July/August_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 0 1 4 METAL-EATING ROBOTS A research team from the Universi- ty of Pennsylvania’s School of Engineer- ing and Applied Science is bridging the gap between batteries and harvesters in the form of a “metal-air scavenger” that combines the best of both worlds. Their new scavenger works like a bat- tery in that it provides power by repeat- edly breaking and forming a series of chemical bonds. But it also works like a harvester as power is supplied by en- ergy in its environment—specifically, the chemical bonds in metal and the surrounding air. The result is a power source that has 10 times more power density than the best energy harvesters and 13 times more energy density than lithium-ion batteries. In the future, this type of ener- gy source could be the basis for a new paradigm in robotics, where machines keep themselves powered by seeking out and “eating” metal—breaking down its chemical bonds for energy. Like a traditional battery, the met- al-air scavenger (MAS) starts with a cathode that is wired to the de- vice it’s powering. Underneath the cathode is a slab of hydrogel. With the hydrogel acting as an electro- lyte, any metal surface it touches functions as the anode of a bat- tery, allowing electrons to flow to the cathode and power the con- nected device. This oxidation re- action takes place only within 100 microns of the surface, so while the MAS may use up all the read- ily available bonds with repeated trips, there is little risk of it doing signif- icant structural damage to the metal it is scavenging. Currently, the winners of Penn’s annual Y-Prize Competition are plan- ning to use metal-air scavengers to power low-cost lights for off-grid homes in the developing world and long-last- ing sensors for shipping containers that could alert to theft, damage, or even human trafficking. upenn.edu . USING SHADOWS TO MAKE ELECTRICITY Researchers from the National University of Singapore (NUS) have found a way to harness shadows to generate electricity. A team from the NUS department of materials science and engineering as well as the physics department created a device called a shadow-effect energy generator (SEG), which makes use of the contrast in il- lumination between lit and shadowed ENERGY TRENDS areas to generate electricity. Their con- cept enables new approaches to gener- ating green energy under indoor light- ing conditions to power electronics. The SEG comprises a set of SEG cells arranged on a flexible and trans- parent plastic film. Each SEG cell is a thin film of gold deposited on a sili- con wafer. Carefully designed, the SEG can be fabricated at a lower cost compared to commercial silicon so- lar cells. Based on laboratory experi- ments, the team’s four-cell SEG is twice as efficient as commercial cells under the effect of shifting shadows. The har- vested energy from the SEG in the pres- ence of shadows created under indoor lighting conditions is sufficient to pow- er a digital watch. In the next phase of research, the team will experiment with materials other than gold to reduce the cost of the SEG. www.nus.edu.sg . The DOE successfully delivered its latest nuclear power system to the Kenne- dy Space Center for NASA’s upcoming Mars 2020 launch. The Multi-Mission Radioisotope Thermoelectric Generator was fueled, built, and tested by DOE’s national laboratories to power the Perseverance rover, the first to use plutoni- um created by Oak Ridge National Laboratory. energy.gov. BRIEF This metal-air scavenger vehicle gets energy from breaking chemical bonds in the aluminum surface it travels over. Courtesy of University of Pennsylvania. This Multi-Mission Radioisotope Thermo- electric Generator will provide electricity for a Mars mission this summer. A novel SEG uses indoor shadows to generate electricity.