PVDF-PBASS Blend Membrane for Low Methanol Crossover

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Solution Overview

Problem

Proton exchange membranes (PEMs) in fuel cells face challenges such as high methanol crossover, mechanical instability, and high costs, particularly with NAFION membranes, which are prone to methanol crossover and have poor reproducibility and mechanical properties when modified by post-polymerization sulfonation methods.

Innovation Solution

A polymeric blend membrane using poly(vinylidene fluoride) (PVDF) as a scaffold with poly(tetrabutylammonium styrene sulfonate) (PBASS) copolymer, synthesized through radical copolymerization and crosslinking, which forms a homogeneous and transparent film with improved proton conductivity and low methanol permeability when blended with PVDF, offering better compatibility and stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If NAFION membranes are used for high proton conductivity, then proton conductivity is improved, but methanol crossover increases significantly

Engineering Contradiction:

Improveproton conductivityVSAvoidmethanol crossover

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent uses composite materials by blending PVDF (hydrophobic scaffold) with PSSA (hydrophilic proton-conducting domains) to create a membrane that simultaneously achieves high proton conductivity and low methanol crossover. The composite structure allows hydrophilic channels for proton transport embedded within a hydrophobic matrix that blocks methanol diffusion.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The membrane exhibits local quality differentiation with hydrophilic regions (PSSA domains) providing proton conductivity and hydrophobic regions (PVDF matrix) preventing methanol crossover. This spatial separation of functions allows the membrane to perform both proton transport and methanol rejection simultaneously in different locations.

Inventive Principle:

Principle #3Local quality

2Use of energy by moving object

If post-polymerization sulfonation is used to modify PVDF, then proton conductivity is improved, but mechanical stability and reproducibility deteriorate

Engineering Contradiction:

Improveproton conductivityVSAvoidmechanical stability and reproducibility

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent applies preliminary action by pre-sulfonating polystyrene to create PSSA before blending with PVDF, rather than performing sulfonation after PVDF membrane formation. This preliminary sulfonation avoids mechanical degradation and ensures reproducible results by eliminating harsh post-treatment steps that compromise membrane integrity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses an intermediary approach by employing a compatibilizer (such as PS-b-PEO block copolymer) to mediate between PVDF and PSSA phases during blending. This intermediary ensures homogeneous distribution and stable morphology, improving reproducibility and mechanical stability while maintaining high proton conductivity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Use of energy by moving object

If hydrophilic content is increased to improve proton conductivity, then proton conductivity is improved, but water swelling increases causing mechanical instability

Engineering Contradiction:

Improveproton conductivityVSAvoidmechanical strength

Core Design Contradiction:

Use of energy by moving objectVSStrength

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent optimizes the weight ratio of PVDF to PSSA to balance proton conductivity and mechanical strength. By carefully controlling the hydrophilic content parameter (PSSA concentration), the membrane achieves sufficient proton conductivity while maintaining mechanical stability and minimizing water swelling.

Inventive Principle:

Principle #35Parameter changes

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 PVDF-PBASS blend membranes exhibit high proton conductivity, low methanol permeability, and enhanced mechanical strength, outperforming NAFION membranes in terms of reproducibility and stability, with improved fuel cell performance and reduced methanol crossover.

Implementation Method 1

the scaffold polymer and the polyacid polymer precursor having matching solubility parameters

Methodology Applied

Scientific EffectSolubility parameter matching: Solvation

Implementation Method 2

efficient permeation of hydronium ions from anode to cathode is crucial

Methodology Applied

Scientific EffectProton conduction: Conduction (electrical)

Implementation Method 3

the body of the membrane should have physical properties consistent with its function, for instance essential properties such as mechanical strength, toughness and flexibility

Methodology Applied

Scientific EffectMechanical strength: Elasticity

Data Source

PatentUS10586995B2Method for the fabrication of homogenous blends of polystyrenesulfonic acid and polyvinylidene fluoride suitable for the application in direct oxidation methanol fuel cells (DMFCs)

Publication Date: 2020.03.10 UNIV OF SOUTHERN CALIFORNIA

AI summary

A membrane electrode assembly includes an anode catalyst layer, a cathode catalyst layer, and a polymeric blend proton exchange membrane interposed between the anode catalyst layer and the cathode catalyst layer. The polymeric blend proton exchange membrane includes a scaffold polymer and a polyacid polymer. The polyacid polymer being formed from a polyacid polymer precursor. Characteristically, the scaffold polymer and the polyacid polymer precursor have matching solubility parameters.