(354f) Pd-Containing MOF-Derived Materials for Hydrogen Sensing

Interest in using hydrogen as a clean and adaptable energy carrier is growing, as the energy economy transitions to more sustainable sources and uses of energy. Safety when using hydrogen energy is a major concern accompanying the growing use of hydrogen. Because hydrogen gas is colorless, odorless, combustible, and can permeate through many materials, hydrogen leak detection is essential for ensuring its safe use. Therefore, the development of hydrogen sensors that have a low detection limit, a wide dynamic range, excellent selectivity, maximal absorption/desorption, and rapid response is urgently needed.

Because of their remarkably large surface area, adjustable pore size, and adaptable chemical activity, which allow for strong hydrogen adsorption and selective detection, metal-organic frameworks (MOFs) are very appealing for hydrogen sensing. Their structure can be modified to favor interactions with hydrogen over other gases, improving both sensitivity and selectivity, and their porous nature permits a large number of active sites. Despite their relatively weak conductivity, MOFs can be combined with conductive materials such as metal nanoparticles or graphene to create efficient electrochemical or chemiresistive sensors. They hold great promise for the creation of next-generation hydrogen sensors due to their capacity for room-temperature operation, structural adaptability, and compatibility with a range of sensing platforms.

Palladium (Pd) is one of the most widely studied and utilized materials in hydrogen sensing because of its exceptional capacity to absorb hydrogen atoms and produce palladium hydride (PdHx) at room temperature. Even at low concentrations, this characteristic enables Pd to respond to hydrogen gas with excellent sensitivity and quick reaction times. Depending on the sensor design, hydrogen molecules that come into contact with palladium dissociate into atoms and permeate into the metal lattice, changing electrical resistance, optical characteristics, or volume in quantifiable ways. Pd is effective for precise detection because of its selectivity for hydrogen, even when other gases are present. It also works well at room temperature, which lowers power consumption and makes it possible to incorporate it into wearable or portable electronics. Overall, palladium is a key component of hydrogen sensing technologies due to its potent interaction with hydrogen and adaptability in nanostructured and hybrid systems.

By combining the remarkable hydrogen affinity of palladium (Pd) with the high surface area and adjustable porosity of metal–organic frameworks (MOFs), the incorporation of Pd into MOFs may greatly enhance their effectiveness in hydrogen sensing. Pd can be added to MOFs as surface decoration or embedded nanoparticles, enabling it to efficiently dissociate hydrogen molecules into atoms, a process that MOFs by themselves usually cannot. After dissociating, hydrogen atoms may interact with or diffuse through the MOF framework, changing its electrical, optical, or structural characteristics in ways that can be measured. This hybrid design facilitates room-temperature functioning, quick response/recovery times, and reusability in as well as improving sensitivity and selectivity toward hydrogen. Furthermore, by dispersing Pd nanoparticles and avoiding agglomeration, the porous MOF matrix preserves reliable sensing capability. The combination of Pd's catalytic and selective hydrogen interaction with MOFs' structural adaptability and adsorption ability allows for the creation of extremely efficient hydrogen sensing systems.

In this project, we synthesized Pd-containing MOFs as a platform for providing high surface area, then carbonized the MOF to create Pd nanoparticles on a porous conductive carbon support. Carbonized MOFs have been extensively explored in other applications like electrocatalysis, membranes, and adsorbents, but have not been developed for hydrogen sensing. Carbonization of a Pd-containing MOF provides a unique way to produce a high-surface-area Pd-decorated porous carbon material that can change resistance in the presence of hydrogen. We found that the response of chemiresistive sensors using these MOF-derived materials was much higher than that of our previously studied Pd nanowire and Pd nanosheet based sensors. Notably, the sensors exhibit a linear response at low hydrogen concentrations, with high response and high resistance. This is qualitatively similar to the behavior of metal oxides in hydrogen sensing, but is effective at low temperature, in contrast to most metal oxide sensors that operate above 200°C. Responses of these MOF-based sensors at room temperature and 50 ℃ will be reported and discussed. Their high resistance and low-temperature operation minimize energy requirements, which is important for microbattery powered systems. The material also provides a low limit of detection of 1 ppm. Other experiments, like XRD, TEM, SEM, BET, TGA, humidity sensor tests and selectivity tests of the sensor toward different interfering gasses (like carbon monoxide, carbon dioxide and methane) are also reported in this work and allow us to fully understand the sensor response.