Search

Electrochemical oxygen reduction reaction (ORR) via the 2e− pathway in an acidic media shows great techno-economic potential for the production of hydrogen peroxide. Currently, carbon-based single-atom catalysts (C-SACs) have attracted extensive attention due to their tunable electronic structures, low cost, and sufficient stability in acidic media. This review summarizes recent advances in metal centers and their coordination environment in C-SACs for 2e−-ORR. Firstly, the reaction mechanism of 2e−-ORR on the active sites of C-SACs is systematically presented. Secondly, the structural regulation strategies for the active sites of 2e−-ORR are further summarized, including the metal active center, its species and configurations of nitrogen coordination or heteroatom coordination, and their near functional groups or substitute groups, which would provide available and proper ideas for developing superior acidic 2e−-ORR electrocatalysts of C-SACs. Finally, we propose the current challenges and future opportunities regarding the acidic 2e−-ORR pathway on C-SACs, which will eventually accelerate the development of the distributed H2O2 electrosynthesis process. [ABSTRACT FROM AUTHOR]

• A facile strategy to construct a similar coordination environment around the metal atom center using CB particles as substrates; • Both a high yield rate of 110.2 mmol g metal −1 h−1 at the potential of 0.3 V vs RHE and a high positive onset potential of 0.65 V vs RHE were achieved. • The active center was revealed for 2e−-ORR, including the Co-C 3 O 1 moiety as the first coordination and the epoxy group at ⑥ site in the second coordination sphere. • The practical application of CB-based SACs was evaluated in a wastewater treatment system including an H 2 O 2 electrolyzer and a Fenton filter. The coordination environment of transition metals in single-atom catalysts (SACs) is crucial for tuning the pathway of the electrocatalytic oxygen reduction reaction (ORR). However, it is significantly difficult to simultaneously and precisely control the first and second coordination structure near the metal active center. Herein, we report that the activated carbon black was used to anchor transition metals' single atoms with a similar first and second coordination structure. As a result, Co-SACs exhibit an extraordinary performance for ORR to produce H 2 O 2 , where a current density of around ∼2.8 mA cm−2 at 0.1 V vs RHE by rotating ring-disk electrodes and a high yield rate of 110.2 mmol g metal −1 h−1 at the potential of 0.3 V vs RHE in a gas diffusion electrodes (GDEs) cell, with a high positive onset potential of 0.65 V vs RHE and a >80% selectivity of H 2 O 2 at the potential range from 0.25 to 0.65 V vs RHE, respectively. The combined experimental observations and theoretical calculations indicate that the catalytic active center lies in the Co-C 3 /O 1 moiety of the adjacent epoxy group. The possible position of the epoxy group in the second coordination sphere was further revealed. Moreover, Co-SACs were employed in an electrocatalytic GDEs cell for distributed generation of H 2 O 2 in the acidic media, and coupling Fe-SACs-based Fenton filter or electro-Fenton setup with the H 2 O 2 electrolytic generator delivers an efficient and distributable wastewater treatment system. Our study provides a promising and alternative route for on-site H 2 O 2 production coupling the practical application process. [ABSTRACT FROM AUTHOR]

Novel one-dimensional (1D) magnetic flower-like CoFe 2 O 4 @Bi 2 WO 6 @BiOBr composite photocatalysts were prepared by electrostatic spinning techniques, calcination, solvothermal and precipitation methods. The microscopic morphology and the structure of the photocatalysts were characterized using XRD, SEM, XPS and BET. The photocatalytic efficiency of the photocatalysts was evaluated by measuring the degradation rate of rhodamine B (RhB). The results showed that the efficiency of CoFe 2 O 4 @Bi 2 WO 6 @BiOBr for 3 h is 92.08%. After three cycles, the value remained at 77.71%, showing excellent photocatalytic stability. Furthermore, the possible mechanism of photocatalytic degradation process was proposed by radical trapping experiment and PL test. This work designed and prepared a prospective photocatalyst for degrading organic matters of water environments. • CoFe 2 O 4 was designed as 1D structure to realize the separation and axial transport of photogenerated charges. • CoFe 2 O 4 as the magnetic core facilitated the recycling of the photocatalyst. • Bi 2 WO 6 was designed as flower-like structure to obtain a larger surface area. • BiOBr was combined with Bi 2 WO 6 to construct a heterojunction. [ABSTRACT FROM AUTHOR]