Contributed by Peter B. Littlewood, Director of the Argonne National Laboratory
At the U.S. Department of Energy’s (DOE) Argonne National Laboratory, approximately 1,400 scientists and engineers work to solve some of our greatest energy challenges. Stresses created by climate change and an aging electric grid, coupled with a national effort to reduce our reliance on petroleum, have increased the demand for revolutionary energy systems that are inexpensive and environmentally friendly.
Solar panels, fuel cells, and batteries provide energy while reducing greenhouse gas emissions and increasing the resilience and flexibility of our energy sources. Argonne researchers are investigating affordable and sustainable materials that can help ensure the wide adoption and long-term success of these technologies.
With access to state-of-the-art facilities—including the Advanced Photon Source and Center for Nanoscale Materials, both DOE Office of Science User Facilities—the laboratory’s chemists, as well as researchers in related disciplines, study the processes that enable energy efficiency, performance, and durability in solar photovoltaics, fuel cells, and batteries as they pursue new materials for these applications.
To find new ways to harness the abundant power of the sun, Northwestern University, in collaboration with Argonne, leads the Argonne-Northwestern Solar Energy Research (ANSER) Center. ANSER is a DOE Energy Frontier Research Center, which brings together teams from multiple institutions to conduct fundamental research for solving “grand challenges.”
ANSER scientists are currently searching for an alternative to silicon solar cells that will reduce the cost and size of solar panels, as well as the energy required to manufacture them. Today’s silicon solar cells operate at about 20 percent efficiency and researchers don’t see a way to significantly, yet affordably, boost the efficiency of silicon. And while silicon makes a good semiconductor for delivering electricity, it absorbs sunlight inefficiently, which means more silicon is needed to build thicker cell layers. Finally, the process to purify silicon for solar cell fabrication is energy-intensive.
One way to expand the scalability of solar energy is to find new chemistries that promote conversion of sunlight into electricity, so scientists can build thinner solar cells made of cheaper, more abundant materials. The challenge: materials with the desired light-absorbing and conductive properties also tend to be more expensive or more toxic. ANSER scientists are researching a number of promising ways to enhance the properties of available non-toxic materials and overcome the hurdles associated with them. Rust-like iron oxides, hybrid perovskites halides, and organic polymers are just a few examples.
Iron oxides are incredibly cheap and plentiful but have poor solar-absorbing and conductive properties in bulk; in thin films, however, these properties are enhanced. Researchers are engineering the surface at the nanoscale to further exploit these properties for improved efficiency.
Hybrid perovskites halides are terrific light-harvesters and have generated positive attention as solar cell contenders, but these hybrids are traditionally lead-based—the solubility of lead in water commands special attention when deploying hybrid perovskites halides in the environment. Researchers are looking to replace the lead with largely non-toxic tin. Finally, organic polymers use no precious elements in the solar cell but currently require potentially toxic heavy metal catalysts for synthesis—researchers are identifying and improving new polymerization techniques that could eliminate the use of heavy metals.
Hydrogen is an energy carrier with enormous potential for wide-scale energy storage and as an automobile fuel. Hydrogen fuel cells, and proton exchange membrane (PEM) fuel cells in particular, work by sending the proton of a hydrogen atom through an electrolyte into the cathode, while the atom’s electrons are diverted around the electrolyte, creating a loop of electricity. When the electrons rejoin the protons in the cathode, they close the electrical circuit and the process produces water as a waste product.
This seemingly simple process, however, requires a special material: the precious metal platinum. In automotive fuel cells, half the cost of the fuel cell stack is spent on platinum, and within each fuel cell, most of this cost is in the cathode, which uses over four times more platinum than the anode.
Argonne scientists are helping reduce and even eliminate the use of platinum in fuel cells with innovative new catalysts. Argonne recently accelerated its efforts in this area by collaborating with DOE’s Los Alamos National Laboratory to create the Electrocatalysis Consortium, which is devoted to finding cheap yet effective alternatives to platinum in fuel cell cathodes—they’re starting with the non-precious elements iron and cobalt and continuing to search for other candidates.
As part of the consortium, scientists will use Argonne’s high-throughput laboratory to fabricate catalysts and electrodes and rapidly assess their structure and performance, aided by insights from techniques such as X-ray imaging and spectroscopy. In previous fuel cell tests, Argonne researchers have demonstrated that nanostructures designed to increase the density of active sites can improve the performance of non-precious metal catalysts. In particular, metal-organic frameworks add a new dimension to the cathode nanostructure to improve performance and power density while also lowering cost.
Better batteries have already revolutionized how we live and work, powering our laptops, cell phones, and electric and hybrid vehicles. Argonne leads DOE’s Battery and Energy Storage Hub, the Joint Center for Energy Storage Research (JCESR), where scientists and engineers from national laboratories, universities, and industry develop new electrochemical systems, battery architectures, and fabrication methods to improve the safety, energy densities, and life cycle of batteries.
Researchers are exploring a few types of battery chemistries that could change how we use and store energy. The lithium ions in lithium-ion (Li-ion) batteries carry with them a single charge, but a battery chemistry known as multivalent intercalation uses ions like magnesium that have more than one charge and could potentially double energy storage capacity.
Another type of battery, called “redox flow,” replaces solid metal electrodes used in many Li-ion batteries today with energy-dense liquid electrodes. In this model, micron-sized polymers and gel-like active materials can be separated across electrodes using commercial technology already available.
Argonne researchers have also created a unique solution for doubling the energy density in a nickel-rich battery cathode. Researchers noticed that when they operated nickel-rich cathodes at higher voltages, energy capacity dropped and damaged the battery life cycle. Splitting the cathode’s nickel particles in half to see what was happening, researchers realized the nickel surface was experiencing stress as it reacted with the lithium. To retain high capacity while improving stability, they created something new: composition gradient particles composed of 80 to 90 percent nickel at the center and a thin gradient of manganese at the surface. Paired with a silicon composite anode that uses a pre-lithiation approach to add a source of lithium to the cell to compensate for the large irreversible capacity loss in the first cycle, Argonne chemists believe the nickel-manganese gradient cathode could double battery capacity in the next three to five years.
Finally, researchers see continued potential with lithium. Lithium-sulfur batteries could be cheaper and more lightweight than current Li-ion batteries, and scientists are studying ways to improve their performance and lifetimes by reducing the build-up of precipitate that can short out the battery.
These efforts in solar energy, fuel cells, and batteries are just a few examples of the world-class research underway at Argonne. Our chemists work closely with the laboratory’s computational and materials scientists, biologists, physicists and engineers, as well as institutional and industrial partners, to find energy solutions that work for everyone—consumers, businesses, cities, and the environment.
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