Understanding the Phase Equilibrium and Kinetics of Electrochemically Driven Phase Transition in CoO_xH_y during Electrocatalytic Reactions

Abstract

Water splitting is one of the most promising methods for mass production of green hydrogen (H2), with the oxygen evolution reaction (OER) being the current main kinetic bottleneck. Cobalt (oxy-)­hydroxides are among the most active electrocatalysts for OER in alkaline electrolytes free from rare-earth metals. However, identifying the active phase of electrocatalysts under operational OER conditions is often difficult, which largely impedes the design of cobalt-based electrocatalysts with improved performance and durability. This lack of understanding is partially contributed by the difficulties in operando characterizations on the details of electrochemically driven phase transitions. In this work, we combine operando Raman spectroscopy and operando optical characterization to investigate the phase equilibrium and kinetics of the phase transition in CoO x H y driven by applied electrochemical driving force. We found an irreversible phase transition during the first electrochemical test, after which phase transition became fully reversible in each following cycle. We further established the relationship between kinetic parameters of the reversible phase transition and applied potential by using the time-resolved operando optical method. Our work provides a precise approach toward a better understanding of the electrochemically driven phase transition in OER electrocatalysts.

Epitaxial Design of Complex Nickelates as Electrocatalysts for the Oxygen Evolution Reaction

“…[35d,69] For example, by using UV-vis spectroelectrochemistry, Baeumer et al found that a NiOOH-like surface monolayer forms on Ni-terminated LNO surfaces, but it is not observed on La-terminated films. [35d] Therefore, advanced in situ/operando electrochemical characterization tools, such as Raman spectroscopy, [70] XAS, [71] AFM, [72] and TEM, [73] need to be performed in the near future to generate insight into the dynamic surface changes of RNO electrocatalysts at the atomic scale and establish new principles for the effective design and use of these materials.…”

σ‐Hole intermolecular interactions between carbon oxides and dihalogens: Ab‐initio investigations

“…Halogen bonding interaction involving CO 2 has been investigated by several groups 31–34 . Yang et al 35 reported that C and O atoms of CO 2 simultaneously interact with XY (X = Cl, Br and Y = F, Cl, and Br) by forming ring‐shaped CO 2 ∙X(Y)∙CO 2 complexes.…”

“…They found that the binding distances and interaction strengths are closely associated with the electronegativity of X and Y atoms and that the optimized geometries and the stretching vibrational frequencies of these complexes are different from the individual (CO 2 ) 2 , CO 2 ∙∙∙XY and YX∙∙∙CO 2 dimer. Zhu et al evaluated the Br···O halogen‐bonding interactions between CO 2 and brominated ion pairs; 32 the results show that the Br∙∙∙O interactions are basically electrostatic in nature and belong to conventional weak halogen bonds. Moreover, the complexes formed between C and O atom of CO and dihalogen molecule (e.g., FCl···CO, Cl 2 ···CO, Br 2 ···CO, BrCl···CO, ClBr···CO, ICl···CO, ClI···CO, IBr···CO, BrI···CO, Cl2···OC, Br 2 ···OC, BrCl···OC, ClBr···OC, ICl···OC, and ClI···OC) have been extensively reported in the previous studies 36–39 .…”