With all the scams and claims of water for fuel we have been covering lately, I thought it timely to feature a couple of Examples of how real scientists are researching more efficient ways of splitting water. No overunity, but all adds to the bigger picture.
Simple solution makes hydrogen production through solar water splitting more efficient and cheaper
Researchers from Delft University of Technology (TU Delft), in collaboration with colleagues from the École Polytechnique Fédéral de Lausanne (EPFL), have found a simple yet very effective solution to greatly increase the efficiency and stability of hydrogen production through solar-driven water splitting. By separating the positive and the negative electrodes using a bipolar membrane, they were able to create local optimal conditions for electrolysis. Furthermore, they achieved this using only Earth-abundant catalysts and solar cells, opening the way for more efficient and stable water-splitting systems at lower cost. They have published their findings in the latest Advanced Energy Materials.
The thought driving Associate Professor dr. Wilson Smith in his research at TU Delft, is that one hours’ worth of sunlight reaching the Earth contains enough energy for one years’ worth of current energy demand worldwide. One of the challenges is being able to store and transport part of that energy for later use. So-called solar fuels could offer a solution, for example by harvesting solar energy and converting it into hydrogen by means of water splitting.
Electrolysis is the process involved, and in order to realize efficient and long term water splitting, having a strong acid around the negative cathode and a strong base around the positive anode would be best. Up until now, most of the commercially available electrolysers run in either a strong acid or a strong base electrolyte. In these systems, the highly corrosive environments limit the choice of catalysts, and they suffer from the constraint of finding a suitable pair of electrodes for the one electrolyte. So far only precious, and therefore expensive, metal catalysts can do that job.
The seemingly simple solution of separating the two electrodes by a specialized membrane, allows for optimization of the process, by offering the electrodes their respective best environments. It also means that Earth-abundant catalysts can be used in the process, making it cheaper, more efficient, and more stable.
The international research team, also including dr. David Vermaas from TU Delft, has shown that using a bipolar membrane in this manner can lead to a water splitting system efficiency of 12.7%. Natural photosynthetic processes in plants run at about 1% efficiency, while an efficiency of 10% is considered to be the starting point for potential commercial viability according to various techno economic analyses. An efficiency of 18% has been achieved for these types of processes, but only using precious metals and other very expensive (and unstable) materials. To be able to achieve this high efficiency while also using all Earth-abundant components in the solar cell and catalysts, makes the achievement an excellent demonstration for this technology. Smith: ‘This is a strong scientific step that can help the transition from lab scale systems into practical devices.’
Potential for other applications
The principle of separating the poles in these types of cells also looks very promising for other applications, according to Smith. ‘Using this bipolar membrane for electrochemical systems, we are now able in theory to click together the optimal half reaction components for processes like pieces of Lego. This has a huge potential for other electrochemical reactions such as the production of ammonia and hydrocarbons, while separating the oxidation half reaction completely. In this next step, we can finally replicate nature and make a truly artificial photosynthetic system that goes well beyond the efficiencies in nature.’
Bipolar Membrane-assisted Solar Water Splitting in Optimal pH, Jingshan Luo*, David A. Vermaas, Dongqin Bi, Anders Hagfeldt, Wilson A. Smith*, and Michael Grätzel
One of the main obstacles in the production of hydrogen through water splitting is that hydrogen peroxide is also formed, which affects the efficiency stability of the reaction and the stability of the production. Dutch and Israelian researchers from Eindhoven University of Technology and the Weizmann Institute have succeeded in controlling the spin of electrons in the reaction and thereby almost fully suppress the production of hydrogen peroxide. They published these findings this week in the Journal of the American Chemical Society. The efficient production of hydrogen paves the way towards water splitting by solar energy.
Hydrogen has been referred to as the fuel of the future but its generation is still not efficient enough. One of the production methods is a photo-electrochemical cell whereby water is split into hydrogen and oxygen under the influence of light. Not only does the reaction require a lot of energy but also hydrogen peroxide is formed as a by-product, leading to the poisoning of one of the electrodes and thus reduced efficiency.
Led by professors Bert Meijer (Eindhoven University of Technology) and Ron Naaman (Weizmann Institute), the researchers are the first to have specifically investigated the role of the spin – the internal magnetic moment – of electrons involved in the oxidation reaction, or the formation of oxygen. Their idea was that if both spins are aligned, the formation of hydrogen peroxide would not occur. That’s because the ground state of hydrogen peroxide – a so-called singlet state – does not allow two electrons with opposite spins. Oxygen, with a triplet ground state, does.
By covering the titanium oxide anode in their photo-electrochemical cell with chiral (molecules that are mirror images of each other) supramolecular structures of organic paint, they were able to inject only electrons with their spins aligned in the process. This work followed former findings by the group of Naaman, that the transmission of electrons through chiral molecules depends on the electrons’ spin. “The effect on water splitting exceeded our expectations,” Ron Naaman says. “The formation of hydrogen peroxide was almost entirely suppressed. We also saw a significant increase in the cell’s current. And because chiral molecules are very common in nature, we expect great implications from this finding.”
Stroke of luck
The researchers are not yet able to say how much more efficient this can make hydrogen production. “Our goal was to be able to control the reaction and to understand what exactly was going on,” explains Bert Meijer. “In some ways, this was a stroke of luck because the supramolecular structures had not originally been intended for this purpose. It goes to show how important supramolecular chemistry is as a fundamental field of research, and we’re very busy optimizing the process.”