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February 21, 2024

Sunlight and wastewater could solve fuel crisis

By TONY WU | October 26, 2013

Many Americans are rather familiar with the current energy crisis. As the world population continues to grow, available fuel deposits and supplies continue to dwindle. Some estimate that the Earth will reach an energy shortage epidemic in the next 50 years.

Furthermore, the burning of fossil fuels release CO2, a gas which is a major contributor to global warming. As a result, researchers across the world are seeking solutions to these immediate problems. Some champion solar power while others seek the use of hydrogen as a fuel source. Recently, the research team at University of California, Santa Cruz, found a way to combine advantages of the two alternatives. Yat Li, a professor at the University of California and lead investigator of the team proposes a hybrid device that will efficiently produce hydrogen in a manner that is both cost-effective and sustainable.

Solar power is based on the concept of the photovoltaic effect. The effect is dependent on certain materials, which when exposed to light, cause an excitation of electrons. These excited electrons can then be converted into electrical energy via electrodes. The iconic image of solar panels harnessing the sunlight is an example of the effect in action.

However, in the device built by the research team led by Li, the solar component is composed of a device called the PEC. The PEC — or photoelectrochemical cell — works by the electrolysis of water.

Instead of using excited electrons to generate electricity, the PEC generates hydrogen and oxygen gas, which can then be burned to generate the necessary heat for power production. Li explains that the PEC is composed of a semiconductor electrode that produces energy necessary for hydrogen production through the absorption of sunlight.

Another interesting part of the novel device is the inclusion of a microbial fuel cell. The concept of a microbial fuel cell is relatively simple. Microbial organisms can break down organic matter, and in the process, generate electrons as a metabolic process. By providing the organisms with the proper environment and energy source, electrons can be continuously produced and, hopefully, harnessed.

The idea of the MFC is not completely foreign but the unique aspect of the device consists of an unusual bacteria. The bacteria is categorized as an electrogenic bacteria. Electrogenic bacteria have the unique ability to transfer electrons generated through metabolism to an external object such as an electrode.

As a result, scientists believe that we can actually harness those electrons and used them to produce hydrogen fuel. In essence, these bacteria are able to generate electricity which can then be utilized in the hydrolysis of water.By combining both the PEC and the MFC into a device, Li showed that a self-sustainable, fuel producing system is viable.

The PEC and the MFC are known for their ability to produce electricity; however, both devices require an external power source to jumpstart the process of hydrolysis since the power generated from each alone is not enough. By combining the two systems, the two components supply enough combined energy to begin the process of hydrolysis. Furthermore, the self-sustained system appears to be a reliable source of hydrogen gas.

When wastewater is added to the MFC and the PEC is exposed to sunlight, the system produces hydrogen gas at 0.05 m^3 every day. The results proved that the concept of a combined PEC-MFC device is possible.

In addition, the MFC has the added benefit of processing wastewater. The wastewater actually becomes clearer and the water quality is measurably improved over the course of two days. The amount of organic compounds present in water declined by 70 percent.

One concern of the device is the decline in hydrogen production as the wastewater becomes purer. As the amount of organic matter decreases, the bacteria can no longer generate enough electricity. However, when the wastewater is replenished, the rate of hydrolysis returned.

Optimistically, this novel device will be the long-awaited sustainable solution for addressing multiple issues, such as wastewater treatment and the energy shortage in one shot.

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