A Theoretical and Experimental Approach for Correlating Nanoparticle Structure and Electrocatalytic Activity

Abstract

The objective of the research described in this Account is the development of high-throughput computational-based screening methods for discovery of catalyst candidates and subsequent experimental validation using appropriate catalytic nanoparticles. Dendrimer-encapsulated nanoparticles (DENs), which are well-defined 1-2 nm diameter metal nanoparticles, fulfill the role of model electrocatalysts. Effective comparison of theory and experiment requires that the theoretical and experimental models map onto one another perfectly. We use novel synthetic methods, advanced characterization techniques, and density functional theory (DFT) calculations to approach this ideal. For example, well-defined core@shell DENs can be synthesized by electrochemical underpotential deposition (UPD), and the observed deposition potentials can be compared to those calculated by DFT. Theory is also used to learn more about structure than can be determined by analytical characterization alone. For example, density functional theory molecular dynamics (DFT-MD) was used to show that the core@shell configuration of Au@Pt DENs undergoes a surface reconstruction that dramatically affects its electrocatalytic properties. A separate Pd@Pt DENs study also revealed reorganization, in this case a core-shell inversion to a Pt@Pd structure. Understanding these types of structural changes is critical to building correlations between structure and catalytic function. Indeed, the second principal focus of the work described here is correlating structure and catalytic function through the combined use of theory and experiment. For example, the Au@Pt DENs system described earlier is used for the oxygen reduction reaction (ORR) as well as for the electro-oxidation of formic acid. The surface reorganization predicted by theory enhances our understanding of the catalytic measurements. In the case of formic acid oxidation, the deformed nanoparticle structure leads to reduced CO binding energy and therefore improved oxidation activity. The final catalytic study we present is an instance of theory correctly predicting (in advance of the experiments) the structure of an effective DEN electrocatalyst. Specifically, DFT was used to determine the optimal composition of the alloy-core in AuPd@Pt DENs for the ORR. This prediction was subsequently confirmed experimentally. This study highlights the major theme of our research: the progression of using theory to rationalize experimental results to the more advanced goal of using theory to predict catalyst function a priori. We still have a long way to go before theory will be the principal means of catalyst discovery, but this Account begins to shed some light on the path that may lead in that direction.

Less Frustration, More Activity—Theoretical Insights into Frustrated Lewis Pairs for Hydrogenation Catalysis

“…However, in order to make them substantially more efficient, and thereby convert them to viable alternatives to traditionally employed metal based catalysts, adopting a computational investigative approach may be the best strategy. This is because there is considerable literature– on significant improvement in efficiency that was achieved when the second generation of existing catalyst systems had been designed based on computational investigations. The current work represents such an approach, where the hydrogenation catalysis by FLPs has been investigated with full quantum chemical calculations, with density functional theory (DFT).…”

Catalysis by Metallic Nanoparticles in Solution: Thermosensitive Microgels as Nanoreactors

“…From eq. (16) one is thus led to (17) Thus, for a fixed efficiency f, the number Nf depends exponentially on GT. If we assume for example a reasonable set of parameters, namely Di/D0 =0.2, a/R0 = 0.1 and ßGT =0.1.…”

Morphology Control and Electro catalytic Activity towards Oxygen Reduction of Peptide‐Templated Metal Nanomaterials: A Comparison between Au and Pt

“…It is worth pointing out that, such template induced synthetic approach is quite common in nanomaterial synthesis. Crooks and coworkers have devoted tremendous efforts on fabrication of noble metal materials by employing a variety of dendrimers as template , . For instances, Pt nanoparticles encapsulated by fourth generation dendrimer were prepared by Ye et al., and the resulting films were electrocatalytically active for ORR .…”

“…Moreover, to achieve enhanced stability, surface ligands or templates have been extensively employed to protect or stabilize the metal core. Such ligands or templates include thiol molecules, DNA, protein, dendrimer as well as peptide . Peptides are polymeric molecules made of amino acids, with 20 natural amino acid residues, the structure of the peptides can be easily fine tuned and versatile functionalities are endorsed through amino acid residues.…”