Fig. 1. (a) Time profiles of photodriven H2O2 production under illumination (λ > 420 nm) of an O2-saturated aqueous solution containing [RuII(4,7-Me2phen)3]2+ (0.20 mM), ScIII(NO3)3 (0.10 M) and NiFe2O4 NPs (0.17 g/L) with diameters of 1300 (black), 120 (blue) and 91 nm (red); (b) Time profile of photodriven H2O2 production under illumination (λ > 420 nm) of an O2-saturated aqueous solution containing Ru(II) (0.20 mM), ScIII(NO3)3 (0.10 M) and NiFe2O4 NPs (0.17 g/L). Ru(II) complex was added to the reaction solution at 50 and 100 h during the visible-light-driven H2O2 production. Reproduced from Ref. [66] with permission from Royal Society of Chemistry (Copyright 2015).

Scheme 1. Photodriven 4e- H2O oxidation combined with 2e- O2 reduction to produce H2O2 with WOC and [Ru(4,7-Me2phen)3]2+ as a photocatalyst. Reproduced from Ref. [50] with permission from Royal Society of Chemistry (Copyright 2013).

Scheme 2. Photocatalytic cycle of photodriven H2O2 production by oxidation of H2O by O2 with Ni(II)[Ru(II)(CN)4(bpy)]. Reproduced from Ref. [68] with permission from Royal Society of Chemistry (Copyright 2017).

Scheme 3. Photocatalytic water oxidation by O2 to H2O2 by double photoexcitation. Reproduced from Ref. [69] with permission from Royal Society of Chemistry (Copyright 2016).

Fig. 2. A two-compartment cell employed for photocatalytic H2O2 production by combining the photocatalytic H2O oxidation and the photocatalytic 2e-/2H+ O2 reduction under visible light illumination. Reproduced from Ref. [69] with permission from Royal Society of Chemistry (Copyright 2016).

Scheme 4. Solar-light-driven H2O2 production with FeO(OH)/ BiVO4/FTO photoanode and CoII(Ch)/CP cathode in water or seawater under simulated 1 sun (AM 1.5G) irradiation. Reproduced from Ref. [79] with permission from American Chemical Society (Copyright 2016).

Scheme 5. (a) Three-dimensional structure; (b) Electronic band structure of g-C3N4/PDI (containing 51% PDI unit); (c) Photocatalytic cycle for H2O2 production from H2O and O2 with g-C3N4/PDI. Reproduced from Ref. [98] with permission from American Chemical Society (Copyright 2016).

Fig. 3. (A) Photoanode and cathode for photoelectrochemical water splitting to H2O2 and H2. (B) Energy diagram of photoelectrocatalytic production of H2O2 and H2 using a WO3/BiVO4 photoanode under solar-light illumination. Reproduced from Ref. [110] with permission from Royal Society of Chemistry (Copyright 2016).

Scheme 6. Proposed mechanism of the photocatalytic oxidation of H2O by DDQ with [(N4Py)FeII]2+ to evolve O2. Reproduced from Ref. [102] with permission from American Chemical Society (Copyright 2019).

Scheme 7. A membraneless one-compartment H2O2 fuel cell in which the anode (2e-/2H+ H2O2 oxidation) and cathode (2e-/2H+ H2O2 reduction) reactions afford the output potential of 1.09 V. Reproduced from Ref. [113] with permission from Royal Society of Chemistry (Copyright 2015).

Fig. 4. A photoelectrode system for production of H2O2 via the 2e-/2H+ H2O oxidation on a WO3/BiVO4 photoanode combined with the 2e-/2H+ O2 reduction on an Au cathode under solar-light illumination. Reproduced from Ref. [111] with permission from John WILEY and Sons (Copyright 2017).

Fig. 5. (A) Reaction diagram of photocatalytic production of H2O2; (B) Composite electrode supported WO3/BiVO4 and Au on a single FTO substrate; (C) Solar-light-driven production of H2O2 on the composite electrode under simulated solar-light illumination in H2O containing KHCO3 (2.0 M) at below 5 °C under O2 and CO2 bubbling with use of a petri dish as a cell; (D) Reaction diagram of photocatalytic production of H2O2 on an Au-supported BiVO4 powder in H2O containing KHCO3 (2.0 M) under O2 and CO2 bubbling. Reproduced from Ref. [111] with permission from John WILEY and Sons (Copyright 2017).

Fig. 6. Plots of I-V (blue) and I-P (red) of a one-compartment H2O2 fuel cell with a FeII3[CoIII(CN)6]2/carbon cloth cathode and a Ni mesh anode. Performance tests were carried out in a pH 1.3 aqueous solution, which was transferred from the CoII(Ch)/CP cathode cell of the two- compartment cells containing 52 mM of H2O2 produced by photocatalytic H2O oxidation by O2 (see also Scheme 4). Reproduced from Ref. [79] with permission from American Chemical Society (Copyright 2016).

Fig. 7. Illustration of a H2O2 MMFC. Reproduced from Ref. [13] with permission from American Chemical Society (Copyright 2020).

Scheme 8. Proposed mechanism of photocatalytic hydroxylation of benzene by combining photodriven production of H2O2 via 4e-/4H+ H2O oxidation and 2e-/2H+ O2 reduction with benzene hydroxylation by H2O2 using [RuII(4,7-Me2phen)3]2+ as a photocatalyst and [(Cp*)CoIII(bpy)(H2O)]2+ as a dual function catalyst for the 4e-/4H+ oxidation of water and hydroxylation of benzene. Reproduced from Ref. [129] with permission from Royal Society of Chemistry (Copyright 2017).

Scheme 9. Coupling of photo- and thermal catalysis by FeII2[RuII(CN)6]@sAl-MCM-41 for photocatalytic hydroxylation of benzene by O2 with H2O. Reproduced from Ref. [133] with permission from American Chemical Society (Copyright 2016).

Fig. 8. External bias-free, PEC H2O2 production by oxidation of H2O by O2 with use of an FeOOH/BiVO4/CIGS solar cell in tandem and CN/rGO film electrode under photoirradiation for chemo- and stereospecific conversion of ethylbenzene to obtain (R)-1-phenylethanol catalyzed by AaeUPO. Reproduced from Ref. [134] with permission from American Chemical Society (Copyright 2019).