Fig 1

The timeline for the development of selective electrocatalysts for 2e− WOR. Adapted from Royal Society of Chemistry 45, 51, 53, 58, Springer Nature 3, 60, 61, Wiley-VCH 49, and American Chemical Society 4, 31, 52, 57."

Fig 2

Schematic of three different WOR pathways on the catalytic surface."

Fig 3

Theoretical studies of WOR electrocatalysts. (a) Different pathways of WOR processes on the LaAlO3 surface. (b) Free energy diagrams of three WOR pathways on LaAlO3. (c) Volcano plots of limiting potentials as a function of ΔGOH*. (d) Pourbaix diagram of 50%–50% Bi-V system in aqueous solution, assuming an ion concentration of 10–5 mol∙kg−1 for both Bi and V. (e) Computational screening strategy to search the most stable perovskite oxide for 2e− WOR at varying pH values. (a–c, e) are adapted from Springer Nature 60. (d) Adapted from Springer Nature 93."

Table 1

Summary of quantitative determination methods of electrochemically generated H2O2."

Fig 4

The in situ Raman characterization for 2e− WOR. (a, b) In situ Raman spectra of BiVO4 and (c, d) BiVO4-Air/V with various applied biases in 1.0 mol∙L−1 NaHCO3 electrolyte. Adapted from Wiley-VCH 100."

Fig 5

Catalysts design based on defect engineering. (a) A diagram illustrating the electrochemical coupling cell for H2O2 production through 2e− ORR and 2e− WOR reactions. (b) High-resolution O 1s XPS spectra and (c) EPR spectra of pristine TiO2 and TiO2−x. (d) Schematic of the synthetic procedures of CaSnO3@CF. DFT calculated free energy diagram of (e) CaSnO3 and (f) CaSnO3-Ov. (g) Schematic of the synthesis of ZnO@CF. (h) Faraday efficiency and (i) H2O2 production rate of ZnO/CNTs@CF-550-2, 600-2 and 650-2. (a–c) are adapted from Elsevier 56. (d–f) are adapted from Wiley-VCH 96. (g–i) are adapted from Elsevier 30."

Fig 6

Catalysts design based on doping engineering. (a) Scanning electron microscopy (SEM) images of undoped and Gd-doped BiVO4. (b) Current density versus potential curves and (c) FE towards H2O2 production for BiVO4 with various Gd doping concentrations. (d) Diagram for the preparation process for five Bi-based oxide electrodes. (e) Current density versus potential curves and (f) FE towards H2O2 production for FTO/Bi2WO6 and FTO/Bi2WO6: 5%Mo electrodes. (a–c) are adapted from American Chemical Society 52. (d–f) are adapted from Wiley-VCH 88."

Fig 7

Catalysts design based on facet engineering. (a–c) SEM images and (d) Schematic of (010), (010)/(110), and (110) facet-terminated BiVO4. (e) XRD patterns of BiVO4 photoanodes with different crystal faces. (f) Current density versus potential curves and (g) FE towards H2O2 production of BiVO4 photoanodes with different crystal faces in 1.0 mol∙L−1 NaHCO3 electrolyte under 1.5G AM illumination. (a–g) are adapted from American Chemical Society 117."

Fig 8

Catalysts design based on interface engineering. (a) Digital images of GC surfaces with both pristine and PTFE-patterned regions were obtained in an electrolyte of 1.0 mol∙L−1 Na2CO3. (b) Measurements of O2 gas bubble adhesive force were conducted on pristine GC, 300-GC, and 200-GC electrodes. The contact angles of O2 bubbles under electrolyte were displayed in the insets. (c) The overall current densities and (d) H2O2 FEs on pristine CFP, CFP-5%, CFP-20% and CFP-60%. (e) The partial current density of ECSA-normalized H2O2 production was plotted against the potential for pristine CFP, CFP-5%, CFP-20% and CFP-60%. (a–e) are adapted from Springer Nature 36."

Fig 9

Four types of electrochemical devices for H2O2 production. (a) Electrolyzer for H2O2 production via 2e− WOR at the anode coupled with HER at the cathode. (b) Electrolyzer for two-side H2O2 production via 2e− WOR at the anode and 2e− ORR at the cathode. (c) Light-driven PEC electrolyzer for H2O2 production via 2e− WOR at the anode coupled with HER at the cathode. (d) Light-driven PEC electrolyzer for two-side H2O2 production via 2e− WOR at the anode and 2e− ORR at the cathode."

Fig 10

Advanced design of electrochemical devices for H2O2 synthesis. (a) Schematic of a membrane-free flow cell for H2O2 electrosynthesis, and (b) the obtained electrochemical H2O2 production performance. (c) Schematic of the light-driven fuel cell with spontaneous H2O2 and electricity generation. (d) The band diagram of BiVO4 with redox potentials for O2/H2O2 and H2O/H2O2 reaction. (a, b) are reprinted from Springer Nature 36. (c, d) are adapted from Wiley-VCH 50."