• Energy Research
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Supercapacitors are fast-charging energy storage devices of great importance for developing robust and climate-friendly energy infrastructures for the future. Research in this field has seen rapid growth in recent years. Therefore, consistent reporting practices must be implemented to enable reliable comparison of device performance. Although several studies have highlighted the best practices for analysing and reporting data from such energy storage devices, there is yet to be an empirical study investigating whether researchers in the field are correctly implementing these recommendations, and which assesses the variation in reporting between different laboratories. Here, we address this deficit by carrying out the first interlaboratory study of the analysis of supercapacitor electrochemistry data. We find that the use of incorrect formulae and researchers having different interpretations of key terminologies are the primary causes of variability in data reporting. Furthermore, we highlight the more significant variation in reported results for electrochemical profiles showing non-ideal capacitive behaviour. From the insights gained through this study, we make additional recommendations to the community to help ensure consistent reporting of performance metrics moving forward.

Abstract This study examines the operating characteristics and durability of a small direct methanol fuel cell (DMFC) stack (volume: 39.6 cm 3 ). To investigate the operating characteristics in a real multi-user operating mode, various load cycles (such as gradual acceleration and deceleration), two operating modes (current mode or voltage mode) and four interrupted operating methods (load on–off, load–methanol on–off, load–air on–off, and load–methanol–air on–off) are used. The durability of the DMFC stack is examined at a constant voltage of 2.4 V (0.4 V per cell) by using the load–methanol–air on–off mode for more than 2000 h. In these tests, the DMFC stack exhibits a rapid, stable and dynamic response regardless of the load cycle and operating mode, though the stack performance and response behaviour vary with the interrupted operating modes. Among the operating modes, the air-interruption modes exhibit better stability and higher performance. Moreover, the load–methanol–air on–off mode provides the stack with good durability and a high performance in a long-term test of 2045 h.

The flow distribution in fuel cells has an important influence on both the power density and efficiency of fuel cell systems. In order to effectively utilize the area, flow distribution should be as homogeneous as possible. In addition, pressure losses should be minimized with regard to the power demand of auxiliary components as pumps and compressors. In polymer electrolyte fuel cells (PEFCs) and direct methanol fuel cells (DMFCs) the flow field is in direct contact with the diffusion layer. The main task of the diffusion layer is to distribute the reactants from the flow field towards the catalyst layer. To prevent diffusion overvoltages, the diffusion layer is in general highly porous and provides high fluxes of the reactants. Consequently, the flow distribution in the flow field can be superpositioned by a flow in the diffusion layer. In this paper, we discuss the interaction between the diffusion layer and the flow field. Experimentally, we characterized different diffusion layers with regard to their diffusion properties as well as different flow fields. Additional simulation studies help to understand the processes and to determine suitable combinations of flow fields and diffusion layers.

Abstract Au/TiO2 is added to a PtRu/C electrode to improve the performance of a direct methanol fuel cell (DMFC). A high-throughput-screening test is performed for the fast screening of the loading of Au/TiO2 on PtRu/C. The electrochemically-active surface area of PtRu/C-Au/TiO2 and PtRu/C is determined from cyclic voltammetry. In CO-stripping and methanol oxidation voltammetry, PtRu/C-Au/TiO2 exhibits better activity for CO and methanol oxidation than PtRu/C. The performance of the DMFC is also improved by addition of Au/TiO2 to the PtRu/C electrode. The CO adsorbed on Pt may move to the surface of the Au/TiO2 by the interaction between PtRu/C and Au/TiO2. The improved performance of the PtRu/C-Au/TiO2 catalyst is explained in terms of preferential oxidation of CO or CO-like poisoning species that are generated during the oxidation of methanol on PtRu/C.

Abstract The internal distributed physicochemical characteristics of a battery significantly affect its performance. However, these properties are difficult to measure experimentally. This study presents a validated three-dimensional (3D) battery model covering the conservation of charge, mass, and energy and the electrochemical reaction of a laminated 10 Ah lithium iron phosphate battery. Using this 3D battery model, the space and time distributions of the internal physicochemical properties of the battery are investigated. The results indicate that the maximum gradients of the properties are at the transition region between the tabs and electrode plates. Thus, the tabs in a battery should be reasonably designed. For this LiFePO 4 /Graphite battery, anode plays a more important role than cathode in the overall overpotential and is likely to be crucial in the sharp decrease of output voltage at the later discharge process. And a higher battery capacity can be obtained by increasing the amount of anode material.

A three-dimensional, two-phase and non-isothermal numerical model has been developed in Part I of this two-article work. In this article, the parameter sensitivity analysis is performed. The influence of 11 major parameters, including the transfer coefficient, exchange current density multiplied by specific area, porosity, diffusion coefficient, absolute permeability and membrane phase conductivity, were investigated on the effect of the global polarization curve. The results show that the PEMFC global polarization curve is influenced by many parameters and the cathode-side parameters are a stronger influence than those on the anode side. Two different groups of parameters are provided which can result in almost the same global polarization curve, showing that the global polarization curve is not sufficient for the validation. Detailed discussion on the PEMFC model validation is conducted, and it is shown by numerical results that the global polarization curve plus the local current density distribution is still not sufficient for the model validation. A three-step validation approach is then proposed which can be expected to give a unique validation. The three steps are: validation of the global polarization curve; validation of the local current density distribution curve and validation of the cathode overpotential versus current density curve. Four further suggestions are proposed in order to solve the validation issue completely. These include the completeness of the data provided, the accumulation of benchmark data and the necessity for introduction of uncertainty analysis.