Photo-Ionic Cells: Two Solutions to Store Solar Energy and Generate Electricity on Demand

A solar energy conversion concept based on the photo-induced separation of a pair of redox species in a biphasic liquid cell is presented. The redox pair is subsequently discharged in an electrochemical flow cell to generate electricity. To illustrate this generic concept, we have revisited the thionine/cobalt EDTA system where, upon light excitation, the excited thionine dye is quenched in the aqueous solution by the [Co(II)EDTA]2- complex to form both [Co(III)EDTA]- and reduced thionine, namely leucothionine, that partitions to the organic phase. As a result, solar energy is converted to a redox pair, leucothionine/[Co(III)EDTA]-. The two immiscible liquid phases are separated and the redox energy is stored in the respective electrolyte solutions. These two solutions can then be electrochemically discharged in a flow cell to generate electricity on demand. The electrode reactions involved are the re-oxidation of leucothionine to thionine in the organic solvent and the reduction of the Co(III) complex in water

Hydrogen evolution across nano-Schottky junctions at carbon supported MoS2 catalysts in biphasic liquid systems

The activities of a series of MoS2-based hydrogen evolution catalysts were studied by biphasic reactions monitored by UV/Vis spectroscopy. Carbon supported MoS2 catalysts performed best due to an abundance of catalytic edge sites and strong electronic coupling of catalyst to support

Mimicking the Microbial Oxidation of Elemental Sulfur with a Biphasic Electrochemical Cell

The lack of an artificial system that mimics elemental sulfur (S8) oxidation by microorganisms inhibits a deep mechanistic understanding of the sulfur cycle in the biosphere and the metabolism of sulfur-oxidizing microorganisms. In this article, we present a biphasic system that mimics biochemical sulfur oxidation under ambient conditions using a liquid|liquid (L|L) electrochemical cell and gold nanoparticles (AuNPs) as an interfacial catalyst. The interface between two solvents of very different polarity is an ideal environment to oxidise S8, overcoming the incompatible solubilities of the hydrophobic reactants (O2 and S8) and hydrophilic products (H+, SO32–, SO42–, etc.). The interfacial AuNPs provide a catalytic surface onto which O2 and S8 can adsorb. Control over the driving force for the reaction is provided by polarizing the L|L interface externally and tuning the Fermi level of the interfacial AuNPs by the adsorption of aqueous anions.</p

Reversible Electrochemical Ion Intercalation at an Electrified Liquid|liquid Interface Functionalised with Porphyrin Nanostructures

Ion intercalation into solid matrices influences the performance of key components in most energy storage devices (Li-ion batteries, supercapacitors, fuel cells, etc.). Electrochemical methods provide key information on the thermodynamics and kinetics of these ion transfer processes but are restricted to matrices supported on electronically conductive substrates. In this article, the electrified liquid|liquid interface is introduced as an ideal platform to probe the thermodynamics and kinetics of reversible ion intercalation with non-electronically active matrices. Zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrins were self-assembled into floating films of ordered nanostructures at the water|a,a,a-trifluorotoluene interface. Electrochemically polarising the aqueous phase negatively with respect to the organic phase lead to organic ammonium cations intercalating into the zinc porphyrin nanostructures by binding to anionic carboxyl sites and displacing protons through ion exchange at neutral carboxyl sites. The cyclic voltammograms suggested a positive cooperativity mechanism for ion intercalation linked with structural rearrangements of the porphyrins within the nanostructures, and were modelled using a Frumkin isotherm. The model also provided a robust understanding of the dependence of the voltammetry on the pH and organic electrolyte concentration. Kinetic analysis was performed using potential step chronoamperometry, with the current transients composed of “adsorption” and nucleation components. The latter were associated with domains within the nanostructures where, due to structural rearrangments, ion binding and exchange took place faster. This work opens opportunities to study the thermodynamics and kinetics of purely ionic ion intercalation reactions (not induced by redox reactions) in floating solid matrices using any desired electrochemical method.</p

Soft-Photoconversion Using Floating Self-Assembled Crystalline Films of Porphyrin Nanostructures

One of many evolved functions of biological cell membranes is to induce and regulate self-assembly of photoactive molecules into efficient light harvesting nanomaterials. Synthetic molecular assemblies at soft interfaces exhibit macroscale long-range order and so provide routes to biomimetic analogues that minimise concentration quenching. Here, we report the facile assembly of free-standing layered crystalline films of zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrin nanostructures that exhibit significant photocurrents in situ at an electrified liquid | liquid interface. This methodology does not require acidic conditions, specialised amphiphilic porphyrins, or the use of additives or external stimuli. The assembly process is driven by an interplay between the hydrophobicity gradient at an immiscible aqueous | organic interface and optimised hydrogen bonding in the formed nanostructure. Highly-ordered interfacial nanostructures may provide a new paradigm for realisation of light-harvesting antennae in artificial photosynthetic technologies