The work has come from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (the Berkeley Lab). The aim of the research is to improve ways for safely storing hydrogen ready for use with fuel cells for vehicles. This comes down to a better understanding of the atomic details of the ultrathin coating put onto nanocrystals. This coating functions as selective shielding; the coating also enhances the performance of hydrogen storage.
The research required the synthesizing and coating of magnesium crystals (tint structures which measure just three nanometers (billionths of a meter) across. This required the application of X-rays and the development of complex computer simulations into order to study how the nanocrystals and the carbon coating (formed from graphene) functioned in synchronicity. The X-ray device used was the Advanced Light Source (a synchrotron). This is one of the world’s brightest sources of ultraviolet and soft X-ray light, a synchrotron light source (which is a source of electromagnetic radiation produced by a storage ring). The device provides multiple and extremely bright sources of intense and coherent short-wavelength light. The computing power came from the supercomputers housed at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC).
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Fuel cells are of great importance for meeting future energy needs, especially in relation to transport in the wake of dwindling (and environmentally polluting) fossil fuels. A fuel cell is a type of electrochemical cell that converts the chemical energy from a fuel into electricity via electrochemical reactions. The reaction is typically with the hydrogen-containing fuel reacting with oxygen.
There are two electrodes in hydrogen fuel cells:
The reaction at the cathode is an oxidation reaction because hydrogen loses electrons, and the reaction at the anode is a reduction reaction because hydrogen ions gain electrons. The overall reaction in the fuel cell is a redox reaction.
A fuel cell differs from a battery in that the fuel cell needs a continuous source of fuel and oxygen in order to sustain the necessary chemical reaction. In contrast, a battery uses chemical energy from chemicals already present in the battery. Theoretically, a fuel cell can produce electricity continuously.
Aside from spacecraft, the main future application of fuel cells is with vehicles, which makes fuel cell development something of interest to vehicle manufacturers and those running large fleets. The use of hydrogen-oxygen fuels cells in vehicles has benefits. This includes zero emissions of carbon dioxide; lower reliance on fossil fuels; and lower ruining costs. Vehicles running from fuel cells are classes of electric vehicle that use a fuel cell, instead of a battery, or in combination with a battery or supercapacitor, to power its on-board electric motor. One of the most common business uses of fuel cell vehicles is forklift trucks used in warehouses.
There are many different types of fuel cells, including polymer electrolyte membrane fuel cells; direct methanol fuel cells; alkaline fuel cells; phosphoric acid fuel cells; molten carbonate fuel cells; solid oxide fuel cells and reversible fuel cells. These fuel cells are classified by the kind of electrolyte they employ. The grouping determines the type of electro-chemical reactions that take place in the cell; other factors include the kind of catalysts required, the temperature range in which the cell operates, and the fuel required.
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The coating used with the new research is reduced graphene oxide (or rGO), which resembles graphene (a one-atom-thin sheet of carbon, which is arrayed in a honeycomb pattern). The rGO carting consists of nanoscale holes that allow hydrogen to pass through while trapping larger molecules at bay. The purpose of the carbon wrapping is to prevent the magnesium from reacting with its environment, which leads to inefficiencies. The resultant layer creates a better solution for trapping more hydrogen.
One of the researchers, Dr. David Prendergast explains to Controlled Environments magazine that the current generation of hydrogen-fueled vehicles power fuel cell engines via compressed hydrogen gas. “This requires bulky, heavy cylindrical tanks that limit the driving efficiency of such cars.” With the new research, Dr Prendergast notes the nanocrystals offer a strong possibility for eliminating such bulky tanks by storing hydrogen within other materials.
Overall the wrapped nanocrystals can chemically absorb pumped-in hydrogen gas at a far higher density than is currently possible using a compressed hydrogen gas fuel tank at the same pressures.
The new research into coatings forms part of the Hydrogen Materials-Advanced Research Consortium (HyMARC) , which was established as part of the Energy Materials Network by the U.S. Department of Energy’s Fuel Cell Technologies Office. The consortium is composed of composed of Sandia National Laboratories, Lawrence Livermore National Laboratory, and Lawrence Berkeley National Laboratory. The HyMARC research activities focus on the thermodynamic and kinetic limitations of storage materials. This area includes mass transport, surface chemistry, and processes at solid-solid interfaces.
A next phase of the research is to use materials that are ideal for real-world hydrogen storage applications. This includes looking at complex metal hydrides, which can also be wrapped in a protective sheet of graphene. These are being considered to boost the hydrogen storage capacity, according to the lead researcher Dr. Liwen Wan.
The research is published in the journal Nano Letters, with the research paper titled “Atomically Thin Interfacial Suboxide Key to Hydrogen Storage Performance Enhancements of Magnesium Nanoparticles Encapsulated in Reduced Graphene Oxide.”
In related graphene news, scientists have devised a simple, sturdy graphene-based hybrid desalination membrane. The device can provide clean water for agriculture and one-day human consumption.
Essential Science
This article is part of Digital Journal’s regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we profiled the work of Austin Russell who is a pioneer in the type of technology that helps cars see. At age 13 Russell pioneered optics and photonics; at 18 he set up the company Luminar, with support from PayPal. Now he is launching an advanced LiDAR system. The week before we investigated the world of telemedicine, weighing up whether it can match face-to-face meetings with medics.
