Zeolitic Metal–Organic Framework with High-Density Hydrophilic Sites for Efficient Proton Conduction

Proton exchange membranes play a key role in fuel cells; however, the development of highly proton-conductive and stable materials still remains a challenge. Herein, a hydrolysis coordination strategy was proposed for the synthesis of a three-dimensional porous metal–organic framework (MOF) [Zn₈Na₄(ImDC)₁₂]. This MOF was structured with an ACO zeolite topology and high-density hydrophilic sites of nitrogen and oxygen. Under high-temperature and humidity conditions (353 K, 76% RH), [Zn₈Na₄(ImDC)₁₂] exhibited proton conductivity as high as 0.016 S cm^–1, outperforming that of most MOF materials reported previously. Mixed-matrix membranes of [Zn₈Na₄(ImDC)₁₂]@CS were fabricated with [Zn₈Na₄(ImDC)₁₂] and a chitosan polymer. The membrane with 10 wt % [Zn₈Na₄(ImDC)₁₂] showed an optimal proton conductivity of 0.051 S cm^–1. This study provides guidance for developing high-performance proton conduction materials.