Electrochemical Instability of Metal–Organic Frameworks: In Situ Spectroelectrochemical Investigation of the Real Active Sites

• Published in: ACS catalysis Vol. 10; no. 1; pp. 81 - 92
• Main Authors: Zheng, Weiran, Liu, Mengjie, Lee, Lawrence Yoon Suk
• Format: Journal Article
• Language: English
• Published: American Chemical Society 03.01.2020
• Subjects: oxygen evolution reaction; in situ UV−vis; cobalt hydroxide; spectroelectrochemistry; in situ Raman; electrochemical stability; ZIF-67
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.9b03790

Despite recent attempts using metal–organic frameworks (MOFs) directly as electrocatalysts, the electrochemical stability of MOFs and the role of in situ-formed species during electrochemistry are elusive. Using in situ spectroelectrochemistry, we present herein a comprehensive discussion on the structural and morphological evolution of MOFs (zeolitic imidazolate framework-67, ZIF-67) during both cyclic voltammetry and amperometry. Dramatic morphological changes exposing electron-accessible Co sites are evident. The intense conversion from tetrahedral Co sites in ZIF-67 to tetrahedral α-Co­(OH)2 and octahedral β-Co­(OH)2, and the formation of their corresponding oxidized forms (CoOOH), is observed during both the electrochemical treatments. Subsequent oxygen evolution reaction suggests the CoOOH produced from α/β-Co­(OH)2 as the dominating active sites, not the metal nodes of ZIF-67. Specifically, the CoOOH from α-Co­(OH)2 is most active (turnover frequency = 0.59 s–1) compared to that from β-Co­(OH)2 (0.06 s–1). Our study demonstrates the importance of examining the electrochemical stability of MOFs for electrocatalyst design.