An acid‐doped ice membrane for selective proton transport

Abstract

Cation exchange membranes need to have high permselectivity for protons to make these membranes suitable for, for example, energy storage devices. Here, we present the proof of concept for a proton selective membrane made of hydrochloric acid-doped ice. The proton selectivity of this acid-doped ice membrane is the result of defects in the ice structure, caused by the acid. Ice membranes were made from different hydrochloric acid concentrations (0.1-2.0 M). The proton permselectivity of all ice membranes was above 99.7% when both Na + and K + were present. The resistivity decreased exponentially with the concentration of acid in the ice membrane, reaching a value of 12 Ω.cm. The ice membranes were tested in an electrochemical cell using the Fe/Fe 2+ and Fe 2+ /Fe 3+ redox couples, and a power density of 7 W/m 2 and OCV of 0.87 V were measured. The resistance of the ice membrane increased with time as protons moved from the ice structure, as determined from the higher pH of the ice after melting. These expelled protons (and corresponding counter charged ions) were not replaced by other mobile cations, indicating a permanent loss in conductivity, but not selectivity. To apply the ice membrane as a selective separator for protons in energy storage devices in the future, the membrane thickness should be reduced and the protons should be retained inside the ice.

Synthesis of highly water‐absorbing chromium oxyhydroxide as a dopant in a hybrid proton‐conducting membrane

“…7 But the high cost, harsh working conditions, and hazardous synthetic process, etc are drawbacks and prompt researchers to create other alternatives. In the field of proton conduction, the current research trend is designing new materials with superior proton conductivity, including phosphoric acid and sulfonic acid derivatives, [8][9][10][11][12] polyoxometalates, [13][14][15][16][17][18][19][20] metal-organic Dongming Cheng and Mengxi Wei contributed equally to this work. frameworks, [21][22][23][24][25][26] covalent-organic frameworks, [27][28][29] and carbon allotropes.…”

Insights and Challenges for Applying Bipolar Membranes in Advanced Electrochemical Energy Systems

“…This sudden pH-jump at the membrane–electrolyte interface requires flow strategies to reduce the concentration polarization and membrane material with extremely high affinity for protons and hydroxide ions over other ions. In principle, such a membrane material exists in the form of an ice-based proton membrane but has obviously limited practical (liquid) water possibilities . Another option is operating with a pure water feed, avoiding the presence of ionic species in the membrane layer and circumventing the challenge to have strong relative affinity in multi-ionic systems. , …”

“…In principle, such a membrane material exists in the form of an ice-based proton membrane but has obviously limited practical (liquid) water possibilities. 54 Another option is operating with a pure water feed, avoiding the presence of ionic species in the membrane layer and circumventing the challenge to have strong relative affinity in multi-ionic systems. 49,50 The surrounding electrolytes affect not only the membrane potential but also the ion crossover across the membrane.…”