Recent Progress on the Catalysts and Device Designs for (Photo)Electrochemical On‐Site H₂O₂ Production

Abstract

Low‐cost and on‐site H2O2 production is desirable for industrial and civilian usage. (Photo)electrochemical H2O2 production is proposed to be a safer, greener, and cheaper strategy for on‐site H2O2 production as compared to the conventional anthraquinone process and the direct thermal synthesis. However, the efficiency, selectivity, and durability of the (photo)electrochemical H2O2 production devices are still not satisfactory. Therefore, there is an urgent need to revisit the (photo)electrocatalyst and device designs for (photo)electrochemical on‐site H2O2 production, thus to rationalize the research thoughts and provide valuable guidance. This review comprehensively summarizes and discusses the mechanism of two‐electron oxygen reduction reaction (2e− ORR) and two‐electron water oxidation reaction (2e− WOR) for H2O2 production, and the current research status on the (photo)electrocatalysts and (photo)electrochemical devices. In particular, the pros and cons of the four types of (photo)electrochemical device designs, which are Type I (2e− ORR + oxygen evolution reaction), Type II (2e− ORR + hydrogen oxidation reaction), Type III (2e− WOR + hydrogen evolution reaction) and Type IV (2e− WOR + 2e− ORR), are discussed in detail. Finally, a practical perspective on the future research directions for the on‐site (photo)electrochemical H2O2 production based on the technical challenges of this technique is provided.

Urea and ammonium fluoride di-nitrogen and Cu & Fe bi-metal co-doped carbon felt as cathode for electro-Fenton degradation of norfloxacin: 1O2-dominated oxidation pathway

“…67 Alternatively, O 2 gets converted to O 2 ˙ − by electrons in the presence of an electric current (eqn (7)), 27 and then ·OH combines with O 2 ˙ − and disproportional reactions occur to produce 1 O 2 (eqn (8) and (9)). 68 When the environment is alkaline, some of the H 2 O 2 may be produced electrochemically from the water in the system (eqn (10)), 69 and the free radical conversion process relies mainly on the leaching of metal ions (eqn (11)–(13)), 70 while the ·OH produced combines with H 2 O 2 to produce O 2 ˙ − (eqn (14)). Overall, it can be seen that the pH environment has a significant effect on the type of ROS produced, and the production of 1 O 2 in an acidic environment is accompanied by the consumption of H + and the production of OH − , while the production of free radicals in neutral and alkaline environments is also accompanied by the production of H + , which is consistent with the monitored changing pattern of pH.…”

Covalent Organic Frameworks Based Electrocatalysts for Two-Electron Oxygen Reduction Reaction: Design Principles, Recent Advances, and Perspective

“…A greater disparity in charge density between the active site and the O 2 molecule enhances the rate of electron transfer from the catalyst to the O 2 molecule. This acceleration not only assists in O 2 adsorption during the ORR process but also facilitates subsequent reactions of the adsorbed O 2 molecules [ 40 ]. According to previous reports, the introduction of heteroatoms with different electronegativities, the surface modification with functional groups of varying electron affinities, the adjustment of linkage bonds and structural units, chelated metal ions, and axial coordination of metal centers can all be used for electronic regulation of active sites.…”

“…Electrocatalytic ORR is an electrochemical reaction occurring at the gas–liquid–solid three-phase interface, which mainly involves the processes of adsorption of O 2 molecules, proton and electron transfer, bond breaking or formation, and product release [ 40 , 41 , 42 ]. Typically, the ORR process can generate H 2 O 2 via the 2e-transfer pathway, as shown in Equations (1) and (2), or generate H 2 O via the 4e-transfer pathway, as shown in Equations (5) and (6) [ 43 ].…”

Advancements and opportunities in piezo-(photo)catalytic synthesis of value-added chemicals

“…Besides the typical perovskite metal oxides, other low-cost piezoelectric metal oxide materials with non-centrosymmetric structures have been developed as catalysts for piezocatalytic production of H 2 O 2 . 77,78 Wen et al constructed a C-layer coated ZnO with a modulated electronic structure, employing it in piezocatalytic H 2 O 2 generation. 68 The interface interaction between the C layer and ZnO modulates the charge distribution at the active centers, and the excellent conductivity of C enhances the surface piezoelectric potential and piezoelectric effect of the material compared to ZnO (Fig.…”