Partial Hydrolysis of Cyanide Coordination Polymers Induced by a Pillar Ligand with Optimized Electrochemical Kinetics for Rechargeable Alkaline Batteries

• Published in: Chemistry : a European journal Vol. 27; no. 71; pp. 17818 - 17823
• Main Authors: Feng, Jie, Zhao, Hongyang, Ali, Wajid, Yin, Dandan, Li, Xinyang, Khan, Nawab Ali, Ding, Shujiang
• Format: Journal Article
• Language: English
• Published: Germany 20.12.2021
• Subjects: coordination polymers; hydrolysis; metal–organic frameworks; rechargeable alkaline batteries; coordination polymers; rechargeable alkaline batteries; hydrolysis; metal-organic frameworks
• DOI: 10.1002/chem.202102746
• ISSN: 0947-6539

Coordination polymers are promising cathode materials for rechargeable alkaline batteries. Therefore, the precise modulation of these cathodes by chemical structure and in‐depth structure transform study is necessary. Here, two model coordination polymer battery cathodes were designed to demonstrate the dynamic structure–performance relationship. We studied the electrochemical performance of two kinds of nickel‐based coordination polymer, comprising a planar 2D cyanide‐bridged network and a 3D cyanide‐bridged network pillared by pyrazine molecules. The 2D coordination polymer showed serious voltage degradation with poor rate capability, whereas the 3D coordination polymer exhibited stable voltage output coupled with high rate at various current densities. The investigation revealed the underlining relationship of plateau voltage degradation and hydrolysis process of electrodes. It was revealed that the pyrazine pillar molecules in the 3D coordination polymer could suppress the hydrolysis and lead to the in situ formation of partially hydrolyzed structure with excellent electrochemical kinetics; this exhibited obvious smaller peak separation (27 mV compared with 149 mV) and hence an almost twofold increase in capacity retention (31.9 to 50.0 %) and energy density retention (18.2 to 35.9 %) at 10 A g−1. Delaying the inevitable: Hydrolysis of MOF and coordination polymer electrode materials in alkaline electrolyte is inevitable. However, we have found that the hydrolysis of cyanide‐bridged nickel‐based coordination polymer electrode materials can be suppressed by the introduction of pillared pyrazine ligands; this optimizes the electrochemical performance. The possible mechanism of partial hydrolysis of electrode materials was proposed, and the hypothesis was justified by ex situ electrochemical and structural characterization.