Toward Understanding the Formation Mechanism and OER Catalytic Mechanism of Hydroxides by In Situ and Operando Techniques

Abstract

Developing efficient and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) remains a significant barrier that needs to be overcome for the practical applications of hydrogen production via water electrolysis, transforming CO2 to value‐added chemicals, and metal‐air batteries. Recently, hydroxides have shown promise as electrocatalysts for OER. In situ or operando techniques are particularly indispensable for monitoring the key intermediates together with understanding the reaction process, which is extremely important for revealing the formation/OER catalytic mechanism of hydroxides and preparing cost‐effective electrocatalysts for OER. However, there is a lack of comprehensive discussion on the current status and challenges of studying these mechanisms using in situ or operando techniques, which hinders our ability to identify and address the obstacles present in this field. This review offers an overview of in situ or operando techniques, outlining their capabilities, advantages, and disadvantages. Recent findings related to the formation mechanism and OER catalytic mechanism of hydroxides revealed by in situ or operando techniques are also discussed in detail. Additionally, some current challenges in this field are concluded and appropriate solution strategies are provided.

Lewis Acid Site Al-Promoted CoAl2O4/CoO Electrocatalyst for Efficient Electrochemical Production of H2O2 toward On-Site Pollutant Degradation

“…Meanwhile, in the first step of O 2 → *OOH, the free energy of CoAl 2 O 4 is still above 0, which is a spontaneous reaction. However, the free energy of Co 3 O 4 is below 0 after the first step and it presents an upward trend in the second step of *OOH desorption to H 2 O 2 resolution (*OOH → H 2 O 2 ), indicating that this is the rate-determining step (RDS) of Co 3 O 4 . , This reveals that the addition of Lewis acid site Al can make the 2-electron ORR process in the cobalt catalytic active site become spontaneous reaction, which is conducive to the progress of ORR. When U = 0.7 V vs RHE, the Δ G *OOH (−0.39 eV) of CoAl 2 O 4 is closer to the optimal value (Δ G *OOH = 0 eV) than that of the Co 3 O 4 (−1.57 eV), indicating that the Lewis acid site Al reduces the energy barrier for the 2-electron ORR process.…”

Transition Metal‐Based Catalysts for Urea Oxidation Reaction (UOR): Catalyst Design Strategies, Applications, and Future Perspectives

“…Deepening our knowledge of the reaction mechanism will also better illuminate the relationship between catalyst structure and its performance. [ 175 ]…”

Novel insight from in‐/ex‐situ investigation toward intercalated water in high‐performance oxygen evolution electrocatalysts and their mechanisms

“…The progress in in-situ/operando methodologies such as XRD analysis, XAS, TEM, Raman spectroscopy, Fouriertransform infrared spectroscopy (FTIR), and even scanning electrochemical microscopy (SECM) have paved the way for investigating the phase transformation, structural reconstruction, and surface rearrangement of OECs under realistic conditions (Figure 10) [136]. With more and more in-situ/operando evidence being provided, in-depth observations of the bulk, near-surface region, interface, and intermediates adsorbed on the surface promoted the understanding of the real active sites/species/ moieties of the electrocatalysts (Table 1) [137][138][139][140]. The as-prepared electrocatalyst is a pre-catalyst whose surface undergoes a dynamic reconstruction under anodic applied potential and generates an activated, amorphous surface addressed as an oxyhydroxide (MOOH) layer [116]; however, the long-range ordered structure at the surface can also be disrupted.…”

“…T A B L E 1 The advantages, disadvantages, and limitations of different in-situ techniques for the catalytic mechanism investigation [139,140].…”