The influence of electrolyte identity upon the electro-reduction of CO2

AbstractThe influence of supporting electrolyte cations on the voltammetric behaviour and product distribution in N-methylpyrrolidone-based carbon dioxide electroreduction systems is investigated. The reduction potentials associated with TBABF4 (0.1M) and corresponding alkali metal (M+) electrolytes; LiBF4, NaBF4 and RbBF4 (focussing mainly on the reduction of the widely employed Li+ species) were established in both the presence and absence of CO2 at polycrystalline noble metal working electrodes. In situ and ex situ Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and qualitative element identification via flame testing were used to aid the assignment of reduction processes. It was established that CO2 reduction products in the metal cationic systems were formed at a much less negative potential than those found with the non-metal cation (−1.5V vs. Ferrocene, c.f. −2.2V), however the resultant alteration of the surface environment was found to deactivate the electrode to further CO2 reduction. The presence of CO2 in solution was found to affect the potential required for the bulk deposition of metal from the electrolyte through the same process. Where TBA+ and M+ were employed simultaneously in the system, the resultant voltammetry shared the majority of features with the pure M+ system with CO2 reduction suppressed at more negative potentials therefore supporting the conclusion that any ‘catalytic effect’ associated with TBA+ is in fact a lack of deactivation given by the M+ system, rather than any enhancement offered by the former

Au Electrodeposition at the Liquid-Liquid Interface: mechanistic aspects

The deposition mechanism of metallic gold was investigated based on charge transfer voltammetry at the water/1,2-dichloroethane (W/DCE) interface, and the corresponding redox voltammetry of the metal precursor in W and the reductant, triphenylamine (TPA), in DCE. The metal precursor was present as Au(III) (AuCl_4^[−]), or Au(I) (AuCl_2^[−]) in W or DCE. Electron transfer could be observed voltammetrically at the interface between W containing both Au precursors and DCE containing TPA. Au particles, formed by constant potential electrolysis at the W/DCE interface, were examined by transmission electron microscopy. It was shown that deposit size could be controlled via the applied potential and time, with specific conditions to form particles of less than 10 nm identified

An electrochemical investigation of electroless deposition : the copper-DMAB system

An electrochemical study of the copper electroless deposition process, using dimethylamine borane as a reducing agent, has been performed, in order to gain further understanding of the mechanism and kinetics of electroless deposition. An in-depth study of the electro-oxidation of dimethylamine borane (DMAB) was additionally carried out, due to its increasing relevance, not only in electroless deposition, but also in fuel cell technology. DMAB oxidation was studied using different experimental techniques such as voltammetry, chronoamperometry, single-crystal electrochemistry and in-situ Fourier Transform infrared spectroscopy, which demonstrated that adsorption of the DMAB molecule, and its intermediates, plays an important role in the oxidation mechanism and kinetics. The initial dissociation process is catalysed by the presence of metallic surfaces and the applied potential. On gold surfaces, DMAB undergoes a three-electron transfer at low overpotentials, with a further oxidation process of up to six electrons occurring at high overpotentials. Chemical interactions with gold oxide produce further oxidation of the DMAB molecule. In the potential region of gold oxide formation, in highly alkaline media, the dimethylamine is also oxidised. The voltammetric behaviour of bipolar cells was studied using model reversible and quasi-reversible redox couples, in conjunction with numerical simulations of the system. DMAB oxidation and copper electrodeposition were studied separately and together using the bipolar cell, providing useful information of the 'coupling' effects between the cathodic and anodic processes of electroless deposition. The ability to quantify side reactions associated with electroless plating, namely hydrogen evolution in the copper-DMAB system, was also demonstrated. The kinetics of the copper-DMAB electroless system was studied in detail, using the electroless bath and a galvanic cell configuration. The fact that the rate of deposition decreased upon the physical separation of the two half-reactions, as well as the observed catalysis of the oxidation of DMAB by copper surfaces, lead to the conclusion that the mixed potential theory (MPT) does not apply to this system. Faradaic efficiencies never reached 100% due to the parasitic side reactions mentioned above; the latter were especially prominent in the early stages of deposition. Crystalline copper films were obtained, with a higher fraction of Cu (111) than expected for polycrystalline copper, while the roughness of the deposits was found to increase with deposition time.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An electrochemical investigation of electroless deposition : the copper-DMAB system

An electrochemical study of the copper electroless deposition process, using dimethylamine borane as a reducing agent, has been performed, in order to gain further understanding of the mechanism and kinetics of electroless deposition. An in-depth study of the electro-oxidation of dimethylamine borane (DMAB) was additionally carried out, due to its increasing relevance, not only in electroless deposition, but also in fuel cell technology. DMAB oxidation was studied using different experimental techniques such as voltammetry, chronoamperometry, single-crystal electrochemistry and in-situ Fourier Transform infrared spectroscopy, which demonstrated that adsorption of the DMAB molecule, and its intermediates, plays an important role in the oxidation mechanism and kinetics. The initial dissociation process is catalysed by the presence of metallic surfaces and the applied potential. On gold surfaces, DMAB undergoes a three-electron transfer at low overpotentials, with a further oxidation process of up to six electrons occurring at high overpotentials. Chemical interactions with gold oxide produce further oxidation of the DMAB molecule. In the potential region of gold oxide formation, in highly alkaline media, the dimethylamine is also oxidised. The voltammetric behaviour of bipolar cells was studied using model reversible and quasi-reversible redox couples, in conjunction with numerical simulations of the system. DMAB oxidation and copper electrodeposition were studied separately and together using the bipolar cell, providing useful information of the 'coupling' effects between the cathodic and anodic processes of electroless deposition. The ability to quantify side reactions associated with electroless plating, namely hydrogen evolution in the copper-DMAB system, was also demonstrated. The kinetics of the copper-DMAB electroless system was studied in detail, using the electroless bath and a galvanic cell configuration. The fact that the rate of deposition decreased upon the physical separation of the two half-reactions, as well as the observed catalysis of the oxidation of DMAB by copper surfaces, lead to the conclusion that the mixed potential theory (MPT) does not apply to this system. Faradaic efficiencies never reached 100% due to the parasitic side reactions mentioned above; the latter were especially prominent in the early stages of deposition. Crystalline copper films were obtained, with a higher fraction of Cu (111) than expected for polycrystalline copper, while the roughness of the deposits was found to increase with deposition time.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Use of voltammetry for in vitro equilibrium and transport studies of ionisable drugs

In this review, we will briefly outline the voltammetric investigations of the transfer of ionisable drugs at the interface between two immiscible electrolyte solutions. The voltammetric techniques enable the determination of some key in vitro properties of ionisable drugs, including partition coefficient, diffusion coefficient and membrane permeability. Some successful applications will be highlighted, together with the background methodologies

Resolution of Li deposition vs. intercalation of graphite anodes in lithium ion batteries - an in situ electron paramagnetic resonance study

In situ electrochemical electron paramagnetic resonance (EPR) spectroscopy is used to understand the mixed lithiation/deposition behavior on graphite anodes during the charging process. The conductivity, degree of lithiation, and the deposition process of the graphite are reflected by the EPR spectroscopic quality factor, the spin density, and the EPR spectral change, respectively. Classical over‐charging (normally associated with potentials ≤0 V vs. Li(+)/Li) are not required for Li metal deposition onto the graphite anode: Li deposition initiates at ca. +0.04 V (vs. Li(+)/Li) when the scan rate is lowered to 0.04 mV s(−1). The inhibition of Li deposition by vinylene carbonate (VC) additive is highlighted by the EPR results during cycling, attributed to a more mechanically flexible and polymeric SEI layer with higher ionic conductivity. A safe cut‐off potential limit of +0.05 V for the anode is suggested for high rate cycling, confirmed by the EPR response over prolonged cycling

[M(CO)4(2,2′-bipyridine)] (M = Cr, Mo, W) as efficient catalysts for electrochemical reduction of CO2 to CO at a gold electrode

Group 6 complexes of the type [M(CO)4(bpy)] (M=Cr, Mo, W) are capable of behaving as electrochemical catalysts for the reduction of CO2 at potentials less negative than those for the reduction of the radical anions [M(CO)4(bpy)].−. Cyclic voltammetric, chronoamperometric and UV/Vis/IR spectro-electrochemical data reveal that five-coordinate [M(CO)3(bpy)]2− are the active catalysts. The catalytic conversion is significantly more efficient in N-methyl-2-pyrrolidone (NMP) compared to tetrahydrofuran, which may reflect easier CO dissociation from 1e−-reduced [M(CO)4(bpy)].− in the former solvent, followed by second electron transfer. The catalytic cycle may also involve [M(CO)4(H-bpy)]− formed by protonation of [M(CO)3(bpy)]2−, especially in NMP. The strongly enhanced catalysis using an Au working electrode is remarkable, suggesting that surface interactions may play an important role, too

On the controlled electrochemical preparation of R4N+ graphite intercalation compounds and their host structural deformation effects

AbstractWe present electrochemical studies of tetraalkylammonium (R4N+) reduction chemistry at Highly Orientated Pyrolytic Graphite (HOPG) and glassy carbon (GC) electrodes. We show that by electrochemically controlled intercalation and formation of a graphite intercalation complex (GIC) into layered HOPG, the irreversible reduction of the tetraalkylammonium cation can be prevented and subsequent de-intercalation of the GIC via the use of potentiostatic control is achievable. R4N+ cations with varying alkyl chain lengths (methyl, ethyl and butyl) have been shown to exhibit excellent charge recovery effects during charge/discharge studies. Finally the effects of electrode expansion on the degree of recovered charge have been investigated and the observed effects of R4N+ intercalation on the graphite cathode have been probed by scanning electron microscopy (SEM) and X-ray diffraction (XRD)

Functionalization of graphene at the organic/water interface

A simple method for the deposition of noble metal (Pd, Au) nanoparticles on a free-standing chemical vapour deposited graphene (CVD GR) monolayer is reported. The method consists of assembling the high purity CVD GR, by transfer from poly (methyl methacrylate) (PMMA), at the organic/water interface. Metal deposition can then proceed using either spontaneous or electrochemically-controlled processes. The resultant graphene-based metal nanoclusters are characterized using atomic force and electron microscopy techniques, and the location of the nanostructures underneath the graphene layer is determined from the position and the intensity changes of the Raman bands (D, G, 2D). This novel process for decoration of a single-layer graphene sheet with metal nanoparticles using liquid/liquid interfaces opens an alternative and useful way to prepare low dimensional carbon-based nanocomposites and electrode materials