Urea ElectrolysisUrea is the main component of human and livestock urine, as well as a key ingredient of fertilizers. There is, as a result, an abundance of urea-rich wastewater. If this wastewater is left untreated and then discharged into rivers, creeks, and lakes, the urea will naturally hydrolyze into pollutants such as ammonia and nitrates. 

In the Center for Electrochemical Engineering Research (CEER), a novel technology has been developed to directly convert urea to hydrogen using electricity (please see below): 

Schematic representation of the direct urea to hydrogen process

Anode reaction:

CO(NH2)2 + 6OH- ----> N2 + 5H2O + CO2 + 6e-

Cathode reaction:

6H2O + 6e- -----> 3H2 + 6OH-

Overall reaction:

CO(NH2)2 + H2O -----> N2 + 3H2 + CO2

These reactions take place at room temperature and under normal pressure conditions. Theoretically, the cell voltage for the electrochemical conversion of urea to hydrogen is only 0.37 V, whereas water electrolysis, a popular electrochemical method to produce hydrogen, requires 1.23 V to split water into hydrogen and oxygen. Hydrogen gas produced from urea electrolysis does not require any further purification.

Advantages

1. Raw material for urea electrolysis is urea-rich wastewater, which is readily available and abundant.

2. This process consumes less energy than conventional steam methane reforming (SMR) and water electrolysis.

3. Hydrogen gas produced from this process is pure and, as such, does not require further purification.

4. In addition to producing hydrogen, urea electrolysis remediates wastewater.

5. Urea electrolysis uses an inexpensive Nickel catalyst.

6. This technology is operated at low temperatures (less than 60°C).

7. Urea electrolysis is compatible with any renewable form of energy, such as solar and wind energy.

8. This technology can be implemented in residential areas, farms, and industry.

Sponsors

Department of Defense through the U.S. Army Construction Engineering Research Laboratory

Publications

1. Botte, G. G. Electrolytic Cells and Methods for the Production of Ammonia and Hydrogen. U.S. Pending Patent 12/250 864, 2007.

2. B.K. Boggs, R.L. King and G.G. Botte, "Urea electrolysis: direct hydrogen production from urine," Chem. Commun., p4859 (2009)

3. D.A. Daramola, D. Singh and G.G. Botte, "Dissociation Rates of Urea in the Presence of NiOOH Catalyst: A DFT Analysis," J. Phys. Chem. A, 114, p11513 (2010)

4. R.L. King and G.G. Botte, "Hydrogen Production via Urea Electrolysis using a Gel Electrolyte," J. Power Sources 196, p2773 (2011)

5. D. Wang, W. Yan and G.G. Botte, "Exfoliated nickel hydroxide nanosheets for urea electrolysis," Electrochem. Commun. 13, p1135 (2011)

6. R.L. King and G.G. Botte, "Investigation of multi-metal catalysts for stable hydrogen production via urea electrolysis," J. Power Sources 196, p9579 (2011)

7. W. Yan, D. Wang and G.G. Botte, "Nickel and cobalt bimetallic hydroxide catalysts for urea electro-oxidation," Electrochim. Acta 61, p25 (2012)

Pee-powered fuel cell turns urine to energy31 October 2011

Urine-powered fuel cells could generate electricity and reclaim essential nutrients directly from human

and animal waste, say UK scientists. The development could make wastewater treatment easier and

cheaper, and provide an abundant source of locally generated power.

The team, led by Ioannis Ieropoulos and John Greenman at the Bristol Robotics Laboratory, developed

microbial fuel cells (MFCs) - which use bacteria to break down organic molecules and generate

electricity - that could run on the organic molecules found in urine, such as uric acid, creatinine and

small peptides. 

Finding the right bacteria to munch these molecules was relatively easy - wastewater treatment plants

routinely employ bacteria to do the job. But the crucial point, says Ieropoulos, is that the current

processes are energy intensive, whereas the fuel cell approach could turn it into an energy-generating

process. Getting the urine on the other hand, required a volunteer. 'It's one of us,' quips Greenman, 'but

we're not going to say which one.'

The bacteria form a robust biofilm on the anode surface of the fuel cell, and pass electrons to the

electrode as they respire and metabolise the fuel molecules in the urine. The team have found that

smaller cells have higher energy densities, 'so we've followed a path of miniaturisation and

multiplication, building stacks of cells,' says Ieropoulos. An individual cell can produce a current of

0.25mA for 3 days from 25ml of urine, so stacks of hundreds or thousands of cells could run on the

amounts of urine available from homes, farms, or public toilets, for example. 'Initially we'd probably be

targeting local microgeneration,' says Greenman.

The microbial fuel cell metabolises organic compounds in urine to produce electricity

The lack of solids - which could clog up the fuel cells - in urine compared to more general wastewater

gives this system a significant advantage, comments Lars Angenent, director of the agricultural waste

management lab at Cornell University in Ithaca, US. But, he points out, there are some issues: 'Firstly,

there is a societal question - do people want to separate their urine?' Although there are modern toilets

that can perform the separation, it would require a social change. 'Then there is the cost issue - they've

shown it can be done, but will it be economical?'

Angenent observes that some research has moved from fuel cells towards electrolysis of the urea in

wastewater to form hydrogen or hydrogen peroxide. These valuable products help balance the device

costs. However, as Ieropoulos explains, the bacteria in their fuel cell can't metabolise urea as fuel, so it

could be possible to pass the urine first through an electrolytic cell to generate hydrogen, then through

the MFC to generate electricity from the other organics.

As well as generating power, the team's MFCs could help reclaim essential nutrients from waste, adds

Greenman. Urine is particularly troublesome in wastewater treatment, since it not only contains organic

compounds, but also high levels of nitrogen, phosphorus and potassium. Treatment plants currently

expend significant effort and energy removing these elements from wastewater, as releasing them

constitutes environmental pollution in the same way as excess fertiliser leaching from agricultural land -

it promotes algal blooms that can choke out rivers and waterways.

The fuel cell bacteria could sequester those salts to grow and divide, but in normal urine the balance of

nutrients is wrong - there isn't enough carbon fuel for them to grow fast enough to take up sufficient

amounts of the other elements. 'But if you balance it by adding a cheap carbon source like acetate,'

says Greenman, 'all the nitrogen, phosphate and potassium is captured into daughter bacteria, which

perfuse out of the MFC and can be filtered out and dug back into the ground as fertiliser.'

Phillip Broadwith