Semi-supervised machine learning approach to select materials for solar thermal application
Dr Julia Melisande Fischer1, Mr Jonathan Perry2,3, Dr Alicia Bayon4, Professor Amanda Barnard5
1CSIRO Data61, Docklands, Australia, 2CSIRO Energy, Newcastle, Australia, 3University of Newcastle, Newcastle, Australia, 4Arizona State University, Tempe, USA, 5 Australian National University, Acton, Australia
Solar thermal hydrogen production is a two-step process. Firstly, a material is heated with sunlight, which removes oxygen from the crystal structure. Secondly, at a lower temperature, hydrogen is produced from water, replenishing the oxygen in the crystal. The chemical space of possible materials, which could cycle these two steps, is endless and mostly unexplored. Additionally, experimental testing is both labour and time-consuming. To address these limitations, we used semi-supervised machine learning to identify novel candidates. Here, the chemical space was restricted to a specific crystal structure called perovskites (ABO₃; A, B metal sites and O oxygen) and the raw materials were chosen to be economically viable and non-toxic. All charge-neutral formulas with up to four different metals on A and B sites were included (350,000 entries). Further, elemental features specific for these perovskites were used. With an extensive literature search, we could identify 84 materials that cycle the reaction and 15 which do not. For additional labels, entries that are in a different crystal structure than perovskite (11576) were also labelled as not cycling. With these inputs, label spreading was used to identify other candidates, which are not intuitive from a chemist’s perspective but close in the data space. In a second step with random forest, the stability in the form of the formation energy was predicted. This resulted in a shorter list of candidate materials that could produce hydrogen, which are currently being experimentally tested.
Meli Fischer is a Postdoctoral-Fellow at CSIRO. She completed her Bachelor and Master of Science in Chemistry at Ulm University, Germany. Afterward, she received an International Postgraduate Scholarship from the University of Queensland and graduated with a Doctor of Philosophy in Chemistry from the Australian Institute of Bioengineering and Nanotechnology.