Brownmillerite Transition Metal Oxide Catalyst for Air Electrodes
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Solution Overview
Problem
Current transition metal oxide catalysts for oxygen evolution reactions (OER) in metal-air secondary batteries are not as active as precious metal catalysts, limiting the charging and discharging efficiency of these batteries.
Innovation Solution
Development of a brownmillerite-type transition metal oxide catalyst, specifically represented by the formula A2B2O5, where A represents Ca, Sr, or rare earth elements, and B1 and B2 are different 3d transition metals, forming a tetrahedral and octahedral structure respectively, which exhibits higher OER activity than Pt catalysts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If precious metal catalysts (Pt, IrO2, RuO2) are used for OER, then high OER activity is achieved, but cost increases and resource scarcity becomes a problem
Solution Approach 1:
The patent replaces expensive precious metal catalysts with non-precious metal transition metal oxides (such as perovskite-type ABO3 and spinel-type AB2O4) that are cheaper and more abundant. These alternative catalysts achieve comparable OER activity (2.0-3.0 mA/cm2 at 1.6V vs RHE) without relying on scarce precious metals like Pt, IrO2, and RuO2, thereby reducing cost and resource dependency while maintaining reliable catalytic performance
Solution Approach 2:
The patent optimizes the electronic structure and composition parameters of transition metal oxides by adjusting the number of eg electrons in the transition metal at the B site (targeting eg electron count close to 1) and modifying the oxide stoichiometry (such as A0.5Ca0.5CoO3-δ). These parameter changes enable non-precious metal catalysts to achieve OER activity levels previously only attainable with precious metals, resolving the contradiction between catalyst cost and catalytic effectiveness
2Quantity of substance
If perovskite-type transition metal oxide (ABO3) catalysts are used, then precious metal content is reduced, but OER activity remains insufficient compared to precious metal catalysts
Solution Approach 1:
The patent employs composite material strategies by combining transition metal oxides with conductive carbon materials (such as acetylene black, carbon nanotubes, or graphene) to create composite catalysts. This composite structure addresses the insufficient OER activity of pure perovskite-type oxides by providing additional active sites and improving electron transport, while maintaining the low-precious-metal advantage. The composite catalysts achieve enhanced OER activity (2.0-3.0 mA/cm2 at 1.6V vs RHE) comparable to precious metal catalysts
3Use of energy by stationary object
If large overvoltage is generated in OER, then charging voltage increases, but charging and discharging efficiency decreases
Solution Approach 1:
The patent replaces conventional catalysts that generate large overvoltage with highly active non-precious metal transition metal oxide catalysts. These alternative catalysts reduce the overvoltage required for OER by providing more efficient reaction pathways, thereby lowering the charging voltage needed and improving overall charging and discharging efficiency without sacrificing catalytic durability
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 brownmillerite-type transition metal oxide catalysts demonstrate OER activity comparable to or exceeding that of Pt, with Ca2FeCoO5 showing a current density of about 6 mA/cm2 at 1.6 V vs RHE, significantly higher than previously reported precious metal oxide catalysts, and maintaining high activity in high-concentration KOH solutions.
Implementation Method 1
a large overvoltage is typically generated in the OER, and therefore, sufficient charging and discharging efficiency has not been obtained at present. Therefore, a highly active OER catalyst that greatly affects the voltage during charging urgently needs to be developed
Data Source
AI summary
A novel transition metal oxide catalyst that is equivalent to precious metal catalysts, and an air electrode and an air secondary battery using this catalyst are provided. The catalyst is a catalyst for an air electrode including a brownmillerite-type transition metal oxide and represented by General Formula (1) below:A2B1B2O5 (1)where A represents Ca, Sr, Ba, or a rare earth element(RE), B1 is a metal atom that forms a tetrahedral structure together with oxygen atoms, and B2 is a metal atom that forms an octahedral structure together with oxygen atoms. Disclosed are an air electrode for a metal-air secondary battery that includes the catalyst, and a metal-air secondary battery that includes an air electrode including the catalyst, a negative electrode including a negative electrode active material, and an electrolyte intervening between the air electrode and the negative electrode.