Valve Metal Anode with Iridium Tin Coating for Oxygen Evolution
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Solution Overview
Problem
Existing anodes for oxygen evolution in industrial electrolysis, particularly in electrometallurgy, face issues with high oxygen overpotential and reduced durability due to corrosion and pollution from aggressive contaminants, especially in high current density applications, and they also contribute to environmental and health concerns with lead-based materials.
Innovation Solution
An electrode comprising a valve metal substrate with a catalytic layer of iridium, tin, and a doping element like bismuth or tantalum, a protective layer of valve metal oxides, and an external layer of valve metal oxides, optimized with specific molar ratios and thermal decomposition processes, which reduces anodic potential and enhances durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lead-based anodes are used for oxygen evolution, then traditional widespread use and simplicity are achieved, but high oxygen evolution overpotential and environmental health concerns occur
Solution Approach 1:
The patent changes the chemical composition parameters of the anode by replacing lead-based materials with valve metal substrates (titanium, zirconium, hafnium) coated with catalytic compositions containing iridium, tin, and doping elements. This parameter change reduces oxygen evolution overpotential while maintaining manufacturing feasibility through established coating techniques.
Solution Approach 2:
The patent employs composite material structures consisting of valve metal substrates combined with catalytic coatings. The composite nature of these anodes (substrate + catalytic layer + protective layer) achieves both low overpotential and high durability, resolving the contradiction between energy efficiency and material performance.
2Loss of energy
If valve metal substrates coated with noble metal catalytic compositions are used, then energy savings are achieved, but operating lifetime is greatly reduced in the presence of aggressive contaminants
Solution Approach 1:
The patent introduces protective layers as intermediary barriers between the catalytic composition and the aggressive electrolyte environment. These protective layers (such as titanium oxide, tantalum oxide, or diamond-like carbon coatings) mediate the interaction by providing chemical stability and resistance to corrosion while allowing the catalytic layer to maintain its low overpotential function.
Solution Approach 2:
The multi-layer composite structure (valve metal substrate + catalytic coating + protective layer) combines materials with complementary properties: the valve metal provides structural stability, the catalytic coating ensures low overpotential, and the protective layer provides corrosion resistance. This composite approach resolves the contradiction between energy efficiency and durability.
3Reliability
If outer coating of valve metal oxides is added to improve durability, then protection against corrosion is achieved, but potential increases to unacceptable values
Solution Approach 1:
The patent employs thin film protective layers that provide adequate protection against corrosion while minimizing the increase in anodic potential. By controlling the thickness and composition of these outer coatings (such as thin layers of titanium oxide or tantalum oxide), the patent achieves durability improvement without unacceptable potential increases.
Solution Approach 2:
The patent optimizes parameters including the thickness, composition, and structure of the protective outer layer to balance durability and potential. By carefully controlling these parameters, the protective layer provides sufficient corrosion resistance while maintaining acceptable anodic potential values for industrial electrolysis applications.
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 a longer operational duration and lower anodic potential, effectively reducing parasitic reactions and ion diffusion, particularly beneficial for decorative chrome plating by minimizing Cr (III) oxidation to Cr (VI), thus improving the quality of chromium metal deposition.
Implementation Method 1
a catalytic layer, a protective layer consisting of valve metals oxides interposed between the substrate and the catalytic layer and an external layer of valve metal oxides, said catalytic layer comprising oxides of iridium, of tin and of at least one doping element M selected between bismuth and tantalum
Implementation Method 2
the presence of the outer valve metal oxide layer, if too thick, increases the potential to unacceptable values
Implementation Method 3
a method for manufacturing an electrode suitable for use as oxygen-evolving anode in electrolytic processes comprising the application in one or more coats of a solution containing precursors of iridium, tin and said at least one doping element M to a valve metal substrate and the subsequent decomposition of said solution by heat treatment in air at a temperature of 480 to 530° C.
Data Source
AI summary
An electrode for electrolytic processes, in particular to an anode suitable for oxygen evolution having a valve metal substrate, a catalytic layer, a protection layer consisting of oxides of valve metals interposed between the substrate and the catalytic layer and an outer coating of oxides of valve metals. The electrode is particularly suitable for processes of cathodic electrodeposition of chromium from an aqueous solution containing Cr (III).