Increasing the Formation of Active Sites on Highly Crystalline Co Branched Nanoparticles for Improved Oxygen Evolution Reaction Electrocatalysis

Abstract

The electrocatalysis of the oxygen evolution reaction (OER) at the surface of oxidized metal electrocatalysts is highly dependent on the structure and composition of the surface oxide. Here, Au core‐ Co branched nanoparticles were synthesized using a cubic‐core hexagonal‐branch growth approach in a slow reductive solution synthesis, resulting in highly crystalline metallic hcp Co branches. Electrochemical surface oxidation of the Co branched nanoparticles resulted in formation of Co(OH)2 that enable the formation of a higher number of active sites under OER conditions compared to Co3O4. Differently from polycrystalline spherical Au−Co core‐shell nanoparticles, the oxidized structure on the Co branched nanoparticle surface is retained with electrochemical cycling, resulting in improved OER activity and stability.

Synthesis of hierarchical metal nanostructures with high electrocatalytic surface areas

“…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.…”

Synthetic Strategies to Enhance the Electrocatalytic Properties of Branched Metal Nanoparticles

“…By deliberately choosing a branch metal that preferentially adopts an hcp structure, such as Ru and Co, and a core that is an fcc metal, bimetallic branched nanoparticles can be synthesized. The versatility of this method has been demonstrated by the well-defined branched nanoparticles formed with different bimetallic combinations, such as Pd-core Ru-branch, , Au-core Ru-branch, Au-core Ni-branch, and Au-core Co-branch, as shown in Figure b–e.…”

“…By deliberately choosing a branch metal that preferentially adopts an hcp structure, such as Ru and Co, and a core that is an fcc metal, bimetallic branched nanoparticles can be synthesized. The versatility of this method has been demonstrated by the well-defined branched nanoparticles formed with different bimetallic combinations, such as Pdcore Ru-branch, 1,24 Au-core Ru-branch, 13 Au-core Ni-branch, 3 and Au-core Co-branch, 40 as shown in Figure 3b−e. Cubic-core hexagonal-branch growth enables catalytically important branched nanoparticle structures to be accessed by hcp materials for the first time, where this was previously dominated by fcc metals.…”

Electrocatalytic activity and surface oxide reconstruction of bimetallic iron–cobalt nanocarbide electrocatalysts for the oxygen evolution reaction

“…Nanoparticle electrocatalysts have attracted considerable interest for the replacement of bulk noble metal oxide catalysts due to their increased surface area to volume ratio, exposure of more active sites to reduce the amount of material needed to undergo reactions like the OER, [12][13][14] and offering a high degree of physical and chemical property tunability for the modulation of catalytic performance. 15,16 In particular, earth-abundant transition metal (TM)-based nanocatalysts have been reported to have comparable electrochemical performance to noble metal-based catalysts.…”