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For the gradual introduction of hydrogen in the energy market, the study of the properties of mixtures of hydrogen with typical components of natural gas (NG) and liquefied petroleum gas (LPG) is of great importance. This work aims to provide accurate experimental (p, rho, T) data for three hydrogen-propane mixtures with nominal compositions (amount of substance, mol/mol) of (0.95 H2 + 0.05 C3H8), (0.90 H2 + 0.10 C3H8), and (0.83 H2 + 0.17 C3H8), at temperatures of 250, 275, 300, 325, 350, and 375 K, and pressures up to 20 MPa. A single-sinker densimeter was used to determine the density of the mixtures. Experimental density data were compared to the densities calculated from two reference equations of state: the GERG-2008 and the AGA8-DC92. Relative deviations from the GERG-2008 EoS are systematically larger than those from the AGA8-DC92. They are within the ±0.5% band for the mixture with 5% of propane, but deviations are higher than 0.5% for the mixtures with 10% and 17% of propane, especially at low temperatures and high pressures. Finally, the sets of new experimental data have been processed by the application of two different statistical equations of state: the virial equation of state, through the second and third virial coefficients, B(T, x) and C(T, x), and the PC-SAFT equation of state.
This work aims to address the technical concerns related to the thermodynamic characterization of gas mixtures blended with hydrogen for the implementation of hydrogen as a new energy vector. For this purpose, new experimental speed of sound measurements have been done in gaseous and supercritical phases of two binary mixtures of nitrogen and hydrogen using the most accurate technique available, i.e., the spherical acoustic resonator, yielding an experimental expanded (k = 2) uncertainty of only 220 parts in 106 (0.022%). The measurements cover the pressure range between (0.5 and 20) MPa, the temperature range between (260 and 350) K, and the composition range with a nominal mole percentage of hydrogen of (5 and 10) mol%, respectively.
From the speed of sound data sets, thermophysical properties that are relevant for the characterization of the mixture, namely the second βa and third γa acoustic virial coefficients, are derived. These results are thoroughly compared and discussed with the established reference mixture models valid for mixtures of nitrogen and hydrogen, such as the AGA8-DC92 EoS, the GERG-2008 EoS, and the recently developed adaptation of the GERG-2008 EoS, here denoted GERG-H2_improved EoS. Special attention has been given to the effect of hydrogen concentration on those properties, showing that only the GERG-H2_improved EoS is consistent with the data sets within the experimental uncertainty in most measuring conditions.
The symmetry or structural stability of ABO3-type perovskite oxides depends largely on the size of ‘A’ and ‘B’ cations, which determines the material properties. The partial substitution of these cations may be used to tune these properties. The ionic sizes and valence states of the cations play an important role in improving the prop- erties of perovskite. In this study, the substitution of La3+ with Sr2+ with a larger ionic radius and Mn3+ with Fe3+ with a similar ionic radius favored both the crystal symmetry and the mixed ionic–electronic conductivity of the perovskite. Electrodes based on La0.7Sr0.3Mn0.5Fe0.5O3 (LSMFO55) exhibited a faradaic behavior with a specific capacity of 330 C g−1 (92 mAh g−1 ) at 12C rate, while this electrode maintained a capacity of 259 C g−1 at 240C (charge or discharge in 15 s). Additionally, exohedral carbon nano-onions (CNO) were introduced as a negative electrode to design an asymmetric hybrid supercapacitor (AHS) with a widened cell voltage. The use of CNO as a negative electrode in the AHS improved the rate capability drastically compared to the use of rGO. This device maintained a good energy density even at an extra-high charging rate (600C) owing to its outstanding rate capability. The high-rate performance of the LSMFO55//CNO AHS can be elucidated by successful fabrication with a mixed ionic–electronic conductive positive electrode and a CNO negative electrode. Tuning the electronic and ionic conductivities by cationic substitution and adopting an appropriate carbon-derived negative electrode (such as CNO) can provide a practical high-rate hybrid device using various perovskites.
CCQM-K118 was an international key comparison on natural gas composition with two types of gases, i.e., a low calorific hydrogen-enriched natural gas and a high calorific LNG type of gas. There were 14 participating laboratories. The traveling standards (i.e., 14 mixtures each) were obtained from an external source and checked for homogeneity and stability before and after the participants' measurements at the two coordinating laboratories. The data evaluation was performed using a consensus value and a laboratory effect model. The results of the participants were benchmarked against a key comparison reference value computed from the largest consistent subset (LCS) of the submitted results, adjusted for the differences between the travelling standards. For the first time in a key comparison in gas analysis, the model included a term to account for excess variability in the LCS. Most of the participants reported one or a few (slightly) discrepant results. Partly this is due to the heterogeneity and heteroscedasticity of the datasets. In all, the results in this key comparison demonstrate the good comparability of the national measurement standards for natural gas composition maintained by the participating NMIs.
Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
The continual increase in energy demand and inconsistent supply have attracted attention towards sustainable energy storage/conversion devices, such as electrochemical capacitors with high energy densities and power densities. Perovskite oxides have received significant attention as anion-intercalation electrode materials for electrochemical capacitors. In this study, hollow nanospheres of nonstoichiometric cubic perovskite fluorides, KNi1-xCoxF3-delta (x = 0.2; delta = 0.33) (KNCF-0.2) have been synthesized using a localized Ostwald ripening. The electrochemical performance of the non-stoichiometric perovskite has been studied in an aqueous 3 M KOH electrolyte to categorically investigate the fluorine-vacancy-mediated charge storage capabilities. High capacities up to 198.55 mA h g-1 or 714.8 C g-1 (equivalent to 1435 F g-1) have been obtained through oxygen anion-intercalation mechanism (peroxide pathway, O-). The results have been validated using ICP (inductively coupled Plasma mass spectrometry) analysis and cyclic voltammetry. An asymmetric supercapacitor device has been fabricated by coupling KNCF-0.2 with activated carbon to deliver a high energy density of 40 W h kg-1 as well as excellent cycling stability of 98 % for 10,000 cycles. The special attributes of hollow-spherical, non-stoichiometric perovskite (KNCF-0.2) have exhibited immense promise for their usability as anion-intercalation type electrodes in supercapacitors.
Continuing our study on (CO2 + O2) mixtures, this work reports new experimental (p, rho, T) data for two oxygen-rich mixtures with mole fractions x(O2) = (0.50 and 0.75) mol·mol−1, in the temperature range T = (250–375) K and pressure range p = (0.5–20) MPa, using a single-sinker densimeter. Experimental density data were compared to two well-established equation-of-state models: EOS-CG and GERG-2008. In the p, T-range investigated, the EOS-CG gave a better reproduction for the equimolar mixture (x(O2) = 0.5), whereas the GERG-2008 performed significantly better for the oxygen-rich mixture (x(O2) = 0.75). The EOS-CG generally overestimates the density, while the GERG-2008 underestimates it. This complete set of new experimental data, together with previous measurements, is used to calculate the virial coefficients B(T, x) and C(T, x), as well as the second interaction virial coefficient B12(T) for the (CO2+ O2) system.
This work aims to address the technical aspects related to the thermodynamic characterization of natural gas mixtures blended with hydrogen for the introduction of alternative energy sources within the Power-to-Gas framework. For that purpose, new experimental speed of sound data are presented in the pressure range between (0.1 up to 13) MPa and at temperatures of (260, 273.16, 300, 325, and 350) K for two mixtures qualified as primary calibration standards: a 11 component synthetic natural gas mixture (11 M), and another low-calorific H2-enriched natural gas mixture with a nominal molar percentage x(H2) = 3 %.
Measurements have been gathered using a spherical acoustic resonator with an experimental expanded (k = 2) uncertainty better than 200 parts in 106 (0.02 %) in the speed of sound. The heat capacity ratio as perfect-gas gammapg, the molar heat capacity as perfect-gas Cp,m pg, and the second betaa and third gammaa acoustic virial coefficients are derived from the speed of sound values. All the results are compared with the reference mixture models for natural gas-like mixtures, the AGA8-DC92 EoS and the GERG-2008 EoS, with Special attention to the impact of hydrogen on those properties. Data are found to be mostly consistent within the model uncertainty in the 11 M synthetic mixture as expected, but for the hydrogen-enriched mixture in the limit of the model uncertainty at the highest measuring pressures.
The limited availability of accurate experimental data in wide ranges of pressure, temperature, and composition is the main constraining factor for the proper development and assessment of thermodynamic models and equations of state. In the particular case of carbon capture and storage (CCS) processes, there is a clear need for data sets related to the (carbon dioxide + oxygen) mixtures that this work aims to address. This work provides new experimental (p, rho, T) data for three binary (CO2 + O2) mixtures with mole fractions of oxygen x(O2) = (0.05, 0.10, and 0.20) mol/mol, in the temperature range T = (250 to 375) K and pressure range p = (0.5 to 13) MPa. The measurements were performed with a high-precision single-sinker densimeter with magnetic suspension coupling. The density data were obtained with estimated expanded relative uncertainties of 0.02 % for the highest densities and up to 0.3 % for the lowest ones.The results were compared to the corresponding results calculated by the current reference equations of state for this kind of mixtures, namely the EOS-CG (combustion gases) and the GERG-2008 equation of state, respectively. The EOS-CG yields better estimations in density than the GERG-2008 equation of state. The results from the EOS-GC model show no systematic temperature dependence. For the GERG-2008 model, however, this criterion is significantly less fulfilled.
Speed of sound is one of the thermodynamic properties that can be measured with least uncertainty and is of great interest in developing equations of state. Moreover, accurate models are needed by the H2 industry to design the transport and storage stages of hydrogen blends in the natural gas network. This research aims to provide accurate data for (CH4 + H2) mixtures of nominal (5, 10, and 50) mol-% of hydrogen, in the p = (0.5 up to 20) MPa pressure range and with temperatures T = (273.16, 300, 325, 350, and 375) K. Using an acoustic spherical resonator, speed of sound was determined with an overall relative expanded (k = 2) uncertainty of 220 parts in 10^6 (0.022%). Data were compared to reference equations of state for natural gas-like mixtures, such as AGA8-DC92 and GERG-2008.
Average absolute deviations below 0.095% and percentage deviations between 0.029% and up to 0.30%, respectively, were obtained. Additionally, results were fitted to the acoustic virial equation of state and adiabatic coefficients, molar isochoric heat capacities and molar isobaric heat capacities as perfect-gas, together with second and third acoustic virial coefficients were estimated. Density second virial coefficients were also obtained.
Most of the experimental density data of the methane−hydrogen binary system available at the time of the development of the equation of state for natural gases and related mixtures, GERG-2008, at temperatures above 270 K were limited to hydrogen contents higher than 0.20 (amount-of-substance fraction). On the contrary, for mixtures with hydrogen contents lower than 0.20, experimental data were limited to temperatures below 270 K. This work intends to close the gap and provides accurate experimental (p, ρ, and T) data for three binary mixtures of methane and hydrogen, (0.95 CH4 + 0.05 H2), (0.90 CH4 + 0.10 H2), and (0.50 CH4 + 0.50 H2), at temperatures of 240, 250, 260, 275, 300, 325, and 350 K, thus extending the range of available experimental data to higher temperatures for mixtures with hydrogen contents lower than 0.20 and, accordingly, to lower temperatures for mixtures with hydrogen contents higher than 0.20. The density measurements were performed by using a single-sinker densimeter with magnetic suspension coupling at pressures up to 20 MPa. Experimental data were compared to the corresponding densities calculated from the GERG-2008 and the AGA8-DC92 equations of state, respectively. The experimental data are within the uncertainty of both equations of state, except at the lower temperatures of 240 and 250 K and pressures over 14 MPa for the mixtures with a hydrogen content of 0.05 and 0.10, respectively. The virial coefficients B(T, x) and C(T, x), as well as the second interaction virial coefficient B12(T) for the methane−hydrogen binary system, were also calculated from the experimental data set at temperatures from 240 to 350 K using the virial equation of state.