Insights into the Enhanced Oxidative Thermal Stability of Nanoparticle Organic Hybrid Materials Developed for Carbon Capture and Energy Storage

Abstract

As a result of the growing need for direct air capture (DAC) and integrated carbon capture and conversion technologies, CO2 capture materials that can withstand a wide range of environmental conditions, including fluctuating ambient temperatures and high concentrations of oxidizing agents (i.e., oxygen and moisture), are critically needed. Liquid-like nanoparticle organic hybrid materials (NOHMs) have been proposed as candidates for DAC and electrolyte additives, enabling sustainable energy storage (i.e., integrated CO2 capture and conversion and flow batteries). Liquid-like NOHMs functionalized with an ionic bond have been shown to display greatly enhanced oxidative thermal stability compared to the untethered polymer. However, previous studies were limited in terms of reaction conditions, and the detailed mechanisms of the oxidative thermal degradation were not reported. In this work, a kinetic thermal degradation analysis was performed on NOHM-I-HPE and the neat polymer, Jeffamine M2070 (HPE), in both non-oxidative and oxidative conditions. NOHM-I-HPE displayed thermal stability similar to the untethered polymer in a nitrogen environment, but interestingly, the thermal stability of the ionically tethered polymer was significantly enhanced in the presence of air. This observed enhancement of oxidative thermal stability is attributed to the orders of magnitude larger viscosity of the liquid-like NOHMs compared to the untethered polymer and the bond stabilization of the ionically tethered polymer in the NOHM canopy. Spectroscopic analyses of the liquid residue revealed that, in the presence of oxygen, the degradation of HPE and NOHM-I-HPE occurs through the formation of trace amounts of carbonyls. This study illustrated that NOHMs can serve as functional materials for sustainable energy storage applications because of their excellent oxidative thermal stability.

Impacts of Bond Type and Grafting Density on the Thermal, Structural, and Transport Behaviors of Nanoparticle Organic Hybrid Materials‐Based Electrolytes

“…Many types of polymers have been shown to be sensitive to thermal degradation in the presence of oxygen. [ 39,41,64,68 ] These results suggest that the presence of oxygen has a significant impact on the degradation behaviors of covalently tethered polymers, while the ionically tethered polymers were much more resistant to oxidative degradation. In our previous work, we showed that the ionic tethering of the HPE canopy to SiO 2 nanoparticles in a higher grafting density and liquid‐like NOHM‐I‐HPE lead to a significant enhancement in the oxidative thermal stability of HPE due to ionic bond stabilization of the N‐terminus and a mass transfer limitation of oxygen.…”

“…In addition, the crystallization temperature of the NOHMs was shifted by ≈20–25 °C to lower temperatures, suggesting that the HPE confinement suppressed its crystallization, as has been reported in the literature. [ 41,57 ]…”

“…In our previous work, a kinetic thermal degradation analysis suggested that the ionic linker groups cause an autocatalytic degradation of the HPE canopy at elevated temperatures. [ 41 ] From the data presented in Figure 3A, it is evident that the covalent tethering of HPE to a SiO 2 nanoparticle enhances its thermal stability in a nitrogen atmosphere, while there is little to no improvement in the thermal stability of the same ionically tethered HPE. The thermal decomposition of the covalently functionalized HPE polymer (HPE + GPC) was very similar to that of the untethered HPE, thus highlighting how the heat shielding effect of the nanoparticle [ 66,67 ] and/or interfacial interactions [ 57 ] with the nanoparticle surface can lead to improvement of the thermal stability of polymers.…”

“…In our previous work, we showed that the ionic tethering of the HPE canopy to SiO 2 nanoparticles in a higher grafting density and liquid‐like NOHM‐I‐HPE lead to a significant enhancement in the oxidative thermal stability of HPE due to ionic bond stabilization of the N‐terminus and a mass transfer limitation of oxygen. [ 39,41 ]…”

“…Ionic liquids, [ 4,6,16,17 ] deep eutectic solvents, [ 3,6,18–21 ] microemulsions, [ 22–26 ] , and nanoparticle organic hybrid materials (NOHMs) [ 9,10,27–30 ] are currently being developed as novel electrolyte materials to improve the performance of various electrochemical systems. In particular, NOHMs consist of a polymer that is either ionically [ 31–38 ] or covalently tethered [ 31–33 ] to a nanoparticle core and possess a number of favorable properties including negligible vapor pressure, [ 31 ] oxidative thermal stability, [ 31,39–41 ] chemical tunability [ 9,42 ] and high ionic conductivity. [ 27,43 ] As a result, NOHMs have been extensively studied as water‐lean CO 2 capture solvents and it has been shown that the organized structure of the polymer canopy in NOHMs leads to significantly less swelling compared to the untethered polymer, upon exposure to CO 2 .…”