Magnesium batteries offer an opportunity to use naturally abundant Mg and achieve large volumetric capacities reaching over four times that of conventional Li-based intercalation anodes. High volumetric capacity is enabled by the use of a Mg metal anode in which charge is stored via electrodeposition and stripping processes, however, electrolytes that support efficient Mg electrodeposition and stripping are few and are often prepared from highly reactive compounds. One interesting electrolyte solution that supports Mg deposition and stripping without the use of highly reactive reagents is the magnesium aluminum chloride complex (MACC) electrolyte. The MACC exhibits high Coulombic efficiencies and low deposition overpotentials following an electrolytic conditioning protocol that stabilizes species necessary for such behavior. Here, we discuss the effect of the MgCl2 and AlCl3 concentrations on the deposition overpotential, current density, and the conditioning process. Higher concentrations of MACC exhibit enhanced Mg electrodeposition current density and much faster conditioning. An increase in the salt concentrations causes a shift in the complex equilibria involving both cations. The conditioning process is strongly dependent on the concentration suggesting that the electrolyte is activated through a change in speciation of electrolyte complexes and is not simply due to the annihilation of electrolyte impurities. Additionally, the presence of the [Mg2(μ-Cl)3·6THF]+ in the electrolyte solution is again confirmed through careful analysis of experimental Raman spectra coupled with simulation and direct observation of the complex in sonic spray ionization mass spectrometry. Importantly, we suggest that the ∼210 cm–1 mode commonly observed in the Raman spectra of many Mg electrolytes is indicative of the C3v symmetric [Mg2(μ-Cl)3·6THF]+. The 210 cm–1 mode is present in many electrolytes containing MgCl2, so its assignment is of broad interest to the Mg electrolyte community.Keywords: electrolyte conditioning; magnesium aluminum chloride complex; magnesium battery electrolyte; magnesium deposition; Mg dimer;

We evaluate hydrofluoroether (HFE) cosolvents with varying degrees of fluorination in the acetonitrile-based solvate electrolyte to determine the effect of the HFE structure on the electrochemical performance of the Li–S battery. Solvates or sparingly solvating electrolytes are an interesting electrolyte choice for the Li–S battery due to their low polysulfide solubility. The solvate electrolyte with a stoichiometric ratio of LiTFSI salt in acetonitrile, (MeCN)2–LiTFSI, exhibits limited polysulfide solubility due to the high concentration of LiTFSI. We demonstrate that the addition of highly fluorinated HFEs to the solvate yields better capacity retention compared to that of less fluorinated HFE cosolvents. Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that HFEs exhibiting a higher degree of fluorination coordinate to Li+ at the expense of MeCN coordination, resulting in higher free MeCN content in solution. However, the polysulfide solubility remains low, and no crossover of polysulfides from the S cathode to the Li anode is observed.Keywords: hydrofluoroether cosolvent; lithium−sulfur battery; solvate electrolyte; sparingly solvating electrolyte; variable-temperature NMR spectroscopy; X-ray photoelectron spectroscopy;

Rechargeable Zn batteries are promising energy storage alternatives for Li-ion batteries in part because of the high specific and volumetric capacities of Zn anodes, as well as their low cost, improved prospects for safety, and the fact that they are environmentally friendly. Development efforts, however, have focused mostly on aqueous electrolyte systems, which are intrinsically limited by the narrow electrochemical potential window of water. As a consequence, the use of alternative non-aqueous electrolytes has attracted a growing level of interest with the hope that they may provide higher operational voltages, which potentially could provide viable pathways to high-energy and high-power density Zn batteries. With regard to the latter, the considerable progress made in developing useful non-aqueous electrolyte chemistries for Zn anodes has not been matched by correlated progress regarding the development of useful cathode materials. In this work, a new series of spinels, ZnAlxCo2–xO4, are reported and their utility as cathode materials for non-aqueous Zn-ion batteries is demonstrated. Full cells constructed using this new spinel as a cathode paired with a metal anode showed capacities over 100 cycles of 114 mAh/g and an onset potential of 1.95 V, which is the highest OCV yet reported for a non-aqueous Zn-ion battery system. The data show that the Zn2+ ions reversibly intercalate into the spinel structure during the charge–discharge processes, a compositional transformation directly correlated with a reversible conversion between Co4+ and Co3+ oxidation states within the lattice. The data illustrate that the Al3+-doped spinel structure is a robust candidate material for use in non-aqueous Zn batteries, suggesting guidelines for the design of more efficient multivalent cathode materials.

Electrodeposition from plating baths containing 3,5-diamino-1,2,4-triazole (DAT) as an inhibitor gives Cu films exhibiting high surface area and high CO2 reduction activities. By changes in the pH and deposition current density, the morphologies of the Cu films are varied to exhibit wire, dot, and amorphous structures. Among these Cu films, the CuDAT-wire samples exhibit the best CO2 reduction activities activity with a Faradaic efficiency (FE) for C2H4 product formation reaching 40% at −0.5 V vs RHE, a FE for C2H5OH formation reaching 20% at −0.5 V vs RHE, and a mass activity for CO2 reduction at −0.7 V vs RHE of ∼700 A/g.Keywords: 3,5-diamino-1,2,4-triazole; CO2 reduction; copper; electrodeposition; ethylene;

Quasi-binary thiophosphate-based solid electrolytes (SEs) are attracting substantial interest for lithium batteries due to their outstanding room temperature ionic conductivities. This work describes reactions occurring at the solid electrolyte (SE)/Au interface during Li deposition and stripping for two exemplary SE materials: β-Li3PS4 (β-LPS) and Li10GeP2S12 (LGPS). We used in situ Raman spectroscopy, along with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to evaluate potential-dependent changes in the chemistry of these materials at active electrode interfaces. For β-LPS, a partially reversible conversion of PS43– to P2S64– was found along with the formation of Li2S during Li deposition and stripping. In contrast, LGPS exhibited only irreversible changes at potentials below 0.7 V vs Li+/Li. The different behaviors likely relate to differences in the structures of the two SE materials and the availability of easily bridged anion components in close proximity. The work shows that SE integrity at interfaces can be altered by applied potential and illustrates important speciations for the interfacial structures that mediate their electrochemical activities.

•Addition of 250 ppm H2O leads to stable charge/discharge in Li-S batteries.•H2O addition results in the formation of a LiOH-rich SEI film.•The film protects the Li anode from polysulfides.•Water is consumed during Li deposition and stripping process.Dissolved polysulfides, formed during Li-S battery operation, freely migrate and react with both the Li anode and the sulfur cathode. These soluble polysulfides shuttle between the anode and cathode – the so-called shuttle effect – resulting in an infinite recharge process and poor Columbic efficiency. In this study, water present as an additive in the Li-S battery electrolyte is found to reduce the shuttle effect in Li-S batteries. Batteries where water content was below 50 ppm exhibited a substantial shuttle effect and low charge capacity. Alternatively, addition of 250 ppm water led to stable charge/discharge behavior with high Coulombic efficiency. XPS results show that H2O addition results in the formation of solid electrolyte interphase (SEI) film with more LiOH on Li anode which protects the Li anode from the polysulfides. Batteries cycled without water result in a SEI film with more Li2CO3 likely formed by direct contact between the Li metal and the solvent. Intermediate quantities of H2O in the electrolyte result in high cycle efficiency for the first few cycles which then rapidly decays. This suggests that H2O is consumed during battery cycling, likely by interaction with freshly exposed Li metal formed during Li deposition.

A highly anisotropic electrodeposition was observed using the hybrid battery electrolyte Mg(BH4)2 with LiBH4 in diglyme. At low overpotentials high aspect ratio platelet morphologies are observed with a strong fiber texture composed of a {10-10} and a {11-20} component, the first evidence of behavior of this kind in magnesium battery electrolytes. At high overpotentials the deposit aspect ratio is indistinguishable but the texture is shown to be primarily composed of a {11-20} fiber texture. The kinetic parameters relative to the relevant crystallographic faces are extracted from electron microscopy images and compared with the observed bulk rate extracted from the electrochemical data. The use of polycrystalline Ag foil substrates with little preferred orientation at the surface allowed highly polycrystalline nucleation at lower overpotentials than that of platinum, likely due to Ag alloying with Mg. Characterization using focused ion beam (FIB) cross-sections with Auger Electron Spectroscopy (AES) elemental analysis confirm that the deposits are primarily Mg although Mg‐Ag alloys of various compositions were observed. It is proposed that the orientation at slow rates of growth is due to the underlying kinetics of adatom diffusion on Mg and that higher rates diminish the phenomenon due to decreased time for adatom diffusion and instead are governed by the rates of adatom formation or more specifically the adatom vacancy formation on the different low-index planes of Mg.

Proton-coupled electron transfer (PCET) reactions are ubiquitous in biochemistry and alternative energy schemes. Natural enzymes utilize quinones in proton transfer chains and energy conversion processes. Here, we utilize a bio-inspired hybrid bilayer membrane system to control the reaction mechanism of a quinone molecule covalently bound to an electrode surface. In particular, by impeding proton access to the quinone moiety, we change the reaction pathway from a PCET process to a pure electron transfer step. We further alter the reaction pathway to a stepwise PCET process by controlling the proton flux through the use of an alkyl proton carrier incorporated in the lipid membrane. By modulating proton availability, we control the quinone reaction pathway without changing the molecular structure of the redox species. This work provides unique insight into PCET reactions and a novel electrochemical platform for interrogating them.

Electrodeposition of Ni or NiFe films exhibiting fractal-like behavior from plating baths containing an inhibitor, such as 3,5-diamino-1,2,4-triazole (DAT), is found to yield oxygen evolution reaction (OER) catalysts for alkaline solutions exhibiting high current densities (100 mA/cm2), high mass activity (∼1200 A/g of catalyst), high stability (>72 h), and low overpotentials (∼300 mV). By changing electrodeposition time, the activity of the catalyst can be tuned, with longer times yielding higher activities. The electrodeposition method works with any conductive substrate yielding unprecedented performance and providing an easy route to high activity catalysts.Keywords: electrocatalyst; electrodeposition; NiFe; oxygen evolution; water splitting

Earth-abundant and inexpensive catalysts with low overpotential and high durability are central to the development of efficient water-splitting electrolyzers. However, improvements in catalyst design and preparation are currently hampered by the lack of a detailed understanding of the reaction mechanisms of the oxygen evolution reaction (OER) facilitated by nonprecious-metal (NPM) catalysts. In this paper, we conducted a kinetic isotope effect (KIE) study in an effort to identify the rate-determining step (RDS) of these intricate electrocatalytic reactions involving multiple proton-coupled electron transfer (PCET) processes. We observed an inverse KIE for OER catalyzed by Ni and Co electrodes. These results contribute to a more complete understanding of the OER mechanism and allow for the future development of improved NPM catalysts.Keywords: electrocatalysis; kinetic isotope effect; nonprecious metal; oxygen evolution reaction; proton-coupled electron transfer; reaction mechanism; water oxidation

Solid-state 7Li and 13C MAS NMR spectra of cycled graphitic Li-ion anodes demonstrate SEI compound formation upon lithiation that is followed by changes in the SEI upon delithiation. Solid-state 13C DPMAS NMR shows changes in peaks associated with organic solvent compounds (ethylene carbonate and dimethyl carbonate, EC/DMC) upon electrochemical cycling due to the formation of and subsequent changes in the SEI compounds. Solid-state 13C NMR spin–lattice (T1) relaxation time measurements of lithiated Li-ion anodes and reference poly(ethylene oxide) (PEO) powders, along with MALDI-TOF mass spectrometry results, indicate that large-molecular-weight polymers are formed in the SEI layers of the discharged anodes. MALDI-TOF MS and NMR spectroscopy results additionally indicate that delithiated anodes exhibit a larger number of SEI products than is found in lithiated anodes.Keywords: graphite anode; Li-ion battery; MALDI TOF MS; NMR; SEI

The solid electrolyte interface (SEI) formed via electrolyte decomposition on the anode of lithium ion batteries is largely responsible for the stable cycling of conventional lithium ion batteries. Similarly, there is a lesser-known analogous layer on the cathode side of a lithium ion battery, termed the cathode electrolyte interface (CEI), whose composition and role are debated. To confirm the existence and composition of the CEI, desorption electrospray ionization mass spectrometry (DESI-MS) is applied to study common lithium ion battery cathodes. We observe CEI formation on the LiMn2O4 cathode material after cycling between 3.5 and 4.5 V vs Li/Li+ in electrolyte solution containing 1 M LiPF6 or LiClO4 in 1:1 (v/v) ethylene carbonate (EC) and dimethyl carbonate (DMC). Intact poly(ethylene glycol) dimethyl ether is identified as the electrolyte degradation product on the cathode surface by the high mass-resolution Orbitrap mass spectrometer. When EC is paired with ethyl methyl carbonate (EMC), poly(ethylene glycol) dimethyl ether, poly(ethylene glycol) ethyl methyl ether, and poly(ethylene glycol) are found on the surface simultaneously. The presence of ethoxy and methoxy end groups indicates both methoxide and ethoxide are produced and involved in the process of oligomerization. Au surfaces cycled under different electrochemical windows as model systems for Li-ion battery anodes are also examined. Interestingly, the identical oligomeric species to those found in the CEI are found on Au surfaces after running five cycles between 2.0 and 0.1 V vs Li/Li+ in half-cells. These results show that DESI-MS provides intact molecular information on battery electrodes, enabling deeper understanding of the SEI or CEI composition.

The adsorbate-induced surface stress during the electrochemical oxidation of CO and NO on Pt is studied with in situ surface stress measurements and density functional theory (DFT) calculations. The changes in the surface stress response, Δstress, demonstrate the interplay between the adsorbed species during the oxidation process, which is determined by the coverage and the nature of the adsorbates. The oxidation of adsorbed CO, COads, shows a nonlinear surface stress response in both acidic and alkaline electrolytes, with the greatest tensile Δstress observed in the beginning of the oxidation where the CO coverage is the highest. Once a significant amount of CO is removed, OH starts to populate the surface and the Δstress becomes compressive. This surface stress development profile—the nonlinear stress development at high COads coverages and the inflection point due to coadsorption of CO and OH—is further interrogated by DFT calculations. While a tensile to compressive switch in Δstress is observed during CO oxidation, the oxidation of another strongly bound diatomic adsorbate, NOads, shows a continuous compressive Δstress. DFT calculations show that this behavior is attributed to the adsorption of the oxidation product, NO3–, which induces a similar magnitude of compressive Δstress compared to that of NOads. Hence, the compressive Δstress from the oxide and hydroxide on the surface governs the surface stress response.

Li–S batteries are a promising next-generation battery technology. Due to the formation of soluble polysulfides during cell operation, the electrolyte composition of the cell plays an active role in directing the formation and speciation of the soluble lithium polysulfides. Recently, new classes of electrolytes termed “solvates” that contain stoichiometric quantities of salt and solvent and form a liquid at room temperature have been explored due to their sparingly solvating properties with respect to polysulfides. The viscosity of the solvate electrolytes is understandably high limiting their viability; however, hydrofluoroether cosolvents, thought to be inert to the solvate structure itself, can be introduced to reduce viscosity and enhance diffusion. Nazar and co-workers previously reported that addition of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) to the LiTFSI in acetonitrile solvate, (MeCN)2–LiTFSI, results in enhanced capacity retention compared to the neat solvate. Here, we evaluate the effect of TTE addition on both the electrochemical behavior of the Li–S cell and the solvation structure of the (MeCN)2–LiTFSI electrolyte. Contrary to previous suggestions, Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that TTE coordinates to Li+ at the expense of MeCN coordination, thereby producing a higher content of free MeCN, a good polysulfide solvent, in the electrolyte. The electrolytes containing a higher free MeCN content facilitate faster polysulfide formation kinetics during the electrochemical reduction of S in a Li–S cell likely as a result of the solvation power of the free MeCN.Keywords: hydrofluoroether cosolvent; in situ Raman spectroscopy; lithium−sulfur battery; solvate electrolyte; sulfur reduction kinetics;

•SHINERS from single crystal Cu reveals intermediates during nitrate reduction.•Nitrate reduction occurs with concomitant oxidation of the Cu surface.•Differences in activity between the different faces are related to differing Cu oxidation susceptibility.•Cl- inhibits Cu surface oxidation and poisons nitrate reduction activity.The origin of different nitrate reduction activity between the (100), (111), and (110) faces of Cu is examined using vibrational spectroscopy and calculations. Shell isolated nanoparticle enhanced Raman spectroscopy (SHINERS) reveals a suite of intermediates from the nitrate reduction process on Cu(100), Cu(111), and Cu(110) including NO2− and HNO. All three faces show similar intermediates, suggesting the same mechanism is operative on all of them. Critical to the reduction pathway on the bare Cu surfaces is the reduction of nitrate to nitrite concomitant with partial oxidation of the Cu surface. This priming action facilitates nitrate reduction and reduces overpotentials, particularly on the Cu(111) and Cu(110) faces, which are more susceptible to oxidation. Decoration of the surfaces with Cl− suppresses nitrate reduction, resulting in higher overpotentials and lower current density. NH3 is observed by SHINERS as a direct nitrate reduction product in the presence of Cl−, rather than NOx species observed on the bare Cu surfaces, indicating a reaction pathway unique from the bare, undecorated surface.

The development of non-precious-metal (NPM) catalysts to replace the Pt alloys currently used in fuel cells to facilitate the oxygen reduction reaction (ORR) is a vital step in the widespread utilization of fuel cells. Currently, the ORR mechanism for NPM catalysts is not well understood, prohibiting the design and preparation of improved NPM catalysts. We conducted a kinetic isotope effect (KIE) study to identify the rate-determining step (RDS) of this intricate electrocatalytic reaction involving multiple proton-coupled electron transfer (PCET) processes. We observed a KIE of about 2 for the ORR catalyzed by a NPM catalyst, which demonstrates that for these electrocatalysts protons are involved in the RDS during ORR. These results contribute to a more complete understanding of the ORR mechanism and suggest that the design of future NPM catalysts must include careful consideration of the role of protons during ORR.

There is a growing interest in alcohol oxidation electrochemistry due to its role in renewable energy technologies. The goal of this work was to develop active non- precious metal electrocatalysts based on the Mo-V-(M)-O (M is Nb, Te) lattice. Selective gaseous alkane oxidation had been previously observed on these catalysts at elevated temperatures above 300 °C. In this study, the activity of the catalysts at lower temperatures, 25–60 °C, was investigated. Hydrothermal conditions were used to synthesize the Mo-V-(M)-O mixed oxides. Physical characterization of the catalysts were obtained by powder X-ray diffraction (XRD), scanning electron micrography (SEM) equipped with energy dispersive X-ray (EDX), transmission electron micrography (TEM), and X-ray photoelectron spectroscopy (XPS). The catalytic activity for the oxidation of cyclohexanol was studied electrochemically. Chronoamperometric studies were used to evaluate the long-term performance of the catalysts. The onset of alcohol oxidative current was observed between 0.2 and 0.6 V versus Ag/AgCl. Gas chromatography–mass spectrometry analysis was used to determine the nature of the oxidative products. The mild oxidation products, cyclohexanone and cyclohexene, were observed after oxidation at 60 °C. The catalytic activity increased in the order Mo-V-O < Mo-V-Te-O < Mo-V-Te-Nb-O. Mo-V-(Te,Nb)-O based electrocatalysts efficiently catalyzed the oxidation of alcohols at low temperatures.

To control proton delivery across biological membranes, we synthesized a photoresponsive molecular switch and incorporated it in a lipid layer. This proton gate was reversibly activated with 390 nm light (Z-isomer) and then deactivated by 360 nm irradiation (E-isomer). In a lipid layer this stimuli responsive proton gate allowed the regulation of proton flux with irradiation to a lipid-buried O2 reduction electrocatalyst. Thus, the catalyst was turned on and off with the E-to-Z interconversion. This light-induced membrane proton delivery system may be useful in developing any functional device that performs proton-coupled electron-transfer reactions.

Mg batteries are an attractive alternative to Li-based energy storage due to the possibility of higher volumetric capacities with the added advantage of using sustainable materials. A promising emerging electrolyte for Mg batteries is the magnesium aluminum chloride complex (MACC) which shows high Mg electrodeposition and stripping efficiencies and relatively high anodic stabilities. As prepared, MACC is inactive with respect to Mg deposition; however, efficient Mg electrodeposition can be achieved following an electrolytic conditioning process. Through the use of Raman spectroscopy, surface enhanced Raman spectroscopy, 27Al and 35Cl nuclear magnetic resonance spectroscopy, and pair distribution function analysis, we explore the active vs inactive complexes in the MACC electrolyte and demonstrate the codependence of Al and Mg speciation. These techniques report on significant changes occurring in the bulk speciation of the conditioned electrolyte relative to the as-prepared solution. Analysis shows that the active Mg complex in conditioned MACC is very likely the [Mg2(μ–Cl)3·6THF]+ complex that is observed in the solid state structure. Additionally, conditioning creates free Cl– in the electrolyte solution, and we suggest the free Cl– adsorbs at the electrode surface to enhance Mg electrodeposition.

We describe a voltammetric and spectroscopic study of Mg electrodeposition/dissolution (MgDep/Dis) in borohydride diglyme electrolyte solution containing Li+ carried out on a Pt ultramicroelectrode (UME, r = 5 μm). The data reveal Li+ cation facilitation that has not been previously recognized in studies made using macroelectrodes. While a single broad, asymmetric stripping peak is expected following MgDep on a Pt macroelectrode in 0.1 M Mg(BH4)2 + 1.5 M LiBH4 diglyme solution on a Pt UME, the stripping reveals three resolved oxidation peaks, suggesting that MgDep/Dis consists of not only a Mg/Mg2+ redox reaction but also contributions from Mg–Li alloying/dissolution reaction processes. Detailed XPS, SIMS, ICP, and XRD studies were performed that confirm the importance of Mg–Li alloy formation processes, the nature of which is dependent on the reduction potential used during the MgDep step. Based on the electrochemical and surface analysis data, we propose an electrochemical mechanism for MgDep/Dis in a borohydride diglyme electrolyte solution that, in the presence of 1.5 M Li+ ions, proceeds as follows: (1) Mg2+ + 2e– ⇌ Mg; (2) (1 – x)Mg2+ + xLi+ + (2 – x)e– ⇌ Mg(1–x)Lix, 0 < x ≤ 0.02; and (3) (1 – y)Mg2+ + yLi+ + (2 – y)e– ⇌ Mg(1–y)Liy, 0.02 < y ≤ 0.09. Most significantly, we find that the potential-dependent MgDep/Dis kinetics are enhanced as the concentration of the LiBH4 in the diglyme electrolyte is increased, a result reflecting the facilitating influences of reduced uncompensated resistance and the enhanced electro-reduction kinetics of Mg2+ due to Mg–Li alloy formation.Keywords: magnesium borohydride; Mg electrodeposition/dissolution; Mg rechargeable battery; Mg−Li alloy; Pt microelectrode; stripping peak

In situ Raman spectroscopy and cyclic voltammetry were used to investigate the mechanism of sulfur reduction in lithium–sulfur battery slurry cathodes with 1 M lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether (TEGDME)/1,3-dioxolane (DIOX) (1/1, v/v). Raman spectroscopy shows that long-chain polysulfides (S82–) were formed via S8 ring opening in the first reduction process at ∼2.4 V vs Li/Li+ and short-chain polysulfides such as S42–, S4–, S3•–, and S2O42– were observed with continued discharge at ∼2.3 V vs Li/Li+ in the second reduction process. Elemental sulfur can be reformed in the end of the charge process. Rate constants obtained for the appearance and disappearance polysulfide species shows that short-chain polysulfides are directly formed from S8 decomposition. The rate constants for S8 reappearance and polysulfide disappearance on charge were likewise similar. The formation of polysulfide mixtures at partial discharge was found to be quite stable. The CS2 additive was found to inhibit the sulfur reduction mechanism allowing the formation of long-chain polysulfides during discharge only and stabilizing the S82– product.Keywords: carbon disulfide; kinetic of polysulfides formation and decomposition; Li−S batteries; partial discharge; Raman spectroscopy; sulfur reduction

In situ EQCM experiments were used to investigate the stability and roughness changes occurring in a sulfur–carbon cathode utilized for a Li–S battery during the charge–discharge process. Results show that the sulfur–carbon cathode gains mass during the first discharge plateau (∼2.4 V) due to the formation of the long chain polysulfides during the discharge (lithiation) process. However, further discharge to below 2.4 V yields an increase in the crystal resistance (Rc) suggesting the sulfur–carbon cathode becomes rougher. During the charge (delithiation) process, the roughness of the sulfur–carbon cathode decreases. Time dependent measurements show that the electrode surface becomes rougher with the deeper discharge, with the change occurring following a step to 1.5 V. The sulfur–carbon cathode exhibits stable Rc and frequency behavior initially, but then becomes rougher in subsequent following cycles.Keywords: crystal resistance; EQCM; Li−S batteries; polysulfide dissolution; roughness of the sulfur−carbon cathode

In this report, we use a hybrid bilayer membrane (HBM) as an electrochemical platform to study anion diffusion through a lipid monolayer. We first append lipid on a self-assembled monolayer (SAM) that contains a covalently bound Cu(I)/Cu(II) redox center. We then perform cyclic voltammetry (CV) using different anions in bulk solution and extract thermodynamic and kinetic information about anion transport. We analyze the results using linear combinations of fundamental chemical trends and determine that anion transport quantitatively correlates to polarity and basicity, a relationship we formalize as the lipid permeability parameter. In addition, we discuss how our findings can be interpreted according to the two leading mechanisms describing ion permeability through lipids. Our results demonstrate that anion transport in a HBM is best described by the solubility-diffusion mechanism, not the pore mechanism.

•Products in Li–S cathodes identified with solid-state 6Li MAS NMR spectroscopy•Long-chain polysulfides are indistinguishable with chemical shift.•Short-chain polysulfides are distinguishable from soluble long-chain products.•T2 relaxation shows that long-chain polysulfides are converted to shorter chain species.•Structural information about Li–S battery products and intermediates is obtained.6Li and 33S solid-state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy was used to identify the discharge products in lithium–sulfur (Li–S) battery cathodes. Cathodes were stopped at different potentials throughout battery discharge and measured ex-situ to obtain chemical shifts and T2 relaxation rates of the products formed. The chemical shifts in the spectra of both 6Li and 33S NMR demonstrate that long-chain, soluble lithium polysulfide species formed at the beginning of discharge are indistinguishable from each other (similar chemical shifts), while short-chain, insoluble polysulfide species that form at the end of discharge (presumably Li2S2 and Li2S) have a different chemical shift, thus distinguishing them from the soluble long-chain products. T2 relaxation measurements of discharged cathodes were also performed which resulted in two groupings of T2 rates that follow a trend and support the previous conclusions that long-chain polysulfide species are converted to shorter chain species during discharge. Through the complementary techniques of 1-D 6Li and 33S solid-state MAS NMR spectroscopy, solution 7Li and 1H NMR spectroscopy, and T2 relaxation rate measurements, structural information about the discharge products of Li–S batteries is obtained.

Fundamental understanding of the oxygen reduction reaction in aqueous medium at temperatures above 100 °C is lacking due to the practical limitations related to the harsh experimental conditions. In this work, the challenge to suppress water from boiling was overcome by conducting the electrochemical investigation under pressurized conditions. A striking improvement in the kinetics of the electrocatalytic reduction of O2 by about 150 fold relative to room temperature and pressure was recorded under an O2 pressure of 3.4 MPa at 200 °C in basic aqueous environment. To deconvolute the combined effect of temperature and pressure, the underlying variables that dictate the observed O2 reduction kinetics of Pt and carbon electrodes were examined individually. O2 availability at the electrode–solution interface was controlled by the interplay between the diffusion coefficient and concentration of O2. Accurate knowledge of the temperature and pressure dependence of O2 availability at the electrode surface, the Tafel slope, the transfer coefficient, and the electrochemical active surface area was required to correctly account for the enhanced O2 reduction kinetics.

We describe in this work Mg electrodeposition and dissolution from a wide range of inorganic ethereal electrolytes consisting of MgCl2 and a second chloride salt. Systematic variations of the cosalt reveal two broad classes of electrolytes, namely, the group 13 electrolytes, which require electrolytic cycling to improve their performance, and electrolytes based on heavy p-block chlorides, which exhibit Mg intermetallic formation. Results from electrospray ionization mass spectrometry demonstrate that Mg deposition and stripping only occur in electrolytes containing Mg multimers. We also explore the role of solvent in determining the electrochemical performance of chloride-based electrolytes. Our analysis establishes thermodynamic parameters that dictate the ability of a solvent to support Mg electrochemistry in the MgCl2–AlCl3 system. In their totality, these results illustrate important electrolyte design guidelines for future Mg-ion batteries.

We used in situ X-ray diffraction, XPS, SEM, and electrochemical methods to interrogate the mechanism of Mg electrodeposition from PhMgCl/AlCl3 (APC) and EtMgCl electrolytes. An open circuit potential (OCP) pause following Mg deposition led to retained enhancement of Mg deposition and stripping kinetics along with lowered overpotentials for both. In situ X-ray diffraction demonstrated that the OCP pause led to a more polycrystalline deposit relative to that without the pause, while SEM presented micrographs that showed smaller deposits with an OCP hold. The improvement is attributed to an “enhancement layer” that formed on the electrode during the OCP hold. Analysis of XPS data suggests that the “enhancement layer” consists of Mg and Cl retained on the electrode surface, possibly following electrode depassivation.

Microcantilever stress measurements are examined to contrast and compare their attributes with those from in situ X-ray absorption spectroscopy to elucidate bonding dynamics during the oxygen reduction reaction (ORR) on a Pt catalyst. The present work explores multiple atomistic catalyst properties that notably include features of the Pt–Pt bonding and changes in bond strains that occur upon exposure to O2 in the electrochemical environment. The alteration of the Pt electronic and physical structures due to O2 exposure occurs over a wide potential range (1.2 to 0.4 V vs normal hydrogen electrode), a range spanning potentials where Pt catalyzes the ORR to those where Pt-oxide forms and all ORR activity ceases. We show that Pt–Pt surface bond strains due to oxygen interactions with Pt–Pt bonds are discernible at macroscopic scales in cantilever-based bending measurements of Pt thin films under O2 and Ar. Complementary extended X-ray absorption fine structure (EXAFS) measurements of nanoscale Pt clusters supported on carbon provide an estimate of the magnitude and direction of the in-operando bond strains. The data show that under O2 the M–M bonds elongate as compared to an N2 atmosphere across a broad range of potentials and ORR rates, an interfacial bond expansion that falls within a range of 0.23 (±0.15)% to 0.40 (±0.20)%. The EXAFS-measured Pt–Pt bond strains correspond to a stress thickness and magnitude that is well matched to the predictions of a mechanics mode applied to experimentally determined data obtained via the cantilever bending method. The data provide new quantitative understandings of bonding dynamics that will need to be considered in theoretical treatments of ORR catalysis and substantiate the subpicometer resolution of electrochemically mediated bond strains detected on the macroscale.

In situ electrochemical stress measurements are used to interrogate changes in oxide structure before and during the oxygen evolution reaction (OER) from Ir, Ni, Co, Au, and Pt electrodes in alkaline electrolyte. Stress evolution during potential cycling reports on changes in oxidation state and oxide forms. Hysteresis observed in the potential-dependent stress from Ir, Au, and Pt electrodes is associated with chemical irreversibility in electrode composition and roughness. Alternatively, Ni and Co exhibit reversible conversion between hydroxide and oxyhydroxide forms during cycling. From the experimentally determined stress, charge passed during electrode oxidation, and Young’s modulus, the change in strain exhibited by Ni and Co electrodes during hydroxide-oxyhydroxide conversion is calculated to be 7.0% and 8.4%, respectively. We also show that the magnitude of change in stress is proportional to the amount of material that is further oxidized.

•Time dependent film formation was monitored by Impedance and Raman Spectroscopy.•Two loops in the Nyquist plot are found on rough surfaces and are related to film growth.•Raman spectra intensity decreases with time, an effect attributed to film formation.The inhibitory effect of Rhodanine (RD) on copper in acidic media has been investigated by electrochemical impedance spectroscopy (EIS) and surface-enhance Raman scattering (SERS) spectroscopy. Roughened copper was used for EIS experiments to better compare with SERS results. The EIS results show two loops in the Nyquist plot, one of which is associated with protective film growth on the rough surface after 1 h. The SERS spectra showed a marked decrease in intensity after 1 h, which is attributed to formation of thick films opaque to the laser. The film thickness after 2 h was determined to be ∼200 nm from atomic force microscopy (AFM).

Cu complexes of 2,2′-dipicolylamine (DPA) were prepared and tested as electrocatalysts for the oxygen reduction reaction (ORR). To study the effect of multinuclearity on the ORR, two Cu–DPA units were connected with a flexible linker, and a third metal-binding pocket was installed in the ligand framework. ORR onset potentials and the diffusion-limited current densities of di- and tricopper complexes of DPA derivatives were found to be comparable to those of the simpler Cu–DPA system. Electrochemical analyses, crystallographic data, and metal-substitution studies suggested that Cu complexes of DPA derivatives reacted with O2 via a binuclear intermolecular pathway but that the Cu center in the third binding site did not participate in the ORR process. This study highlights the viability of Cu–DPA complexes to mimic the T3-site of laccase, and serves as a guide for designing future laccase models.

•Hydrothermal synthesis of Bi2O2S.•Bi2O2S has a smaller band gap than Bi2O3.•Pt, Co3O4/Cr-TPPCl/Bi2O2S/In2O3 used for water splitting.Oxide-chalcogenide semiconductors are proposed in order to attain a smaller band gap and improve efficiencies in comparison to oxides for light induced total water splitting. Dibismuthoxysulfide (Bi2O2S) was synthesized under relatively mild hydrothermal conditions. The synthesized compound was characterized by XRD, SEM and UV–vis DRS techniques. The band gap of 1.5 eV measured is smaller than 2.8 eV of bismuth oxide (Bi2O3). Photoelectrochemical studies showed that it is possible to utilize Bi2O2S and the Bi2O2S/In2O3 composite as n-type semiconductors. Dye modified Bi2O2S/In2O3 showed promise for the catalysis of water splitting.

We compare the electrochemistry of Mg deposition and stripping from Mg(AlCl2EtBu)2 in THF, a common electrolyte used in Mg-ion battery prototypes, with EtMgBr, a simple Grignard reagent. Electrochemical quartz crystal microbalance measurements demonstrate that mass is gained and lost from the electrode with relatively high efficiency. However, the corresponding Coulombic efficiency is considerably less than the expected 100% for early stage cycles. SEM-EDS analysis shows accumulation of Mg and electrolyte constituents after stripping, highlighting the irreversibility of the Mg deposition and stripping process. GC-MS and NMR analysis of electrolytes reveal decomposition of the solvent–electrolyte system. These findings suggest that Mg organohaloaluminates are not ideal for use in robust Mg-ion batteries.

The influence of 3,5-diamino-1,2,4-triazole (DAT) on the electrochemical reduction of carbon dioxide to carbon monoxide on a silver electrode was studied via in situ surface-enhanced Raman spectroscopy (SERS). SERS bands obtained in the absence of DAT indicate potential-dependent adsorption of the CO product to bridge and 3-fold hollow sites. With the addition of DAT, CO adsorption to less-coordinated surface sites was found, including a physisorbed or noncoordinating site that exhibited no significant Stark vibrational shift. Raman peaks associated with adsorbed DAT observed at the same potentials as this species suggest that the ligand promotes weaker CO adsorption, which may be responsible for the high efficiency of the AgDAT catalyst. The observation of potential-dependent methylene stretching vibrations indicates the presence of surface hydrocarbon species while the presence of C–D stretches in deuterated electrolyte confirm that these hydrocarbons are generated as a CO2 reduction byproduct.

We describe in this report the electrochemistry of Mg deposition and dissolution from the magnesium aluminum chloride complex (MACC). The results define the requirements for reversible Mg deposition and definitively establish that voltammetric cycling of the electrolyte significantly alters its composition and performance. Elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDS) results demonstrate that irreversible Mg and Al deposits form during early cycles. Electrospray ionization mass spectrometry (ESI-MS) data show that inhibitory oligomers develop in THF-based solutions. These oligomers form via the well-established mechanism of a cationic ring-opening polymerization of THF during the initial synthesis of the MACC and under resting conditions. In contrast, MACC solutions in 1,2-dimethoxyethane (DME), an acyclic solvent, do not evolve as dramatically at open circuit potential. From these results, we propose a mechanism describing how the conditioning process of the MACC in THF improves its performance by both tuning the Mg:Al stoichiometry and eliminating oligomers.

The oxygen reduction reaction (ORR) is employed in a large number of systems such as fuel cells and air batteries. Currently, the catalyst with the lowest overpotential for the ORR is the enzyme laccase. Laccase only functions at a very narrow pH range, and its large size prevents high current densities. Using copper based catalysts to mimic the ORR activity is an area with many spectroscopic results, but relatively few electrochemical studies. This review catalogs the various copper based ORR catalysts and their activities.Highlights► Mulitcopper oxidases are some of the most efficient oxygen reduction catalysts. ► Coordination chemistry mimics of these enzymes feature nitrogenous ligands. ► Carbon supported Cu complexes of both diamino triazole and tris pyridyl amine are effective ORR catalyst. ► ORR efficacy of Cu complexes in base is better than in acid.

Discharged lithium–O2 battery cathodes are investigated with different catalysts present including Pd, α-MnO2 and CuO, and containing two different electrolyte solvents, 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC) and tetraethylene glycol dimethyl ether (TEGDME). Solid-state 6Li magic angle spinning (MAS) NMR spectroscopy has been used identify lithium products that are formed in the cathodes and differences between products formed with the different catalysts and solvents. There are significant differences in the products formed in Li–O2 cathodes with the two different solvents, EC/DMC and TEGDME. Due to the small chemical shift range of lithium it is difficult to determine exact speciation from 6Li MAS NMR data alone. Fitting of the 6Li NMR peaks with tested Li-oxide powder standards indicates that Li–O2 cathodes discharged in EC/DMC produce primarily Li2CO3 as a lithium product and those discharged in TEGDME produce mainly Li2O2. Solution 2D correlation 1H–13C NMR spectroscopy techniques allow for determination of side-products produced in Li–O2 cathodes.Highlights► 6Li, 13C, and 1H NMR spectroscopy is used to interrogate discharged lithium–O2 battery cathodes. ► 6Li NMR shows Li2O2 is the primary product from batteries with TEGDME solvent. ► Degradation products include lithium formate, lithium acetate, and lithium carbonate.

A series of copper complexes based on the tris(2-pyridylmethyl)amine (TPA) ligand are examined for their oxygen reduction reaction (ORR) activity. Increasing the potential of the CuI/II couple from 0.23 V vs RHE for [Cu(TPA)(L)]2+ to 0.52 V for [Cu(TEPA)(L)]2+ (tris(2-pyridylethyl)amine) at pH 7 or adding a hydrogen-bonding secondary coordination sphere does not increase the onset potential from 0.69 V vs RHE for the ORR. The underlying mechanism for the ORR is determined to be first-order in O2 and second-order in Cu. The rate-determining step is found to not be CuII to CuI reduction, as seen in other systems. The rate-determining step is also not the protonation of an intermediate, but may be the reduction of a hydroperoxo intermediate. Pyrolysis of the Cu complex of TPA affords an inactive material; activity is recovered through addition of intact TPA to the electrode surface.

We examine the properties of microstructured Ge electrodes for Li-ion battery applications. Model-microfabricated single-crystalline Ge electrode structures are used to investigate the effects of Cu coating and partial discharging on cycle life. Results show that the Ge microstructures insert Li more isotropically than do comparable ones comprised of Si. A model Ge microbar electrode with a Cu coating is capable of 95 % coulombic efficiency after 40 cycles when the amount of charge is limited. The microstructured Ge electrode is found to exhibit poor performance at higher delithiation rates (above C/5) relative to microstructured Si electrodes. These results provide an understanding of the effects of electrochemical processes on model-microstructured Ge electrodes which may ultimately aid in the development of advanced anodes for Li-ion batteries.

The synthesis and application of carbon-supported, nitrogen-based organometallic silver catalysts for the reduction of CO2 is studied using an electrochemical flow reactor. Their performance toward the selective formation of CO is similar to the performance achieved when using Ag as the catalyst, but comparatively at much lower silver loading. Faradaic efficiencies of the organometallic catalyst are higher than 90%, which are comparable to those of Ag. Furthermore, with the addition of an amine ligand to Ag/C, the partial current density for CO increases significantly, suggesting a possible co-catalyst mechanism. Additional improvements in activity and selectivity may be achieved as greater insight is obtained on the mechanism of CO2 reduction and on how these complexes assemble on the carbon support.

The coadsorption of water and potassium on a Au(100) surface is examined using variable-temperature Scanning Tunneling Microscopy (STM). The two-layer system initially formed on the reconstructed Au(100) through addition of K is converted into a labyrinthine row structure upon the introduction of water. This structure features KOH molecules likely covered with a water adlayer. Density Functional Theory (DFT) calculations provide further insight into the observed labyrinthine striped structures formed by adsorbed KOH. Images obtained following limited introduction of water feature larger unreacted areas and a more disordered row structure.

We have investigated the potential-dependent assembly of 2,2′-bipyridine molecules on both Au(100) and Au(111) surfaces using a newly developed Shell-Isolated Nanoparticle Enhanced-Raman Spectroscopy (SHINERS) technique. We present potential-dependent SHINERS spectra of 2,2′-bipyridine adsorbed on both surfaces collected under anodic as well as cathodic polarization. A series of processes were characterized by the analysis of the data set with Perturbation Correlation Moving Window Two-Dimensional Spectroscopy (PCMW2D) and Two-Dimensional Correlation Spectroscopy (2DCOS). Exquisite spectral detail was achieved and allowed for the characterization of the complicated ring breathing mode and C–C inter-ring stretching modes that are diagnostic of molecular orientation on the surfaces. Detection of several occluded vibration peaks was also made possible with SHINERS. Analysis reveals that in very negative potentials 2,2′-bipyridine adsorbs in a disordered, mixed state with both π-flat cis and several different vertically N-bound cis orientations, in contrast to previously published reports. Our findings provide insight into 2,2′-bipyridine adsorption on Au single crystals and also powerfully combine SHINERS with two-dimensional correlation analysis to yield a more detailed view of spectral transitions.

The active site of pyrolyzed Fe/N/C electrocatalysts for the oxygen reduction reaction (ORR) has been a source of debate since the initial discovery that these materials demonstrated activity toward the ORR. Here we utilize carbon-supported iron(II) phthalocyanine (FePc) that has been pyrolyzed at 800 °C in the absence and presence of azide in acidic, neutral, and basic environments in order to probe the ORR activity and mechanism of pyrolyzed Fe/N/C materials. The presence of azide served to enhance the ORR activity of this material in neutral electrolyte while having no effect in acid or base. Tafel slope differences in addition to the azide enhancement suggest an iron-centered active site for the ORR in pyrolyzed FePc and potentially other Fe/N/C electrocatalysts.

An in situ electrochemical X-ray absorption spectroscopy (XAS) cell has been fabricated that enables high oxygen flux to the working electrode by utilizing a thin poly(dimethylsiloxane) (PDMS) window. This cell design enables in situ XAS investigations of the oxygen reduction reaction (ORR) at high operating current densities greater than 1 mA in an oxygen-purged environment. When the cell was used to study the ORR for a Pt on carbon electrocatalyst, the data revealed a progressive evolution of the electronic structure of the metal clusters that is both potential-dependent and strongly current-dependent. The trends establish a direct correlation to d-state occupancies that directly tracks the character of the Pt–O bonding present.

Three copper polypyridyl complexes were examined as electrocatalysts for the oxygen reduction reaction (ORR): a Cu–N3 complex, [Cu–[tris(6-methylpyridin-2-yl)methane]-(NCMe)]PF6 (1); a related Cu2N6 derivative, [Cu2–[1,2-bis(6-(bis(6-methylpyridin-2-yl)methyl)pyridin-2-yl)ethane]-(NCMe)2](PF6)2 (2); and the CuN4 species [Cu–[tris(pyridin-2-ylmethyl)amine]](ClO4)2 [3](ClO4)2. Compared to other copper complexes, [3](ClO4)2 exhibits the highest reported ORR onset potential for a Cu complex of 0.53 V vs reversible hydrogen electrode at pH 1. The Cu2N6 hemocyanin model is more active than the CuN3, but both are less active than the CuN4 complex. The results indicate that copper polypyridyl complexes are promising cathode catalysts for ORR.

We examine the effects of p-type and n-type dopants on the lithiation of crystalline Si as related to Li-ion batteries. In situ Raman spectroscopy and electrochemistry are used to investigate two crystallographic faces, (100) and (111), for boron (B) and phosphorus (P) dopants, to monitor the insertion of Li and the associated transition to amorphous Si. Density functional theory calculations are used to investigate the lithiation of doped and undoped crystalline Si bulk and surface models. The experimental and computational results suggest that lithiation voltages are different for P-doped and B-doped Si. The B-doped surfaces are found to insert Li at higher voltages than P- and undoped surfaces but result in less Li insertion. These results provide an understanding of the effects on dopants on the lithiation of silicon which may ultimately aid in the development of alternate anode materials for Li-ion batteries.

We use first principles Density Functional Theory (DFT), cyclic voltammetry (CV), and Raman spectroscopy to investigate the first-cycle electrochemical lithiation of Ge in comparison with Si – both high-capacity anode materials for Li ion batteries. DFT shows a significant difference in the dilute solubility of Li in Si and Ge, despite similarities in their chemical and physical properties. We attribute this difference to electronic, as opposed to elastic, effects. CV and Raman data reveal little dopant dependence in the lithiation onset voltages in Ge, unlike in Si, due to a smaller energy difference between dilute Li insertion in p-type Ge and bulk germanide formation than the corresponding difference in Si. Finally, we show that there is no orientation dependence in lithiation onset voltages in Ge. We conclude that approaches other than microstructuring are needed to fabricate effective electrodes able to take advantage of the higher rate capability of Ge compared to that of Si.Keywords: anode; germanium; lithium ion battery; silicon;

Whether or not the active sites for the oxygen reduction reaction (ORR) in electrocatalysts based on carbon-supported transition-metal complexes are metal-centered has become controversial, especially for heat-treated materials. Some have proposed that the transition metal only serves to form highly active sites based on nitrogen and carbon. Here, we examine the oxygen reduction activity of carbon-supported iron(II) phthalocyanine (FePc) before and after pyrolysis at 800 °C and a carbon-supported copper(II) complex with 3,5-diamino-1,2,4-triazole (CuDAT) in the presence of several anions and small-molecule poisons, including fluoride, azide, thiocyanate, ethanethiol, and cyanide. CuDAT is poisoned in a manner consistent with a Cu-based active site. Although FePc and pyrolyzed FePc are remarkably resilient to most poisons, they are poisoned by cyanide, indicative of Fe-based active sites.Keywords: cathode; fuel cell; heat treated; macrocycle; nonprecious metal catalyst; triazole;

The performance of a novel carbon-supported copper complex of 3,5-diamino-1,2,4-triazole (Cu-tri/C) is investigated as a cathode material using an alkaline microfluidic H2/O2 fuel cell. The absolute Cu-tri/C cathode performance is comparable to that of a Pt/C cathode. Furthermore, at a commercially relevant potential, the measured mass activity of an unoptimized Cu-tri/C-based cathode was significantly greater than that of similar Pt/C- and Ag/C-based cathodes. Accelerated cathode durability studies suggested multiple degradation regimes at various time scales. Further enhancements in performance and durability may be realized by optimizing catalyst and electrode preparation procedures.

This work presents photoelectrochemical characteristics of TlVO4, a previously uncharacterized candidate for photocatalytic water splitting. Additionally, a composite of InVO4 and TlVO4 was synthesized by a facile solution method using orthorhombic InVO4 as a seed for growth of crystallographically similar orthorhombic TlVO4. Photoelectrochemical measurements indicate an increase in photocurrent and more negative flatband potentials for TlVO4 and the InVO4:TlVO4 composite relative to InVO4. Diffuse reflectance UV−visible measurements were used to determine bandgaps of 3.50 eV, 2.94 eV, and 2.98 eV for InVO4, TlVO4, and InVO4:TlVO4, respectively. Density functional theory (DFT) calculations were performed to elucidate the band structures and correlate well with experimental data. The results indicate higher photoelectrochemical activity for TlVO4 and the InVO4:TlVO4 composite relative to InVO4.

Surface-enhanced Raman scattering (SERS) spectra were collected continuously during cyclic voltammetric measurements on silver electrodes in alkaline aqueous solution at room temperature. Three water librational modes as well as the bending mode peak were observed in cathodic potential range. The 2D-COS analysis of spectra collected in LiOH and KOH solutions showed that the librational bands appear prior to the bending band on the cathodic scan, while in CsOH solution the potential dependence of these bands was identical. A comparison of librational band frequencies revealed that the water molecules around Cs+ cations arranged on the electrode surface were poorly hydrogen bonded in contrast to Li+ and K+. The water bending band of spectra collected in LiOH solution was found to be the convolution of two contributions, consistent with a two state model of water arranged on an electrode surface.

A review of the oxygen reduction reaction (ORR) and its use in fuel-cell applications is presented. Discussed are mechanisms of the ORR and implementations of catalysts for this reaction. Specific catalysts discussed include nanoparticles, macrocycles and pyrolysis products, carbons, chalcogenides, enzymes, and coordination complexes. A prospectus for future efforts is provided.

Laccase, a multicopper oxidase, catalyzes the four-electron reduction of oxygen to water. Upon adsorption to an electrode surface, laccase is known to reduce oxygen at overpotentials lower than the best noble metal electrocatalysts usually employed. Whereas the electrocatalytic activity of laccase is well established on carbon electrodes, laccase does not typically adsorb to better defined noble metal surfaces in an orientation that allows for efficient electrocatalysis. In this work, we utilized anthracene-2-methanethiol (AMT) to modify the surface of Au electrodes and examined the electrocatalytic activity of adsorbed laccase. AMT facilitated the adsorption of laccase, and the onset of electrocatalytic oxygen reduction was observed as high as 1.13VRHE. We observed linear Tafel behavior with a 144 mV/dec slope, consistent with an outer sphere single electron transfer from the electrode to a Cu site in the enzyme as the rate-determining step of the oxygen reduction mechanism.Keywords (keywords): biofuel cell; electrochemistry; multicopper oxidase; Tafel slope; voltammetry;

Vibrational sum-frequency generation spectroscopy (SFG) lineshapes of p-cyanobenzenethiol on low-index Ag crystal surfaces are studied as a function of azimuthal rotation by angle ϕ. A broadband multiplex SFG method is used, with a new technique that variably suppresses the non-resonant (NR) background using time-asymmetric time-delayed picosecond laser pulses. When both resonant (R) and NR signals are present, the amplitude and phase of the R line shape can vary significantly with ϕ, leading to dramatic ϕ-dependent variations of the SFG spectrum. The CN-stretch transition of p-cyanobenzenethiol modified Ag(111) and Ag(110) surfaces has an SFG spectrum consisting of a single vibrational resonance R atop a NR background that originates from the metal surface. Using the NR suppression technique, it was found that the R amplitude of the CN-stretch was independent of ϕ on both Ag(111) and Ag(110), which proves that the CN dipole moment is parallel to the surface normal in both cases. We show that it is possible to accurately extract the ϕ-dependence of the R amplitude, the NR amplitude, and the phase difference from SFG spectra by suppressing the NR signal during sample roation, thereby proving that the R contribution from the CN-stretch transition evidence ϕ-invariant behavior on both Ag surfaces.

•Thiol-based additives to Li-S batteries inhibit the formation isolated short chain polysulfides such as S3•-.•These additives also change the kinetics of formation of short chain polysulfides.•Biphenyl-4,4′-dithiol is found to be the best performing electrolyte additive.The discharge and charge mechanisms of the Li-S battery involve the formation of soluble lithium polysulfide species that can diffuse through the battery and cause issues related to capacity fade and poor Coulombic efficiency. In order to control the behavior of the lithium polysulfides, thiol-based electrolyte additives such as biphenyl-4,4′-dithiol (BPD) were used to enhance capacity retention in lithium-sulfur batteries by controlling polysulfide dissolution. In situ Raman spectroscopy, in situ UV–vis spectroscopy, and electrospray ionization mass spectrometry show that an additional sulfur reduction process observed at ~2.1 V vs. Li/Li+ as a result of BPD addition is associated with the formation of BPD-short chain polysulfide complexes such as BPD-Sn anion (1≤n≤4). The interaction between BPD and short chain polysulfide postpones formation of soluble short chain polysulfides and alters the kinetics of the dissolution process. A smooth SEI/Li entangled phase is found on the Li anode with BPD addition. The BPD additive increases the capacity retention of lithium-sulfur batteries, mainly due to the formation of various BPD-polysulfide complexes which prevents polysulfide dissolution. Comparison with other thiol-based additives shows that the optimal additive balances solubility and polysulfide-additive stabilization.

In this study, we examine the mechanism of flip-flop diffusion of proton carriers across the lipid layer of a hybrid bilayer membrane (HBM). The HBM consists of a lipid monolayer appended on top of a self-assembled monolayer containing a Cu-based O2 reduction catalyst on a Au electrode. The flip-flop diffusion rates of the proton carriers dictate the kinetics of O2 reduction by the electrocatalyst. By varying both the tail lengths of the proton carriers and the lipids, we find the combinations of lengths that maximize the flip-flop diffusion rate. These experimental results combined with biophysical modeling studies allow us to propose a detailed mechanism for transmembrane flip-flop diffusion in HBM systems, which involves the bending of the alkyl tail of the proton carrier as the rate-determining step. Additional studies with an unbendable proton carrier further validate these mechanistic findings.

Proton-coupled electron transfer (PCET) reactions are ubiquitous in biochemistry and alternative energy schemes. Natural enzymes utilize quinones in proton transfer chains and energy conversion processes. Here, we utilize a bio-inspired hybrid bilayer membrane system to control the reaction mechanism of a quinone molecule covalently bound to an electrode surface. In particular, by impeding proton access to the quinone moiety, we change the reaction pathway from a PCET process to a pure electron transfer step. We further alter the reaction pathway to a stepwise PCET process by controlling the proton flux through the use of an alkyl proton carrier incorporated in the lipid membrane. By modulating proton availability, we control the quinone reaction pathway without changing the molecular structure of the redox species. This work provides unique insight into PCET reactions and a novel electrochemical platform for interrogating them.