Donor-acceptor polymers push solar hydrogen peroxide production in pure water

Hydrogen peroxide is one of the world’s most versatile chemicals, used everywhere from paper bleaching and disinfection to fuel cells, yet almost all of it is still made by an energy-hungry anthraquinone hydrogenation–oxidation process that also generates considerable toxic by-products. A review published in the journal Catal argues that a family of synthetic organic semiconductors known as donor-acceptor (D-A) conjugated polymers could offer a cleaner route: using sunlight to build H2O2 directly from nothing but water and oxygen, with no sacrificial agents added. The authors, led by Wang Wang and Shaowen Cao, systematically survey the molecular design strategies that have driven this field forward since 2019, when resorcinol–formaldehyde resins were first shown to photocatalyse H2O2 formation via oxygen reduction.

The appeal of the photocatalytic route lies in its simplicity. Semiconductors absorb visible light, generate electron-hole pairs, and shuttle those charges to surface sites where oxygen is reduced to peroxide while water is oxidised. Because the process needs only air, water and light, it avoids harmful by-products and could, in principle, enable decentralised, on-site production of H2O2. The review notes that H2O2 can be formed through the two-electron oxygen reduction reaction (2e⁻ ORR), the two-electron water oxidation reaction (2e⁻ WOR), or a dual-channel pathway combining both. In practice, the most productive configuration reported so far couples the 2e⁻ ORR with the 4e⁻ WOR, although the competing 4e⁻ ORR toward water and the thermodynamically favoured 4e⁻ WOR toward oxygen evolution constantly erode selectivity.

Donor-acceptor polymers are well suited to this task because of how their electronic structure is built. Their backbones alternate electron-rich donor units, such as benzene, biphenyl or triphenylamine derivatives, with electron-poor acceptors such as triazine or bipyridine moieties. The highest occupied molecular orbital sits mainly on the donor, the lowest unoccupied molecular orbital on the acceptor, and the orbital interaction narrows the HOMO-LUMO gap, producing low-bandgap semiconductors that can reach gaps as small as about 1 electron volt. The same electronic interactions promote the separation of photoinduced charges, and the incorporation of D-A units improves crystallinity and charge transport compared with homopolymers, which typically suffer from low charge-carrier mobility. Notably, whether a given moiety behaves as donor or acceptor is relative: cyclooctatetrathiophene acts as an acceptor when paired with triphenylamine but as a donor when condensed with triphenylbenzene.

The first lever the reviewers examine is the tuning of the donor and acceptor units themselves. Ouyang and co-workers attached electron-donating methoxy or electron-withdrawing cyano side groups onto carbazole units in a triazine-carbazole polymer, and the cyano-modified version achieved the highest H2O2 yield of 2534 micromoles per gram per hour, attributed to a shift of hole localisation toward the acetylene linkage that eased exciton dissociation and water oxidation. Zhao et al. folded electron-deficient dihydroxyanthraquinone into a resorcinol–formaldehyde resin, boosting its rate to 1820 micromoles per gram per hour, four times that of the pristine material. Shu et al. went further with a D-A-A type covalent organic framework (COF) carrying an extra acceptor, which lowered exciton binding energy and extended carrier lifetimes, while Hou et al. introduced cyano groups onto biphenyl units in COFs, creating additional charge-transfer channels; the four-cyano variant reached 1601 micromoles per gram per hour.

Even finer structural changes pay dividends. Liao and colleagues built three isomeric COFs differing only in the relative positions of nitrogen atoms in diazine rings, and the optimised TpDz framework delivered 7327 micromoles of H2O2 per gram per hour. Luo et al. expanded molecular planarity and added electron-withdrawing sulfonyl groups in FS-COFs, reaching 3904.2 micromoles per gram per hour under visible light. Yang et al. swapped a single oxygen atom for sulfur in an acceptor, forming COF-Py-S, whose stronger push-pull effect and thiourea active sites lowered the barriers for oxygen adsorption and intermediate desorption, raising the production rate by 2.32 times. Zhu et al. showed that increasing the number of motifs in a molecular junction from two to three prolonged carrier lifetimes a hundredfold, with the three-motif polymer TAS4 producing 4302 micromoles per gram per hour in air without any sacrificial agent.

The chemical linkage joining donor and acceptor units is another powerful dial. Jiang and co-workers embedded non-conjugated hydrazone, partially conjugated imine and fully conjugated vinylene linkages into otherwise comparable two-dimensional COFs. The hydrazone-linked Hz-TP-BT-COF successfully isolated the HOMO and LUMO on donor and acceptor units respectively, and achieved 5700 micromoles per gram per hour with an apparent quantum efficiency of 17.5 percent at 420 nanometres. Sun et al. found that replacing a single atom in a linkage, switching an imine to an azo group, narrowed the bandgap to 1.5 electron volts and produced a 7.9-fold increase in H2O2 generation, reaching 1498 micromoles per gram per hour. Linkage orientation matters too: Yue et al.’s isomeric TB-COF and TA-COF, with reversed imine orientations, reached 5186 and 2387 micromoles per gram per hour respectively, and Yu and co-workers showed that ortho-linked COFs traded a small amount of initial activity for markedly better stability, because a lower water-oxidation barrier reduced oxidative structural damage to the framework.

Topology, the way building units connect in space, also shapes performance. Cheng et al. compared three sp2 carbon-linked COFs with hcb, sql and hxl topologies and found that QP-HPTP-COF had far smaller effective carrier masses than its counterparts, implying much higher mobility. Yue et al. prepared two COFs with identical compositions but different topologies, and the six-arm TBD-COF outperformed the three-arm TBC-COF, 5448 against 4059 micromoles per gram per hour, an effect traced to topological control over charge separation and superoxide generation. Beyond geometry, active-site engineering directs which half-reactions proceed. Lan and co-workers built an oxidation-reduction molecular junction COF in which benzothiadiazole units serve as photoreduction sites and tetrathiafulvalene units as photo-oxidation sites, giving TTF-BT-COF distinct centres for oxygen reduction and water oxidation and the lowest energy barriers for both. Wang et al. introduced fluorine substitutions that created Lewis acid sites for oxygen activation, yielding 1739 micromoles per gram per hour with an apparent quantum efficiency of 5.1 percent at 400 nanometres.

Getting reactants to the active sites is equally decisive, since H2O2 photosynthesis needs steady supplies of protons and dissolved oxygen, and production in pure oxygen far outstrips that in ambient air. Ouyang’s group constructed a self-supporting three-dimensional amorphous D-A polymer whose porous framework lets dissolved oxygen and water diffuse rapidly to catalytic sites while maximising active-site exposure. Chen et al. designed a COF with aligned one-dimensional nanopores whose walls were made hydrophilic by ethoxy side chains, allowing water and dissolved oxygen to penetrate by capillary effect at a water flow rate of up to 2.00 milligrams per gram of dry sorbent per minute. Zhang et al. addressed proton supply separately, using keto-form anthraquinone units in a mechanochemically synthesised COF to shuttle protons toward peroxide-forming intermediates in alkaline media.

The overall picture is one of rapid progress with a long road ahead. Through rational molecular design, H2O2 production rates in pure water have improved by up to two orders of magnitude since 2019, yet most reported photocatalysts still fall below 10 millimoles per gram per hour, and reported solar-to-chemical conversion efficiencies remain no higher than 3 percent, far from industrial requirements. Many D-A polymers also show apparent decay after repeated cycling, likely from structural changes during operation, and scalable synthesis of well-defined polymers remains difficult. The reviewers argue that future work should establish quantitative structure-activity relationships, potentially accelerated by machine learning trained on experimental and high-throughput datasets, and should invest more effort in designing catalytically specific active sites, including spatially separated dual-reaction sites that suppress reverse reactions. As a review, the article consolidates published findings rather than reporting new experiments, but its synthesis makes clear that donor-acceptor polymers have become one of the most credible platforms for sustainable, solar-driven peroxide chemistry.

Subject of Research: Photocatalytic production of hydrogen peroxide from water and oxygen using donor-acceptor conjugated polymer photocatalysts

Article Title: Donor-acceptor conjugated polymers for the photosynthesis of H2O2 in pure water

Article References: Wang, W., Cheng, J., Cheng, B., Luo, G., Xu, J., & Cao, S. (2026). Donor-acceptor conjugated polymers for the photosynthesis of H2O2 in pure water. Catal, 2(1), Article 13. https://doi.org/10.1007/s44422-026-00026-w

Image Credits: AI Generated

DOI: 10.1007/s44422-026-00026-w

Keywords: hydrogen peroxide, donor-acceptor polymers, photocatalysis, covalent organic frameworks, oxygen reduction reaction, water oxidation, solar-to-chemical conversion, molecular engineering, charge separation, mass transfer, sustainable chemistry, Donor-acceptor