Janus Catalyst for Oxygen and Hydrogen Evolution from Water

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Water Electrolysis

One way to perform water splitting is through electrolysis, that is giving energy in form of electric current. The overall reaction takes place as two half reactions, as shown below:

Hydrogen Evolution Reaction (HER)            2 H+ + 2 e → H2

Oxygen Evolution Reaction (OER)                 2 H2O → O2 + 4 e + 4H+

The two half reactions are performed on the surface of two charged plates (electrodes). The electrodes are generally made of metals, and can act as catalysts to improve the efficiency of the reaction processes.

Different materials normally work as catalysts for the HER and OER reactions; for hydrogen production, the most effective catalysts are noble metals, such as platinum, while platinum or iridium oxide are the best catalysts for oxygen evolution. These elements, however, are all quite expensive, and not very abundant. To produce H2 on a large scale, and with an economically viable process, science will need to develop electrodes made of cheaper and more abundant elements.

Hydrogen Catalyst: New Material Developed

The researchers of the Laboratory of Chemistry and Biology of Metals, in co-operation with the CEA, the University of Grenoble and the CNRS (France) have developed a new material to provide a less-expensive catalyst for producing hydrogen from water. The research was performed in cooperation with other institutions of CEA  (LITEN, IRAMIS, LETI), the Paris French College and the Physics Department of Free University Berlin (Germany).

The material developed is a composite, made of cobalt (Co) nanoparticles deposited on a F-doped SnO2 (FTO) substrate – dubbed CoCat by the researchers.

CoCat: Easy Preparation

Dr. Vincent Artero, leading scientist of this study, told Decoded Science how CoCat was prepared:

The nanostructured cobalt was deposited from a solution of Co(NO3)2·6H2O. The FTO substrates were placed in a neutral phosphate solution and, applying an electric current, the deposition took place. The simplicity of the process means it can be easily scaled up for industrial production. Surface analysis showed that the deposited layer is constituted of metallic cobalt, together with cobalt bound to phosphate and hydroxide ions from the deposition solution.”

The cobalt atoms are present in two different forms. Photo by Juan Rubiano.

Double Functionality

Tests performed on CoCat showed that it works as a very good catalyst for the HER process; hence, it can be used to obtain H2 from water.

Its most interesting aspect, however, is that it also works for the OER process, to generate oxygen. According to Dr. Artero:

this is something completely new, never reported before, that makes this material really remarkable. We think that this double functionality is due to the presence of cobalt in two forms, metallic and in a phosphate-based complex.

Materials which can catalyze two opposite reactions, like in this case, are called Janus catalysts.

Hydrogen Production: Great Potential

How important is this new catalyst? It could change everything. According to Dr. Artero: “In principle CoCat could be used for an artificial leaf device, to produce hydrogen.” Not only that, the material isn’t limited to changing water into hydrogen and oxygen. As Dr. Artero said, “this preparation method could potentially be used for other materials, such as semiconductor nanoparticles, opening the doors to new applications.

Sources

S. Cobo et al. A Janus cobalt-based catalytic material for electro-splitting of water. Nature Materials. (2012). Accessed September 9, 2012.

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