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Water splitting is the process of breaking down the chemical compound of water into its constituent elements of hydrogen and oxygen. There are many approaches to water splitting, the most common among them being electrolysis, where an electrical current is passed through water to produce hydrogen and oxygen ions. Though many methods of water splitting are not energy efficient in terms of the energy required to separate hydrogen and oxygen from water versus the energy that can be derived later from the pure hydrogen for fuel, the process is nevertheless seen as a potential alternative to replacing a dependence on fossil fuels. Applications using solar power and new chemical catalysts to split water offer a promising method of producing renewable net energy gains without producing greenhouse gas emissions or other pollutants in the process.
Photocatalytic water splitting using the energy of light, or using other renewable energy sources such as wind power, are now being employed to generate electrical current in new forms of electrolysis. The goal is to create a water splitting system that is entirely fueled by renewable energy sources, such as sunlight, making hydrogen production competitive against fossil fuels. The challenge in the process has been to develop electrodes that are made of inexpensive and durable materials. Cobalt and nickel borate compounds have been found to offer increased efficiency and they are cheap and easy to manufacture. Though these new electrode compounds are safe in commercial solar-fuel producing systems, they cannot yet compete with the efficiency of industrial electrolysis methods that use dangerous alkali compounds as electrolyte solutions.
Water splitting mechanisms that offer the most promise in terms of energy gain are based on the process of photosynthesis that plants use to convert sunlight into chemical energy. While natural systems for this are very slow and artificial systems that mimic it initially had an efficiency of less than 1% when research began on them back in 1972 in Japan, new processes are increasing hydrogen production levels. Japanese researchers in 2007 began coating electrodes made of hydrogenated microcrystalline silicon with nanoparticles of platinum, which further increased the stability and life of the electrodes and their catalytic ability at water splitting.Similar research at the National Renewable Energy Laboratory (NREL) in the United States targets solar to hydrogen efficiency conversion rates of 14% in the year 2015 with an increased durability of electrodes from 1,000 hours in 2005 to 20,000 hours in 2015, as well. As this efficiency increases, the corresponding cost of producing hydrogen fuels decreases, with a US Dollars (USD) per kilogram ($/kg) cost of producing H2 in 2005 at $360/kg down to $5/kg in 2015. Even at this level, water splitting to produce hydrogen is still three to ten times more expensive than generating hydrogen-based fuels from the reformation of natural gas. The research still has some distance to go before it is competitive economically with the established energy sector.