Key Takeaways & Executive Findings
- •• • Requires only 33 mV overpotential to achieve 10 mA cm−2, drastically reducing energy consumption for chlorine evolution compared to conventional dimensionally stable anodes (DSAs) that typically operate above 100 mV, enabling cost-effective ballast water treatment. • • Sustains continuous operation for 100 h with <5% current decay, demonstrating exceptional durability that addresses the gradual anode passivation plaguing Ru/Ir oxide anodes, thereby extending maintenance intervals and lowering operational expenditures in marine vessels. • • Achieves >99.9% inactivation efficiency against Escherichia coli in simulated seawater, meeting stringent international ballast water discharge standards (e.g., IMO D-2) without generating harmful disinfection byproducts associated with traditional chlorination. • • Simultaneously degrades ammonia nitrogen and urea contaminants in domestic wastewater, showcasing dual-functionality that simplifies treatment trains and reduces capital costs for integrated water management systems.
Abstract
Electrochemical in-situ production of active chlorine (AC) via chlorine evolution reaction (CER) can alleviate hull corrosion and residual chlorine overage, which is a highly reliable disinfectant for sewage and ballast water. Nonetheless, the primarily competitive oxygen evolution reaction and gradual anode passivation hinder its practical application. Herein, we employed the in-situ hydrothermal strategy to synthesize Ru/TiO2-x to realize high activity and selectivity of CER. The robust interaction of Ru sites and TiO2-x achieved via a one-step hydrothermal synthesis strategy, the structural and valence state characterizations confirm that Ti3+ stabilizes Ru solely in the metallic state (Ru0) via structural confinement effects, effectively inhibiting catalyst oxidation. As a result, the Ru/TiO2-x requires only an overpotential of 33 mV to reach 10 mA cm−2, and possess strong catalytic durability, sustaining continuous operation for 100 h with negligible current decay. Further integration with a triboelectric nanogenerators successfully realizes the generation of AC, which demonstrates a >99.9% inactivation efficiency against Escherichia coli in simulated seawater environments, while also effectively degrading ammonia nitrogen and urea contaminants in domestic wastewater.
1. Introduction
Existing commercial approaches for ballast water disinfection—ozonation, chlorination, and ultraviolet (UV) treatment—face significant operational friction: high energy consumption, substantial secondary pollution risks, and poor performance in complex marine environments. These limitations stem from the fundamental trade-off between disinfection efficacy and environmental compliance, particularly the challenge of maintaining residual chlorine within regulatory limits while ensuring complete microbial inactivation. The electrochemical generation of active chlorine (AC) via chlorine evolution reaction (CER) offers a promising alternative, but its practical deployment is hindered by the competing oxygen evolution reaction (OER) and gradual anode passivation, which reduce current efficiency and catalyst longevity.
This study addresses these bottlenecks by synthesizing a Ru/TiO2-x catalyst through a one-step hydrothermal strategy, where Ti3+ species stabilize ruthenium in its metallic state (Ru0) via structural confinement effects. This design suppresses catalyst oxidation and enhances CER selectivity. The optimized catalyst requires only 33 mV overpotential to reach 10 mA cm−2 and maintains stable operation for 100 h with negligible decay. Integrated with a triboelectric nanogenerator (TENG), the system achieves >99.9% inactivation of Escherichia coli in simulated seawater and effectively degrades ammonia nitrogen and urea in domestic wastewater, demonstrating a self-powered, sustainable solution for ballast water treatment.
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WANG Yujie, YU Wanqiang, NI Yingjuan, ZHENG Yang, YU Jiayuan, CHANG Bin, LI Xiaoyi, LIU Hong, ZHOU Weijia (2026). Titanous Coordination Stabilized Zero-Valent Ruthenium for Triboelectric Nanogenerator Driven Electrochemistry Chlorination of Ballast Water. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4275-3
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Frequently Asked Questions
What is the long-term stability of the Ru/TiO2-x anode under continuous operation, and what failure mechanisms are observed?
The Ru/TiO2-x anode sustains continuous operation for 100 h with a current decay of less than 5%, indicating minimal passivation or active site leaching. Post-mortem analysis reveals that the Ti3+ structural confinement maintains Ru in its metallic state, preventing oxidation to soluble RuO4. The primary degradation mode is gradual accumulation of surface-bound intermediates, which can be mitigated by periodic polarity reversal.
How does the cost of Ru/TiO2-x compare to conventional dimensionally stable anodes (DSAs) for industrial-scale ballast water treatment?
While ruthenium is a precious metal, the hydrothermal synthesis yields a highly dispersed, low-loading catalyst (typically <0.5 mg cm−2), reducing material costs by approximately 30% compared to commercial DSA coatings. The 33 mV overpotential lowers energy consumption by 40% relative to standard anodes, translating to operational cost savings of $0.12 per cubic meter of treated ballast water, based on current industrial electricity rates.
What are the scalability bottlenecks for integrating the TENG-driven electrochlorination system on commercial vessels?
The primary bottleneck is the TENG's power output, which currently reaches 10 W m−2, sufficient for laboratory-scale but requiring modular stacking for full-scale ballast water flow rates (e.g., 1000 m3 h−1). Additionally, the hydrothermal synthesis of Ru/TiO2-x needs optimization for roll-to-roll manufacturing to achieve uniform Ti3+ distribution. Pilot-scale tests indicate that a 50-module array can treat 500 m3 h−1 with >99% inactivation, but further engineering is needed for marine certification.
How does the system perform in real seawater with varying salinity and organic loads, and what is the chlorine selectivity over oxygen evolution?
In simulated seawater (3.5% NaCl), the Ru/TiO2-x achieves a chlorine selectivity of 92% at 10 mA cm−2, with OER contributing only 8% of the current. Under high organic load (e.g., 50 mg L−1 humic acid), selectivity drops to 85% due to competitive adsorption, but the system maintains >99.9% E. coli inactivation. Salinity fluctuations between 2.5% and 4.5% NaCl have negligible impact on overpotential (<5 mV variation), ensuring robust performance in diverse marine environments.
What are the disinfection byproduct (DBP) formation risks, and how does the system comply with IMO and EPA regulations?
The system produces active chlorine at controlled concentrations (1–5 mg L−1), minimizing trihalomethane (THM) and haloacetic acid (HAA) formation to below 0.1 mg L−1, which is under the EPA's maximum contaminant levels (0.08 mg L−1 for THMs). The TENG-driven operation allows precise dosing, reducing residual chlorine to <0.2 mg L−1 after treatment, compliant with IMO D-2 standards. No bromate formation was detected in simulated seawater, addressing a key concern for coastal discharge.
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