A research team led by Sun Pengzhan, assistant professor in the Institute of Applied Physics and Materials Engineering (IAPME) at the University of Macau (UM), participated in the development of a novel two-dimensional proton-conducting material, angstrom-porous titania monolayer. This novel material, designed for hydrogen-based technologies such as fuel cells, offers high temperature resistance, high proton conductivity, and perfect proton selectivity. It addresses the problem of existing proton-exchange membrane being prone to dehydration and failure at high temperatures. The research has been published in the prestigious journal Nature Communications.

Two-dimensional (2D) materials are considered promising candidates for the development of the next generation of membrane technologies. Unlike traditional three-dimensional materials, these atomically thin materials can effectively sieve different gases, liquids, and ions with high flow rates and selectivity. For example, perfect graphene crystals and single-layer hexagonal boron nitride (hBN) are impermeable to all atoms and molecules except protons. However, these 2D materials exhibit low proton conductivity (less than <1 S cm^-2 at room temperature), do not meet the requirements of industrial applications (>5 S cm^-2) and struggle to maintain stability at intermediate temperatures (200-500°C). Therefore, it is crucial to develop novel 2D proton-conducting materials with high proton conductivity, perfect proton selectivity, and excellent thermal stability.

The research, titled ‘High proton conductivity through angstrom-porous titania’, demonstrates a new approach to precisely fabricate high-density atomic-scale pores across 2D materials. The research team prepared the titania monolayers by delamination of layered bulk titania compound via ion exchange (Fig. 1a, 1b), and negatively charged monovacancies are introduced spontaneously into the basal planes, providing a new route for precise fabrication of high-density angstrom-scale pores.

The research team studied the transmembrane properties of gas and ions under atomic-scale confinement based on the precise fabrication of micro devices. The results show that the angstrom-porous titania crystal is highly permeable to protons but completely impermeable to helium atoms and all other ions (Fig. 2c). It also exhibits a high proton conductivity of about 2.0±0.8 S cm^-2, which is 10 times higher than single-layer hBN and 100 times higher than graphene (Fig 2d). Additionally, the material maintained structural stability at high temperatures of 300℃ for extended periods of time, with the proton conductivity increasing exponentially with temperature, reaching 100 S cm^-2 at 200°C, which is 10 times higher than the industry standard Nafion 117. Furthermore, the material can be assembled on a large scale using techniques such as layer-by-layer electrostatic assembly to form high-quality membranes for industrial applications.

The research was a collaborative effort between research teams from UM, Dalian University of Technology, and the University of Manchester. The first author of the study is Ji Yu, a postdoctoral researcher at UM IAPME. The research was supported by UM (File No: SRG2022-00053-IAPME, MYRG-GRG2023-00014-IAPME-UMDF), the National Natural Science Foundation of China (File No: 52322319), the Science and Technology Development Fund of the Macao SAR (File No: 0063/2023/RIA1).The full text of the study is available at https://doi.org/10.1038/s41467-024-54544-z.