The identification of materials capable of catalyzing the oxygen evolution reaction (OER) in highly acidic electrolytes is a critical bottleneck in the development of many water-splitting technologies. Bulk-scale solid-state compounds can be readily produced using high-temperature reactions and therefore used to expand the scope of earth-abundant OER catalysts capable of operating under strongly acidic conditions. Here, we show that high temperature arc melting and powder metallurgy reactions can be used to synthesize electrodes consisting of intermetallic NiTa that can catalyze the OER in 0.50 M HSO. Arc melted NiTa electrodes evolve oxygen at a current density of 10 mA/cm for >66 h with corrosion rates 2 orders of magnitude lower than that of pure Ni. The overpotential required for pellets of polycrystalline NiTa to produce a current density of 10 mA/cm is 570 mV. This strategy can be generalized to include other first-row transition metals, including intermetallic FeTa and CoTa systems.

Thermodynamic properties of Ba-Bi alloys, including the activity, partial molar entropy and enthalpy, were determined using the electromotive force (emf) technique for fourteen compositions, x Ba = 0.05-0.80. Emf measurements were performed at ambient pressure using a Ba(s)|CaF 2-BaF 2 |Ba(in Bi) or Ba-Bi(x Ba = 0.05)|CaF 2-BaF 2 |Ba(in Bi) electrochemical cells at 723-1073 K. At 773K, activity values of Ba were as low as 6.6 × 10-16 at mole fraction x Ba = 0.05 and approached unity for mole fractions x Ba ≥ 0.80. Stable emf values were observed at mole fractions x Ba = 0.05-0.25, exhibiting less than a 5 mV difference between the heating and cooling cycles. Mole fractions x Ba ≥ 0.30 exhibited increased hysteresis or had an unexpected emf profile due to the formation of metastable phases such as Bi and Ba 5 Bi 3 , confirmed by X-ray diffraction. The Ba-Bi alloys were further characterized using differential scanning calorimetry over the entire composition range. Based on these data, a revised Ba-Bi binary phase diagram is proposed.

The thermodynamic properties of Sr-Bi alloys were determined by electromotive force (emf) measurements to evaluate the viability of liquid bismuth metal as a medium for separating alkali/alkaline-earth fission products from molten salt electrolyte. A Sr(s)|CaF 2-SrF 2 |Sr(in Bi) cell was used to measure emf values at 748-1023 K for thirteen Sr-Bi alloys at mole fractions 0.05 ≤ x Sr ≤ 0.75. Activity values of strontium in bismuth were determined at 788 K, 888 K, and 988 K as well as the partial molar entropy and enthalpy at each composition. Reproducible emf values within ± 5mV were obtained up to x Sr = 0.35 during cooling-heating cycle. At higher mole fractions (x Sr ≥ 0.40), the emf values exhibited increased hysteresis during the thermal cycles due to the strong tendency of the alloys to form meta-stable phases. The non-equilibrium phase behavior of Sr-Bi alloys was verified by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and microstructural analyses. Compared to the existing equilibrium phase diagram, two additional phases of Sr 2 Bi 3 and Sr 4 Bi 3 were identified and discussed. Liquid-state solubility of Sr was 15-40 mol% at 788-988 K and the activity values were as low as 10-13 at 788 K, implying strong chemical interactions between Sr and Bi.

The corrosion inhibition effect of acid extract of the pericarp of the fruit Garcinia mangostana on mild steel in hydrochloric acid medium is studied. Using weight-loss data, corrosion rate (CR) and thermodynamic parameters such as energy of activation for corrosion of mild steel (E), heat of adsorption of the inhibitors on the metal surface (Q) and change in free energy (∆G) are calculated. Adsorption isotherm is also recorded between log C and θ. Electrochemical parameters are evaluated from AC impedance and Tafel polarization studies in the presence and absence of different concentrations of inhibitor. Infra-red spectra are recorded for the extract and the adsorption product to find out the changes in the functional group frequencies of the organic components of the extract. The surface morphological changes are analysed using the SEM images. The entire study shows that the pericarp extract of the fruit G. mangostana is a non-toxic, cost-effective corrosion inhibitor for mild steel in acid medium.

No abstract