Artificial Proton Channel Membrane with Self-Amplified Selectivity for Simultaneous Waste Acid Recovery and Power Generation

Proton channels have both high permeability and selectivity, a property that remains unparalleled by artificial materials yet is highly demanded in many applications, including acid recovery and power generation. This work takes inspiration from the structure and surface chemistry of biological proton channels and presents a method to construct covalent organic framework (COF) membranes consisting of high-performance artificial proton channels. The membrane was purposefully rendered amorphous, which eliminates most of the nanoscale pores and induces high steric hindrance to ions. On the other hand, the channels were functionalized with hydrogen-donating groups, allowing protons to hop fast. Interestingly, we found that the presence of hydrated protons causes additional hindrance to ions and thus self-amplifies the proton selectivity. Consequently, the proton selectivity against toxic heavy metal ions is up to 104, significantly surpassing that of commercial acid-recovery membranes. The permeability is comparable to that of biological proton channels (a few mol m–2 h–1). Such membranes allow us to recycle acid from industrial waste brines by a simple diffusion dialysis process without the risk of toxic ion leakage. At the same time, the entropy released by the proton diffusion can be harvested to generate power, achieving a power density superior to that of most previously reported membranes for osmotic energy harvesting.