Power/Performance Bits: Feb. 23

Sodium batteries from unusual sources; new material for solar fuel cells.

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Apple core batteries

Apple waste could help reduce the cost of energy storage, say researchers seeking an improved sodium-ion at the Helmholtz Institute Ulm of Karlsruhe Institute of Technology.

Sodium-ion batteries are not only far more powerful than nickel-metal hydride or lead acid accumulators, but also represent an alternative to lithium-ion technology, as the initial materials needed are highly abundant, easily accessible, and available at low cost. Hence, sodium-ion batteries are a very promising technology for stationary energy storage systems and could be a highly attractive market in the future.

The new carbon-based material for sodium-ion batteries can be extracted from apples. (Source: KIT/HIU)

The new carbon-based material for sodium-ion batteries can be extracted from apples. (Source: KIT/HIU)

In the researcher’s battery, a carbon-based material which can be produced from the leftovers of apples was developed for the negative electrode and possesses excellent electrochemical properties. So far, more than 1000 charge and discharge cycles of high cyclic stability and high capacity have been demonstrated. Plus, the material is a step towards the sustainable use and exploitation of resources, such as organic waste.

The material developed for the positive electrode consists of several layers of sodium oxides. This active material goes without the expensive and environmentally hazardous element cobalt that is frequently used in active materials of commercial lithium-ion batteries. At the laboratory, the new active material, in which electrochemical energy storage proper takes place, reaches the same efficiency, cyclic stability, capacity, and voltage without any cobalt.

New material for solar fuel cells

Chemists from the University of Texas at Arlington developed new high-performing materials for cells that harness sunlight to split carbon dioxide and water into useable fuels like methanol and hydrogen gas to power cars, home appliances, or energy storage in batteries.

“Technologies that simultaneously permit us to remove greenhouse gases like carbon dioxide while harnessing and storing the energy of sunlight as fuel are at the forefront of current research,” said Krishnan Rajeshwar, UTA distinguished professor of chemistry and biochemistry.

The new hybrid platform uses ultra-long carbon nanotube networks with a homogeneous coating of copper oxide nanocrystals. It demonstrates both the high electrical conductivity of carbon nanotubes and the photocathode qualities of copper oxide, efficiently converting light into the photocurrents needed for the photoelectrochemical reduction process.

“The performance of our hybrid has proved far superior to the properties of the individual materials,” Rajeshwar said. “These new hybrid films demonstrate five-fold higher electrical conductivity compared to their copper oxide counterparts, and generate a three-fold increase in the photocurrents needed for the reduction process.”

The new material also demonstrates much greater stability during long-term photoelectrolysis than pure copper oxide, which corrodes over time.

The research involved developing a multi-step electrodeposition process to ensure that a homogeneous coating of copper oxide nanoparticles were deposited on the carbon nanotube networks. By varying the thickness of the carbon nanotube film and the amount of electrodeposited copper oxide, the researchers were able to optimize the efficiency of this new hybrid material.

Batteries that grow on trees

Scientists at the University of Maryland have a new recipe for batteries: Bake a leaf, and add sodium. They used a carbonized oak leaf, pumped full of sodium, as a demonstration battery’s anode.

One of the roadblocks has been finding an anode material that is compatible with sodium, which is slightly larger than lithium. Some scientists have explored graphene, dotted with various materials to attract and retain the sodium, but these are time consuming and expensive to produce. In this case, they simply heated the leaf for an hour at 1,000 degrees C to burn off all but the underlying carbon structure.

The lower side of the maple leaf is studded with pores for the leaf to absorb water. In this new design, the pores absorb the sodium electrolyte. At the top, the layers of carbon that made the leaf tough become sheets of nanostructured carbon to absorb the sodium that carries the charge.

(Source: University of Maryland)

(Source: University of Maryland)

“The natural shape of a leaf already matches a battery’s needs: a low surface area, which decreases defects; a lot of small structures packed closely together, which maximizes space; and internal structures of the right size and shape to be used with sodium electrolyte,” said Fei Shen, a visiting student in the department of materials science and engineering.

The next step, researchers said, is to investigate different types of leaves to find the best thickness, structure and flexibility for electrical energy storage. They have no plans to commercialize at this time.