June 22nd, 2011
Econintersect: Hydrogen gas is one of the cleanest sources of energy. It can be burned (oxidized) to produce water and thermal energy or it can be combined with oxygen in an electrochemical cell (commonly called a fuel cell) to produce water and electricity. The long standing problem is that hydrogen requires electricity for production so the entire cycle (water + electricity ---> hydrogen + oxygen and the reversal - hydrogen + oxygen ---> electricity) doesn't gain any energy. In fact, because all natural processes are less than 100% efficient, we always get less electricity back than we put in. Follow up:
Follow up:The only way that hydrogen production makes sense is when it is produced with energy that would otherwise be unused (wasted). Some of the sources that have been suggested are surplus output from wind and solar generators during time period when production exceeds the demand from the grid. Hydrogen becomes one of the means of storing the excess energy. Other methods include traditional batteries and pumped hydro storage, among others.
A stumbling block for using solar power to generate hydrogen has been the short life of electrode materials used in the cell that uses the electricity generated in the solar cell to electrolyze water into hydrogen and oxygen. The most abundant material for efficient electrodes are made of silicon, the same material used in the solar cells that genrate the electricity.
A long recognized highly efficient system involves integrating the solar cell and the hydrogen electrode in the same physical structure. The problem eith that idea? Silicon electrode are almost immediately corroded and fail as soon as the process starts.
Materials science engineer Paul McIntyre and chemist Christopher Chidsey at Stanford University have invented a solution. They have found that if the silicon in coated with an ultra-thin coating of titanium dioxide, the solar cell still operates with high efficiency (the coating is transparent) and the electrode producing hydrogen is protected from corrosion.
An additional invention has been incorporated as well. The addition of an ultra-thin layer of iridium creates a catalyst and the generator now produces hydrogen at a much higher rate than previous silicon electrode systems.
The new structure is still in early stage evaluation. According to a report in RD Magazine, tests so far have extended only to eight hours duration. No degradation of performance has been seen. This indicates the new electrodes are at least 16 times better than plain silicon electrodes which all failed in less than 30 minutes.
Note: There are also processes that generate hydrogen from methane and other hydrocarbons including oil and coal. The loss of energy in producing the hydrogen and then converting it to water also exists in the hydrocarbon cycle as well. The cycle from water to water has long been considered the most ideal system with the least environmental impact.