Superprotonic Conductivity in Metal–Organic Frameworks by Charged-Layer-Mediated Proton Conduction

Abstract

F 2 (SO 3 H) 2 manifests a superprotonic conductivity of 2.86 S cm −1 (at 90% RH and 90 °C), a record breaker so far. Supported by joint experimental−theoretical studies, the ultrahigh conductivity originates from conduction by protons rather than ions and is rationalized to result from the enhanced acidity of −SO 3 H by introduction of electronegative −F followed by the formation of double charged layers composed of Li + and −SO 3 − layers after encapsulation of LiCl. Importantly, the effect of charged layers has been verified, and charged-layer-mediated proton conduction is unprecedentedly proposed to fill in the missing pieces in existing proton conduction mechanisms, giving insight into the rational design of superprotonic conducting framework materials potentially applied as proton exchange membranes in fuel cells.

Covalent organic frameworks confining ultra-dense hydrated hydrogen-bond networks for efficient intrinsic proton conduction

“…The Grotthuss mechanism and vehicle mechanism are two well-established mechanisms for proton conduction. 41,42 Protons travel through a network of hydrogen bonds made up of hydrogen molecules in water, following an ordered path through proton hopping. The proton passes through the protonated charge carrier (H 3 O + ) of water to promote the high kinetic energy input of the proton carrier.…”

Imparting Stable and Ultrahigh Proton Conductivity to a Layered Rare Earth Hydroxide via Ion Exchange

“…Excitingly, with increasing test temperature, LRH-H 2 PO 4 − exhibits a high proton conductivity of over 10 −2 S•cm −1 at 80 °C and 95% RH (1.84 × 10 −2 S•cm −1 ), which is one of the highest proton conductivities known for rare earth hydroxides, and a performance that is far superior to that of most crystalline proton conductor materials (Table S1). Up to now, crystalline proton conductor materials with proton-conduction efficiencies exceeding the 10 −2 S•cm −1 level are still rare, including only a few such as LiCl@UiO-66-F 2 (SO 3 H) 2 (2.86 S•cm −1 ), 13 BUT-8(Cr)A (1.27 × 10 −1 S•cm −1 ), 53 PCMOF21/ 2(Tz) (1.17 × 10 −1 S•cm −1 ), 54 MOF-808-4SA-150 (7.89 × 10 −2 S•cm − 1), 32 , pK a = 7.2 in water) in the material but also effectively promote the formation of stable proton transport channels. To validate this observation, we further performed ion exchange with sulfate anions and monohydrogen phosphate anions to form LRH-HPO S17).…”

“…In contrast to amorphous polymers, highly crystalline coordination polymers (CPs), metal–organic frameworks (MOFs), and other crystalline compounds have emerged as promising candidates for proton conductors due to their numerous advantages. − First, these crystalline materials offer a rich variety of geometries, large surface areas, and excellent electrochemical properties. − Second, their well-organized structural frameworks allow for the precise incorporation of various functional groups and the efficient construction and design of proton transport channels. − This enables the controlled realization of desired proton-conduction behavior, ultimately aiding in the establishment of a controllable proton conductivity. − Moreover, the inherent high crystallinity of these compounds plays a crucial role in visualizing proton transport pathways, providing a powerful platform for understanding proton transport mechanisms at the molecular and even atomic levels. Therefore, crystalline compounds hold the potential for making new breakthroughs in the field of proton-conducting materials.…”

Pore size effects on high-efficiency proton conduction in three stable 3D Al-based MOFs modified with imidazole

“…MOFs have rich structural tunability and designability, which also provide a platform for adjusting and controlling proton conductivities. [15][16][17][18] The functional pore cages/channels in MOFs can accommodate various proton carriers and improve their proton conductivities. The thermal and chemical stabilities of MOF-based conductors are crucial for their further applications because most reported MOFs easily collapse under certain testing conditions.…”