ae0c01552_si_002.cif (952.75 kB)

Bioinspired Carboxylate–Water Coordination Polymers with Hydrogen-Bond Clusters and Local Coordination Flexibility for Electrochemical Water Splitting

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posted on 30.10.2020, 14:21 by Junling Chen, Heng Zhang, Bo Li, Jingzhi Yang, Xiongwen Li, Tiexin Zhang, Cheng He, Chunying Duan, Liya Wang
Coordination polymers (CPs) have attracted considerable attention for use in noble-metal-free electrochemical water splitting, for example, by the hydrogen/oxygen evolution reactions (HER/OER). Transition-metal sites with aqueous accessibility and local coordination flexibility are highly desirable in CPs for use as coordination-polymer-based electrocatalysts, but the challenge of structural assembly has limited their development. By analogy with the hydrogen bond cluster around the water-splitting center in photosystem II, the polycarboxylate aryl ether ligand and first-row transition-metal (Co and Ni) salts were employed to assemble CP-based electrocatalysts for water splitting. The obtained monometallic CPs, Co–HL (1) {[Co2(HL)­(H2O)5]·3H2O}n, Ni–HL (2) {[Ni2(HL)­(H2O)5]·3H2O}n, and bimetallic CPs, Co/Ni–HL, with different ratios of Co/Ni ions had semirigid isostructural frameworks and carboxylate–water hydrogen bond clusters around the transition-metal sites. The susceptibility of the hydrogen bond cluster and response of the local coordination environment to stimuli were examined by investigating the thermo-/solvatochromism performance of the CPs. The local hydrogen bond system within the CPs contributes to electron injection and the synergistic bimetallic effect to support electrochemical applications. Among the mono- and bimetallic CP materials, Co/Ni–HL(5:5), with a Co/Ni ratio of 5:5, exhibited the optimal water splitting performance. This bimetallic CP was grown in situ on FeNi foam to improve the conductivity, and the composite material exhibited excellent performance, with overpotentials of 258 mV for the OER and 90 mV for the HER at 10 mA cm–2, a small Tafel slope, and high faradaic efficiency. Overall water splitting generated a current density of 10 mA cm–2 at a voltage of 1.52 V with excellent durability; its performance was comparable to that of state-of-the-art materials for this application.