Electrode Coating for Electrochlorination at Low Temperatures
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Solution Overview
Problem
Existing electrodes for electrochlorination cells, particularly those used in naval ballast water treatment, face inefficiencies in generating active chlorine from dilute sodium chloride solutions at low temperatures and tend to deactivate during cathodic operation, leading to reduced selectivity and operational costs, along with safety and environmental concerns from cathode scaling.
Innovation Solution
A titanium electrode with an inner catalytic coating of tantalum, ruthenium, and iridium oxides and an outer coating of titanium, ruthenium, nickel, iron, or cobalt oxides, applied in a specific composition and roughness profile to enhance anchoring and durability, allowing for efficient active chlorine generation and prolonged operation even at low temperatures and with polarity reversal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If noble metal oxide-coated titanium anodes are used for generating active chlorine from dilute sodium chloride solutions, then the biocidal treatment function is achieved, but the selectivity and efficiency deteriorate at low temperatures and low sodium chloride concentrations
Solution Approach 1:
The electrode uses a composite coating structure with an inner layer containing Ta2O5, RuO2, and IrO2 oxides, and an outer layer containing TiO2, RuO2, and Fe2O3, CoO, or NiO oxides. This composite material composition optimizes both the stability and catalytic activity for active chlorine generation from dilute NaCl solutions at low temperatures, resolving the contradiction between reliability and productivity.
2Duration of action of stationary object
If periodic polarity reversal is implemented to prevent cathode scaling, then the operational continuity is improved, but the electrode deactivation during cathodic operation increases
Solution Approach 1:
The composite coating with specific oxide combinations (Ta2O5, RuO2, IrO2 in inner layer; TiO2, RuO2, Fe2O3, CoO, or NiO in outer layer) provides enhanced resistance to deactivation during cathodic operation, allowing the electrode to maintain reliability while supporting periodic polarity reversal for operational continuity.
Solution Approach 2:
The invention changes the chemical composition parameters of the catalytic coatings to specific oxide ratios and combinations that confer resistance to deactivation during cathodic polarization, enabling the electrode to withstand periodic polarity reversal without significant performance loss.
3Ease of operation
If cathodes are periodically washed with hydrochloric acid to remove scaling, then the cathode surface cleanliness is improved, but safety and environmental issues arise
Solution Approach 1:
The system uses periodic polarity reversal where the electrode itself performs self-cleaning during cathodic operation through local acidification, eliminating the need for external hydrochloric acid washing operations and thereby removing safety and environmental hazards while maintaining ease of operation.
4Reliability
If the titanium substrate is etched to increase roughness for better coating anchoring, then the coating adhesion is improved, but the manufacturing complexity increases
Solution Approach 1:
The invention specifies controlled etching parameters achieving a roughness profile with Ra value of 0.5-2.0 μm, optimizing coating anchoring while controlling manufacturing complexity through defined process parameters rather than uncontrolled complex procedures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The electrode achieves high selectivity and extended operational life in generating active chlorine from dilute sodium chloride solutions, even at low temperatures, with improved durability and reduced deactivation, thereby enhancing the efficiency and cost-effectiveness of electrochlorination processes.
Implementation Method 1
a first inner catalytic coating applied to the substrate containing a mixture of oxides of tantalum, ruthenium and iridium
Implementation Method 2
The electrolysis of seawater or other dilute aqueous solutions of sodium chloride with consequent generation of active chlorine
Implementation Method 3
The titanium substrate has an average roughness value Ra ranging from 4 to 10 μm, in order to favour the optimal anchoring of the catalytic coatings
Data Source
AI summary
The invention relates to an electrode suitable for electrolytic treatments of dilute solutions of sodium chloride even at low temperatures. The electrode can be used in the generation of active chlorine-based biocidal agents in ballast water for marine applications. The electrode has a titanium substrate, an inner catalytic coating containing oxides of tantalum, ruthenium and iridium, and an outer catalytic coating containing oxides of titanium, ruthenium and of at least one of nickel, iron and cobalt.