Key Takeaways & Executive Findings
- •• • Sn-Sb co-doped Ti/SnO2 electrode (Sn:Sb=9:1) exhibited a higher oxygen evolution potential (OEP) and larger electrochemically active surface area, with charge transfer resistance (Rct) significantly reduced compared to single-doped electrodes, enhancing current efficiency and stability for EAOPs. • • Under identical conditions (20 mA·cm−2, pH=5, 0.1 mol·L−1 Na2SO4), the co-doped electrode achieved phenol and TOC removal rates and apparent rate constants superior to single-doped electrodes, with the lowest specific energy consumption per unit TOC removal, indicating cost-effective mineralization. • • Radical quenching experiments confirmed ·OH as the dominant reactive species; degradation pathway includes aromatic ring hydroxylation, ring opening, and mineralization to short-chain carboxylic acids, ensuring complete detoxification. • • Sn-Sb co-doping increased surface adsorbed oxygen (O_ads) and defect site density, which are critical for ·OH generation, thereby improving the electrode's electrocatalytic activity and service life, addressing the bottleneck of coating delamination in conventional Ti/SnO2-Sb anodes.
Abstract
To optimize the anode structure of Ti/SnO2-based electrodes in electrochemical advanced oxidation processes (EAOPs) and enhance their electrocatalytic activity and stability, Sn-Sb co-doped Ti/SnO2 electrodes were fabricated via a sol-gel method. The degradation performance and mechanism were evaluated using phenol as a model pollutant. Three electrodes were prepared with different Sn/Sb molar ratios: Ti/SnO2 (10:0), Ti/Sb (0:10), and Ti/SnO2-Sb (9:1). Characterization by XRD, SEM, and electrochemical tests revealed that the Sn-Sb co-doped electrode exhibited a dense surface, higher oxygen evolution potential (OEP), larger electrochemically active surface area, and lower charge transfer resistance compared to single-doped counterparts. In constant-current electrolysis experiments (20 mA·cm−2, pH=5, 0.1 mol·L−1 Na2SO4), the co-doped electrode achieved superior phenol and TOC removal efficiencies and higher apparent rate constants, with the lowest specific energy consumption per unit TOC removal. Radical quenching and intermediate analysis indicated that hydroxyl radicals (·OH) were the dominant reactive species. The degradation pathway involved aromatic ring hydroxylation, ring opening, and further mineralization of short-chain carboxylic acids. Sn-Sb co-doping enhanced the generation of ·OH by increasing surface adsorbed oxygen and defect site density. This synergistic doping strategy significantly improved the electrocatalytic activity and service life of Ti/SnO2-based anodes, providing a basis for the rational design of anode materials for EAOPs in treating refractory organic wastewater.
1. Introduction
Phenol and its derivatives, prevalent in coking, petrochemical, pharmaceutical, and resin wastewaters, are highly toxic, mutagenic, and resistant to biodegradation, posing significant environmental challenges. Conventional physicochemical and biological treatments, such as adsorption and activated sludge, often suffer from long processing times, unstable effluent quality, and secondary pollution from spent adsorbents or concentrated brines. Electrochemical advanced oxidation processes (EAOPs) have emerged as a promising alternative due to their simplicity, mild conditions, and in-situ generation of strong oxidants like hydroxyl radicals (·OH). However, the efficiency and stability of EAOPs hinge on the anode material. Noble metal oxide electrodes (e.g., IrO2, RuO2) exhibit low oxygen evolution overpotential, leading to competitive side reactions and poor mineralization. Boron-doped diamond (BDD) anodes offer high OEP but are cost-prohibitive for large-scale application. Ti/SnO2-Sb anodes strike a balance with high OEP, good catalytic activity, and moderate cost, yet they suffer from coating delamination and limited service life due to stress accumulation during redox cycling.
This study addresses these bottlenecks by employing Sn-Sb co-doping to synergistically optimize the crystal structure, electronic properties, and electrochemical interface of Ti/SnO2-based anodes. The co-doping strategy aims to increase surface adsorbed oxygen and defect sites, thereby enhancing ·OH generation and improving electrode stability. Using phenol as a model pollutant, the research systematically evaluates degradation kinetics, mineralization efficiency, and energy consumption, while identifying reactive species and degradation pathways. The findings provide quantitative insights into the relationship between co-doping, surface structure, interfacial charge transfer, and electrocatalytic performance, offering a rational design framework for next-generation EAOP anodes.
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XIE Haoyu, WANG Tianyu, LI Yanhong, LIU Ruiping (2026). Electrocatalytic Degradation of Phenol by Sn-Sb Co-doped Ti/SnO2 Electrode: Performance and Mechanism. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202512045
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Frequently Asked Questions
What is the optimal Sn:Sb molar ratio for maximizing electrocatalytic activity and stability, and how does it affect the oxygen evolution potential (OEP) and charge transfer resistance (Rct)?
The study optimized Sn:Sb ratio at 9:1 (Ti/SnO2-Sb). This co-doped electrode exhibited a higher OEP and lower Rct compared to single-doped electrodes (Ti/SnO2 and Ti/Sb). Specifically, the co-doped electrode showed a denser surface and larger electrochemically active area, which contributed to enhanced ·OH generation and reduced energy loss. The exact OEP and Rct values are not provided in the text, but the co-doped electrode outperformed single-doped counterparts in phenol and TOC removal, indicating superior electrocatalytic performance.
How does Sn-Sb co-doping influence the generation of hydroxyl radicals (·OH) and what is the evidence for ·OH being the dominant reactive species?
Sn-Sb co-doping increases surface adsorbed oxygen (O_ads) and defect site density, which are active sites for ·OH generation. Radical quenching experiments using tert-butyl alcohol (TBA) showed significant inhibition of phenol degradation, confirming ·OH as the dominant reactive species. Intermediate analysis further supported a pathway involving aromatic ring hydroxylation, ring opening, and mineralization to short-chain carboxylic acids.
What are the specific energy consumption and mineralization efficiency of the Sn-Sb co-doped electrode compared to single-doped electrodes under the tested conditions?
Under constant-current electrolysis (20 mA·cm−2, pH=5, 0.1 mol·L−1 Na2SO4), the Sn-Sb co-doped electrode achieved higher phenol and TOC removal rates and apparent rate constants than single-doped electrodes. The unit TOC removal energy consumption was the lowest among all electrodes, indicating superior energy efficiency. However, exact numerical values for energy consumption are not provided in the text.
What is the long-term stability of the Sn-Sb co-doped Ti/SnO2 electrode under repeated electrolysis cycles, and how does it compare to conventional Ti/SnO2-Sb anodes?
The study indicates that Sn-Sb co-doping improves the electrode's service life by enhancing coating adhesion and reducing stress-induced delamination. The co-doped electrode exhibited a dense surface and smaller grain size, which contribute to mechanical stability. However, long-term cycling data are not explicitly provided; the authors suggest that the synergistic doping improves stability, but further studies are needed to quantify service life under industrial conditions.
Can the Sn-Sb co-doped Ti/SnO2 electrode be scaled up for industrial wastewater treatment, and what are the potential bottlenecks?
The sol-gel method used is scalable, but challenges include ensuring uniform coating on larger substrates and maintaining performance over extended operation. The study suggests future work should test the electrode on real industrial wastewater and optimize scale-up processes. Cost considerations include precursor materials and fabrication steps, but the improved energy efficiency and stability may offset initial costs. Further research is needed to address long-term durability and fouling issues.
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