Design and reaction study of noble metal nanocatalysts for selective electrochemical CO${_2}$ reduction

Abstract

Nanostructured materials have numerous applications due to their unique physicochemical properties distinct from their bulk counterparts. Then, the rational, systematic design of nanocatalysts has been the holy grail for this field for achieving extreme activity and selectivity on desired reactions. The advanced synthetic techniques of noble metal nanoparticles hold advantages in careful manipulation of morphology and composition. This aspect of catalyst design draws attention to the electrochemical CO${_2}$ reduction reaction (eCO${_2}$RR). The current needs exist to decrease atmospheric CO${_2}$ levels and increase the sustainability of renewable energy technologies also raises interest in eCO${_2}$RR. Noble metals such as Au and Ag are representative catalysts for eCO${_2}$RR to produce CO, where the efficiency can be further enhanced in the form of nanoparticles with tailored structures. Herein, we utilize a vast and rich library of metal nanoparticles with diverse shapes and elemental compositions to direct surface electronic structures and their chemical nature. We build two strategies for nanocatalyst design, generating high-energy facets by overgrowth and inducing bimetallic composition. These approaches aim to increase the active surface sites and enhance the intrinsic activity, resulting in vastly improved catalytic performances of eCO${_2}$RR.In Chapter 2, Au nanostars formed through a simple overgrowth step brought high selectivity and current per mass for the production of CO. This result was the direct consequence of high-indexed Au surfaces, which effectively stabilized the reaction intermediate for CO${_2}$ reduction. In Chapter 3, a series of Au-Ag alloys nanoparticles were synthesized by galvanic replacement. These alloys presented deduction in overpotentials, unexpected from the linear combination of properties observed in each component. This improvement originated from the cooperative effect of Au and Ag to stabilize the *COOH intermediate. The optimal ratio to maximize the bimetallic Au-Ag interface indicated the importance of elemental composition in nanocatalyst design. These modifications of noble metal nanoparticles are generally applicable to mass-scale fabrication, envisioning the rational design of nanocatalysts for practical applications.