Nafion membranes for power generation from physiologic ion gradients†

Abstract

Creatures such as torpedo rays and electric eels showcase the exceptional ability to convert ionic gradients inside their bodies into powerful electrical discharges. In the future, artificial power units capable of reproducing this intriguing biological phenomenon may be able to power active devices, such as pacemakers and prosthetics, directly from ion gradients present in the human body. The present work evaluates the use of proton-selective Nafion membranes to generate electric power from the pH gradient present in the human stomach. First, we characterize two different commercial Nafion membranes by focusing on their ion exchange performance. In particular, we quantify the perm-selectivity of these membranes for various hydrated ions relative to that of the hydronium ion. Our results indicate that the transport of ions in wet Nafion proceeds through water-filled nanochannels, and that proton selectivity can be explained simply by the much larger mobility of protons in water with respect to other ions. Subsequently, we demonstrate a Nafion-based artificial electric organ capable of generating electric power from gastric juices. This power unit is built according to the reverse electrodialysis (RED) scheme, with each cell stack in series capable of generating 134 mV of potential difference and 188 mW m⁻² of power density.