Posted tagged ‘photosynthesis’

Artificial Leaf Solar Power

October 3, 2011

Photosynthesis:

Photosynthesis is the process by which plants, some bacteria, and some protists use the energy from sunlight to produce sugar, which cellular respiration converts into ATP, the “fuel” used by all living things. The conversion of unusable sunlight energy into usable chemical energy, is associated with the actions of the green pigment chlorophyll.

They release molecular oxygen and remove CO2 (Carbon Dioxide) from the air.

ATP: Adenosine Tri-Phosphate (ATP)  Here the energy is stored in living systems; it consists of a Nucleotide (with Ribose sugar) with Three Phosphate groups.

Why is photosynthesis important:

01-photosynthesis-green pigment chlorophyll-ATP-Adenosine Tri-Phosphate

Nearly all living things depend on the energy produced from photosynthesis for their nourishment. Animals need the plants for food as well as oxygen. Only green plants are able to change light energy into chemical energy stored in food, thus they are vital to life on Earth.

Solar cells:

01-solar cells-photovoltaic cells-silicon semiconductor material-silicon cells-solar wall paper

Conventional solar cells are also called as Photo Voltaic Cells. These cells are made out of semiconducting material, usually silicon. When light hits the cells, they absorb energy though photons. This absorbed energy knocks out electrons in the silicon, allowing them to flow. By adding different impurities to the silicon such as phosphorus or boron, an electric field can be established. This electric field acts as a diode, because it only allows electrons to flow in one direction. Consequently, the end result is a current of electrons, better known to us as electricity.


Drawbacks of Solar cells:

They can only achieve efficiencies around 10% and they are expensive to manufacture. The first drawback, inefficiency, is almost unavoidable with silicon cells. This is because the incoming photons, or light, must have the right energy, called the band gap energy, to knock out an electron. If the photon has less energy than the band gap energy then it will pass through. If it has more energy than the band gap, then that extra energy will be wasted as heat.

Artificial Leaf:

Mixing of Photosynthesis + Conventional Solar Cells + Hydrogen Fuel Cell

26 Sept. 2011, Cambridge, MA - MIT professor Daniel Nocera has developed an artificial leaf chip that can split water molecules using light. Photo by Dominick Reuter

This Leaf device combines a commercially available solar cell (Silicon) with a pair of inexpensive catalysts made of Cobalt and Nickel that split water into Oxygen and Hydrogen. The hydrogen can be stored and used as an energy source. (For example to power a fuel cell).

The collection and storage of the sun’s energy as hydrogen fuel is a key step in overcoming one of the limitations of solar power — it generates energy when the sun is shining, but it needs to be stored somewhere to be useful at night and in cloudy weather. Batteries are one place to store the energy, but it is limited. Storing solar energy as hydrogen fuel could be an answer for producing the electricity continuously.

01-bubbles formation-production of electricity from hydrogen bubbles-artificial leaf hydrogen-electricity production


Using this approach, a solar panel roughly one square meter bathed in water could produce enough hydrogen to supply electricity for a house.


Artificial photosynthesis

August 23, 2011

Artificial photosynthesis is one of the newer ways researchers are exploring to capture the energy of sunlight reaching earth.

01-photosynthetic reaction-receive sunlight as photons-transfer energy to a network of pigment protein complexes

Photosynthesis:

01-Photosynthesis-basics-operation-oxygen release-hydrogen splits


Photosynthesis is the conversion of sunlight, carbon dioxide, and water into usable fuel and it is typically discussed in relation to plants where the fuel is carbohydrates, proteins, and fats. Using only 3 percent of the sunlight that reaches the planet, plants collectively perform massive energy conversions, converting just over 1,100 billion tons of CO2 into food sources for animals every year.

Photovoltaic Technology:

This harnessing of the sun represents a virtually untapped potential for generating energy for human use at a time when efforts to commercialize photovoltaic–cell technology are underway. Using a semiconductor–based system, photovoltaic technology converts sunlight to electricity, but in an expensive and somewhat inefficient manner with notable shortcomings related to energy storage and the dynamics of weather and available sunlight.

Artificial Photosynthesis:

01-photosynthesis system-Artificial Photosynthesis-Artificial Photosynthesis Solar energy to produce hydrogen directly used in fuel cell

Two things occur as plants convert sunlight into energy:

  • Sunlight is harvested using chlorophyll and a collection of proteins and enzymes, and
  • Water molecules are split into hydrogen, electrons, and oxygen.

These electrons and oxygen then turn the CO2 into carbohydrates, after which oxygen is expelled.

Rather than release only oxygen at the end of this reaction, an artificial process designed to produce energy for human use will need to release liquid hydrogen or methanol, which will in turn be used as liquid fuel or channeled into a fuel cell. The processes of producing hydrogen and capturing sunlight are not a problem. The challenge lies in developing a catalyst to split the water molecules and get the electrons that start the chemical process  to produce the hydrogen.

There are a number of promising catalysts available, that, once perfected, could have a profound impact on how we address the energy supply challenge:

  • Manganese directly mimics the biology found in plants.
  • Titanium Dioxide is used in dye-sensitized cell.
  • Cobalt Oxide is very abundant, stable and efficient as a catalyst

Artificial Photosynthesis Operation:

01-artificial Photosynthesis-arrays of microwave coated catalysts-split water to make hydrogen or liquid hydrocarbon fuels

Under the fuel through artificial photosynthesis scenario, nano tubes embedded within a membrane would act like green leaves, using incident solar radiation (H³) to split water molecules (H2O), freeing up electrons and oxygen (O2) that then react with carbon dioxide (CO2) to produce a fuel, shown here as methanol (CH3OH). The result is a renewable green energy source that also helps scrub the atmosphere of excessive carbon dioxide from the burning of fossil fuels.

01-artificial photosynthesis solar collector to energy-concentrated solar radiation- convert photosynthesis to Hydrogen and oxygen

History:

Plants use organic compounds that need to be continuously renewed. Researchers are looking for inorganic compounds that catalyze the needed reactions and are both efficient and widely available.

The research has been significantly boosted by the application of nano technology. It’s a good example of the step wise progress in the scientific world.

Studies earlier in the decade showed that crystals iridium efficiently drove the reduction of CO2, but iridium is extremely rare so technology that required its use would be expensive and could never be used on a large scale.

Cobalt crystals were tried. They worked, and cobalt is widely available, but the original formulations weren’t at all efficient.

Things changed with the introduction of nano technology.

The main point is that this unique approach increasing appears to be feasible. It has the advantage of harnessing solar energy in a form that can be stored and used with greater efficiency than batteries and it is at least carbon neutral.