Nitrogen-Doped Carbon Foams Synthesized from Banana Peel and Zinc Complex Template for Adsorption of CO2, CH4, and N2

We report nitrogen-doped, activated carbon foams prepared from banana peels using a self-template method with zinc nitrate, 2-aminophenol, and furfural involved. Importantly, we have extended the banana peel zinc complex soft-template method to investigate the effects of carbonization temperature and postcarbonization CO2 activation on the carbon pore structure, and examined the effect of N-content on the carbon foam's equilibrium adsorption capacity for CO2. The carbon foams contain up to 6.0 wt % nitrogen and feature cellular macroporous structures with BET specific surface areas up to 1426 m2·g-1. The potential of the carbon foams for CO2/N2, CO2/CH4, and CH4/N2 separations was evaluated by measurement of pure fluid adsorption capacities using a gravimetric adsorption apparatus and calculation of adsorption selectivies at a range of conditions using ideal adsorption solution theory (IAST). The adsorption capacities at a 4000 kPa and 298 K were CO2 9.21 mmol·g-1, CH4 5.29 mmol·g-1, and N2 3.29 mmol·g-1

Gravimetric adsorption measurements of helium on natural clinoptilolite and synthetic molecular sieves at pressures up to 3500 kPa

We report helium adsorption capacities and the true specific impenetrable solid volumes of a clinoptilolite-rich Escott zeolite from Werris Creek (Australia), synthetic 3A and 4A zeolites, and carbon molecular sieve 3K-172 measured by a gravimetric method at pressures of (300–3500) kPa and temperatures in the range of (303–343) K. Our helium adsorption procedure extends the previous works by Gumma and Talu [1] to determine the impenetrable solid volume of the adsorbent, which in standard helium pycnometry is determined under the assumption that helium does not adsorb at room temperature. Our results confirm helium adsorption on these solids is small, but not zero: equilibrium helium adsorption capacities measured at 3500 kPa and 303 K were 0.067 mmol/g on Escott, 0.085 mmol/g on 3A, 0.096 mmol/g on 4A and 0.089 mmol/g on 3K-172. The specific solid volumes determined by the Gumma and Talu method were 10–15% larger than the specific solid volumes measured by standard helium pycnometry, and this error can result in uncertainties of 2.6–28% in the equilibrium adsorption capacities of CO2 and N2 measured at high pressures. The uncertainties were largest for N2 on the Escott zeolite, which had the lowest equilibrium adsorption capacity for N2. These results support the need to consider helium adsorption in the characterisation of adsorbents with narrow pore sizes, especially for adsorption processes that involve helium separations at low temperatures and/or high pressures

Gate opening effect of zeolitic imidazolate framework ZIF-7 for adsorption of CH4 and CO2 from N2

We report adsorption isotherms of CO2 and CH4 on the zeolitic imidazolate framework ZIF-7 that exhibit gate opening features associated with a flexible framework structure. This phenomenon has been reported by others for CO2 and light alkanes (e.g. ethane, ethylene, propane), but our study presents for first time experimental data to show that CH4 can also induce a gate opening effect in ZIF-7. Uptakes of CO2, CH4 and N2 on ZIF-7 were measured by a gravimetric adsorption apparatus at temperatures of 303-323 K and pressures up to 4494 kPa. From the CH4 isotherm measured at 303 K the transition pressure for the gate opening in ZIF-7 was estimated as 1245 kPa and the free-energy change associated with the structural phase change was 5.70 kJ mol-1. At an adsorption temperature of 303 K the phase transition pressure for CO2 in ZIF-F was 78 kPa and the free energy change was 2.43 kJ mol-1. The gate opening behaviour observed in this study shows ZIF-7 may have a potential selectivity for CH4 from N2 of more than 10 from an equimolar CH4 + N2 mixture. The equilibrium selectivity of ZIF-7 at 303 K and pressures close to 100 kPa are predicted to be 24 for CO2 from CH4 and 101 for CO2 from N2

Gas storage potential and electrohydraulic discharge (EHD) stimulation of coal seam interburden from the Surat Basin

This paper evaluates the potential methane storage capacity of six clay-rich interburden rock samples from coal seam gas (CSG) wells in the Surat Basin, Australia. Clay minerals identified in all samples included kaolinite, illite, smectite, and illite-smectite mixed-layers. The total organic carbon concentrations in these interburden rocks ranged from 0.66–1.19 wt%, and thus these rocks can be classified as fair to good hydrocarbon source rocks. The effective porosity of the rocks determined from mercury intrusion porosimetry and helium pycnometry varied from 6.8% to 12.5%, and included volumes of micropores and mesopores. The adsorption isotherm results indicated that the average adsorption capacity of six interburden was 3.64 cm3/g, a value corresponding to approximately 20% that of Surat Basin coal. Based on the clay compositions and porosity of the samples, the permeability of these Surat interburden rocks is estimated to be <5 nano Darcy using Yang and Aplin's empirical correlation, which was too low for reliable measurement in our laboratory core flooding apparatus even with a differential pressure of 10 bar applied over a shortened 20 mm length core. However, after stimulation by electrohydraulic discharge (EHD) shockwaves the permeability of one of the interburden samples (S2) increased to 0.6 ± 0.11 mD due to development of fractures and new pores by the EHD stimulation. We characterised the development of the fractures after EHD shockwaves using x-ray computer tomography. The findings of this study suggest that dynamic shockwaves such as those generated by EHD have potential to increase permeability of soft and clay-rich interburden layers in CSG reservoirs and other layered reservoirs. This potentially opens these ultra-tight gas resources to exploitation and recovery

Measurements of helium adsorption on natural clinoptilolite at temperatures from (123.15 to 423.15) K and pressures up to 35 MPa

Helium (He) is an increasingly valuable gas that is relatively difficult to recover: most of the global helium supply is produced through the application of deep cryogenic separation processes to the overheads from a nitrogen rejection unit in an LNG plant. Pressure swing adsorption (PSA) offers an alternative low-cost process for recovering He from natural gas, particularly if a helium selective adsorbent with sufficient capacity could be identified. However, the accurate measurement of the helium equilibrium capacity on narrow pore adsorbents is particularly challenging. Here, the uptake of helium on a natural clinoptilolite-rich Escott zeolite was measured with a volumetric adsorption apparatus at temperatures from 123.15 to 423.15 K and pressures up to 5 MPa, and with a gravimetric adsorption apparatus at temperatures in the range 243.15–423.15 K and pressures up to 35 MPa. We used these two experimental data sets to determine the specific inaccessible solid volume (vs) and true void volume of the Escott zeolite by eliminating the common assumption of zero helium uptake. Instead, the data analysis workflow established by Sircar (2001) and by Gumma and Talu (2003) was applied to the adsorption isotherms measured using the gravimetric apparatus. This led to a specific inaccessible solid volume for the Escott zeolite of 0.462 cm3·g−1, with a maximum helium adsorption capacity of 0.9 mmol·g−1 measured at 253.15 K and 35 MPa. The isosteric heat of adsorption for helium on the Escott zeolite was estimated to be 3.05 kJ·mol−1. The uptake of N2 on the Escott zeolite was also measured; these data were used together with the helium measurements to estimate conditions at which an equilibrium selectivity of 3 for He over N2 might be achieved in an equimolar He + N2 mixture

The role of electrode wettability in electrochemical reduction of carbon dioxide

The electrochemical reduction of carbon dioxide (CO2RR) requires access to ample gaseous CO2and liquid water to fuel reactions at high current densities for industrial-scale applications. Substantial improvement of the CO2RR rate has largely arisen from positioning the catalyst close to gas-liquid interfaces, such as in gas-diffusion electrodes. These requirements add complexity to an electrode design that no longer consists of only a catalyst but also a microporous and nanoporous network of gas-liquid-solid interfaces of the electrode. In this three-dimensional structure, electrode wettability plays a pivotal role in the CO2RR because the affinity of the electrode surface by water impacts the observed electrode reactivity, product selectivity, and long-term stability. All these performance metrics are critical in an industrial electrochemical process. This review provides an in-depth analysis of electrode wettability's role in achieving an efficient, selective, and stable CO2RR performance. We first discuss the underlying mechanisms of electrode wetting phenomena and the foreseen ideal wetting conditions for the CO2RR. Then we summarize recent advances in improving cathode performance by altering the wettability of the catalyst layer of gas-diffusion electrodes. We conclude the review by discussing the current challenges and opportunities to develop efficient and selective cathodes for CO2RR at industrially relevant rates. The insights generated from this review could also benefit the advancement of other critical electrochemical processes that involve multiple complex flows in porous electrodes, such as electrochemical reduction of carbon monoxide, oxygen, and nitrogen.ChemE/Materials for Energy Conversion & Storag

Mitigating Electrolyte Flooding for Electrochemical CO₂Reduction via Infiltration of Hydrophobic Particles in a Gas Diffusion Layer

Achieving operational stability at high current densities remains a challenge in CO2 electrolyzers due to flooding of the gas diffusion layer (GDL) that supports the electrocatalyst. We mitigated electrode flooding at high current densities using a vacuum-assisted infiltration method to embed 200-400 nm-sized polytetrafluoroethylene (PTFE) particles at the interface of the microporous layer (MPL) and carbon cloth in a commercial GDL. In CO2 electrolysis to CO over a silver nanoparticle catalyst on the GDL, the PTFE-embedded GDL not only just exhibited less than 10% of the electrolyte seepage rates observed in untreated GDLs at a current density of 300 mA·cm-2 but also expanded the electrochemical active area across the testing conditions. The PTFE-embedded GDL also maintained a Faradaic efficiency for CO2 electrolysis to CO above 80% for more than 100 h at 100 mA·cm-2, which was a 50-fold improvement in the stable operation time of the electrolyzer. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Materials for Energy Conversion and Storag

Effect of Dispersing Solvents for an Ionomer on the Performance of Copper Catalyst Layers for CO₂ Electrolysis to Multicarbon Products

To explore the effects of solvent-ionomer interactions in catalyst inks on the structure and performance of Cu catalyst layers (CLs) for CO2 electrolysis, we used a “like for like” rationale to select acetone and methanol as dispersion solvents with a distinct affinity for the ionomer backbone or sulfonated ionic heads, respectively, of the perfluorinated sulfonic acid (PFSA) ionomer Aquivion. First, we characterized the morphology and wettability of Aquivion films drop-cast from acetone- and methanol-based inks on flat Cu foils and glassy carbons. On a flat surface, the ionomer films cast from the Aquivion and acetone mixture were more continuous and hydrophobic than films cast from methanol-based inks. Our study’s second stage compared the performance of Cu nanoparticle CLs prepared with acetone and methanol on gas diffusion electrodes (GDEs) in a flow cell electrolyzer. The effects of the ionomer-solvent interaction led to a more uniform and flooding-tolerant GDE when acetone was the dispersion solvent (acetone-CL) than when we used methanol (methanol-CL). As a result, acetone-CL yielded a higher selectivity for CO2 electrolysis to C2+ products at high current density, up to 25% greater than methanol-CL at 500 mA cm-2. Ethylene was the primary product for both CLs, with a Faradaic efficiency for ethylene of 47.4 ± 4.0% on the acetone-CL and that of 37.6 ± 5.5% on the methanol-CL at a current density of 300 mA cm-2. We attribute the enhanced C2+ selectivity of the acetone-CL to this electrode’s better resistance to electrolyte flooding, with zero seepage observed at tested current densities. Our findings reveal the critical role of solvent-ionomer interaction in determining the film structure and hydrophobicity, providing new insights into the CL design for enhanced multicarbon production in high current densities in CO2 electrolysis processes.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Materials for Energy Conversion and Storag

Non-invasive current collectors for improved current-density distribution during CO₂ electrolysis on super-hydrophobic electrodes

Electrochemical reduction of CO2 presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. However, the available electrolyzers suffer from intrinsic problems, like flooding and salt accumulation, that must be overcome to industrialize the technology. To mitigate flooding and salt precipitation issues, researchers have used super-hydrophobic electrodes based on either expanded polytetrafluoroethylene (ePTFE) gas-diffusion layers (GDL’s), or carbon-based GDL’s with added PTFE. While the PTFE backbone is highly resistant to flooding, the non-conductive nature of PTFE means that without additional current collection the catalyst layer itself is responsible for electron-dispersion, which penalizes system efficiency and stability. In this work, we present operando results that illustrate that the current distribution and electrical potential distribution is far from a uniform distribution in thin catalyst layers (~50 nm) deposited onto ePTFE GDL’s. We then compare the effects of thicker catalyst layers (~500 nm) and a newly developed non-invasive current collector (NICC). The NICC can maintain more uniform current distributions with 10-fold thinner catalyst layers while improving stability towards ethylene (≥ 30%) by approximately two-fold.ChemE/Materials for Energy Conversion and Storag