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The instability and expense of anodes for water electrolyzers with acidic electrolytes can be overcome through the implementation of a cobalt-iron-lead oxide electrocatalyst, [Co-Fe-Pb]Ox , that is self-healing in the presence of dissolved metal precursors. However, the latter requirement is pernicious for the membrane and especially the cathode half-reaction since Pb2+ and Fe3+ precursors poison the state-of-the-art platinum H2 evolving catalyst. To address this, we demonstrate the invariably stable operation of [Co-Fe-Pb]Ox in acidic solutions through a cobalt-selective self-healing mechanism without the addition of Pb2+ and Fe3+ and investigate the kinetics of the process. Soft X-ray absorption spectroscopy reveals that low concentrations of Co2+ in the solution stabilize the catalytically active Co(Fe) sites. The highly promising performance of this system is showcased by steady water electrooxidation at 80±1 °C and 10 mA cm-2 , using a flat electrode, at an overpotential of 0.56±0.01 V on a one-week timescale.

Shuttling protons in ammonia synthesis An electrochemical route to ammonia could substantially lower the greenhouse gas emissions associated with the current thermal Haber-Bosch process. One relatively promising option under study involves reductive formation of lithium nitride, which can be protonated to ammonia. However, the ethanol used to date as a local proton source in these studies may degrade under the reaction conditions. Suryanto et al. report the use of a tetraalkyl phosphonium salt in place of ethanol (see the Perspective by Westhead et al. ). This cation can stably undergo deprotonation–reprotonation cycles and, as an added benefit, it enhances the ionic conductivity of the medium. Science , abg2371, this issue p. 1187 ; see also abi8329, p. 1149

Considering the attractive optoelectronic properties of metal halide perovskites (MHPs), their introduction to the field of photocatalysis was only a matter of time. Thus far, MHPs have been explored for the photocatalytic generation of hydrogen, carbon dioxide reduction, organic synthesis, and pollutant degradation applications. Of growing research interest and possible applied significance are the currently emerging developments of MHP-based Z-scheme heterostructures, which can potentially enable efficient photocatalysis of highly energy-demanding redox processes. In this Perspective, we discuss the advantages and limitations of MHPs compared to traditional semiconductor materials for applications as photocatalysts and describe emerging examples in the construction of MHP-based Z-scheme systems. We discuss the principles and material properties that are required for the development of such Z-scheme heterostructure photocatalysts and consider the ongoing challenges and opportunities in this emerging field.

Ferroelectric semiconductors like BiFeO3 are increasingly being investigated for applications in solar energy conversion and storage due to their intrinsic ability to induce ferroelectric polarization-driven separation of the photogenerated charge carriers resulting in above-bandgap photovoltages. Nevertheless, the BiFeO3 has been commonly prepared using complex and expensive fabrication techniques, e.g., epitaxial growth, radio frequency sputtering and pulsed laser deposition, which are not economically viable for large-scale production. Herein, we report a facile and scalable method for the fabrication of porous perovskite BiFeO3 photoanodes, as well as sequential interfacial engineering methods to enhance their photoelectrochemical performance for water splitting. Upon atomic layer deposition of a TiO2 overlayer and photo-assisted electrodeposition of a cobalt oxide/oxyhydroxide co-catalyst, the photocurrent density of the engineered photoanode for oxygen evolution reaction (1 M NaOH) significantly increased from negligible photocurrent of the pristine BiFeO3 to 0.16 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) under simulated 1 sun irradiation (100 mW cm−2, AM1.5G spectrum). Furthermore, such functionalization of the BiFeO3 photoanodes shifts the photoelectrochemical oxidation onset potential by 0.7 V down to 0.6 V vs. RHE. The significantly enhanced photoelectro-oxidation activity is facilitated by the improved charge transfer and electrochemical kinetics.

The results presented herein unambiguously demonstrate that neither nanoparticulate carbon-supported gold, nor bismuth powder are active catalysts for the electrocatalytic dinitrogen reduction, but...

As research on sustainable ammonia synthesis via electrochemical and photochemical N2 reduction progresses to include a wider variety of aqueous and aprotic electrolytes, 1H NMR spectroscopy is inc...

High efficiency and environmental stability are mandatory performance requirements for commercialization of perovskite solar cells (PSCs). Herein, efficient centimeter-scale PSCs with improved stability were achieved by incorporating an additive-free 2,2',7,7'-tetrakis[

Caesium silver bismuth halide double perovskites, in the first instance Cs2AgBiBr6, were recently introduced to the field of emerging photovoltaics as environmentally friendly, non-toxic and thermodynamically stable photoabsorber materials. However, the wide indirect bandgaps of these materials indicate the need for bandgap engineering and enhancing the light absorption to improve the photovoltaic performance. The present work demonstrates that this can be achieved via modification of the double perovskite with sulphide to obtain caesium silver bismuth sulphobromide materials, Cs2AgBiBr6−2xSx, which have been synthesised as pin-hole-free uniform films and systematically investigated herein. Notable enhancements in the intrinsic light absorption for 0 ≤ x ≤ 0.2 are demonstrated, as are the improvements by up to 50% in the photocurrent density of the corresponding thin-film solar cells. The devices based on the films with the nominal composition Cs2AgBiBr5.8S0.1 delivered a short-circuit current density of 3.0 ± 0.3 mA cm−2 and a power conversion efficiency of 1.9 ± 0.1% (cf. 2.1 ± 0.2 mA cm−2 and 1.3 ± 0.1%, respectively, for the control cells based on the sulphide-free Cs2AgBiBr6). Equally important, caesium silver bismuth sulphobromides demonstrate excellent stability against all common environmental stimuli, viz. heat, light, and humidity.

In situ experiments combining X-ray absorption spectroscopy (XAS) and electrochemistry have now become an indispensable tool for understanding the mechanisms of operation, structure, and the modes of degradation of electrocatalysts under operational conditions. Herein, the design of a gas- and liquid-tight spectroelectrochemical cell (SEC) and an experimental protocol for the simultaneous collection of high-quality XAS and electrochemical data are introduced. The effects of the working electrode, loading of active material, and X-ray damage are demonstrated and interpreted by an example of a well-known heterogenite-like cobalt oxide water oxidation catalyst. The SEC permitted reproducible X-ray absorption near edge structure to be collected with a resolution of at least 0.05 eV (equivalent to approximately 0.02 unit oxidation state sensitivity) and allowed X-ray-mediated photoeffects to be examined in detail. Furthermore, tracking of the potential-dependent changes in the oxidation state of a cobalt oxide catalyst with high precision and reproducibility is demonstrated. These in situ XAS data are correlated with a previous detailed electrokinetic analysis to identify the nature of the active state of the heterogenite-like water oxidation catalyst and conclude that metal oxidation states higher than IV are not involved in the catalytic mechanism. Finally, the implications of the significantly different timescales of the probed electron transfer events and the XAS analysis on the interpretation of the in situ spectroelectrochemical data are critically discussed, focusing on the mechanism of the water oxidation reaction.

Electrochemical water splitting with a proton-exchange membrane electrolyte provides many advantages for the energy-efficient production of high-purity H2 in a sustainable manner, but the current technology relies on high loadings of expensive and scarce iridium at the anodes, which are also often unstable in operation. To address this, the present work scrutinises the electrocatalytic properties of a range of mixed antimony-metal (Co, Mn, Ni, Fe, Ru) oxides synthesised as thin films by a simple solution-based method for the oxygen evolution reaction in aqueous 0.5 M H2SO4. Among the noble-metal free catalysts, cobalt-antimony and manganese-antimony oxides demonstrate good stability over 24 h and reasonable activity at 24 ± 2 °C, but slowly lose their initial activity at elevated temperatures. The ruthenium-antimony system is highly active, requiring an overpotential of only 0.39 ± 0.03 and 0.34 ± 0.01 V to achieve 10 mA cm-2 at 24 ± 2 and 80 °C, respectively, and most importantly, remaining remarkably stable during one-week tests at 80 °C. Detailed characterisation reveals that the enhanced stability of metal-antimony oxides water oxidation catalysts can arise from two distinct structural scenarios: either formation of a new antimonate phase, or nanoscale intermixing of metal and antimony oxide crystallites. Density functional theory analysis further indicates that the stability in operation is supported by the enhanced hybridisation of the oxygen p- and metal d-orbitals induced by the presence of Sb.

Ammonia is of emerging interest as a liquefied, renewable-energy-sourced energy carrier for global use in the future. Electrochemical reduction of N2 (NRR) is widely recognised as an alternative to the traditional Haber–Bosch production process for ammonia. However, though the challenges of NRR experiments have become better understood, the reported rates are often too low to be convincing that reduction of the highly unreactive N2 molecule has actually been achieved. This perspective critically reassesses a wide range of the NRR reports, describes experimental case studies of potential origins of false-positives, and presents an updated, simplified experimental protocol dealing with the recently emerging issues., Discovering a sustainable route to ammonia as a fertiliser and as an energy carrier is critically important, but many recent reports on the electrochemical nitrogen reduction are false positives. Here the authors uncover the emerging experimental traps and detail protocols to reliably avoid them.

Previous theoretical work has predicted vanadium and niobium nitrides to be catalytically active toward the electrochemical reduction of dinitrogen to ammonia and inactive for the hydrogen evolutio...

Design of efficient photoelectrodes for water oxidation requires careful optimization of the morphology and structure of a photoactive material to maximize electrical conductivity and balance carrier diffusion length with light penetration depth. Hematite-based photoanodes can theoretically oxidize water at very high rates, as provided by the optimal band-gap, but their performance is limited by the poor charge transport and low charge separation efficiency. Herein, we have developed physically- and chemically-induced morphological and structural tuning procedures, viz. capillary-force-induced self-assembly and corrosion followed by regrowth, which enable significant improvements in the performance of the hematite photoanodes. Specifically, a 24-fold enhancement in the photocurrent density for water oxidation (1 M NaOH) at 1.23 V vs. reversible hydrogen electrode under simulated 1 sun (100 mW cm–2, AM1.5G solar spectrum) irradiation has been achieved. The capillary-force-induced self-assembly improves the crystallinity, promotes preferential orientation of the hematite along the [110] direction, and thereby enhances the electrical conductivity of the material. Subsequent dissolution and regrowth of the hematite nanostructures provide higher light absorption, improve photo-generated charge separation and facilitate photoelectrocatalytic kinetics resulting in the significantly higher photoelectrocatalytic activity. These broadly applicable insights provide a robust set of guidelines for the engineering of efficient photoelectrodes initially made of disordered structures for conversion of solar energy into renewable fuels.

Transparent quasi-interdigitated electrodes (t-QIDEs) were produced by replacing the opaque components of existing QIDEs with indium tin oxide (ITO). We demonstrate their application in the first semitransparent back-contact perovskite solar cell. A device with a VOC of 0.88 V and a JSC of 5.6 mA cm–2 produced a modest 1.7% efficiency. The use of ITO allows for illumination of the device from front and rear sides, resembling a bifacial solar cell, both of which yield comparable efficiencies. Coupled optoelectronic simulations reveal this architecture may achieve power conversion efficiencies of up to 11.5% and 13.3% when illuminated from the front and rear side, respectively, using a realistic quality of perovskite material.

Recent advances in materials science have significantly broadened the range of electrodes available for use in dynamic forms of electrochemistry. In the modern era of dc voltammetry when the kinetic model of electron transfer with coupled chemical reactions was introduced, initial emphasis in theory-experiment comparison was placed on use of the ideal homogenous liquid mercury electrode with significant attention also given to polycrystalline and faceted metal electrodes. Nowadays, there are a plethora of carbon-based electrodes such as glassy carbon, edge and basal plane graphite, boron doped diamond, graphene and carbon nanotubes that may be extremely heterogeneous. These are supplemented by chemical modifications designed for example to improve the efficiency of electrocatalysis. In this review, it is shown that analysis of the higher harmonics available in large amplitude Fourier transformed alternating current voltammetry (FTacV) allows key processes to be detected, that are masked under commonly used dc voltammetric conditions. In particular it is shown how underlying fast electron processes that facilitate carbon dioxide reduction at tin electrodes and oxygen evolution at cobalt based electrodes can be directly detected and analysed for the first time. FTacV also experimentally reveals that structural defects or adatoms can give rise to well-defined higher order ac harmonics suggesting that a fast electron transfer process is associated with the active sites during electrocatalytic oxidation or reduction. Importantly, electron transfer processes often can be evaluated by FTacV in the presence and absence of the electrocatalysis, unlike dc voltammetric methods. The ability to analyse third and higher order ac harmonics that are essentially devoid of background charging current and which allow the electron transfer and catalytic steps to be resolved, presents new opportunities for fundamental advances in understanding complex electrochemical reaction mechanisms taking place at heterogeneous electrodes. Related advantages in studying electron transfer of surface confined metallo-enzymes or proteins in the presence and absence of their catalytically oxidised or reduced biologically relevant substrate partners are also surveyed. Finally, prospects for providing quantitative accounts of complex reactions at highly heterogeneous electrodes by FTacV are considered.

Design of novel efficient light-harvesters for p-type dye-sensitised solar cells (DSSCs) is indispensable for further advances in this photovoltaic technology. Herein, a novel D-π-A (D=donor, π=π-conjugated linker, A=acceptor) sensitiser, ZnP1, featuring an electron acceptor, perylenemonoimide (PMI), connected to an electron donor, di(p-carboxyphenyl)amine (DCPA), through fluorene and a zinc(II) porphyrin with alkyl chains as a π-conjugated bridge is introduced. Spectroscopic and electrochemical characterisation of this dye along with a newly synthesised PMI-free reference dye ZnP0 has been undertaken to demonstrate strong electron coupling between the DCPA donor and PMI acceptor subunits through the porphyrin ring in ZnP1, which redshifts the light absorption onset to the near-IR region. When integrated into p-DSSCs based on a mesoporous nickel(II) oxide semiconductor electrode and a tris(acetylacetonato) iron(III/II) redox mediator, ZnP1 exhibits an onset of the incident photon-to-current conversion efficiency at 800 nm and a power conversion efficiency of up to 0.92 % under simulated 100 mW cm-2 AM 1.5 G irradiation. This is the highest efficiency of the porphyrin-based p-DSSCs hitherto reported.

The present work introduces a rapid low-temperature microwave-assisted synthesis of nickel(iron) layered hydroxides and sulphides that exhibit robust catalytic activity for electrooxidation of alkaline water – the most feasible source of electrons for any renewable fuel synthesis. The procedures require not more than an hour to complete at 120–150 °C with quantitative yields of: (i) few-atomic-layers thick porous sheets of Ni0.75Fe0.25(OH)2+x with surface area ABET = 149 m2 g−1, and (ii) interconnected Ni0.75Fe0.25S2+y particles of few nanometers in size covered with a thin oxide/hydroxide layer having ABET = 87 m2 g−1. These and other morphological and structural features of the materials were inferred from XRD, XPS, Ni- and Fe-edge EXAFS/XANES, TEM/SAED, EDX mapping, SEM, N2 adsorption–desorption, and electrochemical techniques. At lower loadings on the electrode surface (≤0.01 mg cm−2), the specific activity for water (1 M KOH) electrooxidation at 0.3 V overpotential is 210 A g−1 for Ni0.75Fe0.25(OH)2+x, and 384 A g−1 for Ni0.75Fe0.25S2+y, which excels the performance of the best-performing analogues. The enhanced electrocatalytic activity of sulphides over hydroxides is defined by the better electrical conductivity and different nature of the electrochemically active surface species. At higher loadings, the activity of the microwave-synthesised NiFe catalysts is found to be partially limited by agglomeration, though still high enough to enable the water oxidation rate of 10 mA cmgeom−2 at overpotentials of only 0.270 ± 0.005 (flat support) and 0.21 V (foam support) with Ni0.75Fe0.25S2+y. The developed methods offer a new facile strategy for the creation of high-performing multicomponent catalysts.

Metal halide perovskite solar cells (PSC) exhibit outstanding power conversion efficiencies when fabricated as mm-sized devices, but creation of high-performing large-area PSCs that are stable under operating conditions on a sufficiently long timescale still presents a significant challenge. We demonstrate herein that modification of the interface between the perovskite and a spiro-OMeTAD hole-transporting material with commercially available para-substituted benzenethiol molecules facilitates fabrication of cm-sized PSCs with both improved efficiency and stability. Comprehensive analysis using specialised and conventional physical characterisation techniques has been undertaken to demonstrate that band alignment at the perovskite surface can be tuned to improve the solar cell efficiency via adsorption of benzenethiols with a significant dipole moment. Moreover, modification of the perovskite with cyano-substituted benzenethiol enhances charge extraction and reduces charge recombination in the devices. These effects enable improvements in the power conversion efficiency of PSCs from 19.0 to 20.2% and from 18.5 to 19.6% under 1 sun AM 1.5G irradiation with 0.16 and 1.00 cm2 apertures, respectively. Most importantly, benzenethiol-modified perovskite solar cells retain more than 80% of the initial performance after 185 h of continuous operation at 50% relative humidity and 50 °C device temperature under 1 sun irradiation, while devices with no interfacial modification undergo continuous deterioration down to 35% of the initial efficiency. These significant improvements are provided by a very simple and highly reproducibile modification procedure that can be readily adopted in other types of PSCs.

Spray pyrolysis of bismuth(III) tris(4-methylbenzodithioate) toluene solutions containing either silver(I) acetate and 1-octanethiol, or copper(I) acetate and 1,2-ethanedithiol is introduced as a low-temperature solution-based method to produce sub-100 nm thick coatings of α cubic rock salt AgBiS2 or orthorhombic Cu3BiS3, respectively. The structure, morphology and optoelectronic properties of the materials thus obtained have been comprehensively characterised using conventional techniques. Extensive optimisation of the deposition conditions has been undertaken to achieve the formation of uniform, 60–70 nm thick films of densely packed AgBiS2 and Cu3BiS3 crystallites with a typical size of 10–20 nm. Planar photovoltaic devices based on spray-deposited AgBiS2 as a light harvester, ZnO as an electron transporting layer, and spiro-OMeTAD as a hole transporting material produce short-circuit current densities as high as 18.1 ± 0.6 mA cm−2 under 1 sun AM 1.5 G irradiation. The devices are stable without encapsulation under ambient conditions for at least 1 month.

Photosensitising dyes require anchoring groups for attachment to a metal oxide support surface. When a dye-sensitised electrode is designed for applications in aqueous media, e.g. for photoelectrocatalytic water splitting, these anchoring groups must be highly stable towards hydrolysis while retaining sufficient electrical conductivity to sustain efficient transfer of photogenerated charges. With this motivation, we introduce herein a cooperative silanetriolate-carboxylate anchoring combination. A ruthenium(II) tris-bipyridine dye has been functionalised with this dual-anchor through a facile peptide coupling reaction. The photoelectrooxidation performance and stability of mesoporous TiO2 electrodes sensitised with this new dye have been systematically examined in solutions with pH 1–9 in the absence and presence of a sacrificial electron donor and/or buffering electrolyte following a specifically designed testing protocol, which involves comprehensive characterisation of the electrodes and electrolyte solutions by ICP-MS and UV-vis spectroscopy. When compared to the state-of-the-art phosphonate anchoring group, the silanetriolate-carboxylate combination enables approximately 4- and 8-fold enhancements in the rate of sulphite oxidation by the Ru(II) (bipyridine)3-sensitised TiO2 photoanodes under 1 sun irradiation after 2 and 24 hours of reaction, respectively. In the absence of a sacrificial electron donor, photoanodes based on carboxylate- and phosphonate-anchored dyes undergo continuous and rapid degradation under all conditions examined, leading to almost completely bleached electrodes within less than an hour of operation. Conversely, silanetriolate-carboxylate anchoring provides quasi-stable operation with typically less than 10% ruthenium loss from the electrode surface under the same conditions. The analysis undertaken here unambiguously attests to the significantly improved long-term performance of the dye-sensitised photoelectrodes provided by the cooperative anchoring system where silanetriolate provides high stability and carboxylate sustains efficient charge transfer. This furnishes a practical pathway towards the synthesis of photosensitisers capable of stable and efficient operation within photoelectrochemical devices in aqueous environments.

Dye-sensitized photocathodes have been observed on several occasions to sustain light-driven H2 generation without intentionally introduced catalysts. Herein, plausible mechanisms addressing this phenomenon are probed by a combination of long-term photoelectrochemical measurements with concurrent gas chromatography, transient absorption spectroscopy, and inductively coupled mass spectrometry using a perylenemonoimide–sexithiophene–triphenylamine (PMI-6T-TPA) sensitized NiO electrode. The experimental evidence obtained discounts the possibility for direct reduction of hydrogen by the dye and demonstrates that the availability of interfaces between dye molecules and any electrically disconnected NiO particles exposed to the electrolyte solution is critical for photoelectrocatalytic H2 generation. These interfaces are postulated to serve as photoactive sites for the formation of a hydrogen evolution catalyst, e.g., metallic nickel, which can accept photogenerated electrons from the excited dye molecules. The...

Two zeolitic imidazolate frameworks, ZIF-67 and ZIF-8, were interrogated for their redox properties using Fourier transformed alternating current voltammetry, which revealed that the 2-methylimidazolate ligand is responsible for multiple redox transformations. Further insight was gained by employing discrete tetrahedral complexes, [M(DMIM)4]2+ (DMIM = 1,2-dimethylimidazole, M = CoII or ZnII) which have similar structural motifs to ZIFs. In this work we demonstrate a multidirectional approach that enables the complex electrochemical behavior of ZIFs to be unraveled.

Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnOx ) is explored. Physical characterisation of MnOx includes scanning and transmission electron microscopy, and X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopy. This characterisation reveals that the MnOx materials share the structural features of birnessite, yet differ in the degree of structural disorder. Importantly, these biogenic products exhibit strikingly different morphologies that can be easily controlled. Changing the substrate-to-protein ratio produces MnOx either as nm-thin sheets, or rods with diameters below 20 nm, or a combination of the two. Mineralisation in solutions that contain Fe2+(aq) makes solids with significant disorder in the structure, while the presence of Ca2+(aq) facilitates formation of more ordered materials. The (photo)oxidation and (photo)electrocatalytic capacity of the MnOx minerals is examined and correlated with their structural properties.

An efficient hole-transporting material (HTM) is indispensable for high-performing perovskite solar cells (PSCs), which have recently emerged as a breakthrough photovoltaic technology. Here, we demonstrate the capacity of the transition metal complex (6,6′-bis(1,1-di(pyridin-2-yl)ethyl)-2,2′-bipyridine)-iron(II/III) trifluoromethanesulfonate ([Fe(bpyPY4)](OTf)2+x) to act as an additive-free, solution-processable HTM in PSCs based on the formamidinium lead bromide absorber. State-of-the-art physical methods have been employed to characterize [Fe(bpyPY4)](OTf)2+x and, in particular, to demonstrate its significantly higher conductivity compared to that of the conventional HTM spiro-OMeTAD. A maximum power conversion efficiency of 2.2% was obtained for a device employing [Fe(bpyPY4)](OTf)2+x, which is the first evidence of the applicability as a HTM in a PSC of a solid material in which conductivity is provided by a redox transformation of a transition metal.

This work describes the facile microwave synthesis of interlayer expanded, nanosized MoS2 sheets that are vertically aligned on a well-conducting reduced graphene (rGO) support, as confirmed by X-ray diffraction, Raman and X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive X-ray analysis, and high-resolution transmission electron microscopy. Such structure has been predicted to be highly favorable for efficient electrocatalysis of hydrogen evolution by MoS2 but could not be achieved until now. Films deposited from the microwave-synthesized MoS2-rGO composites demonstrate outstanding and stable hydrogen evolution performance in acidic solution. These catalysts exhibit an exchange current density as high as 1.0 ± 0.2 A g–1MoS2-rGO, sustain a current density of 10 mA cm–2 (36 A g–1MoS2-rGO) at an overvoltage of 0.104 ± 0.002 V, and maintain steady performance for many hours. Importantly, our simple synthesis affords several advantages over more sophisticated methods used pr...

We demonstrate that bismuth exhibits no measurable electrocatalytic activity for the nitrogen reduction reaction to ammonia in aqueous electrolyte solutions, contrary to several recent reports on the highly impressive rates of Bi-catalysed electrosynthesis of NH3 from N2.

Non-uniform metal deposition and dendrite formation in high-density energy storage devices reduces the efficiency, safety and life of batteries with metal anodes. Superconcentrated ionic-liquid electrolytes (for example 1:1 ionic liquid:alkali ion) coupled with anode preconditioning at more negative potentials can completely mitigate these issues, and therefore revolutionize high-density energy storage devices. However, the mechanisms by which very high salt concentration and preconditioning potential enable uniform metal deposition and prevent dendrite formation at the metal anode during cycling are poorly understood, and therefore not optimized. Here, we use atomic force microscopy and molecular dynamics simulations to unravel the influence of these factors on the interface chemistry in a sodium electrolyte, demonstrating how a molten-salt-like structure at the electrode surface results in dendrite-free metal cycling at higher rates. Such a structure will support the formation of a more favourable solid electrolyte interphase, accepted as being a critical factor in stable battery cycling. This new understanding will enable engineering of efficient anode electrodes by tuning the interfacial nanostructure via salt concentration and high-voltage preconditioning. Non-uniform metal deposition and dendrite formation reduce the efficiency, safety and life of batteries with metal anodes. The influence of these factors in a sodium electrolyte now shows how a molten-salt-like structure at the electrode surface results in dendrite-free metal cycling at higher rates.

Chemical doping is a ubiquitously applied strategy to improve the charge-transfer and conductivity characteristics of spiro-OMeTAD, a hole-transporting material (HTM) used widely in solution-processed perovskite solar cells (PSCs). Cobalt(III) complexes are commonly employed HTM dopants, whose major role is to oxidize spiro-OMeTAD to provide

Summary Here we introduce the Monash Electrochemistry Simulator (MECSim) software package that allows most aspects of ac voltammetry to be simulated when a single sine wave or a combination of sine waves are superimposed onto a dc ramp. The MECSim software and companion tool kits can be downloaded free of charge from http://www.garethkennedy.net/MECSim.html where there is also instructional documentation. Features accommodated in the simulation model include non-linear background capacitance, uncompensated resistance, Butler–Volmer and Marcus–Hush electron transfer, chemical reactions involving surface confined and solution phase species and stationary or rotating disc electrode mass transport with linear diffusion. Companion tool kits are also provided that allow Fourier transformed ac voltammograms with harmonic analysis to be generated along with other forms of data presentation. The MECSim format in combination with parameter optimisation tool kit also facilitates the implementation of sophisticated forms of experiment-theory comparisons needed to estimate the electrode kinetic and other parameters. MECSim software is computationally efficient and based on flexible code that can be used in cluster computing as well as on a single machine. Typical simulations take seconds to run on a laptop and parameter searches needed to tackle the inverse problem can be achieved efficiently. Capabilities of MECSim are illustrated in this article by comparing simulated results with those obtained experimentally.

Rapid disulfide bond formation and cleavage is an essential mechanism of life. Using large amplitude Fourier transformed alternating current voltammetry (FTacV) we have measured previously uncharacterized disulfide bond redox chemistry in Escherichia coli HypD. This protein is representative of a class of assembly proteins that play an essential role in the biosynthesis of the active site of [NiFe]-hydrogenases, a family of H2-activating enzymes. Compared to conventional electrochemical methods, the advantages of the FTacV technique are the high resolution of the faradaic signal in the higher order harmonics and the fact that a single electrochemical experiment contains all the data needed to estimate the (very fast) electron transfer rates (both rate constants ≥ 4000 s(-1)) and quantify the energetics of the cysteine disulfide redox-reaction (reversible potentials for both processes approximately -0.21 ± 0.01 V vs SHE at pH 6). Previously, deriving such data depended on an inefficient manual trial-and-error approach to simulation. As a highly advantageous alternative, we describe herein an automated multiparameter data optimization analysis strategy where the simulated and experimental faradaic current data are compared for both the real and imaginary components in each of the 4th to 12th harmonics after quantifying the charging current data using the time-domain response.

Ammonia as the source of most fertilizers has become one of the most important chemicals globally. It also is being increasingly considered as an easily transported carrier of hydrogen energy that can be generated from “stranded” renewable-energy resources. However, the traditional Haber–Bosch process for the production of ammonia from atmospheric nitrogen and fossil fuels is a high temperature and pressure process that is energy intensive, currently producing more than 1.6% of global CO2 emissions. An ambient temperature, electrochemical synthesis of ammonia is an attractive alternative approach, but has, to date, not been achieved at high efficiency. We report in this work the use of ionic liquids that have high N2 solubility as electrolytes to achieve high conversion efficiency of 60% for N2 electro-reduction to ammonia on a nanostructured iron catalyst under ambient conditions.

Dye-sensitised photocathodes promoting hydrogen evolution are usually coupled to a catalyst to improve the reaction rate. Herein, we report on the first successful integration of a heterogeneous metal particulate catalyst, viz. , Pt aggregates electrodeposited from acidic solutions on the surface of a NiO-based photocathode sensitised with a p -type perylenemonoimid-sexithiophene-triphenylamine dye (PMI-6T-TPA). The platinised dye-NiO electrodes generate photocurrent density of ca −0.03 mA cm −2 (geom.) with 100% faradaic efficiency for the H 2 evolution at 0.059 V vs. reversible hydrogen electrode under 1 sun visible light irradiation (AM1.5G, 100 mW cm −2 , λ > 400 nm) for more than 10 hours in 0.1 M H 2 SO 4 (aq.). The Pt-free dye-NiO and dye-free Pt-modified NiO cathodes show no photo-electrocatalytic hydrogen evolution under these conditions. The performance of these Pt-modified PMI-6T-TPA-based photoelectrodes compares well to that of previously reported dye-sensitised photocathodes for H 2 evolution.

Photoelectrochemical water splitting into H2 and O2 over a semiconductor-based photocatalyst offers a promising way to achieve the sustainable harvesting and storage of solar energy. However, short diffusion lengths and inefficient separation of the charge carriers in the semiconductors following light absorption result in fast recombination of holes and electrons and eventually poor performance. Herein, we address this problem by integrating an efficient and robust water oxidation catalyst, cobalt oxide (CoOx), into screen-printed TaON photoanodes premodified with TiO2 coatings for better stability. SEM, TEM, and ICP-MS analysis of the Co deposits and electrochemical techniques were used to demonstrate the advantages provided by the photoassisted CoOx electrodeposition method. Specifically, this method allows the selective and facile functionalization of the TiO2-TaON surface with a uniform layer of near-(hemi)spherical CoOx particles having a diameter of 5–15 nm. In comparison to the TiO2-TaON photoanod...

Estimation of thermodynamic and kinetic parameters in electrochemical studies is usually undertaken via comparison of the experimental results with theory based on a model that mimics the experiment. The present study examines the credibility of transient d.c. and a.c. voltammetric theory-experiment comparisons for recovery of the parameters needed to model the ubiquitous mechanism when an electron transfer (E) reaction is followed by a chemical (C) step in the EC process ([Formula: see text]). The data analysis has been undertaken using optimization methods facilitated in some cases by grid computing. These techniques have been applied to the simulated (5% noise added) and experimental (reduction of trans-stilbene) voltammograms to assess the capabilities of parameter recovery of E(0) (reversible potential for the E step), k(0) (heterogeneous electron transfer rate constant at E(0)), α (charge transfer coefficient for the E step), and k(f) and k(b) (forward and backward rate constants for the C step) under different kinetic regimes. The advantages provided by the use of a.c. instead of d.c. voltammetry and data optimization methods over heuristic approaches to "experiment"-theory comparisons are discussed, as are the limitations in the efficient recovery of a unique set of parameters for the EC mechanism. In the particular experimental case examined herein, results for the protonation of the electrochemically generated stilbene dianion demonstrate that, notwithstanding significant advances in experiment and theory of voltammetric analysis, reliable recovery of the parameters for the EC mechanism with a fast chemical process remains a stiff problem.

Inspired by the previously published theoretical findings, the present work aims to assess the electrocatalytic activity of molybdenum(IV) sulfide modified with metallic molybdenum for the nitrogen reduction reaction in aqueous electrolyte solution (0.1 M Li2SO4; pH 3) and in aprotic [C4mpyr][eFAP] ionic liquid electrolyte at ambient temperature. The material of interest was synthesized via a high-temperature partial reduction of MoS2, while electrocatalytic tests followed a previously established robust protocol, which in particular involves strict control over any NH3 and NO3 −/NO2 − contamination at every key step. As expected, no activity was found in aqueous solutions. In aprotic medium, the formation of small amounts of ammonia at low rates was observed and was found to strongly depend on the water concentration and applied potential. However, the amount of electrochemically generated NH3 always reached a particular limit and did not increase further, even when the N2 pressure was increased from 1 to 16 bar. The results suggest rapid blockage of the surface of the investigated electromaterial with NH3, which prevents its operation as a catalyst for the ammonia electrosynthesis.

The synergistic effect of coupling a photooxidation catalyst, tantalum oxynitride, and manganese oxide (MnOx) as electrooxidation catalyst in multi-component photoanodes for water oxidation is explored in near-neutral solutions under visible light irradiation (λ > 400 nm). The anodes have been formed by using different electrochemical methods to deposit MnOx on screen-printed TaON films, pre-modified with TiO2 coatings (TiO2–TaON). By using SEM/EDX, ICP-MS analysis of the amount of Mn deposited and, electrochemical techniques, we demonstrate that selective deposition of fine-structured nm-sized MnOx flakes on the photocatalytically active TiO2–TaON surface is achieved when the electrodeposition is carried out under visible light irradiation, but not in the dark. The MnOx/TiO2–TaON anodes produced using the photo-assisted method exhibit improved activity and better long-term stability during water photooxidation under visible light irradiation when compared to the TiO2–TaON films modified with MnOx in dark. A 7-fold enhancement in the oxidative photocurrent densities under voltammetric and chronoamperometric conditions in 0.1 M Na2SO4 (pH = 6) is observed for the films prepared by the photo-assisted method. The Mn-loading in the best performing films is ca. 0.8 wt% and higher loadings were found to lower the photocatalytic activity. Continuous water photooxidation over MnOx/TiO2–TaON anodes in 0.1 M Na2SO4 (pH = 6) at potentials more positive than ca. 1.0 V vs. reversible hydrogen electrode coarsens the fine structure of the MnOx material, and this structural degradation is mirrored in a slow deterioration of the photocatalyst performance.

The possibility of efficient water electrooxidation sustained by continuous (re)generation of catalysts derived from the oxidative electrodeposition of transition-metal contaminants is examined herein for three natural water samples from Australia and China. The metal composition of the solutions has been determined by inductively coupled plasma optical emission spectrometry, and a range of strategies to produce water-splitting catalysts by means of in situ electrodeposition have been applied. The performance of the resulting electrocatalysts is below the state-of-the-art level owing to large amounts of impurities in the solutions and non-optimal concentrations of naturally available catalyst precursors. Nevertheless, these studies have identified the FePb-based system as a rare example of an electrocatalyst for water oxidation that forms in situ and maintains reasonable activity (≥4.5 mA cm-2 at an overpotential of 0.8 V) in weakly acidic solutions (pH 2.9).

It has become apparent that renewable energy sources are plentiful in many, often remote, parts of the world, such that storing and transporting that energy has become the key challenge. For long-distance transportation by pipeline and bulk tanker, a liquid form of energy carrier is ideal, focusing attention on liquid hydrogen and ammonia. Development of high-activity and selectivity electrocatalyst materials to produce these energy carriers by reductive electrochemistry has therefore become an important area of research. Here, recent developments and challenges in the field of electrocatalytic materials for these processes are discussed, including the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the nitrogen reduction reaction (NRR). Some of the mis-steps currently plaguing the nitrogen reduction to ammonia field are highlighted. The rapidly growing roles that in situ/operando and quantum chemical studies can play in new electromaterials discovery are also surveyed.

Detection and quantification of redox transformations involved in water oxidation electrocatalysis is often not possible using conventional techniques. Herein, use of large amplitude Fourier transformed ac voltammetry and comprehensive analysis of the higher harmonics has enabled us to access the redox processes responsible for catalysis. An examination of the voltammetric data for water oxidation in borate buffered solutions (pH 9.2) at electrodes functionalized with systematically varied low loadings of cobalt (CoOx), manganese (MnOx), and nickel oxides (NiOx) has been undertaken, and extensive experiment-simulation comparisons have been introduced for the first time. Analysis shows that a single redox process controls the rate of catalysis for Co and Mn oxides, while two electron transfer events contribute in the Ni case. We apply a “molecular catalysis” model that couples a redox transformation of a surface-confined species (effective reversible potential, Eeff0) to a catalytic reaction with a substra...

In a natural geochemical cycle, manganese-oxide minerals (MnOx ) are principally formed through a microbial process, where a putative multicopper oxidase MnxG plays an essential role. Recent success in isolating the approximately 230 kDa, enzymatically active MnxEFG protein complex, has advanced our understanding of biogenic MnOx mineralization. Here, the kinetics of MnOx formation catalyzed by MnxEFG are examined using a quartz crystal microbalance (QCM), and the first electrochemical characterization of the MnxEFG complex is reported using Fourier transformed alternating current voltammetry. The voltammetric studies undertaken using near-neutral solutions (pH 7.8) establish the apparent reversible potentials for the Type 2 Cu sites in MnxEFG immobilized on a carboxy-terminated monolayer to be in the range 0.36-0.40 V versus a normal hydrogen electrode. Oxidative priming of the MnxEFG protein complex substantially enhances the enzymatic activity, as found by in situ electrochemical QCM analysis. The biogeochemical significance of this enzyme is clear, although the role of an oxidative priming of catalytic activity might be either an evolutionary advantage or an ancient relic of primordial existence.

Efficient solar-powered water oxidation over the TaON-based anodes requires coupling this photoactive n-type semiconductor to an electrooxidation catalyst to improve the otherwise unsatisfactory activity and stability. Herein, we examine how functionalization with electrodeposited nickel oxide, NiOx , affects the performance of screen-printed TaON photoanodes post-necked with titania (TiO2 -TaON). The effects of the NiOx photo-electrodeposition parameters on the microstructure and photocatalytic performance of the resulting anodes are explored. Enhancements in the transient water oxidation photocurrent densities by sixfold vs. unmodified TiO2 -TaON were achieved with the use of the NiOx /TiO2 -TaON photoanodes. Long-term stability tests reveal a slow but persistent degradation of the performance of the multicomponent photocatalysts under the severely oxidizing conditions of water photo-oxidation coincident with continuous morphological changes in the NiOx deposits.

Remarkable power conversion efficiencies (PCE) of metal–halide perovskite solar cells (PSCs) are overshadowed by concerns about their ultimate stability, which is arguably the prime obstacle to commercialization of this promising technology. Herein, the problem is addressed by introducing ethane-1,2-diammonium (+NH3(CH2)2NH3+, EDA2+) cations into the methyl ammonium (CH3NH3+, MA+) lead iodide perovskite, which enables, inter alia, systematic tuning of the morphology, electronic structure, light absorption, and photoluminescence properties of the perovskite films. Incorporation of

Voltammetric quantification of the electrode kinetics for the quasi-reversible reaction requires detailed experiment–theory comparisons. Ideally, predicted data derived from the theoretical model are fitted to the experimental data by adjusting the reversible potential (E0), heterogeneous electron transfer rate constant at E0 (k0), and charge transfer coefficient α, with mass-transport and other parameters exactly known. However, parameters relevant to mass transport that include electrode area (A), diffusion coefficient (D), and concentration (c), are usually subject to some uncertainty. Herein, we examine the consequences of having different combinations of errors present in A, D, and c in the estimation of E0, k0, and α on the basis of the a.c. (alternating current) voltammetric experiment–theory comparisons facilitated by the use of a computer-assisted parameter optimisation algorithm. In most cases, experimentally reasonable errors (

The scalable synthesis of highly transparent and robust sub-monolayers of Co3O4 nano-islands, which efficiently catalyze water oxidation, is reported. Rapid aerosol deposition of Co3O4 nanoparticles and thermally induced self-organization lead to an ultra-fine nano-island morphology with more than 94% light transmission at a wavelength of 500 nm. These transparent sub-monolayers demonstrate a remarkable mass-weighted water oxidation activity of 2070–2350 A gCo3O4−1 and per-metal turnover frequency of 0.38–0.62 s−1 at an overpotential of 400 mV in 1 m NaOH aqueous solution. This mixed valent cobalt oxide structure exhibits excellent long-term electrochemical and mechanical stability preserving the initial catalytic activity over more than 12 h of constant current electrolysis and 1000 consecutive voltammetric cycles. The potential of the Co3O4 nano-islands for photoelectrochemical water splitting has been demonstrated by incorporation of co-catalysts in GaN nanowire photoanodes. The Co3O4-GaN photoanodes reveal significantly reduced onset overpotentials, improved photoresponse and photostability compared to the bare GaN ones. These findings provide a highly performing catalyst structure and a scalable synthesis method for the engineering of efficient photoanodes for integrated solar water-splitting cells.

Beyond conventional electrically-driven neuronal stimulation methods, there is a growing interest in optically-driven approaches. In recent years, nitrogen-doped ultrananocrystalline diamond (N-UNCD) has emerged as a strong material candidate for use in electrically-driven stimulation electrodes. This work investigates the electrochemical activity of N-UNCD in response to pulsed illumination, to assess its potential for use as an optically-driven stimulation electrode. Whilst N-UNCD in the as-grown state exhibits a weak photoresponse, the oxygen plasma treated film exhibits two orders of magnitude enhancement in its sub-bandgap open circuit photovoltage response. The enhancement is attributed to the formation of a dense network of oxygen-terminated diamond nanocrystals at the N-UNCD surface. Electrically connected to the N-UNCD bulk via sub-surface graphitic grain boundaries, these diamond nanocrystals introduce a semiconducting barrier between the sub-surface graphitic semimetal and the electrolyte solut...