Meta-analysis of electrically conductive membranes: A comparative review of their materials, applications, and performance

A range of conductive materials have been used to develop electrically conductive membranes (ECMs) for use in various applications, including fouling mitigation, selectivity enhancement, electrochemical degradation of contaminants, and surface sensing capabilities. ECMs have been fabricated both as stand-alone porous materials and as composite materials wherein the conductive material is supported on a conventional membrane. In this meta-analysis, we classify composite ECMs from 111 studies based on their physical properties and specific applications in order to identify their material limitations, performance trends, and avenues for future work. During this analysis, two major challenges were identified: the wide variety of test conditions (98 unique pollutants across 193 different experiments) used by researchers, which makes it difficult to perform cross-study comparisons, and a very limited body of ECM research that uses realistic feed sources (e.g., municipal wastewater). Based on this analysis, we propose a set of characterization and performance tests that researchers can use as standards in comparing ECM materials and configurations. To this end, surface conductivity and hydraulic permeability data from 39 studies of various composite ECMs are collected and plotted using Robeson-like analysis to illustrate the respective trade-offs that exist when using graphitic nanomaterials and conductive polymers. Interestingly, metal-based composite ECMs were not subject to the same trade-offs and generally out-performed the other ECMs in terms of conductivity. The conductivity/permeability plots developed herein not only provide a standardized approach for evaluating the performance of composite ECMs, but they can also be used to guide design decisions aimed at achieving specific performance levels.