(6ay) Computational Catalysis Design for Fuel Synthesis

Karamad, M., Stanford University

Heterogeneous catalysis is currently attracting much attention mainly for energy-conversion purposes. In particular, many future energy transformation processes rely on electro-catalysis. Few important examples are oxygen reduction reaction (ORR), CO electrooxidation and the electrochemical reactions of CO2. With advances in density functional theory (DFT) mean, it is now possible to gain some insight into chemical and electrochemical reactions. Moreover, the extraordinary progress in density functional theory (DFT) calculations provides the possibility of computer-based catalyst design. Different approaches have been developed in understanding catalytic activity and selectivity trends as well as designing new catalysts design criteria[1,2]. Probably scaling relations is one of the most important one that could be used in understanding the trends as well as limitations that are exposed by the scaling relations in catalysts performance[1]. My research is using new strategies to design catalysts that do not follow the existing scaling relations. This approach will be extended to other chemical and electrochemical reactions.  

The electrochemical reactions of CO2 are of interest for the synthesis of chemicals and for approaches to decrease global warming[3]. However, there are two main problems associated to this reaction that need to be addressed[4]:

 1) Lack of the catalysts with high activity toward desired reaction products. Cu is the only metal on which CO is reduced to hydrocarbons in significant amounts, albeit accompanied by a very high overpotential making copper an inefficient catalyst for this reaction. To move ahead, new ways to circumvent the scaling relations is needed. My work will utilize existing theoretical and experimental results to discover new catalysts with improved activity using high-throughput computational screening of different compounds. My focus in the screening will be discovering new compounds that could break the existing scaling relations. In another approach, I seek to find new compounds on which CO2 reduction proceeds through a different mechanism. Therefore, scaling relation limitations will not be imposed[5,6]. This approach will be extended to other reactions.   

2) Lack of catalysts with high selectivity towards desired product: CO2 reduction will be in competition with the hydrogen evolution reaction (HER) at all negative potentials where CO2 reduction occurs, and a key criterion for selective catalysts in CO2 reduction will be comparatively poor HER activity in the presence of CO2. However, no strategy to suppress HER has been proposed. My research will focus on designing new catalysts through changing chemical composition of active sites to suppress HER and thereby promote CO2 reduction. In this approach, I will use new strategies that have not been explored so far. One promising approach is functionalizing and tethering the catalysts to suppress hydrogen evolution reaction and improve the catalytic activity at the same time.

The electrochemical reduction of oxygen to hydrogen peroxide is a particularly promising means for continuous on-site production of hydrogen peroxide[7]. However, it would require active, selective and stable materials to catalyse the reaction. Although progress has been made in this respect, further improvements through the development of new electrocatalysts are needed. In particular, designing non-precious electrocatalysts for direct synthesis of hydrogen peroxide is of paramount importance. Using DFT, my research will seek to design new non-precious catalysts for the electrochemical reduction of oxygen to hydrogen peroxide using my atomic scale understanding of ORR.

[1] Abild-Pedersen, F; Greeley, J; Studt, F., et al. Phys Rev Lett 2007, 99, 016105.

[2] Nørskov, JK.; Abild-Pedersen, F; Studt, F., et al. Proc Natl Acad Sci USA 2011; 108 :937–43.

[3] Gattrell, M.; Gupta, N.; Co, A., J. Electroanal. Chem. 2006, 594, 1– 19.

[4] Peterson, A. A.; Nørskov, JK., J. Phys. Chem. Lett. 2012, 3, 251– 258.

[5] Karamad, M.; Tripkovic, V.; Rossmeisl, J., ACS Catal. 2014, 4, 2268– 2273.

[6] Karamad, M.; Hansen, HA.; Rossmeisl J.; Nørskov, JK., ACS Catal. 2015, 5, 4075–4081.

[7] Siahrostami, S.; Verdaguer-Casadevall, A.; Karamad, M., et al. Nat. Mater. 2013, 12 ( 12) 1137– 1143.