We’ve all heard of black gold, but yellow? That could be something new. But of course, in the current climate of ecological fear, a new alternative to crude oil is precisely what we need. Now Geradine Botte from Ohio University, USA suggests we leave our modern prejudices behind and try using our own waste product – urine – as a fuel for the future.
The largest constituent of human urine is urea (see structure in figure 1). It’s a toxic waste product from the breakdown of amino acids under physiological conditions. You’ll notice though, there’s four hydrogen atoms in each molecule. Botte was convinced she could find a way to extract the hydrogens as a gas (H2) from urea. Initially the way to do it wasn’t obvious – it appears, strangely enough, that no one had ever wanted to investigate urine as a H2 source before. Nonetheless, the potential benefits of developing such a procedure drove her relentlessly towards her goal.
Wee is the most abundant waste material on earth. As a rough estimate, a healthy adult produces 1.5 litres of urine each day. Multiplied by the global population, that gives a figure of approximately 9 billion litres of yellow gold each day. If this cheap and abundant waste product could be turned into a fuel for cars easily it could be truly revolutionary.
Botte is now reporting the use of an electrochemical cell to ‘electrolyse’ the urine . This literally translates to ‘split apart using electricity’. By passing an electric current through two Nickel electrodes immersed in a solution of urine, the urea molecules are given enough energy to overcome the power of the chemical bonds holding them together. The molecules can then split apart and the constituent parts collect in the compartments of the cell (figure 1). The researchers showed the cell could produce H2 from artificial wee (urea dissolved in water) and eventually demonstrated it was also effective on the real life stuff.
Figure 1 – A Nickel electrochemical cell for the electrolysis of urea.
You might notice that hydrogen gas isn’t the only product to be expelled from the cell. Nitrogen and potassium carbonate are also given off, and there are questions which would need to be answered over what would happen to these items, especially if the process was used on a large scale to produce fuel.
Nitrogen is a pretty useful gas. Light bulbs are generally filled with nitrogen, so that’s a major sink. Then there’s the Haber process – the reaction of N2 with H2 – to produce ammonia. The Haber process is currently carried out on a massive scale globally as ammonia is a vital constituent of soil fertilisers.
The potassium carbonate is a trickier customer altogether though. Disposing of this might be difficult as it can break down to produce carbon dioxide (CO2) if it comes into contact with water. This could be a significant risk as washing effluent into rivers is how we dispose of most of our chemical waste at the moment. Not only is this unfortunate for the obvious reason that CO2 is a greenhouse gas, but since it’s also fairly acidic the net result of carbonate getting into water supplies is likely to be quite negative for anything which likes living in ponds or rivers.
Although it’s great that we now have a potentially efficient method for producing lots of useful hydrogen, one final question springs to mind. Since this process requires electricity to split the urea molecules apart, wouldn’t it be more efficient to just use the electricity as the power source straightaway? For this reason it seems unlikely that Botte’s brilliant academic discovery will ever become more than that. If in 10 years time we all have our own hydrogen producing cells collecting gas for us to put in our cars, I’ll eat my lab coat.
 B. Boggs, R. King and G. Botte, Chem. Comm., 2009, 4859 – 4861. Check out a freely available .pdf of the original paper here.
 The research was also reported on in a recent RSC press release.