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Category Archives: Photoelectrolysis

Photovoltaic  solar energy  is becoming popular as a source of clean energy and an alternative to fossil fuels to combat climate change. Though the initial cost is expensive people have started realizing the potential of PV solar as  a real alternative to grid power, especially when they can export surplus power to the grid and earn some revenue. It is  a source of income for potential investors as the energy cost keeps rising steadily. The cost of solar panels, batteries and inverters are slowly coming down as the systems get more popular and more competition is created in the market. However, during cloudy days or when the solar hours are less, the power generation by solar panels is considerably low. Moreover, the ‘power in tariff ‘ system is not available in many countries especially in developing countries. Therefore, energy storage becomes an issue. Lead acid batteries serve as storage devices for smaller applications but it becomes expensive for lager systems. Operation and maintenance, replacement and waste disposal are some of the issues with battery storage.

Generating Hydrogen on site using solar power and storing Hydrogen under pressure in a tank is the best method of storing solar energy. The stored Hydrogen can be used to generate power using a Fuel cell as and when we need power. However, the amount of energy required to convert water into Hydrogen using Alkaline Electrolyzer or Solid Polymer Electrolyzer is still high, averaging 5-7 kwhrs/m3.When you calculate the economics of  Hydrogen storage versus battery storage using a computer modeling for a stand alone system, it is clear that Hydrogen storage is more economical and also guarantees an uninterrupted power supply using a Fuel cell.

One US company has developed a Carbon doped Titanium oxide nanopowder visible light photo catalyst to  generates Hydrogen using sun’s light energy. The company claims that it consumes only one-third of the power consumed by PEM Electrolyzer or half of an Alkaline Electrolyzer.It can be easily installed at roof tops and it can generate Hydrogen even at one-third of sunlight because it can effectively use short UV light and blue wave length of suns light because these energetic wavelengths penetrate cloud cover more effectively than the rest of sunlight. A 2mm modular solar panel can be installed on roof top or installed in multi-acre field installations. Even during the absence of sunlight the company claims it can use grid power to generate Hydrogen using its hybrid integral (MMO) Mixed metal oxide Titanium anode as efficiently as PEM Electrolyzer.

While a PEM electrolyzer generates about 1.3kg Hydrogen from a power input of 100Kwhrs, this model can generate about 2.5kg Hydrogen using MMO + TiO2 anode and about 3.8kg using TiO2 alone. (Based on higher heating value of Hydrogen at 39.4 kwhrs/kg).The panel consuming 26.7kwhr power at 1.0Volt DC current at Anode can generate 1.25kg Hydrogen with Electrolysis electrical efficiency at 148%.  This will make Hydrogen fuel a commercial reality because it will consume only 21.36 kwhrs of Dc power to generate 1 Kg Hydrogen. The generated Hydrogen can generate about 15 Kw power using a Fuel cell. This is an elegant solution to generate and store power using sun’s light than Photovoltaic power.

Synthesis of Ammonia is one of the  remarkable achievements of Chemical engineering in forties .It is a precursor for Urea, the fertilizer  that  brought about ‘Green revolution’ in agriculture industry and helped to achieve record food production all over the world. It was a milestone in modern chemistry to synthesis a molecule containing I atom of Nitrogen and 3 atoms of Hydrogen, represented by NH3 called Ammonia. The HeberBosch process for the production of Ammonia is a well established mature, commercial technology.

The process uses a Hydrocarbon source such as Naphtha or Natural gas as the feed stock to generate a synthesis gas composed of Hydrogen and Carbondioxide.The gas mixture is separated into carbon dioxide and Hydrogen using PSA (pressure swing adsorption ) technology. The resulting Hydrogen is used to combine with Nitrogen to synthesize Ammonia.

The chemical reaction can be represented by the following equation.

N2 + 3H2 ———- 2 NH3

The above reaction takes place at a pressure of 100-200 bars and temperature of 300-500C in presence of  catalysts. It is an exothermic (heat releasing) reaction and the catalyst bed is cooled and maintained at 400C to be efficient.But this process of Hydrogen generation using Hydrocarbon emits greenhouse gases. Alternatively, Hydrogen can be generated using different methods using renewable energy sources using water electrolysis. Such process may be used in the future for this application.

Nitrogen is derived from atmospheric air. The air we breathe has about 79% of Nitrogen and 21% Oxygen. But these two gases can be separated by liquefying the air by cryogenic process and distilling them into two fractions. Alternatively, they can separated using pressure swing adsorption or membrane separation process, utilizing their density differences. In either way, Nitrogen can be separated from atmospheric air. By combining the above Hydrogen and Nitrogen, it is possible to synthesis Ammonia on a commercial-scale.

The ammonia can be easily split into Hydrogen and Nitrogen by passing Ammonia through a bed of Nickel catalyst at 200-400C as and when required to generate on site Hydrogen. This Hydrogen can be used for power generation or to run our cars using PEM Fuelcell.As we have seen previously, we are now looking for various sources of Hydrogen, and Ammonia is one of the promising sources for couple of reasons. The process and technology of Ammonia production, transportation and usage is well documented and has been practiced for few decades. It does not emit  greenhouse gases.Liquified Ammonia has been widely used in air-conditioning and refrigeration systems. Ammonia can be easily metered into any system directly from the cylinder.

It is easier to use Ammonia directly into a convention internal combustion engines in place of Gasoline and this technology has already been practiced in 1880. Ammonia is pungent and any leakage can be easily identified. The advantage of using Ammonia as a fuel in cars, it does not emit any smoke  but only water vapour.It can be admixed with Gasoline or used as 100% anhydrous Ammonia. It also helps in reduction of NO2 emission, especially is diesel engines.

Ammonia has a great potential as a source of future fuel provided the sources of Hydrogen comes from water using renewable technologies or by photo electrolysis using direct sunlight.

One of the wonders of Mother Nature is her ability to sustain life on earth with sun light, water and Carbon dioxide from the atmosphere producing food. No toxic chemicals, no polluting gas emissions and no noise. We can only admire the majesty and power of Nature with our  fragile knowledge of science and try to duplicate Nature to satisfy our growing energy needs. Nature produces Carbohydrates C6H12O6 using sun’s light, Carbon dioxide from atmosphere and water by a chemical reaction as shown below:

6H2O + 6 CO2  ———–   C6H12O6 + 6O2

The same Carbon dioxide from the atmosphere is now threatening the globe with warming. Can’t we grow more trees so that all the carbon dioxide emissions from our power plants and cars can be converted into more carbohydrates? It sounds very simple and logical but is it feasible? The carbon dioxide in the atmosphere before industrialization was about 280ppm but it has now increased to 392ppm which is almost double. It has grown roughly 2.2% exponentially in the last decade. It is the highest in the past 800 years and likely higher than in the past 20 million years. (Ref: Wikipedia). Couple of things happened during this period. The industrial and population growth increased rapidly building up carbon dioxide level in the atmosphere and at the same time displacing tropical and rain forests with people and industries; it resulted in the buildup of greenhouse gases to a level, which scientists say are unsustainable. We don’t have enough forest to absorb so much of carbon dioxide.

Alternatively, scientists are now trying to interfere with Nature’s photosynthesis process using micro algae called chlamydomonas reinhardtii that will support the production of Hydrogen instead of Oxygen in a normal photosynthesis reaction. This was based on the discovery that if an algae growing culture medium is deprived of Sulfur, it will generate Hydrogen instead of Oxygen. They also found out that such an algae can thrive in a Carbon source such as Carbon dioxide or even in  Acetic acid medium. They tested the process using a pilot Photo bioreactor and concluded that the cost of producing Hydrogen by this route will be about $ 42/kg.The cost is high compared to the target cost of Hydrogen by DEO  (Department of Energy,USA) at $2.80/kg which is fifteen times lower. However scientists are still working to cut the cost.

Meanwhile scientists are also working on Hydrogen production using Photoelectrolysis.The water electrolysis using Direct current is a known process but the cost of energy in this process is still high. The high cost is due to several stages involved. In the first stage, one has to generate power using PV cells. In the second stage the PV generated electricity will be used to split water electrolyticlly.But scientists are now trying to substitute both the above steps with a single step of utilizing direct sun light to split water into Hydrogen and Oxygen.Thie requires a catalyst known as Photocatalyst which will use light energy instead of electrical energy to split water into elements. Using TIO2 (Titanium dioxide coated electrode) and ultraviolet rays of the sun they believe that a 20m2 PV solar panel can generate about 5m3 of Hydrogen ad 2.5m3 of Oxygen in 24 hours, equal to a power generation capacity of 15kwhrs or roughly about  2.01 gallons of Gasoline from 4 liters of pure water.

Scientists are now  hoping that light energy, more precisely ultraviolet rays from the sun will come to the rescue of human beings in solving one of the greatest  energy crisis  in the history of mankind. At last we can hope to see some ‘light’ at the end of the tunnel.

There is so much discussion about Hydrogen as a source of clean energy because, it is the choice of Nature. Nature has provided us with fossil fuels which are Hydrocarbons, chemically represented by CxHy, Carbon and Hydrogen atoms. In the absence of Hydrogen in a Hydrocarbon, it is nothing but Carbon, which is an inert material. The Hydrocarbon gets its heating value only from the presence Hydrogen atom. The natural gas, now considered as the cleanest form of Hydrocarbon is represented by the chemical formula CH4, containing 25% Hydrogen by weight basis. It represents the largest Carbon to Hydrogen ratio at 1:4.This is the highest in any organic chemicals. In aromatic organic compounds such as Benzene, represented by C6H6, the Hydrogen content is only 7.69%.Even in Sugar which is an organic compound from Nature, represented chemically as C12H22O11 has only 8.27% Hydrogen. But Bioethanol, derived from sugar represented by C2H4OH has almost 11.11% Hydrogen. That is why Ethyl Alcohol known as ‘Bioethanol’ derived from sugar is blended with Gasoline (Hydrocarbon), for using as a fuel in cars in countries like Brazil.

Brazil is the only country that does not depend on imported Gasoline for their cars. The same Bioethanol can also be derived from Corn starch. But the starch should first be converted into sugar before alcohol is derived; that is why it is more expensive to produce Bioethanol from starch than from cane sugar molasses. The climatic conditions of Brazil are more favorable for growing Cane sugar than corn. That is why Brazil is in a more advantageous position than North America, when it comes to Bioethanol. US is one of the largest consumer of Gasoline.US has imported 11.5 million barrels/day of oil in 2010.It has used 138.5 billion gallons of Gasoline (3.30billion barrels) in 2010) according to EIA. (US Energy Information Administration)

It is estimated that Brazil’s sugar based Alcohol is 30% cheaper than US’s corn-based Alcohol. Brazil has successfully substituted Gasoline with locally produced alcohol .They also introduced ‘flexible fuel vehicles’ that can use various blends of Alcohol-Gasoline. Most of the Gasoline used in US has 10% Ethanol blend called E10 and E15, representing the percentage of Alcohol content in Gasoline. Brazil is the largest producers of Bioethanol in the world. Both Brazil and US account for 87.8% of Bioethanol production in the world in 2010 and 87.1% in 2011.Brazil is using Bioethanol blends of various proportions such as E20/E25/E100 (anhydrous alcohol) (Ref: Wikipedia). Almost all cars in Brazil uses Bioethanol blended Gasoline and even 100% anhydrous Bioethanol are used for cars. Brazil has set an example as a ‘sustainable economy introducing alternative fuel’ to the rest of the world. The ‘bagasse’ from cane sugar is also used as a fuel as well in the production of ‘Biogas’, which helps Brazil to meet sustainability on renewable energy and greenhouse gas mitigation.

The above example is a clear demonstration of sustainability because natural organic material such as sugar is the basic building block by which we can build our Sustainable clean energy of the future. The same Bioethnanol can easily be reformed for the production of Hydrogen gas to generate power and run Fuel cell cars. Many companies are trying to use chemicals such as metal Hydrides as a source of Hydrogen. For example, one company successfully demonstrated using Sodium Borohydride for Hydrogen production. Many companies are trying to find alternative sources of Hydrogen generation from water, including Photo-electrolysis using direct solar light and special photo catalyst materials. We know Nature produces sugar by using sun’s light, water and carbon dioxide from air by photosynthetic process. Can man duplicate this natural process and generate Hydrogen at the fraction of the cost by simply using water and sun’s light? The race is already on and only time can tell whether our pursuit for cheap and clean Hydrogen can become a commercial reality or just stay as an elusive dream.




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