Ultrathin Pt Nanowire Network Monolayer for Oxygen Reduction Reaction
Authors: Liu Yang , Zhu Enbo , Huang Jin , Zhang Ao , Huang Yu 
Published: December 2024

Owing to a rising energy demand with the increasing population and development of society, hydrogen fuel cells have attracted considerable attention in electrochemistry research. Compared with the hydrogen oxidation reaction at the anode, the oxygen reduction reaction (ORR) at the cathode exhibits more sluggish kinetics due to its multielectron, multistep reaction mechanism, which is the critical limiting step in hydrogen fuel cells. Therefore, developing catalysts with excellent performance for ORR is essential for developing hydrogen fuel cells. Pt nanomaterials represent the most widely explored ORR electrocatalysts for their high catalytic activities and stabilities in ORR.

The morphology and surface structures of nanocatalysts are critical determinants of their catalytic performance, with both factors profoundly influenced by anisotropy. One-dimensional (1-D) and 2-D anisotropic Pt nanostructures demonstrate enhanced catalytic activity, due to structural anisotropy and larger surface area accessible for catalytic reactions. Owing to their high anisotropy and surface energy, one-dimensional (1-D) and 2-D anisotropic nanostructures are much more challenging to obtain, especially for the cubic lattice adopted by Pt with high symmetry, which leads to challenges in anisotropic growth from seed during colloidal synthesis. Anisotropic assembly of nanoscale building blocks can be an alternative strategy to synthesize anisotropic nanostructures, which may be guided by biomolecules due to their highly specific surface recognition properties.

Here we report extensive macroscale 2-D platinum (Pt) nanowire network (NWN) sheets by a hierarchical self-assembly process with the assistance of biomolecular ligands. 1-D nanowires with a high density of grain boundaries are formed by the assembly of 1.9 nm 0-D Pt nanocrystals, and the interconnection of these 1-D nanowires forms the Pt NWN sheets with a centimeter-scale monolayer network structure extending into centimeter-scale size. The assembly of Pt nanocrystals occurs at the gas/liquid interfaces of the bubbles produced by sodium borohydride (NaBH4) during the synthesis process. The Pt NWN sheets are released at the gas/liquid surface after the rupture of these bubbles and merge into a centimeter-scale monolayer Pt NWN sheet. It is demonstrated that the monolayer Pt NWN sheet exhibits much-improved performance in oxygen reduction reaction (ORR), with 12.0 times and 21.2 times higher specific and mass activities than those of current state-of-the-art commercial Pt/C electrocatalysts. A 21.3 times greater mass activity than that of Pt/C is also observed in the Pt NWN sheet after 15,000 accelerated durability test cycles. The outstanding enhancement of the activity and stability in ORR can be attributed to the high electrochemical surface area and high density of defects formed during assembly.

In summary, we developed an ultrathin monolayer Pt NWN sheet with abundant grain boundaries from the assembly of Pt nanocrystals with the assistance of biomolecules. The Pt NWN sheet has demonstrated outstanding catalytic activity and stability in ORR.