Sustainable solutions to the energy challenge
- Diamond Comms
“Our vision one day is to see such fuel cells commercialised and distributed around Africa and the rest of the world," says Sikhumbuzo Masina, PhD candidate.
[This article is supplied by the START (Synchrotron Techniques for African Research and Technology), a collaborative project between scientists in Africa and the UK working together on research using synchrotron science.]
Globally and locally in Africa, we need sustainable and cost effective solutions to the energy crisis, particularly in the light of climate change, pressures on energy resources and rising energy costs (UN Sustainable Development Goal 7). According to the UN, slightly less than 1 billion people (13% of the global population) are functioning without electricity and 50% of them are found in Sub-Saharan Africa alone.
Our research group in the Molecular Science Institute at the University of the Witwatersrand, South Africa, largely looks at energy materials for alternative energy solutions – from hybrid perovskites (materials that have a potential use in making photovoltaic cells for solar panels which comprise both organic and inorganic constituents) to electroceramics such as fluorite structured material (materials where the metal atoms form a face centred cubic packing, and the non-metals fill in the tetrahedral holes in between the metal ions), to Solid Oxide Fuel Cells, and even some battery anode materials.
This research is supported, in part, by GCRF START through UK-Africa collaborations to find solutions to these global challenges. START helps our group develop expertise in the use of cutting edge synchrotron techniques (through the UK’s synchrotron light source, Diamond) and neutron techniques, in order to characterise energy materials adapted to the needs of the African continent.
Alternative power generation – the case for Solid Oxide Fuel Cells (SOFCs)
SOFCs are electrochemical devices that convert chemical energy directly to electricity without a combustion step. They are highly efficient energy conversion devices, possess fuel flexibility, and demonstrate zero or reduced Carbon dioxide (CO2) emissions when Hydrogen gas (H2) or natural gas are used as fuel respectively.
Achieving efficiencies of close to 80% depending on the power generation mode, SOFCs can be used off-grid which is vital in countries that experience daily power cuts (rolling blackouts or ‘load shedding’), especially in rural areas where access to electricity can be scarce, or even non-existent.SOFCs are versatile – they can be used as an auxiliary, stationary or distributed power sources, which eliminates the need for expensive transmission cables.
In our research, we examine the effect of temperature on the stability, conductivity, thermal expansion and related properties of the materials used in SOFCs. The aim, in the near term, is to design and study the behaviour of materials used in the fuel cells ‘in-situ’, as they operate at various temperatures, in a quest to identify sufficiently stable combinations to allow for further development and ultimately commercialisation (these materials include solid solutions of bismuth oxide, cerium oxide and yttrium oxide).
One such research project is that of Sikhumbuzo Masina, Caren Billing, and Professor David Billing from the Molecular Science Institute at the School of Chemistry, University of the Witwatersrand, South Africa looking at Bi2O3, a potential SOFC electrolyte. Sikhumbuzo describes this research which is the focus of his PhD.
The effects of impurity cations on the average and local structure of Bi2O3, a potential SOFCs electrolyte [1]
My PhD research focuses on studying the effects of impurity cations on the average and local structure of Bi2O3, a potential SOFC electrolyte .This involves adding foreign (impurity) atoms into a material and observing the effect of these atoms on the arrangement of the host atoms and correlating this with the change in physical properties like electric conductivity, as well as thermal expansion and stability.
Bi2O3 in its defect fluorite δ-phase – a certain arrangement of atoms in the fluorite structure where some of the tetrahedral sites are empty (defective) or vacant – is reported to have the highest oxide ion conductivity at 730 °C. However, its local structure has proven inscrutable; it cannot be probed using conventional X-ray diffraction techniques and the four published models have proved inadequate in explaining all our observations and measurements, leaving the fundamental understanding of the real structure property relations of this family of materials as an unresolved enigmatic scientific challenge.
This seemingly insurmountable local structure problem is compounded by the fact that the δ-phase is only stable within a narrow range of 730-824 °C. Substitution of the host atoms by other foreign atoms (Doping) stabilises the δ-phase to room temperature but the oxygen sublattice arrangement undergoes some ordering and degradation of conductivity is observed with long term annealing (Where we heat powder in a furnace at constant temperature for a certain period of time)at temperatures less than 600 °C.
To conjure up solutions to these problems, complimentary local probes such as pair distribution functions (PDFs) and extended X-ray absorption fine structure (EXAFS) techniques are needed to study the local structure in greater detail. These techniques are sensitive to the local environment around a particular atom revealing, for example, the distances and angles between groups of atoms and how they are arranged and vibrate in relation to each other (correlations), hence providing the structure of a material at a more local level.
In our project, we study both the average and local structure (repeat pattern over long distances and local atomic arrangements respectively) of the solid solutions of Bi2O3 which will help elucidate what entails a best fast oxide ion conductor. This will, in turn, help us design solid electrolytes that will enable solid oxide fuel cells to operate at intermediate temperatures (500-800°C) and reduce their capital cost – a current stumbling block to their commercialisation.
Knowledge exchange and collaboration through START Energy Materials Workshops
I attended a very informative START workshop at the University of Cape Town (16-17 Dec 2019) where we heard talks from scientists across the UK and South African Energy Materials community. The workshop was a great platform to build connections with START for future collaborations.
I spoke to Dr Sofia Diaz-Moreno, a Principal Beamline Scientist at Diamond about the options to use the synchrotron to look at the local environment and oxidation states of the metals we are using in our SOFC research at the University of the Witwatersrand.
The workshop also heard from Dr Daniel Bowron, who is the leader of the ISIS Disordered Materials Group. He described the possibility of also applying to ISIS to do neutron-studies on our materials to probe the oxygen environment so that we can understand how the oxygen sublattice would impact these kinds of solid oxide fuel cell devices when used under intermediate temperatures for a very long time.
Footnote:
[1]Sikhumbuzo M. Masina (a), Caren Billing(a), David G. Billing(a,b), (a)Molecular Science Institute, School of Chemistry, University of the Witwatersrand, South Africa; (b) DST-NRF Centre of Excellence in Strong Materials, University of the Witwatersrand, South Africa.
[This article is supplied by GCRF START (Global Challenges Research Fund Synchrotron Techniques for African Research and Technology), a collaborative project between scientists in Africa and the UK working together on research using synchrotron science]