Production of clean energy has been an effort in progress for a long time. As the world currently runs on fossil fuels that are polluting the planet are a finite resource and unsustainable for long term. This has led to the search of alternatives and hydrogen is one of the leading contenders. The problem with hydrogen is that it is an energy carrier instead of an energy source. Pure hydrogen is not found naturally and it consumes energy ( usually generated by fossil fuels ) for production. Now researchers at Pennsylvania State University have developed a way to produce hydrogen that uses no grid electricity, is carbon neutral and could be used at anyplace where there is wastewater near sea water.
The researcher's work revolves around microbial electrolysis cells (MECs) - a technology related to microbial fuel cells (MFCs), which produce an electric current from the microbial decomposition of organic compounds. MECs partially reverse this process to generate hydrogen (or methane) from organic material but they require the some electrical input to do so.
Instead of relying on the grid to provide the electricity required for their MECs, Bruce E. Logan, Kappe Professor of Environmental Engineering, and postdoctoral fellow Younggy Kim, turned to reverse-electrodialysis (RED) to generate electricity using salt water from the North Sea and fresh water from the Rhine and the Penn State team's work follows the principle i.e - extracting energy from the ionic differences between salt water and fresh water.
A RED stack consists of alternating positive and negative ion exchange membranes, with each RED adding to the electrical output. Logan says that using RED stacks to generate electricity has been proposed before but, because they are trying to drive an unfavorable reaction, many membrane pairs are required. To split water into hydrogen and oxygen using RED technology requires 1.8 volts, which would require about 25 pairs of membranes, resulting in increased pumping resistance.
However, by combining RED technology with exoelectrogenic bacteria - bacteria that consume organic material and produce an electric current - the researchers were able to reduce the number of RED stacks required to five membrane pairs.
Previous work with MECs showed that, by themselves, they could produce about 0.3 volts of electricity, but not the 0.414 volts needed to generate hydrogen in these fuel cells. Adding less than 0.2 volts of outside electricity released the hydrogen. Now, by incorporating 11 membranes - five membrane pairs that produce about 0.5 volts - the cells produce hydrogen.
"The added voltage that we need is a lot less than the 1.8 volts necessary to hydrolyze water," said Logan. "Biodegradable liquids and cellulose waste are abundant and with no energy in and hydrogen out we can get rid of wastewater and by-products. This could be an inexhaustible source of energy."
While Logan and Kim used platinum as the catalyst on the cathode in their initial experiments, subsequent experimentation showed that a non-precious metal catalyst, molybdenum sulfide, had 51 percent energy efficiency.
The
Penn State researchers say their results, which are published in the Sept. 19 issue of the
Proceedings of the National Academy of Sciences, "show that pure hydrogen gas can efficiently be produced from virtually limitless supplies of seawater and river water and biodegradable organic matter."
