Perspective on water electrolysis for ozone production: electrocatalyst design and development

Abstract

Electrocatalytic ozone production (EOP) is a new, environmentally friendly, safe and cost-efficient ozone production technology. The slow kinetics and poor stability of conventional catalysts in the EOP process limit its wide application. Consequently, the development and design of novel EOP catalysts are crucial. There have been few reviews on various types of EOP catalysts. Therefore, this paper reviews recent advances on EOP catalysts, categorized by material types. Additionally, the mechanism of EOP is discussed in depth. Finally, we propose constructive implications for future EOP system development. This paper aims to provide an in-depth analysis of the EOP process, summarize and discuss advances in EOP materials, and establish a reliable foundation for future EOP development.

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Wider impact

Other than H₂ and O₂, water electrolysis can also be used for producing ozone for versatile applications. But the slow kinetics and poor stability of conventional catalysts for this reaction limit its widespread applications. Thus far, there have been few reviews on various types of ozone production catalysts. Here we report recent developments in ozone production catalysts categorized by material type. Our paper will provide an in-depth understanding of the ozone production process, summarize and discuss advances, and establish a reliable foundation for future development.

Introduction

Electrocatalytic ozone production (EOP) primarily utilizes specific electrocatalysts to generate ozone by oxidizing oxygen molecules in water under an applied electric current. Typically, water serves as the raw material. Oxygen evolution occurs at the anode surface, and when the applied voltage exceeds a certain threshold, a portion of the oxygen molecules undergo further oxidation to produce ozone.^1–6 Under an electric field, the anode-surface electrocatalyst adsorbs water molecules and induces their dissociation into hydroxide ions and protons.^7–12 Hydroxide ions then lose electrons and protons at the anode to form oxygen, while some oxygen molecules adsorb onto active sites where they lose electrons and protons, triggering an oxidation reaction that yields ozone.

EOP possesses several advantages over other ozone production methods: (i) strong oxidizing ability: ozone is a potent oxidizing agent with a redox potential second only to fluorine. It effectively degrades diverse organic pollutants in water, decomposing large organic molecules into smaller fragments, and ultimately mineralizing them to carbon dioxide and water. This confers significant advantages in wastewater treatment and advanced drinking water purification.^13,14 (ii) Tunable selectivity: by adjusting electrode materials, applied potential, and other parameters, the selectivity of the electrocatalytic reaction can be controlled. This enables preferential reaction of ozone with specific pollutants, enhancing treatment efficiency and resource recovery.¹⁵ (iii) Elimination of secondary pollution: this technology utilizes water as the sole feedstock for ozone generation via electrocatalysis, requiring no chemical additives. It thereby avoids secondary pollution associated with chemical dosing, aligning with environmental sustainability goals.¹³ (iv) Operational simplicity: the EOP system equipment is relatively simple, easy to operate, and easy to automate, reducing labor demand and operating costs. (v) On-site generation: ozone is produced in situ within the target water body, eliminating decomposition and leakage risks during storage/transport while improving utilization efficiency and process safety. (vi) Synergistic compatibility: EOP technology integrates effectively with other water treatment processes (e.g., biological treatment and membrane separation), creating synergistic effects that enhance treatment performance, improve effluent quality, and expand application scope in water treatment.^15,16

Nevertheless, EOP also exhibits disadvantages common to electrocatalytic reactions:^17–26 (i) high energy consumption: the EOP process consumes significant electrical energy. This issue becomes particularly pronounced in large-scale applications, potentially increasing operating costs and limiting deployment in energy-constrained or cost-sensitive settings. (ii) Electrode material limitations: while high-performance electrocatalysts are crucial for EOP, efficient materials (e.g., precious metals and their oxides) face high costs and scarcity. Conversely, economical alternatives typically suffer from inadequate catalytic activity and stability, hindering economic viability and large-scale implementation. (iii) Catalyst instability: during operation, electrode-surface catalysts may experience deactivation, poisoning, or corrosion, leading to performance degradation. Regular replacement or regeneration increases operational costs and maintenance requirements. (iv) Constrained ozone yield: compared to traditional ozone generators, EOP technology produces relatively low ozone concentrations. This limitation restricts its applicability for large-scale industrial production or high-concentration ozone demands. (v) Competing side reactions: undesirable reactions (e.g., hydrogen evolution and oxygen reduction) may occur during EOP, reducing current efficiency, compromising ozone production/utilization, and diminishing overall system performance.

In this paper, we review recent advances in EOP systems, encompassing precious metal-based, nonprecious metal-based, toxic metal-based, and nontoxic metal-based materials (Fig. 1a and b). Additionally, we provide an in-depth discussion of the EOP reaction mechanism and propose forward-looking recommendations to address current system limitations.

Fig. 1 (a) The schematic diagram of EOP catalyst categorization. (b) A timeline of milestone studies in EOP research.^27–34 (c) The general mechanism of EOP.

General mechanism of EOP

Due to the high thermodynamic potential required for EOP, poor catalytic activity under strongly oxidizing conditions, and inherently sluggish reaction kinetics, further complicated by competing oxygen evolution reactions, it is crucial to fundamentally understand the EOP reaction mechanism and investigate catalyst evolution during operation, including active site transformations and deactivation pathways. The general mechanism of EOP is shown in Fig. 1c.

Specifically, the anode reaction for aqueous ozone electrolysis proceeds as follows:³⁵

2H₂O → O₂ + 4H⁺ + 4e⁻ E⁰ = 1.229 V vs. SHE (1)

3H₂O → O₃ + 6H⁺ + 6e⁻ E⁰ = 1.511 V vs. SHE (2)

O₂ + H₂O → O₃ + 2H⁺ + 2e⁻ E⁰ = 2.075 V vs. SHE (3)

The anodic reaction of water splitting comprises two pathways: the four-electron oxygen evolution reaction (OER) and the six-electron EOP. Similar to the OER, EOP reaction mechanisms involve both the adsorbate evolution mechanism (AEM) and lattice oxygen mechanism (LOM).^36–50

Adsorbate evolution mechanism

The AEM pathway for EOP follows the sequence: H₂O → OH* → O* → O₂* → O₃* → O₃. This mechanism primarily involves adsorption/desorption of reactants and intermediates, necessitates a high overpotential to drive the reaction, and is inferred from analogous electrocatalytic reactions like the OER, ORR, etc.:^51–58

H₂O → OH* + H⁺ + e⁻ (4)

OH* → O* + H⁺ + e⁻ (5)

2O* → O₂* → O₂ (6)

O₂* + O* → O₃* → O₃ (7)

Lattice oxygen mechanism

Initially, researchers questioned whether EOP followed a LOM analogous to the classical OER, with no established consensus. The prevailing hypothesis suggested that—conceptually similar to the OER—an EOP LOM pathway would require lattice oxygen participation in ozone-forming steps (e.g., O–O bond formation), rather than relying exclusively on adsorbed oxygen species. This conceptual framework now guides contemporary EOP mechanistic studies. Subsequent research has confirmed LOM in EOP systems, enabling targeted catalyst design.^{27,29,35,59–71}

Jiang et al. demonstrated the correlation between lattice oxygen activity and the crystal facet structure in β-PbO₂, revealing superior ozone generation efficiency on (110) facets. Their work establishes direct involvement of β-PbO₂ lattice oxygen in electrochemical ozone production, rather than exclusive dependence on surface-adsorbed oxygen species.⁷² The enhanced efficiency of (110) facets stems from their higher lattice oxygen activity and favourable electronic structure. Notably, facet-dependent variations in lattice oxygen activation properties govern catalytic activity differences.

EOP catalysts

Synthesis methods

EOP is an efficient and clean method for producing ozone, with its core focus on developing efficient, stable, and economical anode catalysts. These catalysts must selectively oxidize water molecules to produce ozone rather than oxygen under the competition of the OER. The following is an analysis of some major catalyst types and their typical synthesis methods.

Electrodeposition

Electrodeposition, also known as electroplating or electrolytic deposition, is a method that uses electrochemical principles to deposit a layer of metal, alloy, or compound on the surface of a conductive substrate (cathode), as shown in Fig. 2a. It is a very important surface treatment technology and functional material preparation method. In the EOP system, the most commonly used materials for electrodeposition include β-PbO₂ (orthorhombic crystal system), SnO₂, etc.

Fig. 2 The schematic diagram of (a) electrodeposition, (b) pyrolysis and (c) chemical vapor deposition.

Pyrolysis

Pyrolysis is one of the most commonly used and important methods for preparing electrocatalysts (especially carbon-based and non-precious metal electrocatalysts). Its core principle involves high-temperature thermal treatment of carbon- and/or metal-containing precursors under inert or specific atmospheres (Fig. 2b). Through thermal decomposition and structural reorganization, this process generates catalytic materials with specific active sites, high specific surface areas, and excellent conductivity.

As with the thermal decomposition synthesis method for the classic EOP material β-PbO₂, a solution containing lead compounds (such as lead acetate) is coated onto a substrate, and high-temperature thermal decomposition oxidation forms a PbO₂ coating. However, the bonding strength and density are typically inferior to those achieved by electroplating. For SnO₂-based catalysts, the method typically involves repeatedly coating (brushing, dipping, and spraying) a mixture of SnCl₄ and dopants (such as SbCl₃) in hydrochloric acid or alcohol solutions onto a pretreated titanium substrate. After each coating, the substrate is calcined at high temperatures (400–600 °C) for a certain period of time to decompose and oxidize the precursor into a crystalline SnO₂–Sb₂O₅ (or other doped) coating. This process is repeated multiple times to achieve the desired thickness and density.

Chemical vapor deposition

Chemical vapor deposition (CVD) is an important material preparation technology widely used in the preparation of high-performance thin films, coatings, and nanostructured materials. In the field of electrocatalysts, CVD has attracted widespread attention because it can precisely control the composition, structure, and morphology of catalysts, thereby optimizing their activity, selectivity, and stability. The CVD process involves introducing gaseous precursors (compounds containing the target elements) into a reaction chamber, where chemical reactions (pyrolysis, reduction, oxidation, or synthesis reactions) occur on the surface of a heated substrate, resulting in the deposition of solid products onto the substrate while gaseous byproducts are vented from the system (Fig. 2c).

For example, boron-doped diamond (BDD) has the highest known oxygen evolution overpotential, an extremely wide potential window, exceptional corrosion resistance and chemical inertness, low background current, and can efficiently produce ozone with minimal byproducts under specific conditions, making it an ideal material for high-performance EOP. The general synthesis steps are as follows: in a high-temperature (700–900 °C) and low-pressure reaction chamber, a mixture of gases containing a carbon source (such as methane CH₄), a dopant source (such as borane B₂H₆), and hydrogen is introduced. The carbon source undergoes thermal decomposition on the substrate surface, hydrogen atoms etch away non-diamond carbon, and ultimately a polycrystalline boron-doped diamond thin film is deposited on the substrate surface.

The core of electrocatalytic ozone-producing catalysts lies in anode materials with high oxygen evolution overpotential and high stability. The electrodeposition method for β-PbO₂ is currently the most technically mature and widely applied technique. The CVD method for BDD exhibits excellent performance but comes with extremely high costs. The thermal decomposition method also serves as an important alternative or substrate material. Research on novel catalysts (such as doped modifications, composite structures, and other high overpotential oxides) continues, with synthesis methods primarily based on fundamental chemical techniques like hydrothermal, sol–gel, coprecipitation, and electro-deposition, combined with morphology control and composite technologies. The choice of synthesis method must be determined comprehensively based on the specific material system, performance objectives, cost budget, and process feasibility. In actual research, optimizing synthesis parameters (concentration, temperature, time, current/voltage, doping amount, etc.) to achieve optimal performance is of critical importance. In addition, other methods for preparing EOP electrocatalysts are also being developed and applied, such as sol–gel and hydrothermal-assisted electrochemical deposition.

Categories of EOP catalysts

Precious metal-based catalysts. Precious metal-based materials are widely employed in electrocatalysis.^73–79 Among these, platinum (Pt) has been extensively studied for classical reactions (e.g., HER, ORR, OER, etc.). While Pt exhibits EOP activity in neutral electrolyte systems, several drawbacks limit its large-scale application: (i) high cost. (ii) Susceptibility to oxidation/dissolution in strongly oxidizing environments, reducing activity and operational lifetime. (iii) Promotion of competing reactions (e.g., oxygen evolution) during ozone generation, lowering faradaic efficiency. (iv) Surface fouling by impurities or intermediates, decreasing active site availability. (v) Requirement of high overpotentials for effective ozone production, increasing energy consumption. (vi) Environmental impacts from platinum mining/processing and improper catalyst disposal.

Current research addresses these limitations through improving Pt-based catalysts: (i) alloying with other metals to enhance stability and selectivity. (ii) Utilizing high-surface-area supports to improve dispersion. (iii) Engineering nanostructures to increase active sites. (iv) Developing non-precious metal/composite alternatives.

For instance, Gu et al. synthesized Pt single atoms embedded in B/N co-doped carbon nanotubes (Pt-SAs/BNC) (Fig. 3a).³² The Pt-Sas/BNC-3 variant demonstrated exceptional electrochemical activity (Fig. 3b and c) achieving an overpotential of 2.61 V vs. RHE at pH 7. This system yielded 4.8 mg L⁻¹ dissolved O₃ at 3.0 V (Fig. 3d and e) and 15 mg L⁻¹ gaseous O₃ at 50 mA cm⁻² (Fig. 3f), with a faradaic efficiency of 21% (3.0 V) (Fig. 3g and h) and remarkable 100-hour stability (Fig. 3i). XAFS spectroscopy revealed Pt-Sas/BNC-3's local coordination environment, showing Pt in an oxidation state intermediate between Pt foil and PtO₂ without nanoparticle/cluster formation. The Pt atoms occupy graphene double vacancies coordinated to three pyridinic N atoms and one B atom, conferring enhanced structural stability.

Fig. 3 (a) The synthesis schematic of Pt Sas-BNC; (b) polarization curves; (c) Tafel plot; (d) and I dissolved O₃ field; (f) gaseous O₃ field; (g) and (h) Faraday efficiency of O₃; (i) stability curve. Reproduced from ref. 32 with permission from [American Chemical Society], copyright [2021].

Beyond that example, numerous studies report Pt-based catalysts for EOP applications. Hayashi et al. demonstrated a Pt/Ti catalyst achieving 19.7% faradaic efficiency for ozone production,⁸⁰ while Mohamed et al. developed Pt/TaO_y composites exhibiting high EOP activity (FE = 19.3%),⁸¹etc.

As mentioned above, Pt-based EOP catalyst performance can be significantly improved through alloying, support optimization, nanostructure design, and surface modification, simultaneously reducing costs and enhancing stability. Future research should focus on developing novel composite materials and rational structure designs to advance efficient, economical EOP technology.

Non-precious metal-based catalysts

Non-precious metals offer compelling advantages in electrocatalytic reactions, particularly EOP, due to their low cost, resource sustainability, and environmental friendliness.^82–90 Key benefits include low material cost, earth abundance and minimal environmental impact, tunable multifunctionality, enhanced stability, poisoning resistance, facile modification and optimization, scalable production and high innovation potential. Non-precious metals (e.g., Fe, Co, Ni, Mn, Cu, etc.) cost substantially less than precious counterparts (e.g., Pt, Ir, Ru), exhibit high crustal abundance, and require less energy-intensive extraction.^91–98 Their mining/processing reduces ecological disturbance, while end-of-life catalysts enable efficient recycling. Through doping, compositing, or structural engineering, these materials achieve tailored EOP performance while maintaining chemical stability and impurity tolerance under operational conditions.

Nickel- and antimony-doped SnO₂ non-precious metal catalysts show excellent potential for electrocatalytic applications. Xue et al. synthesized Ce–Ni–Sb–SnO₂ catalysts (Fig. 4a) via cerium doping and calcination, achieving exceptional EOP activity.³⁴ Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterization confirmed successful Ce incorporation and synthesis of Ce–Ni–Sb–SnO₂ (Fig. 4b–f). Among tested formulations, Ce–Ni–Sb–SnO₂ demonstrated optimal electrochemical performance (Fig. 4g–i), yielding 8.0 mg L⁻¹ dissolved O₃, 250 mg L⁻¹ gaseous O₃ and 43.9% faradaic efficiency at 250 mA cm⁻² (Fig. 4j–l). Radical quenching experiments (Fig. 4m) elucidated individual radical contributions to efficiency. The system maintained stable operation for 600 h without significant voltage decay (Fig. 4n).

Fig. 4 (a) The synthesis schematic of Ce–Ni–Sb–SnO₂; (b) and (c) SEM images of Ce–Ni–Sb–SnO₂; (d) HRTEM of Ce–Ni–Sb–SnO₂; (e) XRD pattern of Ce–Ni–Sb–SnO₂; (f) elemental mapping of Ce–Ni–Sb–SnO₂; (g) polarization curves; (h) Tafel plot; (i) ECSA plot; (j) dissolved O₃ field; (k) gaseous O₃ field; (l) Faraday efficiency of O₃; (m) effect of free radical quenchers on FE; and (n) stability curve. Reproduced from ref. 34 with permission from [Wiley-VCH], copyright [2023].

While this study effectively demonstrates non-precious metal applications in EOP, it reveals a significant deviation from conventional performance metrics. Typically, dissolved and gaseous O₃ yields in EOP systems are within the same order of magnitude, differing by no more than several-fold. Remarkably, this work reports an unprecedented gaseous O₃ concentration of 250 mg L⁻¹, exceeding dissolved O₃ levels by 31 times and representing the highest value documented in EOP literature. These exceptional findings suggest that future EOP research should not only build upon existing test protocols but may require innovative measurement approaches and willingness to report and validate extraordinary results that challenge current paradigms.

Toxic metal-based catalysts

Toxic metal-based catalysts, particularly lead (Pb), exhibit enhanced EOP activity but suffer from environmental hazards, poor stability, and undesirable side reactions.⁹⁹ During EOP operation, Pb catalysts face critical limitations: (i) potential Pb leaching into aquatic environments causing contamination; (ii) susceptibility to dissolution/corrosion under strong oxidizing conditions; (iii) competing side reactions (e.g., oxygen evolution and metal ion reduction); and (iv) surface poisoning via Pb ion adsorption blocking active sites.

Despite numerous reported catalysts with exceptional EOP activity, β-PbO₂ remains the preferred industrial-scale anode material for ozone production due to its optimal balance of catalytic performance, durability and cost-efficient at high current densities. As a classical EOP catalyst, it has been extensively studied for its high anodic oxidation potential, excellent electrical conductivity, and economic viability. However, prolonged operation under harsh oxidative conditions causes dissolution of β-PbO₂ particles, inducing structural degradation that significantly compromises catalytic activity and operational stability.

Owing to the high EOP selectivity of elemental Pb, researchers frequently modify Pb-based catalysts for enhanced performance, exemplified by β-PbO₂'s adoption in commercial electrolytic water-based ozone generators. Liu et al. synthesized cubic-Pb₃O₄@SiO₂ catalysts through superhydrophobic Pb₃O₄ coating on Si-CH₃-functionalized SiO₂ (Fig. 5a).¹⁰⁰ This material demonstrated exceptional electrochemical activity, yielding 4 mg L⁻¹ gaseous O₃, 16.8% faradaic efficiency, and >100 h operational stability with negligible activity decay (Fig. 5b–g). Complementary ab initio molecular dynamics (AIMD) simulations elucidated the microscopic origin of cubic-Pb₃O₄@SiO₂'s hydrophobicity by modeling three representative configurations (Fig. 5h). By using AIMD simulation to verify surface hydrophobicity, three types of surfaces were compared: Pb₃O₄ (110) (hydrophilic surface), SiO₂ (111) (moderately hydrophilic), and CH₃–SiO₂ (111) (hydrophobic surface). Real water molecule behavior was simulated, and through the evolution of water molecule configuration, surface water layer distance, and radial distribution function, it was analyzed that water molecules on the CH₃–SiO₂ surface formed obvious hydrophobic cavities after 1000 fs, and the water layer separated from the surface. The water molecules on the surface of Pb₃O₄/SiO₂ are tightly adsorbed without the formation of cavities. Hydrophobic cavities provide enrichment space for intermediates, which repel water molecules and reduce the affinity of the electrode surface for water, while enhancing the affinity for gaseous O₂/O₃, promoting ozone generation and diffusion. Experimental and theoretical analyses convergently revealed the fundamental mechanism: Si–CH₃ groups create hydrophobic/oxygen-affinitive microenvironments that enhance active species diffusion at the catalyst-electrolyte interface and oxygen adsorption kinetics—collectively boosting EOP performance.

Fig. 5 (a) The synthesis schematic of cubic-Pb₃O₄@SiO₂; (b) polarization curves; (c) overpotential comparison; (d) Tafel plot; (e) EIS plot; (f) ECSA plot; (g) gaseous O₃ field; (h) and structures by AIMD simulations. Reproduced from ref. 100 with permission from [Elsevier B.V.], copyright [2023].

Numerous additional Pb-based catalysts demonstrate EOP capabilities. For instance, β-PbO₂/Ta₂O₅ achieves a gaseous O₃ yield of 1.65 mg L⁻¹ and dissolved an O₃ yield of 2.75 mg L⁻¹;³¹ PbO₂/bulk porous Pb produces gaseous O₃ at 14 μmol min⁻¹ (equivalent to 31.5 mg L⁻¹ dissolved O₃);²⁹ PbO_x-CTAB exhibits 20.7% faradaic efficiency,¹⁰¹etc. These Pb-containing catalysts show potential to supplant commercial β-PbO₂ while maintaining stable operation at industrial current densities. However, two primary barriers impede their widespread adoption: (i) scalability limitations: current synthesis methods hinder mass production of stabilized catalysts. (ii) Operational instability: structural reconstruction during reaction compromises EOP performance. Therefore, future research should focus on enhancing the stability of Pb-based catalysts by optimizing the structural design and reducing the use of lead to promote the rapid development of efficient and environmentally friendly EOP processes.

Non-toxic metal-based catalysts

The deployment of non-toxic, Pb-free catalysts in EOP holds significant environmental, economic, and sustainability advantages. Through optimized material design and synthesis protocols, these catalysts are poised to drive efficient and eco-friendly ozone production while advancing sustainable electrocatalysis. Among promising Pb-free candidates, MXenes exhibit exceptional EOP applicability due to its high electrical conductivity enabling efficient electron transfer, abundant surface functional groups providing tunable active sites, modifiable electronic structures via compositional engineering, layered architecture with high specific surface area (SSA) maximizing active site exposure and facile synthesis supporting scalable production.^102,103

For instance, Peng et al. designed a series of Nb₂C/Nb₂O₅ catalysts for EOP applications via controlled calcination-reduction synthesis (Fig. 6a).¹⁰⁴ The study uniquely integrated two half-reactions, hydrogen peroxide evolution and EOP, for electrochemical synthesis. Comprehensive characterization (including SEM and TEM) confirmed successful fabrication of these MXene composites (Fig. 6b–g). The optimal catalyst (T-400) demonstrated exceptional performance (Fig. 6i, j and n) with a yield of 5 mg L⁻¹ for gaseous O₃ (Fig. 6h and m), 0.24 mg L⁻¹ for dissolved O₃ (Fig. 6k and l) and robust 30-hour stability in neutral media (Fig. 6o). Mechanistic analysis revealed that oxygen vacancies in T-400 facilitate the formation of an oxygenated OOH* intermediate and enhanced water deprotonation kinetics. This work offers a perspective on the linkages and combinations between electrocatalytic half-reactions.

Fig. 6 (a) The synthesis schematic of Nb₂C/Nb₂O₅; (b) and (c) SEM and TEM images of TT-300; (d) XRD pattern of TT-300; (e) and (f) SEM and TEM images of T-400; (g) XRD pattern of T-400; (h) gaseous O₃ field of Nb₂C/Nb₂O₅; (i) LSV curves; (j) Tafel plot; (k) and (l) dissolved O₃ field; (m) FE of gaseous O₃; (n) EIS plot; and (o) stability curve. Reproduced from ref. 104 with permission from [Elsevier B.V.], copyright [2023].

Beyond classical materials like MXenes, catalysts commonly employed in the ORR, such as ZnO and alloys, have demonstrated applicability in EOP systems.^105–107 This bidirectional catalyst transfer paradigm reveals significant opportunities: EOP materials may be repurposed for other electrocatalytic applications, while established catalysts from related fields can advance EOP technology. Table 1 provides a comparative analysis of recent EOP research literature.

Table 1 Comparison of EOP activity between catalysts

Catalyst	pH	O3^gas	O3^dissoved	FE	j/V	Ref.
FE: Faraday efficiency
Pt-SAs/B–N–C	7	15 mg L^−1	5.5 mg L^−1	26%	50 mA cm^−2	32
β-PbO2/Ta2O5	0	1.65 mg L^−1	2.75 mg L^−1	—	3.5 V	31
PbO2/bulk porous Pb	0	14 μmol min^−1	31.5 mg L^−1	—	5 V	29
Ce–Ni–Sb–SnO2	0	250 mg L^−1	8 mg L^−1	43.9%	250 mA cm^−2	34
e-1.5F-PbO2	0	95 mg h^−1 cm^−2		14.07%	2.2 A cm^−2	33
Pt mesh	7	—	70 wt mg L^−1	31%	1.25 A cm^−2	108
Pt/TaOy	7	320 μmol L^−1		19.3%	1–2.2 V vs. AgCl	81
Pt/Ti	0	33 mg L^−1		19.7%	5 V	80
B doped diamond	7	9 mg L^−1		40%	2.2 V	109
Ga–Ni–Sb–SnO2	0	—	0.15 mmol	64%	2.7 V	110
ZnO/ZnS/C	7	2.75 mg L^−1	0.5 mg L^−1	11%	0.05 A cm^−2	105
Nb2C/Nb2O5	7	5 mg L^−1	0.24 mg L^−1	13%	0.05 A cm^−2	104
PbOx-CTAB-120	7	7 mg L^−1	—	20.7%	0.05 A cm^−2	101
Cubic-Pb3O4@SiO2	7	4 mg L^−1	—	16.8%	0.1 A cm^−2	100
Bi6Pb2Ox	7	11 mg L^−1	9 mg L^−1	13.5%	0.075 mA cm^−2	111
β-PbO2	7	—	2.12 mg L^−1	16.4%	1 A cm^−2	112

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Conclusions and outlook

This review has examined the mechanism of EOP and material systems, yielding the following principal conclusions: (i) Pb-based catalysts remain predominant in industrial EOP applications and (ii) significant potential exists for developing diverse electrocatalyst alternatives.

To address current limitations and future opportunities, we propose:

(i) Advanced in situ/operando characterization: the relatively underdeveloped state of EOP research compared to established electrocatalytic reactions (e.g., ORR, OER, HER, and CRR) has limited the application of sophisticated characterization techniques. This gap impedes mechanistic investigation of catalytic processes, preventing deep probing of chemical transformations and reaction pathways. We therefore recommend comprehensive operando analysis to advance fundamental understanding of EOP systems.

(ii) Alkaline EOP system innovation: current EOP research remains confined to acidic and neutral conditions due to rapid ozone decomposition in alkaline media. Realizing full-pH-operable EOP would profoundly advance both mechanistic understanding and industrial implementation. The competitive OER becomes extremely easy and dominant under alkaline conditions, consuming the majority of the current. At the same time, the conversion of key intermediate ˙OH to O˙⁻ weakens the reaction pathway for generating ozone, and the rapid chemical decomposition of ozone in alkali makes it impossible for even trace amounts to accumulate. To overcome the limitations of alkaline EOP, it is necessary to design electrode materials that resist hydroxyl adsorption or develop non-aqueous systems to avoid OH⁻ interference. The current industrial EOP still relies on acidic systems, and the fundamental reason is the collapse of the lattice oxygen mechanism under alkaline conditions. Consequently, developing effective gas-separation techniques for alkaline environments represents a critical research frontier.

(iii) Pb-free, non-precious catalyst development: while Pb-based systems dominate commercial applications, their environmental toxicity and instability demand alternatives. Similarly, precious metal catalysts face scalability limitations. Hence, the development and design of non-Pb-based and non-precious-metal-based EOP catalysts should not be delayed. Developing Pb-free, non-precious metal EOP catalysts is not only a technical requirement, but also a dual driver of environmental ethics and resource security. Future breakthroughs need to focus on environmentally compatible materials (without heavy metal leaching); rich element high activity design (Fe, Co, and Ni based oxides); and electrode reactor collaborative optimization (such as membrane electrode assembly technology). Only by getting rid of dependence on lead and precious metals can electrocatalytic ozone technology truly achieve green and sustainable applications.

(iv) Next-generation reactor design: conventional electrolyzers dominate current research but suffer from critical limitations, such as prohibitive capital costs, suboptimal structural durability and insufficient operational stability. The improvement of EOP devices can be completed in stages. Primary stage: renovation of the electrolytic cell and optimization of electrodes + addition of pulse power supply + online UV detection. Intermediate stage: building of membrane electrode assembly reactor + split double tank + some control platforms. Advanced stage: development of microfluidic array reactors, combined with AI dynamic regulation. The core of EOP laboratory reactor design is precise control of the “electro-chemical-mass transfer” process. Priority should be given to addressing ozone mass transfer limitations and detection reliability, followed by gradual upgrades to non-aqueous phase systems and intelligence. These shortcomings constrain fundamental research and compromise system efficiency. We therefore urge development of advanced reactor architectures.

Conflicts of interest

There are no conflicts to declare.

Data availability

All source data are provided upon request from corresponding authors.

Acknowledgements

The authors would like to acknowledge the financial support from the National Natural Science Foundation (Grant No. 92163124, 52376193 and 52488201), the Jiangsu Natural Science Foundation (Grant No. BK20230097), and the Fundamental Research Funds for the Central Universities (Grant No. 30920041113 and 30921013103).

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