Dendritic silver self-assembly in molten-carbonate membranes for efficient carbon dioxide capture

Abstract

Membranes for CO₂ capture should offer high permeant fluxes to keep membrane surface area small and material requirements low. Ag-supported, dual-phase, molten-carbonate membranes routinely demonstrate the highest CO₂ fluxes in this class of membrane. However, using Ag as a support incurs high cost. Here, the non-equilibrium conditions of permeation were exploited to stimulate the self-assembly of a percolating, dendritic network of Ag from the molten carbonate. Multiple membrane support geometries and Ag incorporation methods were employed, demonstrating the generality of the approach, while X-ray micro-computed tomography confirmed that CO₂ and O₂ permeation stimulated self-assembly. We report the highest flux of Ag-supported molten-salt membranes to date (1.25 ml min⁻¹ cm⁻² at 650 °C) and ultrahigh permeability (9.4 × 10⁻¹¹ mol m⁻¹ s⁻¹ Pa⁻¹), surpassing the permeability requirement for economically-competitive post-combustion CO₂ capture, all whilst reducing the membrane-volume-normalised demand for Ag by one order of magnitude.