UsCNT-assisted synthesis of water-stable MOF nanosheet for highly proton-conducting membrane

Abstract

Proton exchange membrane (PEM) with ordered and stable pathway is highly desirable for use in proton exchange membrane fuel cells. Porous MOF materials hold great promise for the development of high-performance PEM due to the pre-designable and ordered pore structure, providing regular transfer channel. However, the developed water-stable MOFs usually require hydrophobic pores for stabilizing crystal structure in moisture circumstances. It leads to dramatically declined proton conductivity at low relative humidity (RH) because of severe water loss. Herein, we propose the fabrication of hydrophilic and water-stable MOF nanosheets (usCNT@CuTCPP, ∼2.8 nm) through ultrashort carbon nanotube (usCNT)-assisted self-inhibition crystal growth strategy. Then, ∼ 8.9 μm-thick usCNT@CuTCPP lamellar membrane was prepared by self-stacking of nanosheets. We demonstrate that in-situ incorporation of usCNT could promote membrane hydration, enabling usCNT@CuTCPP-M excellent structural stability in water and remarkable water adsorption and retention ability. This allows the construction of continuous hydrogen-bond networks, thereby affording membrane efficient proton conduction under low RH. Additionally, usCNT@CuTCPP membrane with encapsulation of phytic acid exhibits high proton conductivities of 71 and 124 mS cm−1 under 40% and 100% RH, respectively, superior to Nafion and most porous matrix conductors. The assembled hydrogen fuel cell exhibits high performance over wide RH ranges.