Synthetic Strategies to Enhance the Electrocatalytic Properties of Branched Metal Nanoparticles

Abstract

Conspectus Branched metal nanoparticles have unique catalytic properties because of their high surface area with multiple branches arranged in an open 3D structure that can interact with reacting species and tailorable branch surfaces that can maximize the exposure of desired catalytically active crystal facets. These exceptional properties have led to the exploration of the roles of branch structural features ranging from the number and dimensions of branches at the larger scales to the atomic-scale arrangement of atoms on precise crystal facets. The fundamental significance of how larger-scale branch structural features and atomic-scale surface faceting influence and control the catalytic properties has been at the forefront of the design of branched nanoparticles for catalysis. Current synthetic advances have enabled the formation of branched nanoparticles with an unprecedented degree of control over structural features down to the atomic scale, which have unlocked opportunities to make improved nanoparticle catalysts. These catalysts have high surface areas with controlled size and surface facets for achieving exceedingly high activity and stability. The synthetic advancement has recently led to the use of branched nanoparticles as ideal substrates that can be decorated with a second active metal in the form of islands and single atoms. These decorated branched nanoparticles have new and highly effective catalytic active sites where both branch metal and decorating metal play essential roles during catalysis. In the opening half of this Account, we critically assess the important structural features of branched nanoparticles that control catalytic properties. We first discuss the role of branch dimensions and the number of branches that can improve the surface area but can also trap gas bubbles. We then investigate the atomic-scale structural features of exposed surface facets, which are critical for enhancing catalytic activity and stability. Well-defined branched nanoparticles have led to a fundamental understanding of how the branch structural features influence the catalytic activity and stability, which we highlight for the oxygen evolution reaction (OER) and biomass oxidation. In discussing recent breakthroughs for branched nanoparticles, we explore the opportunities created by decorated branched nanoparticles and the unique bifunctional active sites that are exposed on the branched nanoparticle surfaces. This class of catalysts is of rapidly growing importance for reactions including the hydrogen evolution reaction (HER) and methanol oxidation reaction (MOR), where two exposed metals are required for efficient catalysis. In the second half of this Account, we explore recent advances in the synthesis of branched nanoparticles and highlight the cubic-core hexagonal-branch growth mechanism that has achieved excellent control of all of the important structural features, including branch dimensions, number of branches, and surface facets. We discuss the slow precursor reduction as an effective strategy for ...

Two-Dimensional Nanomaterial-Templated Composites

“…, lattice parameters, dimensionalities, etc .) of both the 2D nanomaterial templates and the secondary nanomaterials, facet-selective growth can be achieved toward the synthesis of novel composites with well-defined structures …”

Synthesis of hierarchical metal nanostructures with high electrocatalytic surface areas

“…There is an important opportunity for such 3D nanostructures because they have the ideal properties for electrocatalytic support materials. First, the nanoscale dimensions create high surface areas, which ensures high exposure of the active catalyst to the reactants (10)(11)(12)(13). Second, the directly connected metal components create a highly conductive material for efficient electron transfer between the catalysts and the electrode (14).…”

“…The formation of branched nanoparticles with two connected components is well known. For example, our group has shown that well-defined branches with dimensions on the tens of nanometers can be grown by carefully selecting a core material that adopts a face-centered cubic (fcc) structure, such as Pd or Au, and a branch material that adopts a hexagonal close-packed (hcp) structure, such as Ru, Co, or Ni (13,(16)(17)(18)(19)(20). In these papers, the hcp branches preferentially grow along the c axis of the crystal structure to form elongated branches directly off the fcc cores.…”

Introducing Stacking Faults into Three-Dimensional Branched Nickel Nanoparticles for Improved Catalytic Activity

“…By tilting, the number of branches was counted from over 100 nanoparticles, giving an average of eight branches per particle (Figure S4c, SI). Such a 3D structure ensures large surface areas and high exposure of active sites for effective catalysis …”

“…Such a 3D structure ensures large surface areas and high exposure of active sites for effective catalysis. 15 The TEM results show that the number of branches and branch length are relatively uniform across all samples, being seven to eight branches per nanoparticle and branch lengths between 250 and 300 nm (Figures 2 and S4, SI). The width of the branch changes as the Au core size increases.…”