H2 H2O Research Articles

Anode humidity trade-offs between proton conductivity and concentration overpotentials in protonic ceramic fuel cell: Experiments and numerical simulations

In protonic ceramic fuel cells (PCFCs), the H2 and H2O partial pressures in the anode side vary along the gas flow direction, particularly during high-fuel-utilization operation. This results in different species conductivities and overpotentials, which renders the quantitative evaluation of local performance based on H2 and H2O mole fractions important. A numerical model is developed that can reflect changes in species conductivities and overpotentials resulting from varying gas mole fractions. The numerical current density–voltage characteristic results obtained numerically agree well with those obtained via measurement in a wide range of H2–H2O gas conditions. Numerical modeling confirms a tradeoff, i.e., higher supply humidity levels result in lower electrolyte resistances but higher concentration overpotentials. The maximum output is achieved at a modest humidification level of 20%. The developed numerical model is particularly useful for optimizing the operating conditions of PCFCs with high fuel utilization.

Metal Poly(heptazine imides) as Multifunctional Photocatalysts for Solar Fuel Production

AbstractSolar‐driven photocatalysis employing particulate semiconductors represents a promising approach for sustainable production of valuable chemical feedstock. Metal poly(heptazine imide) (MPHI), a novel 2D ionic carbon nitride, has been recognized as an emerging photocatalyst with distinctive properties. In this minireview, we first delineate the forefront innovations of MPHI photocatalysts, spanning from synthetic strategies and solving structures to the exploration of novel properties. We place special emphasis on the structural design principles aimed at developing high‐performance MPHI systems toward photocatalytic solar fuel production such as H2 evolution, H2O oxidation, H2O2 production and CO2 reduction. Finally, we discuss crucial insights and challenges in leveraging highly active MPHIs for efficient solar‐to‐chemical energy conversion.

Metal Poly(heptazine imides) as Multifunctional Photocatalysts for Solar Fuel Production.

Solar-driven photocatalysis employing particulate semiconductors represents a promising approach for sustainable production of valuable chemical feedstock. Metal poly(heptazine imide) (MPHI), a novel 2D ionic carbon nitride, has been recognized as an emerging photocatalyst with distinctive properties. In this minireview, we first delineate the forefront innovations of MPHI photocatalysts, spanning from synthetic strategies and solving structures to the exploration of novel properties. We place special emphasis on the structural design principles aimed at developing high-performance MPHI systems toward photocatalytic solar fuel production such as H2 evolution, H2O oxidation, H2O2 production and CO2 reduction. Finally, we discuss crucial insights and challenges in leveraging highly active MPHIs for efficient solar-to-chemical energy conversion.

Enhancing the steam electrolysis by simultaneously regulating the electron and oxygen ion conductivity of la1-xsr1+xfeo4-δ oxides

Ruddlesden-Popper (RP) La1-xSr1+xFeO4-δ(x = 0,0.2,0.4) oxides with different Sr content are investigated as air electrodes for solid oxide electrolytic cells. The increased Sr content in La1-xSr1+xFeO4-δ significantly improves the electronic and oxygen ionic conductivity, enhancing the oxygen evolution reaction (OER) activity and electrochemical performance of steam electrolysis. The polarization resistance of the La0.8Sr1.2FeO4-δ symmetrical cell reaches 1.04 Ω cm2 at 800 °C, and the electrolysis cell delivers a current density of −1709 mA cm−2 at 1.3 V, corresponding to the hydrogen production rates of 714 ml/(cm2 h). Moreover, adding Sm0.2Ce0.8O2-δ (SDC) oxide further improves the steam electrolysis performance due to enhanced three-phase boundary active sites. The electrolysis cell with La0.8Sr1.2FeO4-δ-SDC electrode exhibits excellent stability for over 200 h and cycling durability for 100 h under 750 °C and 1.2 V in 50%H2O–H2 condition.

Investigation of (H2–H2O) partial pressure on the gas-based reduction of fine iron ore in mixed gases (H2–H2O–CO–CO2–N2)

The escalating demand for sustainable, green practices in the steel industry have accentuated the necessity of low-carbon technologies. One of the methods for CO2 mitigation is utilization of H2 in ironmaking process instead of CO-based reducing condition. This research focuses on understanding the utilization of H2 in CO-based iron making process, with an emphasis on the impact of the (H2 + H2O) partial pressure in mixed gases (H2–H2O–CO–CO2) with 10 vol% N2. To control the reducing conditions, the dimensionless indicators denoted oxidation strength (OS, (PH2O+PCO2)/(PH2+PH2O+PCO+PCO2)) and (H2 + H2O) partial pressure in H2–H2O–CO–CO2 (H, (PH2+PH2O)/(PH2+PH2O+PCO+PCO2)) were employed. Based on the reduction behavior and the kinetics analysis, the rate-controlling step of fine iron ore is mixed controlled reaction. It was revealed that a higher H and a lower OS correlate with the promoted internal diffusion of reducing gas and enhanced driving force for reduction, respectively. These characteristics facilitate the reduction rate. Also, reduction rate increased with higher temperature. As a results, the highest rate constant was 0.1863/min at temperature, OS, and H of 1273 K, 0.10, and 0.40. The lowest rate constant was 0.0433/min at temperature, OS, and H of 1073 K, 0.20, and 0.20. The apparent activation energy was calculated to be between 20 and 40 kJ/mol. Additionally, scanning electron microscopy and X-ray diffraction were utilized to analyze the variations in morphological characteristic based on reduction degree and (H2 + H2O) partial pressure in in H2–H2O–CO–CO2 with 10 vol% N2.

A comparative study on transport and interfacial physics of H2/CO2/CH4 interacting with H2O and/or silica by molecular dynamics simulation

Underground H2 storage (UHS), i.e., injecting H2 into subsurface geological formation and its withdrawal when needed, is identified as a promising solution for large-scale and long-term storage of H2. In this study, molecular dynamics (MD) simulation was performed at a typical temperature 320 K with pressure up to 60 MPa to predict H2 transport properties and H2–H2O–rock interfacial properties, which are compared with those of CO2 and CH4. The MD results show that the CH4 profiles of property variations with pressure lie between those of H2 and CO2 and more comparable to CO2. The interaction of H2 with H2O/silica is much weaker than that of CH4 and CO2. It is found that the effect of H2 pressure on altering the water contact angle and interfacial tension is negligible under all conditions. Unlike the multi-adsorption layers of the confined CO2 and CH4, there is only one adsorption layer of H2 confined by silica nano-slit. The planar diffusion of H2 in the confined system is slower than that in the bulk system at pressures lower than 20 MPa. The data and findings of this study will be useful for modeling the multiphase flow dynamics of UHS on reservoir scale, optimizing UHS operation, and assessing the performance of a cushion gas, e.g., CO2 or CH4.

A New 2D Energy Balance Model for Simulating the Climates of Rapidly and Slowly Rotating Terrestrial Planets

Energy balance models (EBMs), alongside radiative–convective climate models and global climate models (GCMs), are useful tools for simulating planetary climates. Historically, planetary and exoplanetary EBMs have solely been 1D latitudinally dependent models with no longitudinal dependence, until the study of Okuya et al., which focused on simulating synchronously rotating planets. Following the work of Okuya et al., I have designed the first 2D EBM (PlaHab) that can simulate N2–CO2–H2O–H2 atmospheres of both rapidly and synchronously rotating planets, including Mars, Earth, and exoplanets located within their circumstellar habitable zones. PlaHab includes physics for both water and CO2 condensation. Regional topography can be incorporated. Here, I have specifically applied PlaHab to investigate the present Earth, early Mars, TRAPPIST-1 e, and Proxima Centauri b, representing examples of habitable (and potentially habitable) worlds in our solar system and beyond. I compare my EBM results against those of other 1D and 3D models, including those of the recent Trappist-1 Habitable Atmosphere comparison project. Overall, the EBM results are consistent with those of other 1D and 3D models, although inconsistencies among all models continue to be related to the treatment of clouds and other known differences between EBMs and GCMs, including heat transport parameterizations. Although 2D EBMs are a relatively new entry in the study of planetary/exoplanetary climates, their ease of use, speed, flexibility, wide applicability, and greater complexity (relative to 1D models) may indicate an ideal combination for the modeling of planetary and exoplanetary atmospheres alike.

The Effect of Adding Aluminium on the Performance of ZnO NRs/PANi in Their Application as Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) is a new renewable energy technology that converts H2O into hydrogen and oxygen gas with the help of sunlight. A photoelectrochemical cell device consists of three main components, one of which is the photoanode. One of the materials that can be used as a photoanode is ZnO which has good electrical properties and is non-toxic. Nanorods-structured ZnO has the advantage of being able to increase light absorption due to its high surface area. However, the resulting performance is still quite low. So it is necessary to make modifications to the photoanode, one of which is by adding aluminium material to ZnO NRs, which has the potential to increase the conductivity of PEC in the production of H2 and O2 in H2O. To overcome the loss of samples during testing, the thin film will be coated with conductive polymers such as polyaniline (PANi), which has high conductivity, can increase photoactive ability, and has good corrosion resistance. In this study, the performance of ZnO NRs/PANi against AZO NRs/PANi will be studied by adding aluminium. The ZnO nanorods were synthesized by Hydrothermal method, Aluminium was deposited on ZnO NRs by DC Magnetron Sputtering method, and PANi was synthesized by polymerization method. From the XRD characterization results, it can be concluded that the addition of aluminium to ZnO NRs/PANi causes an increase in crystallinity and peak shift. SEM characterization shows that the addition of Al to ZnO NRs/PANi causes the porosity value to increase. In addition, UV-Vis characterization showed that the addition of Al material to the ZnO NRs/PANi thin film resulted in a wider range of absorbance of the light spectrum. Then, Cyclic Voltammetry test shows that the addition of aluminium increases the efficiency of the photoelectrochemical.

Reduction of zinc and iron in dust removal ash by H2 generated from lignite pyrolysis

The article describes a process based on the hydrogen recovery of dust removal ash from lignite pyrolysis. The high volatile components in lignite will produce a large amount of H2 during the pyrolysis process, which can replace part of C to reduce zinc and iron oxides in dust removal ash, thereby achieving the goal of reducing carbon consumption. Two methods were used to study the different pyrolysis behaviors of lignite, and it was found that the peak of H2 release was reached at 700 °C. After 1000 °C, the pyrolysis of lignite basically ended, and the final pyrolysis gases were mainly H2, CO, CO2, CH4, and a small amount of CxHy. In addition, the proportion of H2 generated by the full pyrolysis of lignite at 1000 °C in H2–H2O is 84.4 %, and the proportion of CO in the CO–CO2 system is 74 %, which can meet the reduction of zinc and iron oxides in dust removal ash. Based on the principle of minimum free energy and laboratory experiments, zinc oxide is completely reduced to zinc vapor above 906 °C, while the Fe obtained from iron oxide reduction increases with the increase of H2/CO in the system above 810 °C, further confirming the feasibility of this process. The effects of temperature, lignite added amount and holding time on iron reduction and zinc volatilization during the reduction process of dust removal ash was investigated. The results indicate that due to the fast diffusion rate of H2, the reaction rate is greatly increased, which can quickly increase the metallization rate of dust removal ash to over 95 % and the dezincification rate also increases from 19.60 % to about 98.76 % with the increase of carbon content under low temperature (1000 °C) and low carbon content (10 wt %) conditions.

Oxidation of magmas during gain and loss of H2O recorded by trace elements in zircon

Hydroxylation-oxidation reactions of the type H2O + Fe→2+Fe3+ + OH− + 1/2 H2 oxidise Fe2+ in olivine and pyroxenes in oceanic lithosphere prior to subduction and in the supra-subduction-zone mantle wedge and oxidise Fe2+ in silicate melts as dissolved H2O accumulates during magmatic differentiation. Collectively, the coupled hydroxylation-oxidation of melts and of minerals in melt sources tends to produce positive correlations of hydration state and oxidation state of silicate melts, about which there has been much dispute and discussion in literature. We introduce a melt “hygro-barometer” which provides evidence from trace elements in zircon that melt oxidation state rose as dissolved H2O accumulated in fluid-undersaturated residual melts during mafic-to-felsic differentiation at Moho-vicinity depths. Zircon-based measures are consistent with experimental evidence of melt oxidation during gain of dissolved H2O. Examples from many arc igneous complexes demonstrate further oxidation of residual melts as hydrothermal fluid exsolved and segregated during trans-crustal ascent of the magmas. Zircons in those suites show that much of the contrast between redox states of dry mid-ocean-ridge and hydrous arc magmas (especially porphyry copper magmas) develops as H2O is lost during trans-crustal ascent of arc magmas because decompression-induced exsolution and open-system fractional segregation of hydrothermal fluid selectively extracts reduced members of the principal redox couples (H2–H2O, S4+–S6+, Fe2+–Fe3+), thereby raising the oxidation state of residual melt.

Improved La0.8Sr0.2MnO3-δ oxygen electrode activity by introducing high oxygen ion conductor oxide for solid oxide steam electrolysis

The limited oxygen ion conductivity of conventional La0.8Sr0.2MnO3-δ (LSM) electrode has hindered the development of high-performance solid oxide cells. To address this issue, the electrode interface structure of LSM electrode is regulated by incorporating oxides with high oxygen ion conductivity. Specifically, the addition of Dy and Y co-doped Bi2O3-δ oxide (DBY) with a conductivity of 0.34 S cm−1 at 700 °C, which is almost 9 and 20 times higher than conventional SDC and YSZ oxides, has found to substantially reduce the electrode sintering temperature and enhance the transport ability of ion and electron at the interface. As a result, the interface polarization resistance of the LSM/DBY composite electrode is as low as 0.096 Ω cm2 at 700 °C. Finally, a solid oxide cell equipped with an LSM/DBY electrode attains a high power density of 1.78 Wcm−2 in fuel cell mode at 800 °C and 3%H2O–H2, as well as a current density of −1.58 Acm−2 in electrolysis mode under 1.50 V and 50% H2O–H2 condition.

Perovskite/Ruddlesden-Popper composite fuel electrode of strontium-praseodymium-manganese oxide for solid oxide cells: An alternative candidate

Ni migrates from cermet fuel electrodes in SOECs at high overpotentials, prompting interest in alternative electrode materials. Ni-free perovskites with mixed ionic and electronic conductivity are being developed as substitutes for Ni-YSZ- or Ni-CGO-cermet fuel electrodes. However, some perovskite electrodes exhibit poor electrocatalytic activity during steam electrolysis. This study focuses on the synthesis, phase evolution, and cation oxidation state of Sr0.5Pr0.5MnO3 (SPM) perovskite under oxidizing and reducing atmospheres. The electrochemical performance of the SPM electrode is investigated at different steam concentrations (3–50% H2O in H2). Rietveld refinement reveals a phase transformation from Pm-3m (221) to I4/mmm (139) in humidified 5% H2 in N2 gas at 800 °C. XPS measurements indicate that the I4/mmm (139) structure contains more oxygen vacancies, enhancing ionic conductivity and electrocatalytic activity. At 610 ◦C, the SPM electrode with the Pm-3m (221) space group exhibits a low polarization resistance of 0.173 Ω cm2 in 50% H2O in H2 gas. However, forming a Ruddlesden-Popper structure increases polarization resistance at higher temperatures due to a low-frequency reaction. Overall, the SPM electrode shows promising electrocatalytic activity across a wide range of oxygen partial pressure, making it a potential fuel electrode in SOECs.

Speciation and interconversion of atomically dispersed extra-framework Ga in ZSM-5 zeolite

Ga/ZSM-5 has been studied for a long time for its efficiency in catalytic dehydrogenation and conversion of light alkanes. Atomically dispersed extra-framework Ga species, such as [Ga]+(I), [GaH2]+(III), [GaO]+(III), [GaHOH]+(III), [Ga(OH)2]+(III) and [GaH]2+(III), etc. were proposed as reaction centers for such processes. To rationale the observed catalytic performances of Ga/ZSM-5, we investigated the electronic structures of these Ga species and pathways for their interconversion in zeolite channels by first-principles based calculations. Results from thermodynamics calculations at conditions relevant to experiments show that [Ga]+(I) is plausible at high temperature and low PH2O, and [Ga(OH)2]+(III) is plausible at low temperature and high PH2O. On pathways for interconversion of proposed Ga species, the calculated energy and free energy barriers for H2 dissociation and H2O formation are among the highest and correlate with involvement of Ga centers and their coordination with H and O-containing ligands. The coordination of framework O to Ga center are rather flexible, making dynamic formation of undercoordinated Ga species feasible at operation conditions and these species may attend subsequent chemical processes. We expect the findings would help to understand the formation and evolution of atomically dispersed reaction centers in zeolite channels under operation conditions.

Covalent Organic Frameworks Based Heterostructure in Solar‐To‐Fuel Conversion

AbstractPhotocatalytic reactions for fuel generation are crucial for the world's energy needs. Covalent‐Organic‐Frameworks (COFs) have been extensively studied as promising designable photocatalysts for these reactions due to their efficient visible‐light absorption, suitable energy‐band structure, facilitated intramolecular charge separation, and fast mass transfer. However, the activities of pristine COFs remain unsatisfactory, due to intermolecular charge recombination. Recently, COF‐based heterostructures, which combine COFs with metal‐sulfides, metal‐oxides, carbon materials, or MOFs, have attracted increasing attention for enhancing solar‐to‐fuel conversion efficiency by facilitating interfacial photo‐generated carrier separation, sensitizing wide‐gap semiconductors, and promoting surface redox reactions. Thus, a review of the state‐of‐the‐art progress of COF‐based heterostructure photocatalysts in reactions such as H2 evolution, CO2 reduction, O2 evolution, H2O splitting and CO2 splitting is crucial for the design of new photocatalysts to promote solar‐to‐fuel conversion. In this review, the COF‐based heterostructures photocatalysts are highlighted based on their synthesis, properties, and reasons for enhanced activities. Moreover, design principles are raised for such photocatalysts for each fuel generation reaction, based on insights into related research. Finally, this review is concluded by proposing future trends for COF‐based heterostructures photocatalysts, with attention to the design of COFs and supports, analyzing the photocatalytic reaction dynamics, together with considering practical applications.

Predictive model for the intra-diffusion coefficients of H2 and O2 in vapour H2O based on data from molecular dynamics simulations

ABSTRACT Available data from experiments and molecular simulations for the intra-diffusivities of H and O in HO, and for the self-diffusivity of pure HO (at pressure and temperature conditions in which the solvent is in the vapour phase) are compared against calculations based on the Chapman-Enskog theory or other semi-empirical/semi-theoretical methods. A novel methodology is proposed to extrapolate the intra-/self-diffusivities data computed from molecular dynamics simulations at low pressures. The extrapolated values are used to further refine the recently-proposed [Tsimpanogiannis et al., J. Chem. Eng. Data, 66, 3226-3244, (2021)], molecular simulation based correlation of intra-/self-diffusivities as a function of pressure and temperature with the solvent being in the vapour phase.

Nanoscale-mixed ZnNiCu hydroxide composite catalyst for improved photocatalytic hydrogen evolution

The advantage of a complex catalyst in which several catalysts are mixed is that the overall reaction rate can be efficiently increased by increasing each sub-reaction rate. Each constituent catalyst in the complex catalyst must be as well-mixed as possible—while maintaining high catalytic activity—owing to the short reaction time of these sub-reactions. This study reports a facile synthetic method to mix two catalysts homogeneously at the nanoscale while keeping their crystal structure intact. ZnNiCu hydroxide nanoplates with a mixed crystal structure composed of ZnNi and ZnCu hydroxides, which could promote H2O dissociative adsorption and H2 desorption, respectively, were synthesized by a simple cation exchange of ZnO nanoparticles and a precursor mixture of Ni and Cu. ZnNi and ZnCu hydroxides in the nanoplates were mixed at the nanoscale while maintaining their respective crystal structures; density functional theory calculations show that these structures could effectively perform H2O dissociative adsorption and H2 desorption, respectively, resulting in high activity in the overall photocatalytic hydrogen evolution reaction.

Interfacial Tensions, Solubilities, and Transport Properties of the H2/H2O/NaCl System: A Molecular Simulation Study.

Data for several key thermodynamic and transport properties needed for technologies using hydrogen (H2), such as underground H2 storage and H2O electrolysis are scarce or completely missing. Force field-based Molecular Dynamics (MD) and Continuous Fractional Component Monte Carlo (CFCMC) simulations are carried out in this work to cover this gap. Extensive new data sets are provided for (a) interfacial tensions of H2 gas in contact with aqueous NaCl solutions for temperatures of (298 to 523) K, pressures of (1 to 600) bar, and molalities of (0 to 6) mol NaCl/kg H2O, (b) self-diffusivities of infinitely diluted H2 in aqueous NaCl solutions for temperatures of (298 to 723) K, pressures of (1 to 1000) bar, and molalities of (0 to 6) mol NaCl/kg H2O, and (c) solubilities of H2 in aqueous NaCl solutions for temperatures of (298 to 363) K, pressures of (1 to 1000) bar, and molalities of (0 to 6) mol NaCl/kg H2O. The force fields used are the TIP4P/2005 for H2O, the Madrid-2019 and the Madrid-Transport for NaCl, and the Vrabec and Marx for H2. Excellent agreement between the simulation results and available experimental data is found with average deviations lower than 10%.

Effect of multi-component gases on the behavior and mechanism of carbon deposition in hydrogen-rich blast furnaces

Hydrogen-rich blast furnace is considered an advanced technology in the iron and steel industry for reducing carbon emissions at the source. The CO utilization is instead reduced due to the severe carbon deposition behavior after hydrogen enrichment. This paper quantitatively investigated the effect of CO–H2–H2O–N2 multi-component on carbon deposition behavior, and a formation mechanism of deposited carbon was proposed finally. The results revealed that the optimum temperature range for carbon deposition was about 470–900 °C, and the maximum rate of carbon deposition was reached at 550–700 °C. At 600 °C, the carbon deposition rate for 100%CO and 40%CO–60%N2 were 0.54 g/d and 0.13 g/d, respectively. The aggravating effect of H2 to carbon deposition was 5.2 times that of H2O. Whereas the carbon deposition will be constrained in low CO and high H2 environment. The SEM showed that the morphology of the deposited carbon was filamentous, its formation mechanism on the iron surface is: (a) Adsorption of gases on the iron surface, (b) Formation of Fe3C layer, (c) Deposition of graphite layer, (d) Decomposition of Fe3C layer, (e) Formation of Fe3C–Fe + C (diss.) catalytic particles, (f) Formation of filamentous carbon, (g) Carbon activity in metallic Fe-filamentous carbon.

Highly efficient unitized regenerative hydrogen peroxide cycle cell with ultralow overpotential for renewable energy storage

The potential large-scale applications of intermittent renewable energy sources require inexpensive, efficient, and less-resource-demanding energy storage systems to achieve grid balancing. Conventional unitized regenerative fuel cells (URFCs) based on the H2–H2O cycle are promising but suffer from high overpotential and low energy efficiency. Here we demonstrate a highly efficient unitized regenerative hydrogen peroxide cycle cell (UR-HPCC) for the renewable energy storage. The prototype utilizes a carbon-based platinum group metal-free catalyst containing atomically dispersed Co and N dopants (Co–N–C) as the bifunctional oxygen electrode catalyst for the hydrogen peroxide oxidation reaction (HPOR) and two-electron oxygen reduction reaction (2e-ORR) in H2O2 electrolyzer and fuel cell modes, respectively. Further, this prototype exhibits a close-to-zero overpotential with remarkably high round-trip efficiency of over 90%, which is attributed to the ideal catalytic properties of Co–N–C toward HPOR and 2e-ORR. The thermodynamic analysis of these single-intermediate reactions indicates the intrinsic superiority of UR-HPCC in energy efficiency and reversibility over conventional URFCs, thus facilitating the development of future sustainable distributed generation and energy storage systems.

Is Stokes-Einstein relation valid for the description of intra-diffusivity of hydrogen and oxygen in liquid water?

In this study, all available data from experiments and molecular simulations for the intra-diffusivities of H2 and O2 in H2O, and for the self-diffusivity of pure H2O are analyzed to examine the validity of the Stokes-Einstein relation. This analysis is motivated by the significant amount of work devoted through the years for improving the predictions of intra- and self-diffusivities in binary and multi-component mixtures relevant to chemical and environmental processes. Here, we calculate the slopes s and t corresponding to the ln(D)vs.ln(Tη) and ln(DT)vs.ln(1η) plots, respectively, where D is the intra-diffusivity, η the viscosity, and T the temperature of the systems. Our results show that s and t deviate from unity no matter if the experimental or simulation data are used. This means that the Stokes-Einstein relation is violated for the binary systems of H2 and O2 with H2O, and for pure H2O. Although prior studies mainly focused on re-evaluating the parameter A of the SE-based semi-theoretical/semi-empirical approaches expressed as D=ATη, our results indicate that reliable predictions for the intra- and self-diffusivities can be achieved by improving the accuracy of the prediction of slopes s and t.