Progress to hydrogen fuel produced from sunlight

A team of Renewable Energy experts from the University of Exeter has pioneered a new technique to produce hydrogen from sunlight to create a clean, cheap and widely-available fuel.

The team developed an innovative method to split water into its constituent parts – hydrogen and oxygen – using sunlight. The hydrogen can then be used as a fuel, with the potential to power everyday items such as homes and vehicles.

Crucially, hydrogen fuel that can be created through this synthetic photosynthesis method would not only severely reduce carbon emissions, but would also create a virtually limitless energy source.

The ground-breaking new research centers on the use of a revolutionary photo-electrode – an electrode that absorbs light before initializing electrochemical transformations to extract the hydrogen from water – made from nanoparticles of the elements lanthanum, iron and oxygen.

The researchers believe this new type of photo-electrode is not only cheap to produce but can also be recreated on a larger scale for mass and worldwide use.

Goatguy Comment

Mr. Govinder Pawar neatly portrays the potential of LaFeO₃ to catalyze (solar → hydrogen (direct)) as being potentially critical for its role to accelerate replacement of fossil fuels in the near-term future. He does not delve into hydrogen’s intrinsic gotchas. There is no convenient liquid form of hydrogen; the pressurized gas — like all pressurized flammable gasses — is dangerous (but perhaps not fatally so, irony aside). Yet, the tech stands out because it IS direct path.

The other problem is that if a single compound creates both H₂ and O₂ in the same reaction zone, they’ll mix. And as we know mixtures of hydrogen gas and oxygen gas are quite famously explosive. Rather more-so than The Hindenburg zeppelin disaster. Now, it isn’t entirely unreasonable that the components could be readily separated in situ with a simple arrangement of porous membranes: hydrogen loves to permeate and diffuse thru membranes, and oxygen isn’t so inlined. We’ve experienced this with party balloons: tight today, deflated tomorrow. If you fill a balloon tho’ with air, note that it usually doesn’t deflate very much per day. Diffusion!

Also notably missing are efficiency numbers. Just exactly how numerically efficient is the lanthanum iron oxide photodissociation catalyst? After all its fine to say ‘’wonderfully efficient’’, compared oh, to a block of clay, but realistically ‘’efficient’’ is a competitive continuüm, which today has silicon sitting near 20% direct sunlight —> electrons. And while 20% doesn’t sound high to just about anyone, consider that “corn” is less than 0.5% efficient. Corn grows like crazy. 0.5%. In fact, I know of no vascular plants that exceed 1% efficiency. Not even venerable switchgrass.

GoatGuy

Research Paper link, abstract and conclusion for Solar Fuel Production

Nature Scientific Reports – Unbiased Spontaneous Solar Fuel Production using Stable LaFeO3 Photoelectrode

Photoelectrochemical (PEC) water splitting to produce solar fuel (hydrogen) has long been considered as the Holy Grail to a carbon-free hydrogen economy. The PEC concept to produce solar fuel is to emulate the natural photosynthesis using man made materials. The bottle-neck in realising the concept practically has been the difficulty in identifying stable low-cost semiconductors that meet the thermodynamic and kinetic criteria for photoelectrolysis. We have fabricated a novel p-type LaFeO3 photoelectrode using an inexpensive and scalable spray pyrolysis method. Our nanostructured LaFeO3 photoelectrode results in spontaneous hydrogen evolution from water without any external bias applied. Moreover, the photoelectrode has a faradaic efficiency of 30% and showed excellent stability over 21 hours. From optical and impedance data, the constructed band diagram showed that LaFeO3 can straddle the water redox potential with the conduction band at −1.11 V above the reduction potential of hydrogen. We have fabricated a low cost LaFeO3 photoelectrode that can spontaneously produce hydrogen from water using sunlight, making it a strong future candidate for renewable hydrogen generation.

In summary, they have developed a stable p-type LaFeO3 photoelectrode with a coral like nanostructure by a novel and inexpensive spray pyrolysis technique with a post annealing step, which yields a photocurrent density of 0.16 mA/cm2 at 0.26 V vs. RHE. Chronoamperometric studies showed that the LaFeO3 film provides a stable p-type response over a 21 hour period. Optical and impedance data showed that the material is able to straddle the redox potential of water, with the valance band at 1.29 V and conduction band at −1.11 V, and a bandgap of 2.4 eV. IPCE studies revealed that the photoelectrode had an APCE of 3.5%. Water splitting test was conducted in a custom made reactor vessel, where the working electrode and Pt counter electrode was connected by a single looped wire, without any external bias being applied. This in turn yielded 0.18 μmol/cm2 hydrogen after six hours during the first cycle with faradaic efficiency of 30%. To the best of our knowledge this is the first time hydrogen has been produced spontaneously during a water splitting test without any external bias being applied using LaFeO3 photoelectrode as a single material. These findings demonstrate that LaFeO3 is a potential candidate to act as a photoelctrode for unassisted PEC water splitting to generate solar fuel (hydrogen) cost effectively. However further work is required to investigate and improve slow charge carrier dynamics and low light absorption challenges of LaFeO3 photoelectrodes.

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