Key Takeaways & Executive Findings
- •• Carbon electrodes enable efficient 2e− oxygen reduction for on-site H2O2 synthesis, offering a safer and greener alternative to the anthraquinone process. • The three-phase interface and electrode wettability are critical factors determining H2O2 production rate and electrode stability. • Material modification strategies that enhance 2e− selectivity also influence wettability, linking catalyst design to interfacial performance. • Future research should focus on overcoming current limitations in carbon electrode stability and selectivity for practical applications.
Abstract
Electrocatalytic oxygen reduction by a 2e− pathway enables the instantaneous synthesis of H2O2, a process that is far superior to the conventional anthraquinone process. In recent years, the electrocatalytic synthesis of H2O2 using carbon electrodes has attracted more and more attention because of its excellent catalytic performance and superior stability. The relationship between material modification, wettability and the rate of H2O2 synthesis and service life is considered together with the three-phase interface. The structure of the carbon electrodes and the principles of electrocatalytic H2O2 synthesis are first introduced, and four major catalysts are reviewed, namely, monolithic carbon materials, metal-free catalysts, noble metal catalysts and non-precious metal catalysts. The effects of the metal anode and the electrolyte on the three-phase interface are described. The relationship between carbon electrode wettability and the three-phase interface is described, pointing out that modification focusing on improving the selectivity of the 2e− pathway can also impact electrode wettability. In addition, the relationship between the design of the components in the electrochemical system and their effect on the efficiency of H2O2 synthesis is discussed for carbon electrodes. Finally, we present our analysis of the current problems in the electrocatalytic synthesis of H2O2 for carbon electrodes and future research directions.
1. Introduction
Hydrogen peroxide (H2O2) is widely used as an oxidizing agent, bleaching agent, disinfectant, polymer initiator, and cross-linking agent in various fields such as papermaking, textiles, chemical synthesis, military, electronics, food, pharmaceuticals, cosmetics, environmental protection and metallurgy[1]. Hydrogen peroxide is usually prepared by electrolysis, from anthraquinone, or by isopropanol oxidation[2]. However, there are many drawbacks to the above methods. For example, electrolysis requires high electricity cost and produces more by-products[3]. The anthraquinone method requires direct contact with H2, which is a significant safety hazard[4]. Isopropanol oxidation is carried out at high temperatures, which is unsafe as there are explosive mixtures inside the equipment when flammable and combustible isopropanol is mixed with hydrogen peroxide, and in addition the storage and transport also presents significant economic and safety challenges[5].
In-situ synthesis of hydrogen peroxide is a safe, stable, and economical “green” method. The synthesis of hydrogen peroxide via a two-electron pathway oxygen reduction reaction (ORR) using a carbon electrode does not require an intermediate purification or separation step and is stable[6]. It is more cost-effective than the anthraquinone method, and the product can be used directly without any contamination, which can improve the safety and economic benefits to a certain extent, resulting in “green” chemistry[7]. The method is based on the principle of a two-electron oxygen reduction reaction between oxygen and solution at the three-phase interface of a carbon electrode to produce hydrogen peroxide. The rate of hydrogen peroxide synthesis can reflect the catalytic efficiency of the three-phase interface to some extent, and the lifetime of the electrode indicates the stability of the three-phase interface. In general, the features of three-phase interface can be judged by the activity potential, electron transfer, and mass diffusion[8].
Based on these facts, this paper aims to summarize the factors affecting the synthesis of hydrogen peroxide on carbon electrodes in the perspective of the three-phase interface. Firstly, chemical and physical modification will directly affect the properties of the three-phase interface, and therefore the synthesis of hydrogen peroxide. Based on the understanding of the above mechanism, the effects of the structure of the carbon electrode, the modification means of the catalytic layer material[9], the metal anode and electrolyte, the wettability of the material on the three-phase interface, and the performance of the carbon electrode are discussed. Finally, the current challenges and future research directions for synthesis of hydrogen peroxide on carbon electrodes are presented.
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HUANG Xian-huai, YANG Xin-ke, GUI Ling, LIU Shao-gen, WANG Kun, RONG Hong-wei, WEI Wei (2024). Carbon electrodes for the electrocatalytic synthesis of hydrogen peroxide: A review. New Carbon Materials. https://doi.org/10.1016/S1872-5805_N
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Frequently Asked Questions
What is the main advantage of using carbon electrodes for H2O2 synthesis?
Carbon electrodes enable the electrocatalytic synthesis of hydrogen peroxide via a two-electron oxygen reduction pathway, offering a safer, more economical, and greener alternative to the conventional anthraquinone process, with the ability to produce H2O2 on-site without intermediate purification.
How does the three-phase interface affect H2O2 production?
The three-phase interface, where gas (oxygen), liquid (electrolyte), and solid (electrode) meet, is crucial for the two-electron oxygen reduction reaction. Its properties, such as activity potential, electron transfer, and mass diffusion, directly influence the rate of H2O2 synthesis and the stability of the electrode.
What role does electrode wettability play in the electrocatalytic synthesis?
Electrode wettability affects the three-phase interface by influencing the contact between the electrolyte, oxygen, and the catalytic sites. Proper wettability ensures efficient mass transport and gas diffusion, which is essential for high H2O2 production rates and long-term electrode stability.
What are the main types of catalysts reviewed for carbon electrodes?
The review covers four major catalyst types: monolithic carbon materials, metal-free catalysts, noble metal catalysts, and non-precious metal catalysts, each with distinct advantages and challenges for selective H2O2 synthesis.
What are the future research directions for carbon electrodes in H2O2 synthesis?
Future research should focus on improving the selectivity and stability of carbon electrodes, optimizing the three-phase interface through material modification, and addressing challenges related to large-scale implementation and practical applications.
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