The Energy Control Thin Film Group of the Materials Research Institute for Sustainable Development at Japan's National Institute of Advanced Industrial Science and Technology (AIST), which is based in Nagoya City, Japan, developed a technology to switch a transparent glass to a mirror by using a gaschromic (GC) technology and exhibited it at nanotech 2013.
GC technologies does not use electricity but use gas to control the optical properties of a material. This time, Mg-Ca, which is an alloy of magnesium (Mg) and calcium (Ca), and palladium (Pd), which functions as a catalyst for Mg-Ca, were put between two glass plates.
At this point, it reflects light like a mirror. But when H2 is added to it, Mg absorbs H2 and becomes MgH2, making the glass transparent. On the other hand, when O2 in the air is added to the glass, it takes H2 from MgH2 and becomes H2O, making the glass reflect light like a mirror.
The group had long been engaged in the research of this technology by using a double glass having a wide gap and a hydrogen cylinder for supplying H2. However, from the viewpoints of practicality and safety, it is not an option to use a hydrogen cylinder.
H2 supplied from moisture in air
The group realized that there was a gap of about 0.1mm between the two glass plates without inserting a spacer between them about a year ago. With that gap, the required amount of H2 is small.
Therefore, the group decided to obtain H2 by electrolyzing moisture in the air and confirmed that it was possible to switch between the mirror and transparent states by using this method. As a result, the state of the glass can be electrically switched as if an EC technology is used. Also the thickness of the double glass was drastically reduced, increasing the chance of commercialization.
However, when H2 is supplied by electrolyzing moisture in the air, it takes time to switch the state of the glass (about one minute from the mirror state to the transparent state and about five minutes from the transparent state to the mirror state). When H2 is supplied by using a hydrogen cylinder, it takes only 5-20 seconds to switch the state of the glass, AIST said.