The ionomer content in the catalyst layer is a crucial design factor that affects the performance of polymer electrolyte membrane fuel cells (PEMFCs). However, the optimal ionomer content can vary based on the surrounding humidity levels. This study systematically evaluated the influence of the ionomer-to-carbon (I/C) ratio (0.00, 0.55, and 0.91) on PEMFC performance under fully humidified (RH 100%) and low-humidity (RH 25%) conditions. Membrane-electrode assemblies (MEAs) were fabricated using a spray coating technique, and their electrochemical properties were analyzed through polarization curves and electrochemical impedance spectroscopy (EIS). Under RH 100%, the MEA with an I/C ratio of 0.55 achieved the highest peak power density of 519.8 mW/cm², indicating a successful balance between proton conductivity and gas transport. Conversely, under RH 25%, the best performance of 203.9 mW/cm² was observed at an I/C ratio of 0.91. This shift is attributed to improved water retention at higher ionomer content, which reduced membrane dehydration and lowered both ohmic and Faradaic resistances. These findings highlight the dual role of the ionomer in facilitating proton transport and managing water balance, emphasizing the necessity of optimizing the I/C ratio according to operating conditions for stable and high-performing PEMFC operation.

Chronic wounds necessitate periodic treatment and management due to their potential for serious complications. Recently, ultrasonic mist therapy has been introduced to treat chronic wounds efficiently. This therapy requires a noncontact spraying method to prevent side effects such as bacterial infections and pain. Therefore, research is needed on a spray nozzle tip that can effectively transmit ultrasonic energy to the wound target with misted cleaning solution mobility in a specific direction and at an appropriate speed. The performance of the nozzle tip is greatly affected by the flow characteristics inside it. Computational fluid dynamics (CFD) is a powerful tool to analyze these characteristics in detail. The behavior of the mist was analyzed in a simulation based on discrete phase model methodology in an unsteady state. Valid design parameters enabling noncontact cleaning were determined by setting the design parameters of the nozzle tip`s internal flow path and measuring the spraying speed of the mist using CFD analysis. Through the simulation results, information on the sprayed skin surface and spray characteristics are measured. Lastly, we present a nozzle tip design guide optimized for ultrasonic mist therapy.

The demand for flexible electronic materials used in wearable devices has experienced a significant surge in recent years. Wearable devices typically incorporate an electronic material or system that can be mounted on a human body. It is imperative that these materials are composed of substances compatible with the human body. Consequently, numerous studies have been undertaken to develop flexible electronic devices with various performance capabilities. In this study, nanowire patterns were manufactured on nanofibers and utilized as patches. To create a nanowire pattern, a direct-write spraying process was employed to investigate changes in electrical characteristics using process variables. The process involved depositing silver nanowires on the surface of nanofibers using a pneumatic spray nozzle. Generated patterns were found to be suitable for use as sensors capable of withstanding skin-attached deformation.

Exteriors of structures (apartments, buildings, bridges, dams, power plants, etc.) are subject to deterioration and damage (cracks, rust, etc.), mainly due to thermal expansion/contraction and environmental humidity. The damages shorten the lifespan of structures and cause unnecessary reconstruction, increasing social costs. The existing damage maintenance methods, which are directly constructed by the workers, have problems such as reduced work efficiency, increased work cost, lack of timely maintenance, and high work risks. In this paper, a spraying device attached to a drone for active and flexible maintenance of structures is developed. To simplify maintenance, the device consists of a solenoid motor, detachable parts for maintenance agent, and a lightweight-designed frame, manufactured with a 3D printer. In particular, the lever mechanism that amplifies the pushing force of the solenoid motor is designed to spray the maintenance agent when a switch comes into contact with the exterior of the structure. The prototype of a spraying device is attached to a commercial drone (Mavic3, DJI) and tested for effectiveness in structure maintenance. It demonstrates successful, cost-effective maintenance of structural damages in less than 10 minutes.

In Korea, water spraying to suppress the dust during building dismantling operations has been done manually by human laborers, considered extremely dangerous since it often causes fatal accidents. Abroad, however, water spraying machines have been developed and used in construction sites instead of workers to prevent such serious industrial accidents. In this study, the first domestic water spraying machine is suggested. Since the spraying machine should have a novel dust tracking function, an optimal structure and mechanism should be designed to guarantee its motion performance. The motion for target tracking is achieved by the 2 DOF (Degrees of Freedom) structure comprising a linear and a rotary actuator. Then, the geometric analysis was performed to provide a sufficient kinematic workspace. Through the dynamic performance simulation, the optimal actuator capacities could be selected to generate an appropriate acceleration. The geometric and dynamic performance was evaluated by the extensive motion experiments. With this study, it is expected that an advanced water spraying machine can be developed only with domestic technologies to protect construction laborers from potentially dangerous accidents.