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The use of Deep Neural Networks (DNNs) for the classification of electrochemical mechanisms using simulated voltammograms with one cycle of the potential for training has previously been reported. In this paper, it is shown how valuable additional patterns for mechanism distinction become available when a new DNN with advanced architecture is trained simultaneously on images obtained from three cycles of potential using tensor inputs. Significant improvement relative to the single cycle training in achieving correct classification of E, EC1st and EC2nd mechanisms (E = electron transfer step, C1st and C2nd are first and second order follow up chemical reactions, respectively) is demonstrated with noisy simulated data for conditions where all mechanisms are close to chemically reversible and hence difficult to distinguish even by an experienced electrochemist. Challenges anticipated in applying the new DNN to classification of experimental data are highlighted. Directions for future development are also discussed.

[Pt{(p-BrC6F4)NCH═C(Cl)NEt2}Cl(py)] (1Cl) is the product of the hydrogen peroxide oxidation of the PtII anticancer agent [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] (1). Insights into electron delocalization and bonding in [Pt{(p-BrC6F4)NCH═C(Cl)NEt2}Cl(py)]+ (1Cl+) obtained by electrochemical oxidation of 1Cl have been gained by spectroscopic and computational studies. The 1Cl/1Cl+ process is chemically and electrochemically reversible on the short time scale of voltammetry in dichloromethane (0.10 M [Bu4N][PF6]). Substantial stability is retained on longer time scales enabling a high yield of 1Cl+ to be generated by bulk electrolysis. In situ IR and visible spectroelectrochemical studies on the oxidation of 1Cl to 1Cl+ and the reduction of 1Cl+ back to 1Cl confirm the long-term chemical reversibility. DFT calculations indicate only a minor contribution to the electron density (13%) resides on the Pt metal center in 1Cl+, indicating that the 1Cl/1Cl+ oxidation process is extensively ligand-based. Published X-ray crystallographic data show that 1Cl is present in only one structural form, while NMR data on the dissolved crystals revealed the presence of two closely related structural forms in an almost equimolar ratio. Solution-phase EPR spectra of 1Cl+ are consistent with two closely related structural forms in a ratio of about 90:10. The average g value for the frozen solution spectra (2.0567 for the major species) is significantly greater than the 2.0023 expected for a free radical. Crystal field analysis of the EPR spectra leads to an estimate of the 5d(xz) character of around 10% in 1Cl+. Analysis of X-ray absorption fine structure derived from 1Cl+ also supports the presence of a delocalized singly occupied metal molecular orbital with a spin density of approximately 17% on Pt. Accordingly, the considerably larger electron density distribution on the ligand framework (diminished PtIII character) is proposed to contribute to the increased stability of 1Cl+ compared to that of 1+.

Excessive reliance on fossil fuels has led to the release and accumulation of large quantities of CO

The development of Cu-based catalysts for the electrochemical CO2 reduction reaction (eCO2 RR) is of major interest for generating commercially important C2 liquid products such as ethanol. Cu is exclusive among the eCO2 RR metallic catalysts in that it facilitates the formation of a range of highly reduced C2 products, with a reasonable total faradaic efficiency but poor product selectivity. Here, a series of new sulfide-derived copper-cadmium catalysts (SD-Cux Cdy ) was developed. An excellent faradaic efficiency of around 32 % but with a relatively low current density of 0.6 mA cm-2 for ethanol was obtained using the SD-CuCd2 catalyst at the relatively low overpotential of 0.89 V in a CO2 -saturated aqueous 0.10 m KHCO3 solution with an H-cell. The current density increased by an order of magnitude under similar conditions using a flow cell where the mass transport rate for CO2 was greatly enhanced. Ex situ spectroscopic and microscopic, and voltammetric investigations pointed to the role of abundant phase boundaries between CdS and Cu+ /Cu sites in the SD-CuCd2 catalyst in enhancing the selectivity and efficiency of ethanol formation at low potentials.

Advanced data analysis tools such as mathematical optimisation, Bayesian inference and machine learning have the capability to revolutionise the field of quantitative voltammetry. Nowadays such approaches can be implemented routinely with widely available, user-friendly modern computing languages, algorithms and high speed computing to provide accurate and robust methods for quantitative comparison of experimental data with extensive simulated data sets derived from models proposed to describe complex electrochemical reactions. While the methodology is generic to all forms of dynamic electrochemistry, including the widely used direct current cyclic voltammetry, this review highlights advances achievable in the parameterisation of large amplitude alternating current voltammetry. One significant advantage this technique offers in terms of data analysis is that Fourier transformation provides access to the higher order harmonics that are almost devoid of background current. Perspectives on the technical advances needed to develop intelligent data analysis strategies and make them generally available to users of voltammetry are provided.

The α-[S2W18O62]4–/5– and α-[S2W18O62]5–/6– polyoxometalate (POM) reduction processes at boron-doped diamond (BDD) disk electrodes in acetonitrile (0.50 M [n-Bu4N][PF6]) have been investigated usin...

Large amplitude Fourier transform alternating current (FTAC) voltammetry has been used to parameterise the electrode kinetics associated with the reduction of α-[S2W18O62]^(4-) in acetonitrile ([n-...

Polyoxometalates (POMs) have been proposed as electromaterials for lithium-based batteries because they provide access to multiple electron transfer reactions coupled to fast lithium ion transport ...

Addition of low concentrations of water to an aprotic solvent can lead to large changes in the thermodynamics of some electrode processes. In contrast, the impact of water addition on the electrode...

There has been a rapid growth in the use of metal-organic framework (MOF) materials as electrocatalysts. However, simple anodic stripping analysis reveals that some well-known previously reported stable MOFs are in fact unstable at the negative potentials used to catalytically reduce CO2 in aqueous electrolyte media. Thus, it is the resulting metal nanoparticles derived from reduction of the MOFs rather than the MOFs themselves that are the electrocatalysts. The results reported herein therefore suggest that stability data and the origin of the activity for MOF electrocatalysts may need careful re-evaluation and that suitable strategies are needed to ensure that stable MOF electrocatalysts have been synthesized. The use of the readily accessible stripping analysis method provides a powerful tool to assess MOF stability under turnover conditions.

The power of Fourier-transformed large amplitude alternating current voltammetry (FTACV) has been applied to parameterize the reduction of the phosphotungstate [PW11O39{Sn(C6H4)C≡C(C6H4)(N3C4H10)}]...

Cu is a catalyst that can electrochemically reduce CO2 to a variety of industrially important carbon products, but often with poor selectivity and low current density. Alloying Cu with other metals...

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Use of carefully designed computer supported parameterisation methods in voltammetric studies can provide highly robust and accurate methods for simultaneously quantifying the large number of parameters present in complex electrochemical reactions. In this study, a computer program has been developed to parameterise large amplitude AC voltammetric data using mathematical optimisation in combination with Bayesian inference algorithms for calculating posterior distributions of parameters and hence uncertainties in parameter values. The computer program has been applied to objective functions, relevant to total AC current, frequency domain data in the form of the power spectrum derived from Fourier transformation and multivariate based methods using the resolved harmonic data. The robustness of the objective functions have been confirmed and Bayesian inference methods have been validated using “noisy” synthetic and experimental data for the [Fe(CN)6]3−/4− reduction process in aqueous 3.0 M KCl electrolyte at a gold electrode. It was found that the harmonic based Bayesian inference methods outperformed other methods in parameterisation of the thermodynamics and electrode kinetics of the close to reversible [Fe(CN)6]3−/4− process due to their ability to compensate for non-ideality in the modelling and the superior parameter sensitivities available in the higher harmonics. The computer supported and heuristic methods were compared. Their advantages and limitations are discussed.

The development of Cu-based catalysts for the electrochemical CO

Two-dimensional (2D) materials are attractive catalysts for the electrochemical reduction of carbon dioxide reaction (eCO2 RR) by virtue of their tunable atomic structures, abundant active sites, enhanced conductivity, suitable binding affinity to carbon dioxide and/or reaction intermediates, and intrinsic scalability. Herein, recent advances in 2D catalysts for the eCO2 RR are reviewed. Structural features and properties of 2D materials that contribute to their advanced electrocatalytic properties are summarized, and strategies for enhancing their activity and selectivity for the eCO2 RR are reviewed. Prospects and challenges of applications of 2D catalysts for the eCO2 RR on an industrial scale are highlighted.

The rational design of binuclear Au(I)–Au(I), Au(II)–Au(II), and Au(I)–Au(III) complexes requires an understanding of how the redox states interconvert. Herein, the electrochemical interconversion of the three oxidation states I, II, and III is reported on the voltammetric (cyclic and rotating disk electrode) time scales for binuclear gold complexes containing C6F4PPh2 as a ligand, to demonstrate for the first time formation of a binuclear Au(II)–Au(II) from a Au(I)–Au(III) complex. Results are supported by bulk electrolysis and coulometry with reaction products being identified by 31P NMR and UV–vis spectroscopy. All electrochemical processes involve an overall two-electron charge-transfer process with no one-electron intermediate being detected. Importantly, the kinetically rather than thermodynamically favored isomer [Au2IIX2(μ-2-C6F4PPh2)2] is formed on redox cycling of [XAuI(μ-2-C6F4PPh2)(κ2-2-C6F4PPh2)AuIIIX] (X = Cl, ONO2). Finally, a mechanism is proposed to explain the simultaneous change of coor...

A simple one-pot method has been developed to synthesize a palladium/cuprous oxide-copper (Pd/Cu2 O-Cu) material with a well-defined structure, by modification of Cu2 O-Cu with Pd through a galvanic replacement reaction. Compared with the well-known copper/cuprous oxide (Cu/Cu2 O) catalysts, the Pd/Cu2 O-Cu material can catalyze the electroreduction of CO2 into C1 products with much higher faradaic efficiencies at lower overpotentials in a CO2 -saturated 0.5 m NaHCO3 solution. In particular, the highest faradaic efficiencies of 92 % for formate and 30 % for methane were achieved at -0.25 and -0.65 V (vs. the reversible hydrogen electrode), respectively. The improvement is suggested to be the result of a synergistic effect between PdH and the catalytically active copper sites during electrochemical CO2 reduction.

Uniting the advantages of molecular and heterogeneous catalysts, a continuing effort in heterogeneous catalysis, has often proved to be challenging. This work introduces a facile strategy to obtain molybdenum-oxo functional groups strongly anchored on metallic copper support through in situ electrochemical reduction of a cuprous oxomolybdate thin film resulting from electroless plating. The oxomolybdate modified copper electrode exhibits enzyme-like activity and excellent stability for the hydrogen evolution reaction over the entire pH range, together with excellent mechanical properties and cost effectiveness that are needed for commercial applications, including seawater electrolysis. In situ Fourier transformed ac voltammetric study revealed two underlying MoIV/III and MoIII/II processes that are responsible for the high catalytic activity of the material. This study opens up a new avenue for designing advanced heterogeneous catalysts for a greener future using a broad range of oxometalates.

Three new crystallographically characterized compounds were prepared in high yield from reactions between [Cp2Co]PF6 (Cp = cyclopentadiene) and lithium salts of the radical anion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF41–) or the dianionic TCNQF42–. The two [Cp2Co]TCNQF4 compounds (1 and 2) with 1:1 stoichiometry were found to be polymorphic, α and β. Remarkably, the syntheses only differed by the presence of a small amount of neutral TCNQF4 in the case of polymorph β (2). The role of the TCNQF4 has been rationalized on the basis of a transient intermediate, postulated as [Cp2Co](TCNQF4)2. Compound 3 contains TCNQF42– and crystallized as [Cp2Co]Li(TCNQF4). This material highlights a novel coordination mode for the Li+ cation that participated in the formation of a metal–organic framework accommodating the [Cp2Co]+ cation. All complexes were comprehensively characterized by Fourier transform infrared spectroscopy, UV–vis spectroscopy, and electrochemistry. Polymorph β (2) has a condu...

Estimation of parameters of interest in dynamic electrochemical (voltammetric) studies is usually undertaken via heuristic or data optimization comparison of the experimental results with theory based on a model chosen to mimic the experiment. Typically, only single point parameter values are obtained via either of these strategies without error estimates. In this article, Bayesian inference is introduced to Fourier-transformed alternating current voltammetry (FTACV) data analysis to distinguish electrode kinetic mechanisms (reversible or quasi-reversible, Butler-Volmer or Marcus-Hush models) and quantify the errors. Comparisons between experimental and simulated data were conducted across all harmonics using public domain freeware (MECSim).

The solution-based synthesis of the coordination polymer, CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane), which exists in two phases, has predominately used acetonitrile (MeCN) as the solvent. However, our knowledge on the growth and properties of CuTCNQ in other solvents remains limited. In this work, the synthesis of CuTCNQ on Cu foil in two protic (MeOH, EtOH) as well as four aprotic (MeCN, DMSO, DMF, THF) solvents has allowed us to obtain new insights into the important role of the reaction medium in the spontaneous crystallization of CuTCNQ in discrete morphologies and phases. A new electrochemical method for phase identification also has been developed to support this study. Findings reveal that (i) the solvents with higher dielectric constants favor CuTCNQ crystallization; (ii) irrespective of the solvent, use of high temperature (60 °C vs. 25 °C in conventional synthesis) promotes CuTCNQ crystallization and facilitate conversion of phase I to phase II; (iii) phase I CuTCNQ possess enhanced redox catalysis (ferricyanide reduction by thiosulfate) performance over phase II CuTCNQ; and (iv) the amount of catalyst is not necessarily the most important factor for driving catalytic reactions, and other factors, such as, morphology, redox characteristics and solvent in which the CuTCNQ is synthesized may dictate the overall catalytic performance. These findings emphasize the importance of understanding the influence of parameters, such as, solvent and temperature in CuTCNQ synthesis as a means of providing materials with improved catalytic activity.

Metallic bismuth (Bi) is an electrocatalyst that promotes CO2 reduction to formate. However, a substantial overpotential is needed to achieve a high formate faradaic efficiency along with a large catalytic current density, and this hinders its practical application. In this work, a facile strategy has been developed to obtain lattice-dislocated Bi nanowires on copper foam (Cu foam@BiNW) through in situ electrochemical transformation of an electroless plated Bi film on copper foam after thermal treatment in air. The Cu foam@BiNW is found to be a highly active electrocatalyst for CO2 reduction to formate at a low overpotential, reaching a faradaic efficiency for formate (FEformate) of 95% and a formate partial current density of ∼15 mA cm−2 at −0.69 V vs. RHE. High FEformate values of above 93% were also maintained over a potential range from −0.69 V to −0.99 V vs. RHE. A Fourier transformed ac voltammetric study revealed that unlike other Bi materials, the rate determining step for CO2 reduction on the Cu foam@BiNW electrode is the reduction of protonated CO2˙− radical anion, which indicates the presence of new catalytic active sites on the BiNWs. The high CO2 reduction activity of the Cu foam@BiNW electrode is attributed to the high intrinsic activity arising from the presence of crystal lattice dislocations on the twisted Bi nanowires and the large catalytic surface area associated with the porous structure. This work demonstrates the use of crystal defect engineering to improve the efficiency of electrocatalytic CO2 reduction on Bi metal.

Alternating current (AC) voltammetric techniques are experimentally powerful as they enable Faradaic current to be isolated from non-Faradaic contributions. Finding the best global fit between experimental voltammetric data and simulations based on reaction models requires searching a substantial parameter space at high resolution. In this paper, we estimate parameters from purely sinusoidal voltammetry (PSV) experiments, investigating the redox reactions of a surface-confined ferrocene derivative. The advantage of PSV is that a complete experiment can be simulated relatively rapidly, compared to other AC voltammetric techniques. In one example involving thermodynamic dispersion, a PSV parameter inference effort requiring 7,500,000 simulations was completed in 7 h, whereas the same process for our previously used technique, ramped Fourier transform AC voltammetry (ramped FTACV), would have taken 4 days. Using both synthetic and experimental data with a surface confined diazonium substituted ferrocene derivative, it is shown that the PSV technique can be used to recover the key chemical and physical parameters. By applying techniques from Bayesian inference and Markov chain Monte Carlo methods, the confidence, distribution, and degree of correlation of the recovered parameters was visualized and quantified.

This paper describes the effect of thermodynamic and kinetic dispersion on numerical simulations of three different surface-confined voltammetry experiments, ramped FTACV, Purely sinusoidal voltammetry (PSV) and direct current voltammetry (DCV), and the differences between the dispersed and non-dispersed cases. Dispersion in this case refers to a range of observed values for the thermodynamic driving force and reaction rate of a redox reaction (thermodynamic and kinetic dispersion respectively) . This has been acknowledged as a complicating factor of voltammetry experiments for some time. We demonstrate that thermodynamic dispersion has a far stronger effect than kinetic dispersion, and detail the ways in which kinetic dispersion can be resolved under such conditions. The work is novel in its comparison of three separate voltammetry techniques, and a focus on how to determine the presence of dispersion through computational analysis of experimental voltammetry data alone; previous work has required specific experiments designed to distinguish between dispersed and non-dispersed cases.

The paper includes a thorough charac-terisation of a technique called Purely Sinusoidal Voltammetry (PSV). This technique is usedto infer reaction parameters about a surface-linked redox process, and the characterisationeffort involves both computational and experimental methods.

Polyoxometalates (POMs) have been proposed as electromaterials for lithium-based batteries because they provide access to multiple electron transfer reactions coupled to fast lithium ion transport processes and high stability over many redox cycles. Consequently, knowledge of reversible potentials and Li

Chalcopyrite (CuFeS2) passivation during hydrometallurgical copper extraction is attributed to multiple competing mechanisms that are still not completely understood. Here we have studied the interfacial solution chemistry in situ at polarised chalcopyrite and chalcocite, using scanning electrochemical microscopy (SECM). It was observed that the copper species detected at an ultramicroelectrode (UME) positioned at the mineral:solution interface vary between the two minerals, and are dependent upon both the potential of the mineral and the polarisation time. Cu species formed in the presence of sulfide, derived from incomplete oxidation of chalcopyrite, are observed on the UME tip positioned above chalcopyrite under conditions where passivation may occur, in contrast to Cu(II) in the presence of sulfate under conditions where leaching is facile. Only Cu(II) in the presence of sulfate is observed at the interface of chalcocite. These observations via interfacial voltammetry provide experimental support to mechanistic studies on chalcopyrite leaching, and provide new information to complement previous in situ studies which have mostly focused on interfacial solids.