A thermodynamic model for calculating the mass action concentrations of structural units in Fe-Si binary melts based on the atom-molecule coexistence theory, i.e., the AMCT-N i model, has been developed and verified through comparing with the reported activities of both Si and Fe in the full composition range of Fe-Si binary melts at temperatures of 1693, 1773, 1873, and 1973

Knowledge of atomistic structures at solid/liquid interfaces is essential to elucidate interfacial processes in chemistry, physics, and materials sciences. The (Ö3´Ö7) structure associated with a pair of sharp reversible current spikes in the cyclic voltammogram on a Au(111) electrode in sulfuric acid solution, represents one of the most classical structures at electrode/electrolyte interfaces. Although more than ten adsorption configurations have been proposed by more than ten groups in the past four decades, the atomistic structure remains ambiguous and is consequently an open problem in electrochemistry and surface science. Herein, by combining high-resolution electrochemical scanning tuning microscopy, electrochemical infrared and Raman spectroscopies, and in particular, the newly developed quantitative computational method for electrochemical infrared and Raman spectra, we unambiguously reveal that the adstructure is Au(111)(Ö3´Ö7)-(SO4•••w2) with a sulfate anion (SO4*) and two structured-water molecules (w2*) in a unit cell, and the crisscrossed [w•••SO4•••w]n and [w•••w•••]n hydrogen-bonding network comprises the symmetric adstructure. We further elucidate that the electrostatic potential energy dictates the proton affinity of sulfate anions, leading to the potential-tuned structural transformations. Our work enlightens the structural details of the inner Helmholtz plane and thus advances our fundamental understanding of the processes at electrochemical interfaces.

The electro-oxidation of p-aminothiophenol (PATP) on gold electrodes has been investigated by means of density functional theory. A combination of thermodynamic calculations and surface Raman and infrared (IR) spectral simulations has allowed us to reveal the electro-oxidation mechanism and reaction products of PATP on gold electrodes in acidic, neutral, and basic solutions. PATP can be first oxidized to the radical cation PATP(NH2 •+) or the neutral radical PATP(NH•) depending on the pH of aqueous solutions, and this is the rate-determining step. The radical cation or neutral radical can then transform to the dimerized products through a radical coupling reaction. In the acidic medium, the radical cation reacts with its resonance hybrid through a N–C4 coupling to form 4′-mercapto-N-phenyl-1,4-quinone diimine (D1), which can further undergo hydrolysis to yield 4′-mercapto-N-phenyl-1,4-quinone monoimine (D2). In the neutral medium, the neutral radical reacts with its resonance hybrid through the N–C2(6) coupling to form 4,4′-dimercapto-N-phenyl-1,2-quinone diimine (D3). In the basic medium, the neutral radical reacts with its resonance structure through the N–N coupling to form 4,4′-di­mercapto­azo­benzene (D4). The adsorbed dimer products exhibit reversible redox properties. The calculated standard electrode potentials of the above four species decrease in the order D3, D1, D2, and D4. Finally, the characteristic bands for the surface Raman and IR spectra of D1 to D4 redox pairs are clearly assigned. This study provides mechanistic insight into the electrochemical reaction properties of PATP on metal electrodes.