Electrocatalytic Activity and Selectivity - a Density Functional Theory Study

Mohammadreza Karamad

Research output: Book/ReportPh.D. thesis

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The focus of the current PhD thesis is to design new electro-catalysts, by changing the morphology and composition of the catalysts, to tune the electro-catalytic performance. We use Density Functional Theory (DFT) calculations, to examine activity, selectivity and stability of the designed electro-catalysts towards two appealing electrochemical reactions: 1)electroreduction of CO2 to hydrocarbons and alcohols, and 2) electrochemical production of hydrogen peroxide, i.e. H2O2, from its elements i.e. H2 and O2. The thesis is divided into three parts: In the first part, electro-catalytic activity of different Pt/Cu(111) systems forming by incorporating some quantities of Cu into first and second layers of Pt(111) including Surface Alloys (SA), Cu Overlayer (OL) and Near Surface Alloy (NSA) is considered. This study shows how the reactivity of Pt(111), i.e. interaction with adsorbates, changes by the location of Cu atoms into different layers of Pt(111). While the presence of Cu into the surface layer strengthens the interaction between surface and adsorbates, the presence of Cu atoms into the subsurface layer has the opposite effect. These findings can be used to design new electro-catalysts for electrochemical reactions. We consider electrochemical oxidation of CO as a test reaction to evaluate the catalytic activity of different Pt/Cu(111) systems, and find unique agreement between experiments and DFT calculations. In the second part, we tackle two associated remarkable problems to the electrochemical reduction of CO2 at the cathode side: 1) high overpotential that hinders this reaction from being an energy efficient process, and 2) low selectivity towards desired reaction products. We have taken two approaches to improve the selectivity and activity in the reduction of CO2. Firstly, we create the isolated sites that are active for CO2 reduction and surrounded by inactive elements towards both hydrogen evolution reaction (HER) and CO2 reduction to direct the selectivity towards favorable products. In the next step, using this concept we screen for suitable catalysts. Our screening includes viii both metallic and functionalized graphene catalysts. Secondly, we considered CO2 reduction on RuO2, which has a distinctive catalytic activity and selectivity compared to Cu to get insight into mechanistic pathway of the CO2 reduction. Finally, in the last part, we have taken advantage of the isolated active site concept to tune the activity and selectivity for oxygen reduction towards H2O2 production. We screen for new catalysts that exhibit both high catalytic activity and selectivity by constructing activity volcano plots for ORR towards water and H2O2. Moreover, the stability of these catalysts is examined. Our model predicts Pt–Hg as a promising catalyst with unprecedented combination of activity, selectivity and stability.
Original languageEnglish
PublisherDepartment of Physics, Technical University of Denmark
Number of pages261
Publication statusPublished - 2013

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