Rice University researchers have been experimenting with layers of graphene separated by nanotube pillars of boron nitride. This construct appears to be the most suitable material to store hydrogen fuel in cars. The prototype meets U.S. Department of Energy standards for storage materials designed to make hydrogen vehicles efficient and practical. Cars running on hydrogen are part of the ‘green energy’ solutions being put forward by scientists and policy makers.
The research was led by Dr. Rouzbeh Shahsavari and is based on a computer model. By running multiple computations, Dr. Shahsavari found that pillared graphene structures are very resilient; by adding boron nitride nanotubes to the equation, this provided strong three-dimensional architecture. Based on the computer predictions, a working model was constructed.
Graphene is a one atom thick form of graphite. The material has several useful properties relating to strength, flexibility and conductivity (it conducts electricity at room temperature like a superconductor at near-absolute zero).
With the new construct the use of pillars provide spaces for hydrogen atoms. Efficiency is boosted by capturing hydrogen atoms and holding them between the pillar spaces. A vehicle engine would then use the trapped hydrogen as required. The use of pillared boron nitride graphene provides a surface area of 2,547 square meters per gram. The material should be able to withstand 1,500 charge-discharge cycles.
The hydrogen is retained, chemically due to weak van der Waals forces (attraction and repulsions between atoms, molecules, and surfaces). In addition to being fuel efficient, the new material is also recyclable.
Further trials are underway to boost the efficiency still further. This involves adding oxygen or lithium, which could boost the hydrogen binding capabilities of the pillar structures. Indications are oxygen-doped boron nitride graphene could capture and retain 11.6 percent of its weight in hydrogen, resulting in an overall capacity of 60 grams per liter. This is at ambient temperature.
Dr. Shahsavari explains in a research note: “Adding oxygen to the substrate gives us good bonding because of the nature of the charges and their interactions”, adding “oxygen and hydrogen are known to have good chemical affinity.”
The findings are published in the American Chemical Society journal Langmuir. The research is titled “Oxygen and Lithium Doped Hybrid Boron-Nitride/Carbon Networks for Hydrogen Storage.”
