March 25, 2023

Greener fuels only take in hydrogen from water and light; know more

Researchers at the Department of Chemistry at the University of North Carolina at Chapel Hill, USA, have designed silicon nanowires that can convert sunlight into electricity, splitting water into oxygen and hydrogen gas, which is a more environmentally friendly alternative to fossil fuels.

Fifty years ago, scientists showed for the first time that liquid water could be split into oxygen and hydrogen gas using electricity generated by lighting a semiconductor electrode.

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While solar-generated hydrogen is a promising form of clean energy, low efficiencies and high costs have prevented the introduction of commercial solar-powered hydrogen plants.

An economic-feasibility analysis indicates that the use of electrode paste made of nanoparticles instead of a solid-state solar panel design can reduce costs significantly, making solar-powered hydrogen competitive with fossil fuels.

However, most existing catalysts based on light-activated particles, also known as photocatalysts, can only absorb UV radiation, which limits their energy conversion efficiency under sunlight.

James Cahoon, Ph.D. PhDs in chemistry at the Hyde Family Foundation in UNC-Chapel Hill’s College of Arts and Sciences, and their colleagues in the department, are working on the chemical synthesis of semiconducting nanomaterials with unique physical properties that could enable a variety of technologies, from solar cells to solid-state memory. Cahoon is the corresponding author of the findings published February 9 in the journal Nature.

Cahoon and his team designed new nanowires that contain multiple solar cells along their axis so that they can produce the energy needed to split water.

This design is unprecedented in previous reactor designs and allows silicon to be used for the first time in a PSR.

Taylor Tetsworth, a postdoctoral researcher in Cahoon’s lab

Silicon absorbs visible and infrared light. Historically, it has been the best choice for solar cells, also known as photovoltaics and semiconductors, because of these and other properties, including their abundance, low toxicity, and stability.

With its electronic properties, the only way to perform wireless water separation with silicon particles is to encode multiple photoelectric cells into each particle. This can be achieved by generating molecules that contain multiple interfaces, called junctions, between two different forms of silicon – p-type and n-type semiconductors.

Previously, Kahun’s research focused on the upward structure and spatial control of silicon with boron for pe-type nanowires with phosphorus for n-type nanowires to impart desired geometries and functionality.

We have used this approach to create a multi-junction water-splitting class of nanoparticles. They combine the physical and economic advantages of silicon with the optical advantages of nanowires, which have a diameter smaller than the wavelength of the absorbed light,” Kahun said.

“Because of the inherent asymmetry of the wire junctions, we were able to use a photoelectrochemical method to selectively deposit catalysts at the ends of the wires to allow water separation.”

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Featured image: Leonidas Santana/Shutterstock

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