A Perspective on the Applications of Triphasic Gas Storage in Electrochemical Systems

Microporous materials store gases under dry conditions (e.g., hydrogen or oxygen via physisorption), but in some cases microporous materials also show triphasic (e.g., in a solid|gas|liquid system) gas storage in the presence of humidity/water. This is exploited recently to enhance gas solubility in aqueous media (in microporous deposits or in "microporous water") aided by microporous materials. Data obtained from NMR spectroscopy shows stored H₂ within particles of a polymer of intrinsic microporosity (PIM-1) suspended in water, which supports the concept and conclusions of triphasic gas storage derived from accelerated electrochemical reactions. This can be important for accelerating both electrocatalytic gas evolution as well as gas-consuming electrocatalytic processes (e.g., in O₂ to H₂O₂ or N₂ to NH₃ conversions). Comparison can be made between this observed acceleration in electrocatalysis and enzyme-catalytic processes in nature, where enzymes are equipped with "gas tunnel" transport, for example, for producing ammonia in nitrogenases. This perspective examines this analogy and focuses primarily on the use of i) metal-organic frameworks (MOFs) and ii) polymers of intrinsic microporosity (PIMs). Gas binding under wet and dry conditions is contrasted. Reactions involving oxygen reduction, nitrogen reduction, hydrogen evolution/oxidation, and related applications in triphasic energy storage are discussed.