From Chemical Gardens to Fuel Cells: Generation of Electrical Potential and Current Across Self‐Assembling Iron Mineral Membranes

Abstract

We examine the electrochemical gradients that form across chemical garden membranes and investigate how self‐assembling, out‐of‐equilibrium inorganic precipitates—mimicking in some ways those generated in far‐from‐equilibrium natural systems—can generate electrochemical energy. Measurements of electrical potential and current were made across membranes precipitated both by injection and solution interface methods in iron‐sulfide and iron‐hydroxide reaction systems. The battery‐like nature of chemical gardens was demonstrated by linking multiple experiments in series which produced sufficient electrical energy to light an external light‐emitting diode (LED). This work paves the way for determining relevant properties of geological precipitates that may have played a role in hydrothermal redox chemistry at the origin of life, and materials applications that utilize the electrochemical properties of self‐organizing chemical systems.

From Chemical Gardens to Chemobrionics

“…While the system is in disequilibrium, however, chemical gardens can be thought of as analogous to membrane fuel cells; in effect, utilizing a selectively permeable membrane with inner and outer surfaces of different composition separating two solutions of contrasting reduction potential E h and pH. 63,151 In a real membrane fuel cell, the catalytic electrodes on either side of the semipermeable membrane would be of specific composition designed to catalyze reactions in either half of the cell, and electrical potential would be applied to those electrodes to drive the reactions. It is not yet known whether chemicalgarden systems that generate their own electrical potential, with possibly charged or redox active membrane surfaces (such as iron sulfides), might also be able to drive chemical reactions in this fashion, but it is a possibility inviting further experimentation.…”

The fertile physics of chemical gardens

“…together electrically in series could light a small LED device. 8 In certain reaction systems, the fuel-cell analogy is enhanced by the catalytic properties of the tube or precipitate wall; for example, a tube of redox-active material could both generate an electric potential from ion gradients and drive reduction or oxidation of some other component in the surrounding solution. Such possibilities naturally lead one to consider materials applications like using chemical-garden precipitates as electrode materials or electrocatalysts, and they can also help with understanding similar phenomena in natural systems.…”

Nitrogen Oxides in Early Earth's Atmosphere as Electron Acceptors for Life's Emergence

“…Electro-geochemical gradients would have been imposed across inorganic precipitates between the mildly acidic, CO 2 -rich Hadean seawater and the alkaline hydrothermal fluid laden with H 2 and CH 4 , products of serpentinization and hydrothermal leaching, respectively (Russell et al, 1989;Barge et al, 2015). Nitschke and Russell (2013) suggested that the first carbon fixation pathway operated through the process of denitrifying methanotrophic acetogenesis-a putative variant of the ancient acetyl-coenzyme A pathway still used by anaerobic microbes-in which H 2 reduces CO 2 to CO, and CH 4 is oxidized through methanol to a methylene entity before being reduced and thiolated to give CH 3 SH.…”