New Energy Storage Device Stores Solar Energy in Chemical and Electromechanical Form

21 November 2017

Richard Kaner and Maher El-Kady in Kaner's office. Kaner  is holding a replica of a new energy storage and conversion  device they developed.  Source: Reed Hutchinson/UCLARichard Kaner and Maher El-Kady in Kaner's office. Kaner is holding a replica of a new energy storage and conversion device they developed. Source: Reed Hutchinson/UCLA

A team of researchers at the University of California Los Angeles (UCLA) has designed an integrated solar-powered system that can create and store electrical energy and chemical energy simply by harvesting solar energy to create hydrogen fuel.

Richard Kaner and Maher El-Kady from UCLA developed an energy storage cell driven by solar energy that can create electrical energy and store it in a supercapacitor, and also create hydrogen (chemical energy) by the process called water electrolysis.

"Hydrogen is a great fuel for vehicles: It is the cleanest fuel known, it's cheap and it puts no pollutants into the air -- just water," said Richard Kaner, the study's senior author and a UCLA distinguished professor of chemistry and biochemistry, and of materials science and engineering. "And this could dramatically lower the cost of hydrogen cars."

The device can be very useful in remote areas where energy is not readily available, and also in big cities that could store surplus energy from the electrical grid.

"People need fuel to run their vehicles and electricity to run their devices," Kaner said. "Now you can make both electricity and fuel with a single device. If you could convert electricity to hydrogen, you could store it indefinitely," said Kaner, who also is a member of UCLA's California NanoSystems Institute.

Nowadays, more than 95 percent of hydrogen is produced worldwide by converting fossil fuels into hydrogen. This process releases an enormous amount of carbon dioxide into the atmosphere. "Hydrogen energy is not 'green' unless it is produced from renewable sources,” said El-Kady, a UCLA postdoctoral researcher and a co-author of the research. Using solar cells and abundantly available elements to split water into hydrogen and oxygen has enormous potential for reducing the cost of hydrogen production and that approach could eventually replace the current method he added.

Schematics of the new storage device. Source: UCLASchematics of the new storage device. Source: UCLA

How the device was built?

Normally a fuel cell or a supercapacitor is manufactured with only two electrodes, one positive and one negative. The device created by Kaner and his team have a third electrode used as a supercapacitor (to store electrical energy) and to create hydrogen by splitting water into oxygen and hydrogen – the process called water electrolysis. The power source of the three electrodes is a solar cell connected to the three electrodes. The energy produced by the solar cell can be stored in one of two ways: electrochemically (electrical energy in a battery or a supercapacitor) and chemically (as hydrogen).

The electrodes were fabricated at the nanoscale. This provides the greatest surface area for water to be in contact with, so more hydrogen is produced, and it provides bigger storage area to contain electrical charges. The chemical reaction to split water into hydrogen and oxygen uses cobalt, iron and nickel, three elements very abundant and less expensive than precious materials (platinum and others) used today to produce fuel cells. This combination of Ni-Fe-Co has excellent electrochemical properties as an active electrode material in supercapacitors and also as a catalyst for water electrolysis.

In addition, the production of hydrogen using this device can be stored at normal temperature and pressure. "For hydrogen cars to be widely used, there remains a need for a technology that safely stores large quantities of hydrogen at normal pressure and temperature, instead of the pressurized cylinders that are currently in use," said Mir Mousavi, a co-author of the paper and a professor of chemistry at Iran's Tarbiat Modares University.

The results of the research was published in the journal, Energy Storage Materials. An abstract can be found here.

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