Electrochemical Ammonia and Hydrogen Production from Polymer-Immobilized Nitrogenase Enzymes

Grant # 08F-04
Principal Investigator: Johna Leddy
Student:
Organization: The University of Iowa
Technical Area: Renewable Energy

Public Abstract

The majority of power generated worldwide is from combusting fossil fuels. The sustainability of and environmental impacts of this non-renewable process are severe. The state of Iowa has been a major contributor to reducing the dependency on fossil fuels for energy consumption through ethanol production and use as a fuel. Other alternative fuels and power generation systems are needed, however, to cope with increasing energy demands.

Ammonia shows promise for use in power generation, however it is costly to produce and very few methods of using it as a fuel are developed. Iowa is well accustomed and equipped to using ammonia as a fertilizer and can use existing infrastructure for transportation and storage of ammonia. With further research into more financially and energetically cost-effective ways to produce and use ammonia, Iowa can further its stride toward energy independence and in leading our nation and world in ways to reduce carbon footprint and provide for future energy needs.

To address the need for alternative methods of ammonia synthesis, this proposal aims to design and test a device that harnesses nature’s existing cellular machinery (i.e. plant cell enzymes) to generate ammonia and small amounts of hydrogen at ambient temperatures and pressures. The proposed ammonia-generating device consists of an electrode modified with a polymer that contains nitrogenase enzymes harvested from blue-green algae. Certain strains of blue-green algae are known to catalytically convert atmospheric nitrogen to ammonia and hydrogen. After establishing and optimizing a culture of nitrogen-fixing cyanobacteria (blue-green algae) and harvesting the nitrogenase enzymes, these enzymes are immobilized in a polymer attached to an electrode. Enzymes are often longer-lived and more productive when immobilized than in their natural state.

The biochemical process of fixing nitrogen to produce ammonia requires a significant amount of cellular energy. In this system, the electrode will supply much the energy required to drive the reaction at ambient temperatures and pressures. The ammonia and hydrogen collected from this catalytic process can be stored, fed into machines and devices requiring fuel, or used to fertilize Iowa crops. Based upon biological and electrochemical methods, the device should catalytically generate ammonia and hydrogen from atmospheric nitrogen and is called a bioelectrocatalytic device. Ideally, the energy expended in powering this reaction will be significantly lower than that of commercial ammonia cracking technology.

We anticipate to develop the system and optimize the variables to produce ammonia proportional to the amount of enzyme immobilized. This system would be functional in both the daylight and at nighttime and will be able to tolerate a decent range of temperatures. We anticipate the cost-to-benefit analysis of this device (considering fiscal and environmental costs) will show the bioelectrocatalytic device is an equitable investment for Iowa.