Spray-coated Electrodes Research Articles

Mechanical Properties of PEMFC Electrodes According to Fabrication Methods

Electrodes in a polymer electrolyte membrane fuel cell (PEMFC) are the crucial element performing electrochemical reactions and are the most vulnerable mechanically. Various operating conditions (freeze-thaw, start-up, shut down) generate buckling, cracks, and delamination in electrodes. These mechanical failures not only directly affect the performance of the PEMFC cell but also act as a fatal factor in shortening the lifespan. Therefore, understanding and improving the mechanical properties of electrodes is essential for designing high-durability PEMFCs. Furthermore, the fabrication method of electrodes is a factor that causes not only performance but also distinct mechanical property differences since it determines their internal structure and surface characteristics. However, evaluating the mechanical properties of electrodes has been challenging because they are fragile and hard to separate from substrates. Therefore, this study evaluated the intrinsic mechanical behaviors of the electrodes according to fabrication methods via a free-standing tensile test. The effect of fabrication methods was analyzed for blade coating and spray coating methods used universally from industry to laboratory. The difference in mechanical properties between the two methods was identified by analyzing the internal structure and distribution of ionomer agglomerate. For blade-coated electrodes, modulus (372.5 MPa) and elongation (2.44%) were 2-2.7 times higher than spray-coated electrodes (172.9 MPa,0.9%). The difference in mechanical properties originated from the electrodes’ surface and internal structures. Blade-coated electrodes were composed of smaller pores and volume than the spray coating using FIB-SEM. The modulus ratio according to the internal structure through finite element analysis (using ABAQUS software) was consistent with the actual experimental value. In addition, blade-coated electrodes have high elongation and strength because they enable uniform stress transmission with a smooth surface and uniform ionomer binder distribution (analyzed by HAADF-STEM and EDS). This study contributes to a better understanding of the mechanical properties of electrodes according to the fabrication methods and provides guidelines for mechanical improvement. Figure 1

Spray-coated electrodes could create greener, cheaper batteries

Spray-coated electrodes could create greener, cheaper batteries

Scalable Paper Supercapacitors for Printed Wearable Electronics

Printed paper-based electronics offers solutions to rising energy concerns by supplying flexible, environmentally friendly, low-cost infrastructure for portable and wearable electronics. Herein, we demonstrate a scalable spray-coating approach to fabricate tailored paper poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/cellulose nanofibril (CNF) electrodes for all-printed supercapacitors. Layer-by-layer spray deposition was used to achieve high-quality electrodes with optimized electrode thickness. The morphology of these electrodes was analyzed using advanced X-ray scattering methods, revealing that spray-coated electrodes have smaller agglomerations, resulting in a homogeneous film, ultimately suggesting a better electrode manufacturing method than drop-casting. The printed paper-based supercapacitors exhibit an areal capacitance of 9.1 mF/cm2, which provides enough energy to power electrochromic indicators. The measured equivalent series resistance (ESR) is as low as 0.3 Ω, due to improved contact and homogeneous electrodes. In addition, a demonstrator in the form of a self-powered wearable wristband is shown, where a large-area (90 cm2) supercapacitor is integrated with a flexible solar cell and charged by ambient indoor light. This demonstration shows the tremendous potential for sequential coating/printing methods in the scaling up of printed wearables and self-sustaining systems.

Spray-Coated Multiwalled Carbon Nanotube Composite Electrodes for Thermal Energy Scavenging Electrochemical Cells.

Spray-coated multiwalled carbon nanotube/poly(vinylidene fluoride) (MWCNT/PVDF) composite electrodes, scCNTs, with varying CNT compositions (2 to 70 wt %) are presented for use in a simple thermal energy-scavenging cell (thermocell) based on the ferro/ferricyanide redox couple. Their utility for direct thermal-to-electrical energy conversion is explored at various temperature differentials and cell orientations. Performance is compared to that of buckypaper, a 100% CNT sheet material used as a benchmark electrode in thermocell research. The 30 to 70 wt % scCNT composites give the highest power output by electrode area-seven times greater than buckypaper at ΔT = 50 °C. CNT utilization is drastically enhanced in our electrodes, reaching 1 W gCNT(-1) compared to 0.036 W gCNT(-1) for buckypaper. Superior performance of our spray-coated electrodes is attributed to both wettability with better use of a large portion of electrochemically active CNTs and minimization of ohmic and thermal contact resistances. Even composites with as low as 2 wt % CNTs are still competitive with prior art. The MWCNT/PVDF composites developed herein are inexpensive, scalable, and serve a general need for CNT electrode optimization in next-generation devices.