulting in a composite named HHTP@ZIF-67, via a simple one-step solvothermal method. The obtained HHTP@ZIF-67 possesses a Brunauer-Emmett-Teller surface area of 2013.9 m 2 g −1 and displays m...

Highly Selective CO2 Electroreduction to CH4 by In Situ Generated Cu2O Single‐Type Sites on a Conductive MOF: Stabilizing Key Intermediates with Hydrogen Bonding

“…To further confirm the role of the uncoordinated hydroxyl groups of the HHTP ligand towards the formation of CH 4 , the physical mixture of the commercial Cu 2 O and HHTP was conducted for CO 2 RR. As shown in Figure S14, almost doubled FE of CH 4 at each potential after addition of HHTP were achieved, indicating that the hydroxyl‐rich environment is beneficial for improving the selectivity of CH 4 [25–30] …”

“…These intermediates, if detached from active sites before accomplishing the eight electron‐transfer process for CH 4 generation, would give rise to other products such as CO and CH 3 OH. Interestingly, hydrogen bonds could stabilize specific intermediate to change the pathway towards the formation of target products [25–30] . Therefore, introducing intermolecular interaction with hydrogen bonds in reaction system could stabilize specific intermediates and make the reaction proceeding to the expected pathway.…”

Conductive 2D metal-organic framework for high-performance cathodes in aqueous rechargeable zinc batteries

“…Electrical conductivity (0.2 S cm −1 , four-point probe, single crystal) 28 and large pores (~2 nm) facilitate electron and Zn 2+ ion transport to active sites. In particular, we anticipate that the redox activity of the quinoid units of HHTP 28–30 with Zn 2+ insertion will promote the performance of the cathode.…”

Alkali‐Etched Ni(II)‐Based Metal–Organic Framework Nanosheet Arrays for Electrocatalytic Overall Water Splitting

“…[ 18,19 ] Despite few of efforts including synthesis of ultrathin 2D layers or introduction of conductive materials in channels for exposing more active sites or improving their conductivity, the electrocatalytic activity enhancement is still not prominent. [ 20,21 ] Thus, it is desired to rationally design or optimize the structure and composition of MOFs to improve water spitting activity.…”