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Ionic diodes are components in ionic circuits for AC‐electricity driven desalination and ion extraction processes. Independent of the ionic diode type/mechanism, achieving ionic current rectification at high ionic strengths is challenging but important, for example in seawater desalination and treatment of brine. Here, the butylation of a molecularly rigid (glassy) polymer of intrinsic microporosity (PIM‐EA‐TB) is shown to give anionic diodes with ultrahigh rectification effects (associated with interfacial resistivity) even in high ionic strength aqueous 2 M NaCl solution. The effect is rationalised based on polymer structure affecting ion transport. [ABSTRACT FROM AUTHOR]

Protonation of the molecularly rigid polymer of intrinsic microporosity PIM-EA-TB can be coupled to immobilisation of Fe(CN)63−/4− (as well as immobilisation of Prussian blue) into 1–2 nm diameter channels. The resulting films provide redox-active coatings on glassy carbon electrodes. Uptake, transport, and retention of Fe(CN)63−/4− in the microporous polymer are strongly pH dependent requiring protonation of the PIM-EA-TB (pKA ≈ 4). Both Fe(CN)64− and Fe(CN)63− can be immobilised, but Fe(CN)64− appears to bind tighter to the polymer backbone presumably via bridging protons. Loss of Fe(CN)63−/4− by leaching into the aqueous solution phase becomes significant only at pH > 9 and is likely to be associated with hydroxide anions directly entering the microporous structure to combine with protons. This and the interaction of Fe(CN)63−/4− and protons within the molecularly rigid PIM-EA-TB host are suggested to be responsible for retention and relatively slow leaching processes. Electrocatalysis with immobilised Fe(CN)63−/4− is demonstrated for the oxidation of ascorbic acid. [ABSTRACT FROM AUTHOR]

A film of the polymer of intrinsic microporosity PIM‐7 is coated onto a glassy carbon electrode and the resulting effects on electron transfer reactions are studied for three different types of processes: (i) aqueous solution based, (ii) solid state surface immobilised, and (iii) electrocatalytic processes on electrodeposited palladium. The effects on reactivity for hydroquinone oxidation in aqueous phosphate buffer are shown to be linked to microporosity causing a slightly lower rate of mass transport without detrimental effects on electron transfer and reaction kinetics. Next, water‐insoluble microcrystalline anthraquinone is immobilised directly into the PIM‐7 film and shown to give a chemically reversible reduction process, which is enhanced in the presence of PIM‐7, when compared to the case of anthraquinone immobilised directly onto bare glassy carbon. Electrodeposition of a film of nano‐palladium is demonstrated to give catalytically active electrodes for the reduction/oxidation of protons/hydrogen, the reduction of oxygen, and for the oxidation of formic acid and methanol. With the PIM‐7 film applied onto palladium, a mechanical stabilisation effect occurs. In addition, both the hydrogen insertion and the hydrogen evolution reactions as well as formic acid oxidation are enhanced. Effects are discussed in terms of PIM‐7 beneficially affecting the interfacial reaction under triphasic conditions. The microporous polymer acts as an interfacial "gas management" layer. [ABSTRACT FROM AUTHOR]

Hydrogen oxidation and oxygen reduction are two crucial energy conversion reactions, which are shown to be both strongly affected by the presence of intrinsically microporous polymer coatings on electrodes. Polymers of intrinsic microporosity (PIMs) are known to possess extremely high internal surface area and ability to bind gases under dry conditions. It is shown here that both, hydrogen‐ and oxygen gas binding into PIMs, also occurs under wet or "triphasic" conditions in aqueous electrolyte environments (when immersed in 0.01 M phosphate buffer at pH 7). For two known PIM materials (PIM‐1 and PIM‐PY), nanoparticles are formed by an anti‐solvent precipitation protocol and then cast as a film onto platinum or glassy carbon electrodes. Voltammetry experiments reveal evidence for hydrogen and oxygen binding. Both, PIM‐1 and PIM‐PY, locally store hydrogen or oxygen gas at the electrode surface and thereby significantly affect electrocatalytic reactivity. The onset of oxygen reduction on glassy carbon is shifted by 0.15 V in the positive direction. One for three: Due to their hydrophobic and molecularly rigid nature, intrinsically microporous polymers affect the conditions for gas|liquid electrolyte|solid electrode triphasic reactions. [ABSTRACT FROM AUTHOR]

The one-step vacuum carbonization synthesis of a platinum nano-catalyst embedded in a microporous heterocarbon (Pt@cPIM) is demonstrated. A nitrogen-rich polymer of an intrinsic microporosity (PIM) precursor is impregnated with PtCl62- to give (after vacuum carbonization at 700 °C) a nitrogen-containing heterocarbon with embedded Pt nanoparticles of typically 1-4 nm diameter (with some particles up to 20 nm diameter). The Brunauer-Emmett-Teller (BET) surface area of this hybrid material is 518 m2 g-1 (with a cumulative pore volume of 1.1 cm3 g-1) consistent with the surface area of the corresponding platinum-free heterocarbon. In electrochemical experiments, the heterocarbon-embedded nano-platinum is observed as reactive towards hydrogen oxidation, but essentially non-reactive towards bigger molecules during methanol oxidation or during oxygen reduction. Therefore, oxygen reduction under electrochemical conditions is suggested to occur mainly via a 2-electron pathway on the outer carbon shell to give H2O2. Kinetic selectivity is confirmed in exploratory catalysis experiments in the presence of H2 gas (which is oxidized on Pt) and O2 gas (which is reduced on the heterocarbon surface) to result in the direct formation of H2O2. [ABSTRACT FROM AUTHOR]

Ionic diode phenomena occur at asymmetric ionomer | aqueous electrolyte microhole interfaces. Depending on the applied potential, either an 'open' or a 'closed' diode state is observed switching between a high ion flow rate and a low ion flow rate. Physically, the 'open' state is associated mainly with conductivity towards the microhole within the ionomer layer and the 'closed' state is dominated by restricted diffusion-migration access to the microhole interface opposite to the ionomer. In this report we explore a 'heterojunction' based on an asymmetric polymer of intrinsic microporosity (PIM) | Nafion ionomer microhole interface. Improved diode characteristics and current rectification are observed in aqueous NaCl. The effects of creating the PIM | Nafion micro-interface are investigated and suggested to lead to novel sensor architectures. [ABSTRACT FROM AUTHOR]

[Display omitted] • First observation of electroosmotic flow in polymers of intrinsic microporosity. • Employing NMR to monitor water transport through a microhole membrane. • Rectified water transport associated with ionic diode characteristics. • Water transport via "piston mechanism" linked to the molecularly rigid polymer backbone. Tertiary-amine-based Polymers of Intrinsic Microporosity (PIMs) provide a class of highly porous molecularly rigid materials for the electrochemical transport of both ionic and neutral species. Here, the transport of water molecules together with chloride anions (i.e. the electroosmotic drag coefficient) is studied for the intrinsically microporous polyamine PIM-EA-TB immersed in aqueous 0.01 M NaCl (i) when protonated for pH < 4 or (ii) when not protonated for pH > 4. Preliminary data suggest that in both cases a high electroosmotic drag coefficient is observed based on direct H 2 O transport into a D 2 O-filled compartment (quantified by 1H-NMR). For PIM-EA-TB there is a strong pH dependence with a higher electroosmotic drag coefficient in less acidic solutions (going from approx. 400 H 2 O per anion at pH 3 to approx. 4000 H 2 O per anion at pH 7), although the underlying absolute rate of water transport at a fixed voltage of −1 V appears to be essentially pH independent. Water transport through the PIM-EA-TB microchannels is rationalised based on the relative populations of chloride anions and of water in the micropores (essentially a 'piston' mechanism). [ABSTRACT FROM AUTHOR]

“Heterojunction” ionic diodes based on a Nafion cation conductor and a polymer of intrinsic microporosity (PIM) interfaced at a 6 μm thickness polyethylene-terephthalate (PET) film with 20 μm diameter microhole exhibit rectification effects in cation (K + ) flux. When combined with the precipitation reaction of potassium cations with perchlorate anions to give insoluble KClO 4 (solubility product ca. 1.05 × 10 −2 M 2 at 25 °C) at the PIM | Nafion interface, inversion of the rectification/diode effect occurs and the formerly “open” state changes into a “closed” state due to blocking of ion flow. The localised interfacial precipitation reaction is due to up to three orders of magnitude accumulation of K + at the PIM | Nafion interface and shown to be fast and reversible. The effects of K + /ClO 4 − concentration and of Na + interference are considered. The blocking process within the heterojunction ionic diode is suggested to be dynamic/fast and potentially useful as a diode sensor mechanism based on solubility product dependent precipitation. [ABSTRACT FROM AUTHOR]

Anion uptake and charge transport in a polymer of intrinsic microporosity (here PIM-EA-TB) is investigated for three cases: (i) the oxidation of ferrocene embedded into a thin film of PIM-EA-TB on a glassy carbon electrode, (ii) the reduction of protons absorbed into a thin film of PIM-EA-TB on a platinum electrode, and (iii) the potential-driven transport of anions and protons in an asymmetrically deposited free-standing PIM-EA-TB membrane working as a current rectifier or “ionic diode”. In all three cases the competing effects of the diameter and hydrophobicity (size and hydration energy) of the anion are important. For free-standing membranes very high ionic diode rectification ratios (> 10 3 at ± 1 V) are observed in particular for thicker deposits of PIM-EA-TB and for chloride or perchlorate containing electrolyte. [ABSTRACT FROM AUTHOR]

• PIMs can be employed as artificial SEI layer in batteries to avoid dendrimer growth. • PIMs can be employed in fuel cells to stabilise catalysts and to allow gas diffusion. • PIMs can be employed in redox flow systems to stop unwanted cross-over of redox species. • PIMs can be employed in photoelectrochemical hydrogen producing systems to capture and guide hydrogen. Polymers of intrinsic microporosity (or PIMs) have emerged as practical film or membrane materials for a range of electrochemical technologies. Fundamentally, PIMs are based on highly rigid polymer backbone structures, which are inefficient for packing into solid films or structures. Poor packing in the solid is linked directly to (i) good solubility and processability, (ii) to glassy structures with persistent microporosity, (iii) to interesting permeation and separation properties for ions and for neutral molecular species, and (iv) to pore retention during pyrolysis. Further modification by cross-linking, introduction of charged functional groups, and hybrid material formation has been reported for applications in batteries, capacitors, fuel cells, and flow energy storage systems. This mini-review highlights recent applications suggested for PIMs in electrochemical energy systems. [ABSTRACT FROM AUTHOR]