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All-vanadium redox flow battery (VRFB) is a promising energy storage technique. Flow fields play a crucial role in distributing the electrolyte into the electrode uniformly, but their performance characteristics under different electrode parameters are still unclear. In this work, taking the total pressure drop and total overpotential as performance characterizations, the influence of electrode parameters and operating conditions on the performance of serpentine flow field (SFF) and interdigitated flow field (IFF) are experimentally investigated. It is found that the battery with IFF exhibits lower pressure drop than that with SFF because of the shunt effect of IFF on electrolyte. In terms of promoting the uniform distribution of the electrolyte into the electrode, the SFF outperforms IFF when the electrode porosity is higher than 0.810, but the performance of SFF and IFF could be reversed as the electrode porosity decreases to 0.714, indicating that there may be a performance reversal between SFF and IFF when the electrode porosity decreases from 0.810 to 0.714. Moreover, the increase of current density, the decrease of electrolyte input, and the decrease of electrode thickness strengthen the performance reversal at low electrode porosity. The results well explain the debate on the superiority of IFF and SFF and the discussion on the preference between flow fields and electrode thickness in literatures and provide guidance for the selection of optimal flow field in VRFBs.

With the development of applications for microelectromechanical system (MEMS) components and micromachining technology, planar microelectrodes have attracted considerable interest. To study the discharge characteristics of these structures, planar microelectrodes with a variety of plate-shaped and needle-shaped microelectrode structures fabricated from indium tin oxide (ITO) and copper (Cu) with microelectrode gaps ranging from 5 to 35 µm were manufactured using MEMS technology in this study. Experiments carried out in atmospheric air show that the microelectrode configuration has a crucial impact on the discharge current, breakdown voltage, and current response to varying electrode gaps. The electrode surface area plays a significant role in the discharge characteristics of planar microelectrodes, which is a factor dominating the discharge current and breakdown voltage. The commonly used formulas in macroscale corona discharge cannot be directly applied to planar microelectrodes. Planar microelectrodes fabricated with Cu on Si substrates have larger discharge currents, higher breakdown voltages, and better resistance to breakdown strength than ITO ones on quartz substrates under nA-scale current, while ITO damaged microelectrodes because of breakdown can still discharge when accompanied by different discharge characteristics.

Novel three-dimensional (3D) continuously graded phononic crystals (CGPCs) have been designed, and fabricated by 3D printing. Each of the CGPCs is an entity instead of a combination of several other samples, and the porosity distribution of the CGPC along the incident direction is nearly linear. The sound absorption characteristics of CGPCs were experimentally investigated and compared with those of uniform phononic crystals (UPCs) and discretely stepped phononic crystals (DSPCs). Experimental results show that CGPCs demonstrate excellent sound absorption performance because of their continuously graded structures. CGPCs have higher sound absorption coefficients in the large frequency range and more sound absorption coefficient peaks in a specific frequency range than UPCs and DSPCs. In particular, the sound absorption coefficients of the CGPC with a porosity of 0.6 and thickness of 30 mm are higher than 0.56 when the frequency is 1350–6300 Hz and are all higher than 0.2 in the studied frequency range (1000–6300 Hz). CGPCs are expected to have potential application in noise control, especially in the broad frequency and low-frequency ranges.