Speeding protons with metal vacancies

Summary

Proton exchange membranes (PEMs) find applications not only in fuel cells and sensors but as chemical filters and in biological systems. In particular, the Nafion (Chemours Company) PEM, which consists of sulfonated tetrafluoroethylene–based fluoropolymer-copolymer, is widely used in practical electrochemical processes. It has a high proton conductivity up to 0.2 S/cm below 80°C and high relative humidity (RH) (>93%) (1), but its conductivity drops severely at higher temperatures or at low RH (below 50%). On page 596 of this issue, Qian et al. (2) report a new class of proton membranes assembled from two-dimensional (2D) layered transition-metal phosphorus trichalcogenide (TMPTC) nanosheets in which metal vacancies boost ion conductivity. These membranes exhibit a proton conductivity of ∼0.95 S/cm at 90°C and 98% RH but still have a conductivity of 0.26 S/cm even at 60% RH.

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