Hydrogen economics: Formative times

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  • Published: Jun 15, 2016
  • Author: David Bradley
  • Channels: NMR Knowledge Base
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Hydrogen can be released efficiently from liquid formic acid for use in fuel-cell powered vehicles. Proof of principle utilised nuclear magnetic resonance (NMR) spectroscopy to follow the catalytic chemistry involved in the process.

Hydrogen can be released efficiently from liquid formic acid for use in fuel-cell powered vehicles. Proof of principle utilised nuclear magnetic resonance (NMR) spectroscopy to follow the catalytic chemistry involved in the process.

Researchers have never considered formic acid as a viable source of hydrogen as fuel for fuel cells because it needs to be heated to such a high temperature to cause decomposition and in so-doing generates by-products. However, as with many chemical processes a catalyst to lower the activation energy often means a reaction can occur at a useful rate without heat. Now, Richard O'Hair of the University of Melbourne, Australia, and an international team of collaborators have developed a molecular catalyst that causes formic acid to release hydrogen and carbon dioxide gases at a relatively low temperature of just 70 degrees Celsius and no other waste products.

O'Hair, working with Philippe Dugourd of the University of Lyon, France, Philippe Maitre of the University of Paris South, France, Vlasta Bonačić-Koutecký at the Humboldt-University Berlin, Germany, and Roger Mulder of CSIRO Manufacturing, suggests that this new catalyst represents a new route to the hydrogen economy, given its high selectivity as confirmed by the team's NMR work on the reaction.

Emission control

"One of the grand challenges for chemists today is to develop perfect chemical reactions that proceed with 100 per cent yield and 100 per cent selectivity without forming any waste products," O'Hair explains. "With formic acid, the aim was to transform it into hydrogen and carbon dioxide, which could really lend itself to the important practical applications of hydrogen energy in the transport sector."

The team originally used a suite of mass spectrometry based techniques and density functional theoy (DFT) calculations to examine gas-phase reactions of a series of silver complexes and examined their reactions with formic acid until they had identified the right catalyst to manipulate a strict degradation of formic acid that released only hydrogen and carbon dioxide. While the study successfully produces hydrogen and CO2, the ultimate aim of future research will be to ensure any derivative source of hydrogen produces zero emissions.

Refuelling the automotive industry

Athanasios Zavras, O'Hair's graduate student on the study and first author, explains how having the initial gas-phase results validated using NMR was an exciting moment in the study. He prepared solutions containing well-defined amounts of each silver complex and tracked progress with incremental increases in the reaction temperature from 25 degrees Celsius upwards. "There was no reaction for a while, but we persevered and at 70 degrees Celsius, we unequivocally identified the production of hydrogen gas and carbon dioxide. It was an extremely exciting moment."

The emergence of hydrogen-powered vehicles is currently hindered by the safety and storage aspects of containing and carrying the gas. But, liquid sources, such as formic acid, could be used in a future refuelling infrastructure not dissimilar to today's petroleum-based fuel supplies.

O'Hair concedes that while the new catalyst design is an important step forward in addressing our hydrogen energy needs, there are still many barriers to overcome, such as the fact that carbon dioxide is a by-product. There would need to be a way to trap this gas and perhaps regenerate formic acid from it as sustainable feedstock for the fuel supply. The research, published in the journal Nature Communications was funded by the Australian Research Council.

"A key concept that we have introduced in this work is that fundamental gas-phase studies can be used to direct the search for new types of metal complexes that promote related reactivity in solution," O'Hair told SpectroscopyNOW. "In our work we started with the idea of using silver hydride as a catalyst, and through several iterations we found the right combination of ligand to switch on the desired reaction. Thus a second key concept from our study is that ligands can have a vital role in reshaping the scaffold of a metal cluster to activate its reactivity towards a substrate (in this case formic acid)." He adds that the researchers are "excited about applying both of these concepts to other types of substrates and are currently working on inventing a new class of reactions for organic synthesis."

Related Links

Nature Commun 2016, 7, 11746: "Ligand-induced substrate steering and reshaping of [Ag2(H)] scaffold for selective CO2 extrusion from formic acid"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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