A team of researchers has engineered silicon nanowires that can produce hydrogen from water and sunlight. Hydrogen is a greener alternative to fossil fuels. The nanowires, developed by researchers from the University of North Carolina at Chapel Hill, can split water into oxygen and hydrogen gas, and hence, convert sunlight into electricity.
The study describing the findings was recently published in the journal Nature,
In 1972, scientists first demonstrated that liquid water can be split into oxygen and hydrogen gas using electricity produced by illuminating a semiconductor electrode. Hydrogen generated using solar power is a promising form of clean energy. However, low efficiencies and high costs are hurdles to the introduction of commercial solar-powered hydrogen plants.
Why nanoparticles?
If scientists use a slurry of electrodes made from nanoparticles instead of a rigid solar panel design, it can substantially lower costs, an economic feasibility analysis suggests. This would make solar-produced hydrogen competitive with fossil fuels. However, a drawback of most existing particle-based light-activated catalysts, also called photocatalysts, is that they can only absorb ultraviolet radiation. This limits the energy-conversion efficiency of the setup under solar illumination.
James Cahoon, the corresponding author on the paper, and his colleagues have been working on the chemical synthesis of semiconductor nanomaterials with unique physical properties that can enable a range of technologies, from solar cells to solid-state memory, a computer memory that is stored within a hardware device and has no moving parts.
Why is silicon a preferred choice for solar cells?
The researchers designed new silicon nanowires to have multiple solar cells along their axis. These solar cells could produce a large amount of energy needed to split water.
Silicon absorbs both visible and infrared light, and has historically been a top choice for solar cells, also referred to as photovoltaic cells and semiconductors, due to some exceptional properties of the element, such as low toxicity and stability. Furthermore, silicon is abundantly available in the environment.
How do silicon nanowires produce hydrogen?
Since silicon has electronic properties, one can drive water splitting wirelessly with silicon particles by encoding multiple photovoltaic cells in each particle. The researchers generated particles that contain multiple interfaces, called junctions, between two different forms of silicon. They took p-type and n-type semiconductors. A p-type semiconductor consists of boron or indium, and allows current to flow along the material from hole to hole but only in one direction. An n-type semiconductor is doped with arsenic, antimony or phosphorus, and uses electrons as charge carriers.
Hence, the silicon nanowires can convert light into electricity to split water into hydrogen and oxygen. The light-activated nanoreactors, when integrated with co-catalysts, produced hydrogen gas under visible and infrared light.