Separating the effects of experimental noise from inherent system variability in voltammetry: the [[Fe(CN)6]3−/4−_6]^{3-/ 4-} process

Recently, we have introduced the use of techniques drawn from Bayesian statistics to recover kinetic and thermodynamic parameters from voltammetric data, and were able to show that the technique of large amplitude ac voltammetry yielded significantly more accurate parameter values than the equivalent dc approach. In this paper we build on this work to show that this approach allows us, for the first time, to separate the effects of random experimental noise and inherent system variability in voltammetric experiments. We analyse ten repeated experimental data sets for the $[$Fe(CN)$_6]^{3-/ 4-}$ process, again using large-amplitude ac cyclic voltammetry. In each of the ten cases we are able to obtain an extremely good fit to the experimental data and obtain very narrow distributions of the recovered parameters governing both the faradaic (the reversible formal faradaic potential, $E_0$, the standard heterogeneous charge transfer rate constant $k_0$, and the charge transfer coefficient $\alpha$) and non-faradaic terms (uncompensated resistance, $R_u$, and double layer capacitance, $C_{dl}$). We then employ hierarchical Bayesian methods to recover the underlying "hyperdistribution" of the faradaic and non-faradaic parameters, showing that in general the variation between the experimental data sets is significantly greater than suggested by individual experiments, except for $\alpha$ where the inter-experiment variation was relatively minor. Correlations between pairs of parameters are provided, and for example, reveal a weak link between $k_0$ and $C_{dl}$ (surface activity of a glassy carbon electrode surface). Finally, we discuss the implications of our findings for voltammetric experiments more generally.Comment: 30 pages, 6 figure

Lead-free Magnetic Double Perovskites for Photovoltaic and Photocatalysis Applications

The magnetic spin degrees of freedom in magnetic materials serve as additional capability to tune materials properties, thereby invoking magneto-optical response. Herein, we report the magneto-optoelectronic properties of a family of lead-free magnetic double perovskites Cs_{2}AgTX_{6} (T = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu; X=Cl, Br, I). This turns out to provide an extremely fertile series, giving rise to potential candidate materials for photovoltaic(PV) applications. In conjunction with high absorption coefficient and high simulated power conversion efficiency for PV applications, few compounds in this series exhibit novel magnetic character useful for spintronic applications. The interaction between magnetism and light can have far-reaching results on the photovoltaic properties as a consequence of the shift in the defect energy levels due to Zeeman effect. This subsequently affects the recombination rate of minority carriers, and hence the photoconversion efficiency. Moreover, the distinct ferromagnetic and anti-ferromagnetic ordering driven by hybridization and super-exchange mechanism can play a significant role to break the time-reversal and/or inversion symmetry. Such a coalescence of magnetism and efficient optoelectronic response has the potential to trigger magnetic/spin anomalous photovoltaic (non-linear Optical) effect in this Cs$_{2}$AgTX$_{6}$ family. These insights can thus channelize the advancement of lead-free double perovskites in magnetic/spin anomalous photovoltaic field as well.Comment: 9 pages, 5 figures, 1 tabl

Electrochemical evidence that pyranopterin redox chemistry controls the catalysis of YedY, a mononuclear Mo enzyme

A long-standing contradiction in the field of mononuclear Mo enzyme research is that small-molecule chemistry on active-site mimic compounds predicts ligand participation in the electron transfer reactions, but biochemical measurements only suggest metal-centered catalytic electron transfer. With the simultaneous measurement of substrate turnover and reversible electron transfer that is provided by Fourier-transformed alternating-current voltammetry, we show that Escherichia coli YedY is a mononuclear Mo enzyme that reconciles this conflict. In YedY, addition of three protons and three electrons to the well-characterized "as-isolated" Mo(V) oxidation state is needed to initiate the catalytic reduction of either dimethyl sulfoxide or trimethylamine N-oxide. Based on comparison with earlier studies and our UV-vis redox titration data, we assign the reversible one-proton and one-electron reduction process centered around +174 mV vs. standard hydrogen electrode at pH 7 to a Mo(V)-to-Mo(IV) conversion but ascribe the two-proton and two-electron transition occurring at negative potential to the organic pyranopterin ligand system. We predict that a dihydro-to-tetrahydro transition is needed to generate the catalytically active state of the enzyme. This is a previously unidentified mechanism, suggested by the structural simplicity of YedY, a protein in which Mo is the only metal site

Can Laminated Carbon Challenge Gold? Toward Universal, Scalable, and Low-Cost Carbon Electrodes for Perovskite Solar Cells

While perovskite solar cell (PSC) efficiencies are soaring at a laboratory scale, these are most commonly achieved with evaporated gold electrodes, which would present a significant expense in large-scale production. This can be remedied through the use of significantly cheaper carbon electrodes that, in contrast to metals, also do not migrate through the device. To this end, the present work investigates simple-to-prepare aluminum-supported carbon electrodes derived from commercially available, inexpensive materials that can be applied onto various hole-transporting materials and enable photovoltaic performances on par with those provided by gold electrodes. Successful integration of the new carbon-based electrode into flexible devices produced by a roll-to-roll printing technology by both pressing and lamination is demonstrated. However, temperature cycling durability tests reveal that the use of carbon electrodes based on commercial pastes is hindered by incompatibility of adhesive additives with the key components of the PSCs under heating. Resolving this issue, tailor-made graphite electrodes devoid of damaging additives are introduced, which improve the PSC stability under temperature cycling test protocol to the level provided by benchmark gold electrodes. The study highlights current challenges in developing laminated carbon electrodes in PSCs and proposes strategies toward the resolution thereof.This work was funded by the Australian Centre for Advanced Photovoltaics and Australian Renewable Energy Agency. A.N.S. also acknowledges the financial support from the Australian Research Council (Centre of Excellence CE140100012; Future Fellowship FT200100317). Monash Centre for Electron Microscopy (MCEM) and Melbourne Centre for Nano fabrication (MCN) are acknowledged for providing access to their facilities. The authors are grateful to Dr T. Zhang, A. Surmiak, Dr. N. Peris, Dr. D. Senevirathna, and Dr. N. Pai from Monash University for the experimental support throughout this study

Solution processable direct bandgap copper-silver-bismuth iodide photovoltaics : compositional control of dimensionality and optoelectronic properties

Altres ajuts: SRR acknowledges the support from "laCaixa" Foundation (ID 100010434; LCF/BQ/PI20/11760024). Open access publishing facilitated by Monash University, as part of the Wiley - Monash University agreement via the Council of Australian University Librarians.The search for lead-free alternatives to lead-halide perovskite photovoltaic materials resulted in the discovery of copper(I)-silver(I)-bismuth(III) halides exhibiting promising properties for optoelectronic applications. The present work demonstrates a solution-based synthesis of uniform CuAgBiI thin films and scrutinizes the effects of x on the phase composition, dimensionality, optoelectronic properties, and photovoltaic performance. Formation of pure 3D CuAgBiI at x = 1, 2D CuAgBiI at x = 2, and a mix of the two at 1 < x < 2 is demonstrated. Despite lower structural dimensionality, CuAgBiI has broader optical absorption with a direct bandgap of 1.89 ± 0.05 eV, a valence band level at -5.25 eV, improved carrier lifetime, and higher recombination resistance as compared to CuAgBiI. These differences are mirrored in the power conversion efficiencies of the CuAgBiI and CuAgBiI solar cells under 1 sun of 1.01 ± 0.06% and 2.39 ± 0.05%, respectively. The latter value is the highest reported for this class of materials owing to the favorable film morphology provided by the hot-casting method. Future performance improvements might emerge from the optimization of the CuAgBiI layer thickness to match the carrier diffusion length of ≈40-50 nm. Nonencapsulated CuAgBiI solar cells display storage stability over 240 days

2023 Roadmap on ammonia as a carbon-free fuel

The 15 short chapters that form this 2023 ammonia-for-energy roadmap provide a comprehensive assessment of the current worldwide ammonia landscape and the future opportunities and associated challenges facing the use of ammonia, not only in the part that it can play in terms of the future displacement of fossil-fuel reserves towards massive, long-term, carbon-free energy storage and heat and power provision, but also in its broader holistic impacts that touch all three components of the future global food-water-energy nexus

Biological Earth observation with animal sensors

Space-based tracking technology using low-cost miniature tags is now delivering data on fine-scale animal movement at near-global scale. Linked with remotely sensed environmental data, this offers a biological lens on habitat integrity and connectivity for conservation and human health; a global network of animal sentinels of environmen-tal change