Deciphering the linear relationship in the activity of the oxygen reduction reaction on Pt electrodes:A decisive role of adsorbates

Despite substantial efforts in developing high-performance catalysts for the oxygen reduction reaction(ORR),the persistent challenge lies in the high onset overpotential of the ORR,and the effect of the elec-trolyte solution cannot be ignored.Consequently,we have systematically investigated the impact of adsorbate species and concentration,as well as solution pH,on the ORR activity on Pt(111)and Pt(poly)electrodes.The results all tend to establish a linear quantitative relationship between the onset potential for ORR and the adsorption equilibrium potential of the adsorbate.This finding indicates the decisive role of adsorbates in the onset potential for ORR,suggesting that the adsorption potential of adsorbates can serve as an intuitive criterion for ORR activity.Additional support for this conclusion is derived from experimental results obtained from the oxygen evolution reaction on Pt(poly)with different adsorbate species and from the hydrogen evolution reaction on Pt(111)with iodine adsorption.We further propose both an empirical equation for the onset potential for ORR and the concept of a potential-regulated adsor-bate shielding effect to elucidate the influence of adsorbates on ORR activity.This study provides new insights into the high onset overpotential of the ORR and offers potential strategies for predicting and enhancingORRactivity inthefuture.

The anodic dissolution kinetics of Mg alloys in water based on ab initio molecular dynamics simulations

The corrosion susceptibility of magnesium(Mg)alloys presents a significant challenge for their broad application.Although there have been extensive experimental and theoretical investigations,the corrosion mechanisms of Mg alloys are still unclear,especially the anodic dissolution process.Here,a thorough theoretical investigation based on ab initio molecular dynamics and metadynamics simulations has been conducted to clarify the underlying corrosion mechanism of Mg anode and propose effective strategies for enhancing corrosion resistance.Through comprehensive analyses of interfacial structures and equilibrium potentials for Mg(0001)/H_(2)O interface models with different water thicknesses,the Mg(0001)/72 H_(2)O model is identified to be reasonable with−2.17 V vs.standard hydrogen electrode equi-librium potential.In addition,utilizing metadynamics,the free energy barrier for Mg dissolution is calculated to be 0.835 eV,enabling the theoretical determination of anodic polarization curves for pure Mg that aligns well with experimental data.Based on the Mg(0001)/72 H_(2)O model,we further explore the effects of various alloying elements on anodic corrosion resistance,among which Al and Mn alloying elements are found to enhance corrosion resistance of Mg.This study provides valuable atomic-scale insights into the corrosion mechanism of magnesium alloys,offering theoretical guidance for developing novel corrosion-resistant Mg alloys.

Origin of symmetry breaking in the seed-mediated growth of bi-metal nano-heterostructures

Seed-mediated growth is the most general way to controllably synthesize bimetal nano-heterostructures. Despite successful instances through trial and error were reported, the way for second metal depositing on the seed. namely whether the symmetry of resulted nano-heterostructure follows the original crystal symmetry of seed metal, remains an unpredictable issue to date. In this work, we propose that the ther- modynamic factor, i.e., the difference of equilibrium electrochemical potentials （corresponding to their Fermi levels） of two metals in the growth solution, plays a key role for the symmetry breaking of bimetal nano-heterostructures during the seed-mediated growth. As a proof-of-principle experiment, by revers- ing the relative position of Fermi levels of the Pd nanocube seeds and the second metal Au with changing the concentration of reductant （L-ascorbic acid） in the growth solution, the structure of as-prepared prod- ucts successfully evolved from centrosymmetric Pd@Au core-shell trisoctabedra to asymmetric Pd-Au hetero-dimers. The idea was further demonstrated by the growth of Ag on the Pd seeds. The present work intends to reveal the origin of symmetry breaking in the seed-mediated growth of nano-heterostructures from the viewpoint of thermodynamics, and these new insights will in turn help to achieve rational con- struction of bimetal nano-heterostructures with soecific functions.