Role of cobalt phthalocyanine on the formation of high-valent cobalt species revealed by in situ Raman spectroscopy

Abstract

Owing to the enhanced kinetics for the formation of the O–O bond, the high-valent cobalt species have been identified as the highly-efficient active center for oxygen evolution reaction (OER). However, the generation of the high-valent cobalt species is thermodynamically unfavorable under OER conditions. Herein, the π-conjugated molecule (cobalt phthalocyanine, CoPc) was decorated on Co-MOF-74 (denoted as Co-MOF-74@CoPc) to accelerate the formation of the high-valent cobalt species under OER. The obtained Co-MOF-74@CoPc displays a low overpotential of 291 mV and robust long-term stability (210 h) at 10 mA cm⁻² in 1.0 M KOH. XPS and Raman characterizations show the strong electronic interaction between Co-MOF-74 and CoPc and XAS indicates that the CoPc regulates the local coordination environment of Co-MOF-74. Furthermore, in situ Raman spectroscopy reveals that CoPc can promote the transformation of Co-MOF-74 to α-Co(OH)₂ species under the low potential, which then facilitates the generation of disordered CoOOH and Co(IV)O₂ species during the water oxidation process, endowing Co-MOF-74@CoPc with outstanding OER performance. This work provides a new avenue for the design of high efficiency electrocatalysts for OER.