Water splitting is a process of breaking down water into hydrogen and oxygen. It has potential as an alternative to fossil fuels, with solar energy and chemical catalysts offering promising methods. The challenge is to develop cheap and durable electrodes. Research is increasing efficiency, but it is still more expensive than generating hydrogen-based fuels from natural gas.
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 of which is electrolysis, where an electric current is passed through water to produce hydrogen and oxygen ions. While many water splitting methods are not energy efficient in terms of the energy required to separate the hydrogen and oxygen from water compared to the energy that can be derived later from pure hydrogen as a fuel, the process is nonetheless seen as a potential alternative to replacing a dependency on fossil fuels. Applications using solar energy and novel chemical catalysts to split water offer a promising method for producing net renewable energy gains without producing greenhouse gas emissions or other pollutants in the process.
The photocatalytic splitting of water using light energy or using other renewable energy sources such as wind power is now being employed to generate electric current in new forms of electrolysis. The goal is to create a water splitting system that is powered entirely by renewable energy sources, such as sunlight, making hydrogen production competitive with fossil fuels. The challenge in the process has been to develop electrodes made from cheap and durable materials. Compounds of cobalt and nickel borate have been found to offer higher efficiency and are cheap and easy to produce. While these new electrode compounds are safe in commercial solar fuel production systems, they still cannot compete with the efficiency of industrial electrolysis methods that use hazardous alkali compounds as electrolyte solutions.
The water splitting mechanisms that offer the most promise for energy gain are based on the process of photosynthesis that plants use to convert sunlight into chemical energy. While natural systems are very slow to do this, and man-made systems that mimic it initially had an efficiency of less than 1% when research began on them in 1972 in Japan, new processes are increasing levels of hydrogen production. Japanese researchers in 2007 began coating hydrogenated microcrystalline silicon electrodes with platinum nanoparticles, which further increased the stability and durability of the electrodes and their catalytic ability to split water.
Similar research at the National Renewable Energy Laboratory (NREL) in the United States aims for solar to hydrogen efficiency conversion rates of 14% in the year 2015 with increased electrode life from 1,000 hours in 2005 to 20,000 hours in 2015 As this efficiency increases, the corresponding cost of producing hydrogen fuels decreases, with a cost in US dollars (USD) per kilogram ($/kg) of producing H
2
in 2005 at $360/kg up to $5/kg in 2015. Even at this level, splitting water to produce hydrogen is still three to ten times more expensive than generating hydrogen-based fuels since the reform of the
natural gas
. Research still has some distance to go before it is economically competitive with the established energy sector.
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