Development of Structure–Property Relationships for Ammonium Transport through Charged Organogels

TL;DR

This paper explores how to design better membranes for ammonia fuel cells by studying how ammonium moves through different gels.

Contribution

The study introduces a new approach to controlling ammonium transport by systematically varying membrane properties.

Findings

Higher crosslinking density in membranes reduces ammonium permeability.

At maximum crosslinking, ammonium permeability remains consistent regardless of water content or monomer hydrophobicity.

These findings suggest ways to design membranes that minimize ammonium crossover in electrochemical cells.

Abstract

Ammonia is a promising carbon-free fuel, but current methods to produce ammonia are energy intensive. New methods are thereby needed, with one promising method being electrochemical nitrogen reduction cells. Efficient cell operation requires robust catalysts but also efficient membrane separators that permit the selective transport of ions while minimizing the transport of the products across the cell. Commercial membranes have an unknown morphology which makes designing improved cells challenging. To address this problem, we synthesized a series of membranes with controlled crosslinking density and chemical composition to understand their impact on ammonium transport. Higher crosslinking density led to lower ammonium permeability. At the highest crosslinking density, similar ammonium permeability was observed independent of the water volume fraction and hydrophobicity of the monomers. These results suggest new directions to develop membranes with reduced ammonium crossover to improve the efficiency of these electrochemical cells.

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