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Making Fuel From Seawater

Apart from the sun and wind, there is another promising renewable energy source that might soon be used as fuel. Seawater is abundant, replenishable, and conveniently available. There has been a flurry of experiments in recent years to test its efficacy as a fuel.

The idea behind the seawater-to-fuel concept is simple and consists of breaking down seawater into its constituent elements to reuse them as energy sources. The breakdown process yields carbon dioxide and hydrogen, both of which can be combined to produce jet fuel. Alternately, hydrogen can used to make fuel cells to power automobiles and provide energy storage options.

As with other technologies, the military was the first organization to test it. In March 2013, the Naval Research Lab Center of Corrosive Science used a proprietary electrochemical device to extract CO2 and hydrogen from seawater and power a jet. They were able to pull 97% of carbon dioxide from seawater at a cost of $3 to $6 per gallon. Now the laboratory plans to use a commercial chain reactor to spread the use of the technology.     

There are three problems in the process used to convert seawater to fuel. The first one is the power associated with the process. The electricity required to deconstruct seawater into its constituents is significant and mainly derived from fossil fuel sources, making the entire process expensive for the organization implementing it as well as the environment. There might be a workaround, however, if a renewable energy source is used to generate power for the process. For example, the NRL plans to use nuclear-powered aircraft for the conversion process to alleviate power requirements.

The second problem is the process’ skewed efficiency ratio. It will take an enormous amount of seawater in order to produce jet fuel to power military aircraft. According to a 2010 report, it will take 8,900,000 cubic meters of seawater to produce 100,000 gallons of jet fuel in a day. The final problem with the production process for seawater from jet fuel is that it produces harmful waste. Approximately 25% of output in the process used by the U.S. military consisted of methane, a gas which contributes to global warming.

Since the US military’s experiments, a new team of researchers is tackling problems associated with conversion of seawater to fuel from multiple angles. At Columbia University, Daniel Esposito has developed a rig (see pic above) powered by solar panels to separate out hydrogen and oxygen from seawater through electrolysis. In an interview with Hakai Magazine, Esposito explained the innovations in his rig. His team has designed an electrolysis unit without membranes to reduce the inefficiencies resulting from clogging of pores of a membrane. He envisages massive hydrogen rigs, similar to oil rigs, floating in the future. Unlike oil rigs, which transport oil through pipelines and tankers, hydrogen from such rigs may also be transported using blimps or hot air balloons.

Researchers at the University of Central Florida have developed a new nanomaterial that can significantly reduce electricity for the process. Professor Yang Yang at the University of Central Florida and his team have developed a new photocatalyst that can harvest fuel from seawater more efficiently as compared to other commonly-used catalysts. The process builds off commonly-used photocatalysts, such as titanium dioxide. A film of titanium dioxide has nanocavities filled with molybdenum disulfide etched onto its surface. The latter can convert a greater spectrum of bandwidth of light to energy, according to Prof. Yang.

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