A team from UCLA and colleagues from Tarbiat Modares University and Shahed University in Iran have devised an integrated solar-powered system for both electrochemical energy storage and water electrolysis.
They synthesized a nickel-cobalt-iron layered double hydroxide (Ni-Co-Fe LDH) on a nickel foam substrate using a fast, one-step electrodeposition approach. The Ni-Co-Fe LDH exhibited excellent electrochemical properties both as an active electrode material in supercapacitors, and as a catalyst in the oxygen evolution reaction (OER) for water splitting. A paper on their work is published in the journal Energy Storage Materials.
Employed as the positive electrode in a supercapacitor, along with activated carbon as the negative electrode in an asymmetric configuration, the ultrathin and porous Ni-Co-Fe LDH nanoplatelets delivered an ultrahigh specific energy of 57.5 Wh kg−1 with specific power of 37.9 kW kg−1 and an excellent cycle life.
As an OER electrocatalyst, Ni-Co-Fe LDH exhibited superior electrocatalytic performances with a very low overpotential of 0.207 V versus a reference hydrogen electrode (RHE) at 10.0 mA cm−2, and a small Tafel slope of 31 mV dec−1.
The team attributed the superior energy storage and catalytic OER properties of the Ni-Co-Fe LDH nanoplatelet array to both the synergistic effects among the metal species and the unique mesoporous structure of the LDH that provides facilitated charge/ion diffusion pathways and more available active sites.
Traditional hydrogen fuel cells and supercapacitors have two electrodes: one positive and one negative. The device developed at UCLA has a third electrode that acts as both a supercapacitor, which stores energy, and as a device for splitting water into hydrogen and oxygen. All three electrodes connect to a single solar cell that serves as the device’s power source, and the electrical energy harvested by the solar cell can be stored in one of two ways: electrochemically in the supercapacitor or chemically as hydrogen.
People need fuel to run their vehicles and electricity to run their devices. Now you can make both electricity and fuel with a single device. —Richard Kaner, senior author and a UCLA distinguished professor of chemistry and biochemistry, and of materials science and engineering
Combining a supercapacitor and the water-splitting technology into a single unit, Kaner said, is an advance similar to the first time a phone, web browser and camera were combined on a smartphone. The new technology may eventually lead to new applications that even the researchers haven’t considered yet, Kaner said.
The researchers designed the electrodes at the nanoscale to ensure the greatest surface area would be exposed to water, which increases the amount of hydrogen the device can produce and also stores more charge in the supercapacitor. Although the device the researchers made would fit in the palm of your hand, Kaner said it would be possible to make larger versions because the components are inexpensive.
Resources
Yasin Shabangoli, Mohammad S. Rahmanifar, Maher F. El-Kady, Abolhassan Noori, Mir F. Mousavi, Richard B. Kaner (2017) “An integrated electrochemical device based on earth-abundant metals for both energy storage and conversion,”Energy Storage Materials doi: 10.1016/j.ensm.2017.09.010