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We develop a computationally efficient scheme to determine the potentials of zero charge (PZC) of metal-water interfaces with respect to the standard hydrogen electrode. We calculate the PZC of Pt(111), Au(111), Pd(111) and Ag(111) at a good accuracy using this scheme. Moreover, we find that the interface dipole potentials are almost entirely caused by charge transfer from water to the surfaces, the magnitude of which depends on the bonding strength between water and the metals, while water orientation hardly contributes at the PZC conditions. DOI: 10.1103/PhysRevLett.119.016801 Metal-water interfaces are of great technological importance in many energy storage and conversion devices such as fuel cells and batteries. Fundamentally, they are the primary subjects for studying electrochemical processes (i.e., electrocatalysis and corrosion) in electrochemistry and play a crucial role in the development of electric double layer (EDL) theories (i.e., Gouy-Chapman-Stern model). Direct probing of structures and dynamics of the interfaces at a molecular level is extremely challenging for experiment. First principles simulations, on the other hand, can offer detailed microscopic information on the interfaces. However, due to high computational costs, it was not long ago that ab initio modeling of metal-water interfaces became affordable [1,2].Potential of zero charge (PZC) is a fundamental concept in the EDL theories, defined as the potential at which no excess charge exists on metal surfaces, and deviation from the PZC will lead to attraction of counterions to the surfaces, building up the EDL [3]. Because of its significance to the microscopic understanding of an EDL and interfacial potentials, numerous experimental techniques have been developed to determine the PZC of metal electrodes, e.g., surface tension methods, capacitance measurement methods, CO charge-displacement methods, etc [4]. Despite repeated efforts, many measurements are still subject to uncertainties because of difficulties in preparing single crystal electrodes and excluding specific adsorption of electrolyte ions [5][6][7]. In the presence of specific adsorption, electrochemists distinguish the subtlety between the potential of zero total charge (PZTC) and the potential of zero free charge (PZFC), and only the latter is an intrinsic property of metal electrodes [8].First principles calculation of well-defined metal surfaces is ideal for determining the PZFC. There are two issues in computational methods. First, how is the solvent treated in the simulation models? In the literature, water has often been treated with either an implicit dielectric continuum [9][10][11] or some representations of static water structures for efficiency [12]. It, however, has been reported that the dynamics of water on surfaces has significant effects on interface potentials [13]. As yet, very few studies have modeled full metal-water interfaces and accounted for water dynamics using density functional theory based molecular dynamics (DFTMD) [14,15]. Second, how are th...

Electrified solid/liquid interfaces are the key to many physicochemical processes in a myriad of areas including electrochemistry and colloid science. With tremendous efforts devoted to this topic, it is unexpected that molecular-level understanding of electric double layers is still lacking. Particularly, it is perplexing why compact Helmholtz layers often show bell-shaped differential capacitances on metal electrodes, as this would suggest a negative capacitance in some layer of interface water. Here, we report state-of-the-art ab initio molecular dynamics simulations of electrified Pt(111)/water interfaces, aiming at unraveling the structure and capacitive behavior of interface water. Our calculation reproduces the bell-shaped differential Helmholtz capacitance and shows that the interface water follows the Frumkin adsorption isotherm when varying the electrode potential, leading to a peculiar negative capacitive response. Our work provides valuable insight into the structure and capacitance of interface water, which can help understand important processes in electrocatalysis and energy storage in supercapacitors.

Oriented external electric fields (OEEFs) offer a unique chance to tune catalytic selectivity by orienting the alignment of the electric field along the axis of the activated bond for a specific chemical reaction; however, they remain a key experimental challenge. Here, we experimentally and theoretically investigated the OEEF-induced selective catalysis in a two-step cascade reaction of the Diels-Alder addition followed by an aromatization process. Characterized by the mechanically controllable break junction (MCBJ) technique in the nanogap and confirmed by nuclear magnetic resonance (NMR) in bottles, OEEFs are found to selectively catalyze the aromatization reaction by one order of magnitude owing to the alignment of the electric field on the reaction axis. Meanwhile, the Diels-Alder reaction remained unchanged since its reaction axis is orthogonal to the electric fields. This orientation-selective catalytic effect of OEEFs reveals that chemical reactions can be selectively manipulated through the elegant alignment between the electric fields and the reaction axis.

Investigating the chemical nature of the adsorbed intermediate species on well-defined Cu single crystal substrates is crucial in understanding many electrocatalytic reactions. Herein, we systematically study the early stages of electrochemical oxidation of Cu(111) and polycrystalline Cu surfaces in different pH electrolytes using in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). On Cu(111), for the first time, we identified surface OH species which convert to chemisorbed “O” before forming Cu2O in alkaline (0.01 M KOH) and neutral (0.1 M Na2SO4) electrolytes; while at the Cu­(poly) surface, we only detected the presence of surface hydroxide. Whereas, in a strongly acidic solution (0.1 M H2SO4), sulfate replaces the hydroxyl/oxy species. This results improves the understanding of the reaction mechanisms of various electrocatalytic reactions.

The study of the oxygen reduction reaction (ORR) at high-index Pt­(hkl) single crystal surfaces has received considerable interest due to their well-ordered, typical atomic structures and superior catalytic activities. However, it is difficult to obtain direct spectral evidence of ORR intermediates during reaction processes, especially at high-index Pt­(hkl) surfaces. Herein, in situ Raman spectroscopy has been employed to investigate ORR processes at high-index Pt­(hkl) surfaces containing the [011̅] crystal zonei.e., Pt(211) and Pt(311). Through control and isotope substitution experiments, in situ spectroscopic evidence of OH and OOH intermediates at Pt(211) and Pt(311) surfaces was successfully obtained. After detailed analysis based on the Raman spectra and theoretical simulation, it was deduced that the difference in adsorption of OOH at high-index surfaces has a significant effect on the ORR activity. This research illuminates and deepens the understanding of the ORR mechanism on high-index Pt­(hkl) surfaces and provides theoretical guidance for the rational design of high activity ORR catalysts.

It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel-cell catalysts. Surface enhanced Raman spectroscopy( SERS) is ap owerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range,h owever,u sing it to probe practical nanocatalysts remains extremely challenging. Herein, shell-isolated nanoparticle-enhanced Raman spectroscopy( SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt 3 Co nanocatalyst structures.D irect spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt 3 Co in both acidic and basic environments.D ensity functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt 3 Co surface accounts for enhanced ORR activity.This work shows SHINERS is ap romising technique for the realtime observation of catalytic processes.

Unraveling the atomistic structures of electric double layers (EDL) at electrified interfaces is of paramount importance for understanding the mechanisms of electrocatalytic reactions and rationally designing electrode materials with better performance. Despite numerous efforts dedicated in the past, a molecular level understanding of the EDL is still lacking. Combining the state-of-the-art ab initio molecular dynamics (AIMD) and recently developed computational standard hydrogen electrode (cSHE) method, it is possible to realistically simulate the EDL under well-defined electrochemical conditions. In this work, we report extensive AIMD calculation of the electrified Pt(111)-H ad /water interfaces at the saturation coverage of adsorbed hydrogen (H ad ) corresponding to the typical hydrogen evolution reaction conditions. We calculate the electrode potentials of a series of EDL models with various surface charge densities using the cSHE method and further obtain the Helmholtz capacitance that agrees with experiment. Furthermore, the AIMD simulations allow for detailed structural analyses of the electrified interfaces, such as the distribution of adsorbate H ad and the structures of interface water and counterions, which can in turn explain the computed dielectric property of interface water. Our calculation provides valuable molecular insight into the electrified interfaces and a solid basis for understanding a variety of electrochemical processes occurring inside the EDL.