Presenter 1: Julia (Meli) Fischer (PhD, AIBN)
Title: Computational results on Cobalt and Platinum paired single-atom catalysis for the oxygen reduction reaction
Abstract: A single-atom catalyst (SAC) refers to an isolated single metal atom, stabilized in a solid substrate, which functions as an active centre for heterogeneous catalysis. The main advantage is a reduced amount of expensive, rare metals. Paired SAC is the combined effect of two single atoms adjacent to each other. It is widely known, that the best electrochemical catalyst for the oxygen reduction reaction (ORR) is Pt. With the experimental group of Prof. Xiangdong Yao, we have shown that the combination of Co and Pt paired SAC of the ORR outperforms Pt metal catalyst. The distribution of metal distances and their chemical environment was tested. Based on this information, model structures were constructed with density functional theory (DFT). Co and Pt atoms in nitrogen doped graphene with different sized vacancies were used to vary the metal-metal distances. The free energies of intermediate species of the OOR were calculated to determine the mechanism on these systems. Further to compare the results to the experiments, the overpotentials were determined. This potential is the difference in voltage for the reaction to experientially occur and the thermodynamically expected value. Both calculations and experiments conclude to an enhanced activity for the ORR, with a lowered overpotential for a combined CoPt system compared to Pt paired SAC. Further, the charge density differences and the density of states show that the enhancement is due to an increased electron accumulation around Co. Leading to a d-orbital contiguous under the Fermi level.
Presenter 2: Tim McCubbin (PhD, AIBN)
Title: Dynamic metabolic flux analysis of Propionibacterium fermentation of a wild-type and genome-shuffled strain
Abstract: Propionibacteria are naturally high propionate (PA) producers and candidate organisms for the industrial-scale biological production of this carboxylic acid. However, to be competitive with the traditional petrochemical approach a yield of 0.6 g PA/g glucose is required, which surpasses the capabilities of the best natural producing strain, P. acidipropionici 55737. Recently, we developed a strain through genome-shuffling, known as WGS7, which exceeds this yield target by more completely catabolising substrates and reducing the production of by-products. However, the strain is genetically similar to P. acidipropionici 55737 and it is unclear how metabolism has been altered to favour PA production. To gain a deeper understanding of the WGS7 phenotype, metabolic modelling was performed using dynamic metabolic flux analysis (DMFA) to characterise the highly dynamic nature of the propionibacteria fermentation. Mathematical models of metabolism were first formulated for each strain. A series of mathematical approaches were then utilised to reduce the degrees of freedom of these models to zero while maintaining the most accurate representation of the true metabolic network possible, which includes a novel algorithm to perform a robust thermodynamic metabolic flux analysis. DMFA was performed on these final networks and gave new insights into both the native propionibacteria fermentation and underlying cause of the WGS7 phenotype.