Ultra-High Proton Conductivity iHOF Based on Guanidinium Arylphosphonate for Proton Exchange Membrane Fuel Cells

Abstract

The development of high-performance proton exchange membrane fuel cells (PEMFCs) is crucial yet challenging. Enrichment of proton transport pathways by doping ionic hydrogen-bonded organic frameworks (iHOFs) in Nafion matrix is important for further development of high-performance PEMFCs. In this work, an iHOF material (iHOF-9) based on arylphosphonate anions and guanidinium cations with the three-dimensional (3D) hydrogen-bonded network was synthesized, which exhibits an ultrahigh proton conductivity of 4.38 × 10–2 S·cm–1 at 90 °C and 98% RH. In addition, by mixing iHOF into Nafion matrix, we have fabricated the high-performance hybrid membranes, and the maximum proton conductivity value can achieve 6.61 × 10–2 S·cm–1 for 9%-iHOF-9/Nafion membrane at 90 °C and 98% RH. iHOF-9/Nafion membranes were used to fabricate the proton exchange membranes for application in H2/O2 fuel cells. The maximum power density of 9%-iHOF-9/Nafion reached 1092.07 mW·cm–2 after stabilization for 10 h at 80 °C and 100% RH, which is a 33.99% improvement compared to the recast Nafion membrane. This work doped ultrahigh conductivity iHOF into the Nafion matrix as an emerging proton exchange membrane material, injecting new possibilities for the development of new energy sources.

Controllable Synthesis and Ultrahigh Anisotropic Single-Crystal Proton Conduction of a Hydrogen-Bonded Organic Framework

“…These values exceeded that of 9.62 × 10 −2 S cm −1 of Nafion, three pure HOFs, and even the reported HOFs composite membrane materials (Table S7). 4,31,32 The activation energy (E a ) for GC-2/Nafion and GC-3/Nafion and GC-4/Nafion membranes was calculated to be 0.11, 0.15, and 0.15 eV, respectively, indicating that protons migrate mainly through Grotthuss mechanisms (Figure 5d).…”

“…The composite membranes were prepared according to the literature. , A 5 wt % Nafion solution (4 mL) and 2-propanol (4 mL) were rotary evaporated to 4 mL at 50 °C. Then, the powdered HOF (10 mg) was dispersed uniformly into the above solution and stirred for 3 h. The obtained solution was poured into a 35 mm Petri dish and dried in a vacuum oven at 60 °C to obtain the corresponding film.…”

“…24,26,28−30 flexibility and reconfigurability of hydrogen bonds can create new proton-exchange paths due to the synergistic effect as HOFs composited with other materials. 4,21,31,32 In this study, we have synthesized four guanidiniumcarboxylic acid adducts, or HOFs, by using a series of multinitrogen guanidinium with different chain lengths and 1,2,4,5benzenetetracarboxylic acid as organic components. The resultant materials, with formulae [(CN undergoes a single-crystal-to-single-crystal (SCSC) transformation to a more stable GC-2 with a number of the ordered 1D hydrophilic channels constructed by the continuous hydrogen-bonded chains, and highly anisotropic single-crystal proton conduction is observed in GC-2 with an ultrahigh proton conductivity of 1.78 × 10 −2 S cm −1 along the channels at ambient temperature and 98% RH.…”

“…Despite this, only a handful of HOFs are currently utilized in the field of proton conductivity, with even fewer being used in the study of single-crystal proton conductivity. ,,− Notably, the constituents of HOFs are typically organic components, making them highly compatible with organic polymers like Nafion for the preparation of lightweight proton conduction membranes. Moreover, the flexibility and reconfigurability of hydrogen bonds can create new proton-exchange paths due to the synergistic effect as HOFs composited with other materials. ,,, …”

A Sodium-Based Phosphonates Metal–Organic Framework with Superprotonic Conductivity

“…Therefore, deliberate attempts are being made to develop high-performance and low-cost PEMs for fuel cells. In recent years, a series of crystalline materials, such as metal–organic frameworks (MOFs), − covalent–organic frameworks (COFs), , and hydrogen-bonded organic frameworks (HOFs), − have emerged as potential PEM materials. Such crystals have a designable and tunable structure and are also highly crystalline.…”