Solving Goldilocks’ Dilemma

Solving Goldilocks’ Dilemma

Professor Sean Smith, Dr Xin Tan, Dr Hassan Tahini and Dr Prasenjit Seal at the Integrated Materials Design Centre (IMDC) from the UNSW School of Chemical Engineering are using supercomputers at Australia’s National Computing Infrastructure (NCI) centre to pinpoint the ‘sweet spot’ of new carbon capture and hydrogen storage materials.

Current materials for capturing carbon from power plant exhaust tend to bind COtoo effectively. This causes problems when the carbon needs to be released again for sequestration or recycling.

“If the material binds to CO2 too strongly, which is the basic problem with current materials, then you have to heat them up to a high temperature to pull the COoff, and that costs money,"  explains chief investigator Professor Smith.

“We have the same problem for hydrogen storage materials, which should ideally load up hydrogen quickly at the gas station and then release it on demand for an automobile’s fuel cell – they won’t load quickly if the H2 binding is too weak; but they won’t release on demand if the binding is too strong. It’s a ‘Goldilocks problem’.”

The IMDC team are taking a novel computational approach to the search for new materials. They have identified several materials that adopt stronger binding with CO2 and H2 when exposed to electrical charge. 

CO2 Capture Schematic “Normally, if you put the gas in contact with these materials there is very weak binding. But if you put an electrical charge on the materials, suddenly they bind CO2 and H2  quite effectively,” says Professor Smith. “And if you then remove the charge, the gas is released.”

The result is a material whose binding with the gas can be ‘switched’ on and off by modulating electrical charge, 
side-stepping the expensive heating requirements of current industry materials.

However, these new charge-responsive materials come with a hurdle of their own.

“One of the materials we’re looking at now, for example, is boron nitride, which is a semiconductor with a very large bandgap. That means it takes a lot of voltage to put enough charge on, and there is a cost to that,” says Professor Smith.

“What we’re using NCI to do is search for materials that have a similar capacity to bind CO2 but with a much smaller bandgap – so the cost of charging will be much less.” 

The team is running first principles electronic structure calculations on the NCI’s flagship supercomputer Raijin to work out exactly how each new material interacts with CO2 and with H2, predicting the binding strength and voltage response profile to pinpoint a material with ideally balanced properties.

“These are very numerically intensive calculations, which demands that we have access to a facility such as the NCI’s Raijin” explains Professor Smith.

“There is no other way you can do this work. The market potential of the technology is so huge that if we don’t do it first then another team in another country will. UNSW needs to get there first.”

 

References:
  1. Xin Tan, Liangzhi Kou, Hassan A Tahini, Sean C Smith, “Conductive Graphitic Carbon Nitride as an Ideal Material for Electrocatalytically Switchable CO2 Capture”, Scientific Reports5, 17636 (2015).
  2. Xin Tan, Liangzhi Kou, Hassan A. Tahini, Sean C. Smith, “Charge Modulation in Graphitic Carbon Nitride: An Electrocatalytically Switchable Approach to High-Capacity Hydrogen Storage”,ChemSusChem8, 3626-3631 (2015).

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