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We present a scheme to extract the adsorption energy, adsorbate interaction parameter and the saturation coverage from temperature programmed desorption (TPD) experiments. We propose that the coverage dependent adsorption energy can be fit using a functional form including the configurational entropy and linear adsorbate-adsorbate interaction terms. As one example of this scheme, we analyze TPD of CO desorption on Au(211) and Au(310) surfaces. We determine that under atmospheric CO pressure, the steps of both facets adsorb between 0.4-0.9 ML coverage of CO*. We compare this result against energies obtained from five density functionals, RPBE, PBE, PBE-D3, RPBE-D3 and BEEF-vdW. We find that the energies and equilibrium coverages from RPBE-D3 and PBE are closest to the values determined from the TPD.

The production of molecular hydrogen by catalyzing water splitting is central to achieving the decarbonization of sustainable fuels and chemical transformations. In this work, a series of structure-making/breaking cations in the electrolyte were investigated as spectator cations in hydrogen evolution and oxidation reactions (HER/HOR) in the pH range of 1 to 14, whose kinetics was found to be altered by up to 2 orders of magnitude by these cations. The exchange current density of HER/HOR was shown to increase with greater structure-making tendency of cations in the order of Cs+ < Rb+ < K+ < Na+ < Li+, which was accompanied by decreasing reorganization energy from the Marcus-Hush-Chidsey formalism and increasing reaction entropy. Invoking the Born model of reorganization energy and reaction entropy, the static dielectric constant of the electrolyte at the electrified interface was found to be significantly lower than that of bulk, decreasing with the structure-making tendency of cations at the negatively charged Pt surface. The physical origin of cation-dependent HER/HOR kinetics can be rationalized by an increase in concentration of cations on the negatively charged Pt surface, altering the interfacial water structure and the H-bonding network, which is supported by classical molecular dynamics simulation and surface-enhanced infrared absorption spectroscopy. This work highlights immense opportunities to control the reaction rates by tuning interfacial structures of cation and solvents.

© 2018 American Chemical Society. The CO2 electroreduction reaction (CO2RR) is a promising avenue to convert greenhouse gases into high-value fuels and chemicals, in addition to being an attractive method for storing intermittent renewable energy. Although polycrystalline Cu surfaces have long been known to be unique in their capabilities of catalyzing the conversion of CO2 to higher-order C1 and C2 fuels, such as hydrocarbons (CH4, C2H4, etc.) and alcohols (CH3OH, C2H5OH), product selectivity remains a challenge. Rational design of more selective catalysts would greatly benefit from a mechanistic understanding of the complex, multiproton, and multielectron conversion of CO2. In this study, we select three metal catalysts (Pt, Au, Cu) and apply in situ surface enhanced infrared absorption spectroscopy (SEIRAS) and ambient-pressure X-ray photoelectron spectroscopy (APXPS), coupled to density-functional theory (DFT) calculations, to get insight into the reaction pathway for the CO2RR. We present a comprehensive reaction mechanism for the CO2RR and show that the preferential reaction pathway can be rationalized in terms of metal-carbon (M-C) and metal-oxygen (M-O) affinity. We show that the final products are determined by the configuration of the initial intermediates, C-bound and O-bound, which can be obtained from CO2 and (H)CO3, respectively. C1 hydrocarbons are produced via OCH3,ad intermediates obtained from O-bound CO3,ad and require a catalyst with relatively high affinity for O-bound intermediates. Additionally, C2 hydrocarbon formation is suggested to result from the C-C coupling between C-bound COad and (H)COad, which requires an optimal affinity for the C-bound species, so that (H)COad can be further reduced without poisoning the catalyst surface. It is suggested that the formation of C1 alcohols (CH3OH) is the most challenging process to optimize, as stabilization of the O-bound species would both accelerate the formation of key intermediates (OCH3,ad) but

We present a joint theoretical-experimental study of CO coverage and facet selectivity on Au under electrochemical conditions. With in situ attenuated total reflection surface-enhanced IR spectroscopy, we investigate the CO binding in an electrochemical environment. At 0.2 V versus SHE, we detect a CO band that disappears upon facet-selective partial Pb underpotential deposition (UPD), suggesting that Pb blocks certain CO adsorption sites. With Pb UPD on single crystals and theoretical surface Pourbaix analysis, we eliminate (111) terraces as a possible adsorption site of CO. Ab initio molecular dynamics simulations of explicit water on the Au surface show the adsorption of CO on (211) steps to be significantly weakened relative to the (100) terrace due to competitive water adsorption. This result suggests that CO is more likely to bind to the (100) terrace than (211) steps in an electrochemical environment, even though Au steps under gas-phase conditions bind CO∗ more strongly. The competition between water and CO adsorption can result in different binding sites for CO∗ on Au in the gas phase and electrochemical environments.

Understanding and controlling the (electro) chemical reactions between positive electrodes and electrolytes is essential to enhance the cycle life and safety of Li-ion batteries. Previous computational and experimental studies have shown that greater capacity loss of LiNixMnyCo1-x-yO2 (NMC) with increased Ni content can be attributed to the enhanced chemical oxidation of carbonate solvents by dehydrogenation and increased salt decomposition. In this study, we examine the role of a diphenyl carbonate (DPC) additive on the interfacial reactivity of LiNi1/3Mn1/3Co1/3O2, LiNi0.6Mn0.2Co0.2O2, LiNi0.8Mn0.1Co0.1O2 (NMC111, NMC622 and NMC811). Diffuse reflectance infrared Fourier Transform (DRIFT) spectroscopy on NMCs showed that adding DPC in the electrolyte suppressed signals associated with dehydrogenation of ethylene carbonate (EC) from LiNi1/3Mn1/3Ni1/3O2 to LiNi0.8Mn0.1Ni0.1O2 (NMC111 to NMC811). In addition, having DPC in the electrolyte was accompanied with less PF6- salt anion decomposition to form less-fluorine coordinated species such as lithium nickel oxyfluorides or PF3O-like species as revealed by combined infrared spectroscopy and X-ray Photoelectron Spectroscopy (XPS) for Ni-rich NMCs. Such observations are in agreement with previous work showing that DPC can increase the cycling performance of NMC811. The reduced reactivity between NMC such as NMC811 and electrolyte with DPC can be attributed to the formation of surface reaction products from the electrochemical oxidation of DPC occurring at lower voltages compared to the chemical oxidative dehydrogenation of carbonates. This hypothesis is supported by in situ infrared spectroscopy measurements, which revealed electrochemical oxidation of diphenyl carbonate upon charging at 3.9 VLi, accompanied by the detection of a feature around 1824 cm-1 attributed to organic oxidation products adsorbed on the oxide surface, and a stable electrode/electrolyte interface on NMC811 at higher voltages.

Understanding (electro-)chemical reactions at the electrode–electrolyte interface (EEI) is crucial to promote the cycle life of lithium-ion batteries. In this study, we developed an in situ Fourier-transform infrared spectroscopy (FT-IR) method, which provided unprecedented information on the oxidation of carbonate solvents via dehydrogenation on LiNixMnyCo1−x−yO2 (NMC). While ethylene carbonate (EC) was stable against oxidation on Pt up to 4.8 VLi, unique evidence for dehydrogenation of EC on LiNi0.8Co0.1Mn0.1O2 (NMC811) at voltages as low as 3.8 VLi was revealed by in situ FT-IR measurements, which was supported by density functional theory (DFT) results. Unique dehydrogenated species from EC were observed on NMC811 surface, including dehydrogenated EC anchored on oxides, vinylene carbonate (VC) and dehydrogenated oligomers which could diffuse away from the surface. Similar dehydrogenation on NMC811 was noted for EMC-based and LP57 (1 M LiPF6 in 3 : 7 EC/EMC) electrolytes. In contrast, no dehydrogenation was found for NMC111 or surface-modified NMC by coatings such as Al2O3. In addition, while the dehydrogenation of solvents was observed in 1 M electrolytes with different anions, they were not observed on NMC811 in the concentrated electrolyte (EC/EMC with 3.1 M LiPF6), indicating lithium coordination could suppress dehydrogenation. Dehydrogenation of carbonates on NMC811 accompanied with rapid growth of interfacial impedance with increasing voltage revealed by electrochemical impedance spectroscopy (EIS), while the electrode–electrolyte combinations without dehydrogenation did not show significant impedance growth. Therefore, minimizing carbonate dehydrogenation on the NMC surface by tuning electrode reactivity and electrolyte reactivity is critical to develop high-energy Li-ion batteries with long cycle life.

RuO2-based electrodes have been extensively studied for several electrochemical reactions. Earlier literature works claim RuO2-based catalysts to be active also for the electrocatalytic conversion of CO2 to methanol with high selectivity at very low overpotentials. Here we report a thorough investigation of RuO2 films and particles for the electrocatalytic reduction of CO2. The different experimental configurations explored in our work showed that H2 is basically the only reaction product under CO2 reduction conditions in contrast to earlier reports. In situ surface enhanced infrared absorption spectroscopy (SEIRAS) measurements revealed that CO bound to the RuO2 surface, albeit acting solely as spectator species. Our experiments indicated that adsorbed CO cannot be reduced further to methanol or other CO2 reduction products.