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

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 alpha-Co(OH)(2) and octahedral beta-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 alpha/beta-Co(OH)(2) as the dominating active sites, not the metal nodes of ZIF-67. Specifically, the CoOOH from alpha-Co(OH)(2) is most active (turnover frequency = 0.59 s(-1)) compared to that from beta-Co(OH)(2) (0.06 s(-1)). Our study demonstrates the importance of examining the electrochemical stability of MOFs for electrocatalyst design.