Posted tagged ‘chemical energy’

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.

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


HOW FUEL CELL WORK?

August 23, 2011

An electrochemical reaction occurs between hydrogen and oxygen that converts chemical energy into electrical energy.

01-how fuel cell works-proton exchange membrane-hydrogen fuel cell

Think of them as big batteries, but ones that only operate when fuel—in this case, pure hydrogen—is supplied to them. When it is, an electrochemical reaction takes place between the hydrogen and oxygen that directly converts chemical energy into electrical energy. Various types of fuel cells exist, but the one automakers are primarily focusing on for fuel cell cars is one that relies on a proton-exchange membrane, or PEM. In the generic PEM fuel cell pictured here, the membrane lies sandwiched between a positively charged electrode (the cathode) and a negatively charged electrode (the anode). In the simple reaction that occurs here rests the hope of engineers, policymakers, and ordinary citizens that someday we’ll drive entirely pollution-free cars.

Here’s what happens in the fuel cell: When hydrogen gas pumped from the fuel tanks arrives at the anode, which is made of platinum, the platinum catalyzes a reaction that ionizes the gas. Ionization breaks the hydrogen atom down into its positive ions (hydrogen protons) and negative ions (electrons). Both types of ions are naturally drawn to the cathode situated on the other side of the membrane, but only the protons can pass through the membrane (hence the name “proton-exchange”). The electrons are forced to go around the PEM, and along the way they are shunted through a circuit, generating the electricity that runs the car’s systems.

Using the two different routes, the hydrogen protons and the electrons quickly reach the cathode. While hydrogen is fed to the anode, oxygen is fed to the cathode, where a catalyst creates oxygen ions. The arriving hydrogen protons and electrons bond with these oxygen ions, creating the two “waste products” of the reaction—water vapor and heat. Some of the water vapor gets recycled for use in humidification, and the rest drips out of the tailpipe as “exhaust.” This cycle proceeds continuously as long as the car is powered up and in motion; when it’s idling, output from the fuel cell is shut off to conserve fuel, and the ultra capacitor takes over to power air conditioning and other components.

A single hydrogen fuel cell delivers a low voltage, so manufacturers “stack” fuel cells together in a series, as in a dry-cell battery. The more layers, the higher the voltage. Electrical current, meanwhile, has to do with surface area. The greater the surface area of the electrodes, the greater the current. One of the great challenges automakers face is how to increase electrical output (voltage times current) to the point where consumers get the power and distance they’re accustomed to while also economizing space in the tight confines of an automobile.