Hydrogen gas is being seriously pursued as an environmentally safe form of energy to power our modern world. Combustion of pure hydrogen produces water vapour as a by-product, although its gaseous state elicits storage issues, as an energy source it’s hard to beat.
Electrolysis of water, the use of an electric current to make hydrogen has been around for 218 years, as such, it is a very established process. Currently researchers at Penn State are working on generating hydrogen from water without adding an electrical current, and so far their efforts have yielded impressive results.
Modifying a process called reverse-electrodialysis, -RED-, they have managed to apply their technology to hydrolyze water at an efficiency of 58 – 60%. This equates to 0.8 to 1.6 cubic metres of hydrogen for every cubic meter of liquid pumped though the system each day, all without any energy from the grid.
The reverse-electrodialysis, “stack” consists of ion exchange membranes, both positive and negative, that are assembled in an alternating configuration. Additional stacks of membranes in the RED assembly produce an increasing electrical yield. These ion exchange membranes, as the title implies, develop an electrical potential due the “ionic difference” between salt and fresh water.
The basis for their chemical process uses sea water, river water, and the biodegradable organic matter found in waste water. The driving force behind the increased hydrogen production falls on a tiny biological agent. A specific type of bacteria is harnessed to generate the voltages required to hydrolyze water and produce hydrogen in conjunction with RED technology.
These bacteria are identified as exoelectrogenic, this means that the micro- organism itself generates an electric current as it consumes the organic material in the waste water. Without this added energy boost, the RED stack would require a minimum of 25 pairs of membranes which greatly increase resistance to flow of the fluids through the membranes causing increased pressure and an overall decrease in efficiency.
Comparatively, research has established that microbial fuel cells can produce 0.3 volts of electricity. It requires 0.414 volts to generate hydrogen. Without added electricity the microbial fuels cells cannot produce hydrogen by themselves. Incorporating the microbes into a RED stack consisting of 11 membranes, in five pairs, increases the combined voltage to the level needed.
As the exoelectrogenic bacterium consumes the organic material flowing through the RED membrane it produces the needed 0.5 volts of electric current. This increase in efficiency allows for a very impressive amount of hydrogen to be produced by a relatively simple process.
Bruce E. Logan, Kappe Professor of Environmental Engineering, at Penn State and postdoctoral fellow, Younggy Kim, the driving forces behind this advent in technology point to the global abundance of wastewater, seawater, and freshwater. Professor Logan notes, “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.”
A hydrogen economy, in the not so distant future, may see the light of day.
Lorne Oja can be reached at lorne@solartechnical.ca