RuO2 Catalysts for Electrocatalytic Oxygen Evolution in Acidic Media: Mechanism, Activity Promotion Strategy and Research Progress
Abstract
:1. Introduction
2. Reaction Mechanism
2.1. Adsorbate Evolution Mechanism (AEM)
2.2. Lattice Oxygen Oxidation Mechanism (LOM)
3. Activity and Stability Enhancement Strategies
3.1. Heterostructure Construction
3.2. Heteroatom Do**
3.3. Defect Engineering
3.4. Morphology Engineering
4. Summary and Outlook
- (1)
- Reaction mechanism. Understanding the correlation between the activity/stability and local structure is central to the design of efficient RuO2-based OER catalysts. The deactivation and dissolution of RuO2-based catalyst was studied by advanced technical means to provide guidance for the synthesis of more efficient OER electrocatalyst and the in-depth understanding of catalytic mechanism. Although in situ Raman and Operando XAS techniques can be used to record the oxidation states, geometry, electronic structures, and interfaces of catalysts, the diversity and complexity of active stages make it difficult to interpret the factors controlling and influencing catalytic reactions. In addition, the existing operando techniques can only capture quasi-stable active sites, while reaction intermediates typically have picosecond lifetime. Therefore, the development of more advanced techniques to study the electrocatalytic reaction process combined with theoretical simulation to better reveal the true and accurate electrochemical process will be of great help in improving the understanding of the acidic OER mechanism of RuO2-based catalyst.
- (2)
- Activity and durability. Laboratories primarily use CV, CA, and CP to evaluate the stability of RuO2-based OER catalysts, but these methods ignore mass transport, electrode spacing, and fluid flow effects. Ru dissolution caused by over-oxidation in OER process is generally considered to be the main cause of deactivation of RuO2-based materials. And the stability degradation found in these validation methods can be caused not only by catalyst degradation, but also by catalyst interface separation or active site coverage. The development of accelerated deactivation test systems is necessary to provide information on long-term stability performance at high current densities and high temperatures that will be more useful for practical applications [124]. As applications are often required to operate at high current densities and high temperatures, accelerated deactivation test systems are required to rapidly assess catalyst degradation under these conditions. By accelerating the catalyst deactivation process, test times can be reduced, and the harsh environments of practical applications can be simulated, allowing catalyst stability data to be obtained more quickly, which can help researchers better understand the mechanisms of catalyst degradation and provide guidance on how to improve catalyst stability. In addition, the Accelerated Deactivation Test of RuO2-based catalyst can take into account important factors in practical applications, such as mass transfer, electrode spacing and fluid flow.
- (3)
- Industrial applications. The small-scale durability under laboratory conditions cannot meet the requirements of industrial electrolytes. For large-scale PEM electrolysis applications, the catalyst shall be manufactured using scalable and industrially acceptable methods. Precise computer-aided 3D printing techniques can help construct complex structures, accelerating mass/charge/ion transport rates and enhancing activity and stability. Conductive substrates play a key role in delivering activity and stability, but common substrates are not stable in acids. By using acid oxidized and/or doped substrates, we can improve the corrosion resistance of the substrate, or an alternative substrate with excellent corrosion and oxidation resistance such as Ti or Ta foam could be an effective solution. Depositing conductive layers can inhibit the formation of insulating TiO2 layers to further enhance stability. The selection of appropriate OER substrate electrodes significantly impacts catalyst passivation/detachment, substrate-catalyst interactions, and stability performance. Testing in three-electrode configurations significantly differs from industrial applications in terms of operation conditions. To bridge the gap between material development and industrial applications, it is crucial to perform membrane electrode assembly (MEA) testing under relevant industrial conditions as early as possible and further understand the operational conditions and other components essential for designing an optimal working environment for MEAs.
Author Contributions
Funding
Sample | Overpotential @10 mA cm−2 | Tafel Slope | Reference |
---|---|---|---|
Ni-RuO2 | 214 | 42.6 | [1] |
Ru@V-RuO2/C | 176 | 45.6 | [15] |
Nb0.1Ru0.9O2 | 201 | 47.9 | [21] |
Mn0.73Ru0.27O2−δ | 208 | 65.3 | [22] |
Nd0.1RuOx | 211 | 50 | [43] |
W0.2Er0.1Ru0.7O2−δ | 168 | 66.8 | [44] |
SS Pt RuO2 HNSs | 228 | 51 | [45] |
In-RuO2/G | 187 | 46.2 | [46] |
Bi0.15Ru0.85O2 | 200 | 59.6 | [47] |
La-RuO2 | 208 | 57.4 | [48] |
Re0.06Ru0.94O2 | 190 | 45.5 | [49] |
S-RuO2 | 219 | 54.2 | [50] |
Ru0.6Sn0.4O2 | 245 | 61.8 | [51] |
RuO2/CoOx | 240 | 70 | [52] |
a/c-RuO2 | 205 | 48.6 | [53] |
Ru@RuO2 | 198 | 42.6 | [54] |
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© 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
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Bai, J.; Zhou, W.; Xu, J.; Zhou, P.; Deng, Y.; **ang, M.; **ang, D.; Su, Y. RuO2 Catalysts for Electrocatalytic Oxygen Evolution in Acidic Media: Mechanism, Activity Promotion Strategy and Research Progress. Molecules 2024, 29, 537. https://doi.org/10.3390/molecules29020537
Bai J, Zhou W, Xu J, Zhou P, Deng Y, **ang M, **ang D, Su Y. RuO2 Catalysts for Electrocatalytic Oxygen Evolution in Acidic Media: Mechanism, Activity Promotion Strategy and Research Progress. Molecules. 2024; 29(2):537. https://doi.org/10.3390/molecules29020537
Chicago/Turabian StyleBai, Jirong, Wangkai Zhou, **nan Xu, Pin Zhou, Yaoyao Deng, Mei **ang, Dongsheng **ang, and Yaqiong Su. 2024. "RuO2 Catalysts for Electrocatalytic Oxygen Evolution in Acidic Media: Mechanism, Activity Promotion Strategy and Research Progress" Molecules 29, no. 2: 537. https://doi.org/10.3390/molecules29020537