Theoretical Investigation of the Oxygen Reduction Reaction over Platinum Catalysts Supported by Multi‐Edged Vertically Aligned Carbon Nanofiber for Electrocatalyst Preparation

Abstract

Vertically aligned carbon nanofibers (VACNFs) are promising supports for oxygen reduction reaction (ORR) electrocatalysts in fuel cells. Although experimentally these catalytic systems have shown great potential, there is lack of molecular understanding of the catalytic sites and reaction mechanisms. This work investigated the origin of the ORR reactivities of the platinum catalysts on multi‐edged VACNFs (Pt/VACNF) using a multiscale modeling approach combining Density Functional Theory (DFT) and classical Molecular Dynamics (MD) simulations. Based on the ReaxFF potential, all nanoscale Pt particles (Pt55, P100, and Pt147) are stabilized by the open edges located axially along the VACNF walls. The calculated first‐shell coordination numbers, CN ${CN}$ , of surface Pt atoms are 6.63, 7.27, and 7.85, respectively, suggesting that the percentage of low coordination sites increases as the particle size decreases. The adsorption energies of OOH, O, and OH on Pt55 were systematically probed using DFT calculations. These adsorption energies retain a linear correlation against the generalized coordination numbers ( CN‾ ${\overline{CN}}$ ). For Pt nanoparticles supported on VACNF, we found that the OOH and OH bind stronger than on Pt (111) by 0.14 and 0.17 eV, respectively, which can hinder the ORR activity with lower limiting potential than Pt (111). Our theoretical prediction is in good agreement with the linear sweeping voltammetry that revealed a left shift of the half‐wave potential.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

“…According to as-developed CN theories, a negative relation between CN and corresponding adsorption strength is commonly found in diverse catalyst systems with multiple adsorbates. Generally, the active sites with higher CN tend to have stronger detaching ability of overbinding intermediates and thus exhibiting more superior ORR catalysis. ,− Many relevant concepts, like generalized coordination number − and orbitalwise coordination number, have emerged to help lucubrate the mechanism how a coordination environment affects the shape of d -band and the position of d -band center or how it jumps out of the classic d -band theory to influence adsorption energy directly.…”

Introduction of Surface Modifiers on the Pt-Based Electrocatalysts to Promote the Oxygen Reduction Reaction Process

“…With the participation of O 2 , H + , and metal atoms in ORR process, the adsorption/desorption of oxygen-containing species (O ad , OOH ad , OH ad ) and the formation of H 2 O molecules on the surfaces of Pt-based nanoparticles (NPs) indicate that the ORR process is extremely sensitive to the surface properties of electrocatalysts [21][22][23][24]. Surface engineering is regarded as a reasonable way to enhance the catalytic performance, which introduces foreign species (such as carbon, silicon, organic compounds and ionic liquids) to modify the reaction interfaces of surface Pt atoms [25][26][27][28][29].…”