Raising Green Hydrogen Extraction Efficiency

The single biggest problem currently with renewable energy is that the sources are not consistent or predictable. A cloudy or windless day and less energy is generated, and the power grid has to be supplemented by other means. Most of these other ways of generating power, such as coal, oil and natural gas are major contributors to climate change. Nuclear power is controversial, and because of that, the time for new nuclear power stations to be built and become operation is extensive. Hydrogen has been proposed as a replacement fuel to cut the generation of greenhouse gases. It has also been suggested as an interim step in the transition to electric vehicles, until the technology for faster charging and the charging infrastructure is in place. Some automotive manufacturers, particularly Toyota have heavily invested in hydrogen as a greener fuel for vehicles. In some cases, such as heavy industrial vehicles and aeroplanes, hydrogen has even been suggested as a more permanent replacement for fossil fuels. However, not all hydrogen is so good for the environment. Hydrogen can be produced in many ways and the current methods of production also tend to produce greenhouse gas emissions.

The UK’s National Grid website has a directory of the different types of hydrogen production ranging from black or brown hydrogen that produces hydrogen from black coal or lignite to green and yellow hydrogen, which have no emissions. The most common form of hydrogen production at the moment is grey hydrogen, where natural gas or methane is used. Ideally all hydrogen would be made through using surplus renewable energy to electrolyse water. These newer technologies, and still being developed.

The University of Michigan has developed a new type of solar panel which is nearly ten times more efficient than the current method of generating green hydrogen, with a conversion rate of 9%. The new solar panel conversion method mimics a step in natural photosynthesis to convert water into hydrogen and oxygen. The new method is expected to cut the cost of sustainable hydrogen by quite a margin. Solar panels have layers of semiconductor materials, which is the most expensive part of the panel. The team from University of Michigan, led by Zetian Mi, U-M professor of electrical and computer engineering, has developed a way of shrinking that semiconductor material by more than 100 times while still being able to withstand the power of concentrated sunlight. The solar panel uses the highest parts of the solar spectrum to split the water, and the lower parts of the spectrum to encourage the reaction. The indium gallium nitride nanostructure-based semiconductor catalyst is grown onto a silicon surface. The design is also unique in that it improves with use.

The high temperatures from the concentrated sunlight quicken the water splitting process, and stop the hydrogen and oxygen recombining. An insulating layer on top of the panel keeps the temperature at 75 ^oC, warm enough to help encourage the reaction while also being cool enough for the semiconductor catalyst to perform well.

The researchers will now attempt to improve the efficiency and to achieve ultrahigh purity hydrogen that can be directly fed into fuel cells.

University of Michigan