(371d) Control of Nanoparticle Interfaces for Electrocatalytic Applications

There has been growing interest to drive energy and chemical transformations via the use of renewable electricity to address sustainability challenges. The success of the approach rests on the use of the right materials to efficiently catalyze chemical reactions. Thus, intense efforts have focused on studying nanoparticles as electrocatalysts. However, the scope of such efforts is often limited to studying and correlating with the surface properties of materials, for instance, the surface coordination and the exposed facets of nanoparticles. Electrochemical processes at heterogeneous surfaces are reactions at solid-liquid interfaces; thus, understanding how the solid interacts with the constituents of the liquid phase (i.e., solvent molecules and electrolyte ions) as part of an electrochemical reaction as well as being able to manipulate that interaction in favor of a catalytic reaction is critical.

In this talk, two examples that highlight the importance of controlling the electrochemical interface of nanoparticles will be presented. The first example presents a discovery of a unique nanoparticle interface, that is the Nanoparticle/Ordered-Ligand Interlayer (NOLI). In contrast to a tethered-ligand structure typically considered, the NOLI consists of a nanoparticle surface and a detached ligand layer in the vicinity that creates a gap in between. It exhibits pseudocapacitance by the desolvation of cations at the interlayer. Furthermore, by the synergistic act of the desolvated cation and the negatively charged metal surface, CO₂ activation by noble metal nanoparticles is improved with CO₂-to-CO catalytic turnover enhanced by two orders of magnitude compared to a pristine metal surface and CO selectivity reaching 99%. The fundamental insights of the NOLI could be translated to a more practical configuration where the NOLI-based gas-diffusion electrode achieved nearly unit CO selectivity up to a high current density of 400 mA/cm² in neutral media.

The second example illustrates the need for a closer understanding of the interfacial processes taking place at electrochemically active solid-liquid interfaces. Electrooxidation of biomass-derived polyols have been investigated using platinum nanoparticles as electrocatalysts. Developing ways to harness biomass-derived compounds electrochemically can facilitate the penetration of renewables to the biomass sector whose related advances have been limited. By the continuous alteration of applied potentials, Pt nanoparticles exhibit turnover for polyol (C₃-C₆) oxidation enhanced by more than an order of magnitude as well as an unusual selectivity shift toward secondary alcohol oxidation. It is found that the interaction between the Pt surface and surrounding water eventually leads to its surface oxidation limiting catalytic activity at fixed potentials under steady state. Thus, the continuous switch between oxidative and reductive potentials allows exploiting the short-lived high activity state of Pt nanoparticles otherwise difficult to maintain in typical conditions.

The two works illustrate the complexity of electrochemical interfaces and present novel methods to modulate the interfacial properties of nanoparticles used as catalysts. With the increased awareness of the critical role played by other external factors beyond the surface of materials, a thorough understanding and control of the interface fundamental to electrochemical reactions will greatly advance electrochemistry research and its application for sustainability.