An improper designed flow field of a polymer electrolyte fuel cell (PEFC) can cause the maldistributions, resulting in the reduction of PEFC performance and lifetime. Although there are several ...researches investigating the effect of flow field design, the parallel in series flow fields have, however, received a very low attention. In this study, a numerical investigation on the distributions in six different flow field designs over 5 cm2 PEFC has been systematically carried out using CFD techniques via ANSYS FLUENT software to study the effect of different flow field configurations and number of channels. The results revealed that, for a small-size PEFC, the flow fields with less number of channels provided both a better uniformity and cell performance. Although the number of channels affects the small-size PEFC performance much greater than the flow field geometric configurations, the further investigation revealed that the influence of configurations will be greater as the number of channels increases. In addition, with the same number of channels, the parallel in series flow fields performed better than the multi-channel serpentine flow fields in both uniformity and water management aspects as their geometry provided higher reactant flow velocity.
•The effect of different flow fields and number of channels on PEFC performance.•In a small-size PEFC, a longer channel path is better in uniformity and performance.•The number of channels affects cell performance greater than flow field design.•The effect of flow field design was stronger as the number of channels increased.•Parallel in series flow fields performed better than serpentine flow fields.
Cyclic voltammetry is a very useful tool for estimating several parameters such as electron transfer kinetics, diffusivity of active species, and effective surface area in a redox system. In cyclic ...voltammetry modeling, a simulated cyclic voltammogram is usually treated by neglecting the nonlinear effects of an electrical double layer and ohmic resistance. However, this approach leads to inaccurate prediction of such parameters. In this study, numerical modeling, including the combined effects of ohmic resistance, constant phase element, mass transfer, and faradaic processes, of cyclic voltammetry was carried out to show that, using this approach, nonlinear behaviors of the time-domain response of cyclic voltammetry can be encompassed. The model showed a good agreement with the experimental measurements. Furthermore, the numerical investigation of ohmic resistance and constant phase element effects on a cyclic voltammogram were performed.
•Effects of CPE and ohmic resistance are encompassed in the proposed model.•The model conveniently helps separating the faradaic and non-faradaic currents.•The faradaic and non-faradaic currents are coupled through the ohmic drop effects.•CPE and ohmic resistance significantly affect cyclic voltammetry responses.
In this study, we demonstrate that the utilization of modeling CV offers a promising new quantitative approach for elucidating charge storage mechanisms in two categories: diffusion-controlled and ...capacitive-controlled processes. Furthermore, we compared the results with Dunn's and Trasatti's methods, highlighting discrepancies and limitations in these approaches. Our research underscores the importance of constructing models that accurately represent the entire CV system, enabling a deeper understanding of charge storage mechanisms. Consequently, our findings pave the way for the advancement of more efficient and effective energy storage technologies.
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•CV data were simulated and compared with conventional relationships.•Highlighting the advantages and limitations of using conventional approaches.•Studying the impact of resistance and CPE exponent on charge storage mechanisms.•Emphasizing the significance of further developing CV models.
As electrochemical energy storage continues to gain importance, researchers have been exploring novel materials and electrode designs to enhance performance. While these innovations have significantly improved the performance of energy storage devices, the specific mechanisms responsible for their success remain unclear. One powerful tool for gaining insights into how modifications to the electrode can enhance cell performance is cyclic voltammetry (CV). However, interpreting CV data can be challenging, and simple analytical relations are often inadequate for accurate assessment. Moreover, different analytical methods can yield conflicting results, leading to confusion within the research community and hindering progress in the field. To address these challenges, our study aims to investigate the contributions of surface and diffusion-controlled processes to charge storage in supercapacitor applications. We will employ conventional methods to examine how these processes can lead to the misinterpretation of CV data and identify the advantages and limitations of different analytical approaches. Our research underscores the importance of developing models that faithfully replicate the system of interest to gain insights into charge storage mechanisms. By identifying these key factors, our findings could pave the way for the development of more efficient and effective energy storage technologies.
An electrical double layer typically behaves as a constant phase element (CPE) rather than a pure capacitor. To separate the non-faradaic current contributed by the electrical double layer from the ...total current, which is obtained from cyclic voltammetry using modeling, the CPE parameters—the CPE parameter (Y0) and the CPE exponent (γ)—need to be determined. In this work, a semi-theoretical equation for directly evaluating the CPE parameters from cyclic voltammetry experiments was developed by investigating cyclic voltammetry performed under a narrow potential window. The experiments were performed using a ferri/ferrocyanide solution with a cylindrical graphite electrode. The obtained parameters were quantitatively different from those obtained from electrochemical impedance spectroscopy analysis. However, the obtained parameters were in an excellent agreement with cyclic voltammograms. This suggested that to model a non-faradaic current using a CPE in cyclic voltammetry, it is important to evaluate the CPE parameters using cyclic voltammetry. An application of the CPE parameters for simulating cyclic voltammograms that contain both faradaic and non-faradaic currents is also presented. The results show that the model can satisfactorily simulate entire cyclic voltammograms.
In Thailand, Napier grass is expected to play an important role as an energy resource for future power generation. To accomplish this goal, numerous areas are required for Napier grass plantations. ...Before introducing crops, the land potential of the country and the impact of crops on the environment should be assessed. The soil and water assessment tool (SWAT) model is very useful in investigating crop impacts and land potential. Unfortunately, the crop growth parameters of Napier grass are yet to be identified and, thus, conducting effective analysis has not been possible. Accordingly, in this study, parameter calibration and SWAT model validation of Napier grass production in Thailand was carried out using datasets from eight sites with 93 samples. Parameter sensitivity analysis was performed prior to parameter calibration, the results of which suggest that the radiation use efficiency and potential harvested index are both highly sensitive. The crop growth parameters were calibrated in order of their sensitivity index ranking, and the final values were obtained by reducing the root mean square error from 10.77 to 1.38 t·ha−1. The validation provides satisfactory results with coefficient of determination of 0.951 and a mean error of 0.321 t·ha−1. Using the developed model and calibrated parameters, local Napier grass dry matter yield can be evaluated accurately. The results reveal that, if only abandoned area in Thailand is used, then Napier grass can provide roughly 33,600–44,900 GWh of annual electricity, and power plant carbon dioxide (CO2) emissions can be reduced by approximately 21.2–28.3 Mt-CO2. The spatial distribution of estimated yield obtained in this work can be further utilized for land suitability analysis to help identify locations for Napier grass plantations, anaerobic digesters, and biogas power plants.
Napier grass is an energy crop that is promising for future power generation. Since Napier grass has never been planted extensively, it is important to understand the impacts of Napier grass ...plantations on local energetic, environmental, and socioeconomic features. In this study, the soil and water assessment tool (SWAT) model was employed to investigate the impacts of Napier grass plantation on runoff, sediment, and nitrate loads in Songkhla Lake Basin (SLB), southern Thailand. Historical data, collected between 2009 and 2018 from the U-tapao gaging station located in SLB were used to calibrate and validate the model in terms of precipitation, streamflow, and sediment. The simulated precipitation, streamflow, and sediment showed agreement with observed data, with the coefficients of determination being 0.791, 0.900, and 0.997, respectively. Subsequently, the SWAT model was applied to evaluate the impact of land use change from the baseline case to Napier grass plantation cases in abandoned areas with four different nitrogen fertilizer application levels. The results revealed that planting Napier grass decreased the average surface runoff and sediment in the watershed. A multidisciplinary assessment supporting future decision making was conducted using the results obtained from the SWAT model; these showed that Napier grass will provide enhanced benefits to hydrology and water quality when nitrogen fertilizers of 0 and 125 kgN ha−1 were applied. On the other hand, the benefits to the energy supply, farmer’s income, and CO2 reduction were highest when a nitrogen fertilization of 500 kgN ha−1 was applied. Nonetheless, planting Napier grass should be supported since it increases the energy supply and creates jobs while also reducing surface runoff, sediment yield, nitrate load, and CO2 emission.
•A framework for suitability analysis of biogas power plants is proposed.•MCDA is applied to assess suitability level for Napier grass-based power plants.•Obtaining yield distribution from SWAT model ...is proposed.•The framework is tested and evaluated in Southern Thailand.
Napier grass is a promising energy crop owing to its advantages over other energy crops; however, when determining sites for the power plants utilizing Napier grass as a feedstock, relevant data are required. The spatial distribution of the Napier grass dry matter yield (DMY) is among these important data. Unlike agricultural residues, the spatial distribution of the DMY cannot be obtained through surveys or statistical data. In this study, a methodology for locating biogas power plants utilizing Napier grass as a feedstock is proposed. A geographic information system and analytic hierarchy process are used to evaluate land suitability for biogas power plants based on environmental and socioeconomic criteria. The spatial distribution of the DMY is integrated with the land suitability map to locate suitable sites for biogas power plants. The proposed approach is applied to southern Thailand because the region lacks self-sufficient power generation. The results reveal that, five biogas power plants that utilize Napier grass from abandoned areas can be established with a total contracted capacity of 420 MW. Based on this analysis, introducing Napier grass-based biogas power plants could significantly help reduce the dependency on imported electricity. Stakeholders are recommended to treat this study as a tool to be utilized before implementing new dedicated energy crops.
This work investigated different conceptual models for electric motorcycles, which are electric motorcycles with a home charging system, electric motorcycles using a battery swapping system, and ...electric motorcycles with battery swapping and photovoltaic systems, in four Southeast Asia countries. The current research focused on analyzing the impact of factors such as the number of battery packs in a swapping station, variation in battery swapping demand, the season, and photovoltaic panel size on energy utilization and carbon emissions associated with the entire energy supply chain. The objective of the current study was to evaluate and compare the well-to-wheel emissions using these different conceptual models, considering the varying energy mixes in four countries with a significant prevalence of motorcycle ownership, Thailand, Vietnam, Malaysia, and Indonesia. The results revealed that by using a 3 kW photovoltaic system, the dependency on grid energy can be significantly reduced and thus provide the highest benefits in terms of reduction of fossil fuel use and CO2 emissions. Although switching from internal combustion engine motorcycles to electric motorcycles could substantially reduce carbon emissions, it is only feasible when the primary resources used for generating electricity are sufficiently clean or battery swapping stations are equipped with a 3 kW photovoltaic system. In these four countries, electric motorcycles with battery swapping systems could accelerate the transition to a net-zero carbon emission society by reducing CO2 emissions by around 2.6–3.0 Mt-CO2 per year in the right environment. Prioritizing the decarbonization of power generation should be the primary focus, considering its critical role as a bottleneck within the system. The findings of this research hold significant value for decision-makers and investors who are actively pursuing smart city development and aiming to harness the potential of renewable energy sources.
Although the constant phase element (CPE) parameters have been found to vary with DC bias voltage in electrochemical impedance spectroscopy measurement, to date, the CPE parameters are assumed to be ...constant within the voltage window in cyclic voltammetry (CV) simulation. This leads to failure in predicting the voltammetric response of a double layer in some cases. In this study, the voltage-dependent CPE and ohmic parameters are used to simulate the capacitive current. The results show good agreement with the experimental measurements of commercial electrical double layer capacitors. The model is extended to predict the response of a system involving both Faradaic and capacitive currents by combining the conventional physicochemical transport model with circuit analysis to include effects of the resistances and CPE. To accurately predict the entire CV responses, a modified Randles circuit with an additional resistance connected in series with the CPE is proposed to be an equivalent circuit of the system. Furthermore, the closed-form analytical solution of the time-domain response of CPE under CV conditions is also derived and presented to gain better understanding of the CPE response. Using the derived equation, CV can serve as an alternative approach for determining the CPE parameters.
•The adjoint variable method is used to optimize the structure of a porous reactor.•Diffusion fields formed by topology optimization facilitate mass transport.•The developed model is investigated ...under various dimensionalities.•The overall reaction rate is enhanced in a topologically optimized layout.•The local entropy generation rate by different mechanisms is evaluated.
Several studies attempted to enhance the performance of various reaction-diffusion systems, such as electrodes of electrochemical devices, by modifying the spatial distribution of porosity throughout the porous reactor. However, research is proceeding without knowing the theoretical limitation of the improvement. To connect optimization techniques with a well-established theoretical approach, this paper presents topology optimization for the design of diffusion fields in reaction-diffusion systems together with entropy generation analysis using nonequilibrium thermodynamics. Topology optimization of porosity distribution in reaction-diffusion systems was carried out using the adjoint variable methods. The optimization problem was formulated to maximize the reaction in the design domain. The results obtained from the investigation under various dimensionalities were compared and discussed. A formula for the local entropy generation of reaction-diffusion systems was derived and used to assess the topology optimization results. While the findings showed an insignificant difference between the overall reaction rate of 0D and 1D cases, optimization of higher dimensionalities (2D and 3D) considerably enhanced the overall reaction rate. The results revealed that the optimum porosity distribution corresponds to the most uniform and minimum entropy generation.
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