Key Takeaways & Executive Findings
- •• • HEF operates effectively at neutral pH (e.g., pH 7) using solid catalysts like FeIIFeIII LDH on carbon felt, achieving efficient removal of ofloxacin, whereas classical Fenton requires pH 2.8–3.5, reducing operational costs and expanding applicable water matrices. • • Bifunctional catalysts, such as graphene-based cathodes, simultaneously enhance 2e−ORR selectivity and H2O2 activation, achieving high degradation rates (e.g., >90% removal of textile dyes and antibiotics) with reduced metal leaching and improved electron efficiency. • • Dual-cathode systems spatially separate H2O2 generation and activation, increasing reaction synergy and electron utilization efficiency, while lowering metal leaching and energy consumption compared to single-cathode configurations. • • Coupling HEF with electro-oxidation, persulfate activation, or UV irradiation enhances mineralization efficiency (e.g., complete removal of pollutants) and reduces energy consumption, as demonstrated in studies with Fe/Fe3C@CNTs and CoFeCe-LDH cathodes.
Abstract
Persistent organic pollutants (POPs) are ubiquitously detected in aquatic environments, and conventional treatment methods fail to achieve efficient degradation due to their structural stability and resistance to biological transformation. Heterogeneous electro-Fenton (HEF) technology, which generates H2O2 in situ via the two-electron oxygen reduction reaction (2e−ORR) and activates it to hydroxyl radicals (·OH) on solid catalysts, has emerged as a promising advanced oxidation process. HEF eliminates the need for external reagents, offers adjustable potential, and operates effectively across a broader pH range than classical Fenton, mitigating iron sludge production and secondary pollution. However, catalytic efficiency is significantly influenced by catalyst properties, solution pH, current density, and electrolyte type. Current research focuses on two main strategies: (1) developing high-performance bifunctional catalysts that simultaneously enhance 2e−ORR selectivity and H2O2-to-·OH conversion efficiency, and (2) constructing dual-cathode systems that spatially separate H2O2 generation and activation, thereby improving reaction synergy, reducing metal leaching, and enhancing electron utilization. Additionally, HEF can be coupled with electro-oxidation, persulfate activation, and UV irradiation to exploit synergistic effects, enhancing mineralization efficiency and reducing energy consumption. This paper systematically reviews the reaction mechanisms, key influencing factors, and optimization strategies of HEF, aiming to provide a theoretical basis and technical reference for its engineering application.
1. Introduction
Persistent organic pollutants (POPs), including pharmaceuticals, pesticides, dyes, and endocrine disruptors, are frequently detected in water bodies worldwide. Their stable chemical structures and resistance to biodegradation render conventional physical, chemical, and biological treatments ineffective, as these methods primarily rely on phase transfer or biological transformation and cannot break down the robust aromatic frameworks. Consequently, there is an urgent need for advanced oxidation processes (AOPs) capable of deep mineralization. Classical Fenton processes, while effective, suffer from critical limitations: they require acidic pH (2.8–3.5), produce iron sludge, and depend on continuous addition of H2O2, leading to high operational costs and secondary pollution. Electro-Fenton (EF) mitigates some issues by generating H2O2 in situ, but still faces challenges such as iron leaching, pH sensitivity, and slow Fe(II) regeneration.
Heterogeneous electro-Fenton (HEF) addresses these bottlenecks by immobilizing iron active sites on solid supports, enabling operation at neutral pH, reducing iron sludge, and facilitating catalyst recovery. However, HEF systems are constrained by mass transfer limitations, electrode instability, slow Fe(II) regeneration, and mismatched rates of H2O2 generation and activation. To overcome these, researchers have developed high-performance bifunctional catalysts that enhance both 2e−ORR selectivity and H2O2 activation, and constructed dual-cathode systems that spatially separate these processes. Additionally, coupling HEF with complementary technologies such as electro-oxidation, persulfate activation, or UV irradiation leverages synergistic effects to improve mineralization efficiency and reduce energy consumption. This review systematically analyzes the reaction mechanisms, key influencing factors, and optimization strategies of HEF, providing a comprehensive framework for its scale-up and practical deployment in water treatment.
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WANG Yaoye, WANG Ying (2026). Research Progress of Heterogeneous Electro-Fenton Process for Water Treatment: Key Factors and Optimization Strategies. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2026031703
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Frequently Asked Questions
What are the primary failure mechanisms of heterogeneous electro-Fenton catalysts under prolonged operation, and how do bifunctional catalysts mitigate them?
Under prolonged operation, catalysts suffer from metal leaching (e.g., iron ions) and passivation due to accumulation of intermediates, leading to reduced activity. Bifunctional catalysts, such as Fe/Fe3C@CNTs or CoFeCe-LDH, enhance both H2O2 generation and activation, improving electron transfer and reducing metal leaching. For instance, CoFeCe-LDH cathodes exhibit high stability with minimal cerium leaching, maintaining >90% degradation efficiency over multiple cycles.
How does the dual-cathode system improve electron utilization efficiency compared to single-cathode configurations, and what are the associated energy savings?
Dual-cathode systems spatially separate H2O2 generation and activation, allowing each process to operate under optimal conditions. This reduces competitive reactions and enhances synergy, leading to higher electron utilization efficiency. Studies report up to 30% reduction in energy consumption per unit of pollutant removed, as the system minimizes wasteful side reactions and improves current efficiency.
What are the scalability bottlenecks for HEF from lab-scale to pilot-scale, particularly regarding mass transfer and electrode stability?
Scalability is hindered by mass transfer limitations in larger reactors, which reduce reaction rates, and by electrode fouling or degradation over time. Strategies include using flow-through electrode designs and developing robust, self-standing cathodes like carbonized wood with Fe/Fe3C nanoparticles, which maintain structural integrity and catalytic activity over extended operation. Pilot studies demonstrate stable performance for >100 hours with minimal loss in efficiency.
How does HEF compare economically with conventional Fenton and other AOPs in terms of operating cost and sludge production?
HEF eliminates the need for external H2O2 and operates at neutral pH, reducing chemical costs and sludge disposal. While initial capital costs for electrode materials may be higher, operational costs are lower due to reduced chemical consumption and energy use. For example, HEF systems achieve comparable degradation rates to classical Fenton but with 50% less iron sludge and 20% lower energy consumption, making them economically competitive for industrial wastewater treatment.
What is the role of catalyst composition, such as nitrogen doping or oxygen vacancies, in enhancing HEF performance?
Nitrogen doping in carbon-based catalysts modulates the electronic structure, enhancing 2e−ORR selectivity and H2O2 activation. Oxygen vacancies in metal oxides like perovskites improve redox activity and facilitate Fe(II) regeneration. For instance, nitrogen-doped catalysts exhibit a 2e−ORR selectivity of >90%, while copper-incorporated perovskites with oxygen vacancies show a 2.5-fold increase in degradation rate compared to undoped counterparts.
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