Flexible and Safe Additives-Based Zinc-Binder-Free-Hierarchical MnO2 -Solid Alkaline Polymer Battery for Potential Wearable Applications.

The next-generation flexible wearable electronics are among the most rapidly growing industries due to their extended use in everyday applications resulting in an increased demand for cheaper, safer, and flexible energy storage devices. This study aims to investigate and enhance the overall performance of a Zn-MnO2 alkaline battery and make it suitable for safe and flexible wearable applications. To achieve high cyclability and performance of the cathode, issues of low active-material availability for redox reactions and inactive-phase formations are overcome by fabricating a binder-free hierarchical (increased surface area) additives (enabled reversible compound formation) based MnO2 cathode. Furthermore, zinc/stainless steel composite anode (to reduce anode shape changes) and calcium hydroxide coated polymer electrolyte (to stop zincate ion transfer) are used to improve cyclability. By assembling the above mentioned layers, excellent rate capabilities, high-capacity utilization (487 mAh g-1 ), long cycling stabilities (1000 cycles with 70% retention), and high energy density (400 Wh kg-1 ) are achieved. Moreover, bending, hammering, puncturing, and lighting up an light emitting diode are conducted (under flat, bent, and cut) to demonstrate the cells' safety, flexibility, and robustness. The successful findings in this study can chart new pathways to the development of safe, flexible, and cost-effective next-generation energy storage sources for wearables.

Evaluation of STEM Engagement Activities on the Attitudes and Perceptions of Mechanical Engineering S-STEM Scholars.

Since 2009, the mechanical engineering (ME) scholarship-science technology engineering and mathematics (S-STEM) Program at the University of Maryland Baltimore County (UMBC) has provided financial support and program activities to ME undergraduate students aiming at improving their retention and graduation rates. The objective of this study is to identify program activities that were most effective to help students for improvements. Current ME S-STEM scholars were asked to complete a survey that measures their scientific efficacy, engineering identity, expectations, integration, and sense of belonging, as well as how program activities impact their attitudes and perceptions. Analyses of 36 collected surveys showed that scholars reported high levels of engineering identity, expectations, and sense of belonging. However, further improvements were needed to help students in achieving scientific efficacy and academic integration into the program. Results demonstrated that pro-active mentoring was the most effective method contributing to positive attitudes and perceptions. The implemented S-STEM research-related activities and internship were viewed favorably by the scholars in helping them establish their scientific efficacy and engineering identity, and understand their expectations and goals. Community building activities were considered helpful for them to integrate into campus life and improve their sense of belonging to the campus and program. Scholars identified mentoring, research related activities, internships, and social interaction with faculty and their peers as important factors for their retention and graduation. Although the sample size was small in the study, we believe that the cost-effective activities identified could be adopted by other institutions to further improve students' retention and graduation rates in engineering programs.

Establishing the Need to Broaden Bioengineering Research Exposure and Research Participation in Mechanical Engineering and Its Positive Impacts on Student Recruitment, Diversification, Retention and Graduation: Findings From the UMBC ME S-STEM Scholarship Program.

The objectives of this study were to evaluate the current status of exposure to bio-engineering research in community college (CC) students and University of Maryland Baltimore County (UMBC) students, and to estimate relationships between research activities sponsored by the Mechanical Engineering (ME) S-STEM Scholarship Program and improvement in student enrollment/diversification, retention rates, and graduation rates. The analysis drew on data from ME undergraduate academic records at UMBC from 2008 to 2019. A survey was designed to assess the research exposure of CC and UMBC students and their evaluation of the research components included in recruitment and curriculum activities. Results show that exposure to research measured by attending a research seminar was low for the participants, around 37% for CC students and 21% for ME students at UMBC. The survey results indicate the positive impact of the scholarship programs at UMBC on the research exposure and research experience. The impact is more evident in students who originally transferred from a CC. The large increase in recruited female and CC students over the past 10 years indicated that the research-related activities of the ME S-STEM program played an instrumental role in those increases. Because of the research-related activities, the ME S-STEM program achieved retention and graduation rates higher than those in the ME undergraduate program (89% versus 60% for the 6 year graduation rate), as well a higher percentage of students enrolled in graduate school (30% versus 10%). We conclude that there is still a need to implement research-related activities in the ME undergraduate program, starting with student recruitment and continuing through the academic program. Results suggest that there is a positive impact of ME S-STEM research activities on student diversification, retention rates, and percentage of our graduates who are pursuing graduate degree.

Thermoelectric properties enhancement of p-type composite films using wood-based binder and mechanical pressing.

Thermoelectric generators (TEGs) fabricated using additive manufacturing methods are attractive because they offer the advantages of scalability, lower cost, and potentially higher power density than conventional TEGs. Additive manufacturing of TEGs requires active thermoelectric particles to be dispersed in a polymer binder to synthesize printable slurries, and printed films to be subsequently subjected to a long and high temperature curing to enhance their thermoelectic properties. A large amount of polymer binder present in composite films results in a sizable loss in the electrical conductivity. In addition, a long and high-temperature film curing results is a slow and energy intensive fabrication process. In this work, we demonstrate the feasibility of using a small amount (≤10-3 wt ratio) of novel nanofiber cellulose (NFC) as a binder to provide sufficient adhesion strength to hold the TE particles together in the composite films. We also demonstrate a pressure induced densification process to enhance the thermoelectic properties of printed composite films. This novel approach has the potential to fundamentally transform the manufacting method for printing TEGs by eliminating the need of long-duration and high-temperature curing. A higher applied pressure leads to a compact packing and densification of films resulting in an improvement in the electrical conductivity. The highest power factor achieved for best performing p-type thermoelectric-NFC composite film subjected to pressure induced densification is 611 µW/m-K2.

High Conductivity and Electron-Transfer Validation in an n-Type Fluoride-Anion-Doped Polymer for Thermoelectrics in Air.

Air-stable and soluble tetrabutylammonium fluoride (TBAF) is demonstrated as an efficient n-type dopant for the conjugated polymer ClBDPPV. Electron transfer from F- anions to the π-electron-deficient ClBDPPV through anion-π electronic interactions is strongly corroborated by the combined results of electron spin resonance, UV-vis-NIR, and ultraviolet photoelectron spectroscopy. Doping of ClBDPPV with 25 mol% TBAF boosts electrical conductivity to up to 0.62 S cm-1 , among the highest conductivities that have been reported for solution-processed n-type conjugated polymers, with a thermoelectric power factor of 0.63 µW m-1 K-2 in air. Importantly, the Seebeck coefficient agrees with recently published correlations to conductivity. Moreover, the F- -doped ClBDPPV shows significant air stability, maintaining the conductivity of over 0.1 S cm-1 in a thick film after exposure to air for one week, to the best of our knowledge the first report of an air-stable solution-processable n-doped conductive polymer with this level of conductivity. The result shows that using solution-processable small-anion salts such as TBAF as an n-dopant of organic conjugated polymers possessing lower LUMO (lowest unoccupied molecular orbital), less than -4.2 eV) can open new opportunities toward high-performance air-stable solution-processable n-type thermoelectric (TE) conjugated polymers.

High-performance dispenser printed MA p-type Bi(0.5)Sb(1.5)Te(3) flexible thermoelectric generators for powering wireless sensor networks.

This work presents a novel method to synthesize p-type composite thermoelectric materials to print scalable thermoelectric generator (TEG) devices in a cost-effective way. A maximum ZT of 0.2 was achieved for mechanically alloyed (MA) p-type Bi0.5Sb1.5Te3 (8 wt % extra Te additive)-epoxy composite films cured at 250 °C. A 50% increase in Seebeck coefficient as a result of adding 8 wt % extra Te in stoichiometric Bi0.5Sb1.5Te3 contributed to the increase in ZT. To demonstrate cost-effective and scalable manufacturing, we fabricated a sixty element thermoelectric generator prototype with 5.0 mm × 600 µm × 120 µm printed dimensions on a custom designed polyimide substrate with thick metal contacts. The prototype TEG device produced a power output of 20.5 µW at 0.15 mA and 130 mV for a temperature difference of 20 K resulting in a device areal power density of 152 µW/cm(2). This power is sufficient for low power applications such as wireless sensor network (WSN) devices.

Enhanced performance of dispenser printed MA n-type Bi2Te3 composite thermoelectric generators.

This work presents performance advancements of dispenser printed composite thermoelectric materials and devices. Dispenser printed thick films allow for low-cost and scalable manufacturing of microscale energy harvesting devices. A maximum ZT value of 0.31 has been achieved for mechanically alloyed (MA) n-type Bi2Te3-epoxy composite films with 1 wt % Se cured at 350 °C. The enhancement of ZT is a result of increase in the electrical conductivity through the addition of Se, which ultimately lowers the sintering temperature (350 °C). A 62 single-leg thermoelectric generator (TEG) prototype with 5 mm ×700 µm × 120 µm printed element dimensions was fabricated on a custom designed polyimide substrate with thick metal contacts. The prototype device produced a power output of 25 µW at 0.23 mA current and 109 mV voltage for a temperature difference of 20 °C, which is sufficient for low power generation for autonomous microsystem applications.