Anita M. D’ Angelo

Not all oxygen vacancies are equal, yet metal oxide catalysts are usually designed as if they were. In perovskite fuel-cell cathodes, oxygen vacancies near redox-active and redox-inactive cations play distinct roles in oxygen reduction reaction, ion transport and hydration, but they are usually lumped into one bulk-averaged property. By partially substituting Y with less electronegative Yb in the benchmark BaCo _0.4 Fe _0.4 Zr _0.1 Y _0.1 O _{3− δ} cathode, we reveal that oxygen vacancies near redox-inactive Y/Yb control the vacancy formation near redox-active Co/Fe, and that water in air unlocks such formation. In dry air, the vacancies near Y/Yb can switch off their inductive effects and thus block the formation of vacancies near Co/Fe, whereas in humid air, these vacancies tend to be occupied by water, unlocking the inductive effect and promoting active vacancies. This water-unlocked formation of vacancies near Co/Fe doubles the oxygen reduction reaction activity in humid air and enables a protonic ceramic fuel cell to generate a peak power density of 700 mW cm ^− 2 at 600°C and a stable operation beyond 2,450 h. Our findings suggest that oxygen vacancies are not independent but coupled, with water acting as a switch that turns this coupling into new active sites.

Protonic ceramic fuel cells (PCFCs) are one of the promising routes to generate power efficiently from various fuels at economically viable temperatures (500–700°C) due to the use of fast proton conducting oxides as electrolytes. However, the power density and durability of the PCFCs are still limited by their cathodes made from solid metal oxides, which are challenging to address the sluggish oxygen reduction reaction and susceptibility to CO₂ simultaneously. Here, we report an alternative approach to address this challenge by developing a new melt-solid interface through the in situ alkali metal surface segregation and consecutive eutectic formation at perovskite oxide surface at PCFC operating temperatures. This new approach in cathode engineering is successfully demonstrated over a lithium and sodium co-doped BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ perovskite as the model material. Our experimental results unveil that the unique in situ formed melt-solid surface stabilises the catalytically active phase in bulk and promotes catalytically active sites at surface. Our novel engineered melt-solid interface enhanced the stability of the cathode against poisoning in 10% CO₂ by a factor of 1.5 in a symmetrical cell configuration and by a factor of more than two in PCFC single cells.

Metal substituted dodecaborate anions can be coupled with alkali metal cations to have great potential as solid-state ion conductors for battery applications. A tin atom can replace a B–H unit within an unsubstituted dodecaborate cage to produce a stable, polar divalent anion. The chemical and structural change in forming a stannaborate results in a modified crystal structure of respective group 1 metal salts, and as a result, improves the material's ion conductivity. Li₂B₁₁H₁₁Sn shows high ion conductivity of ∼8 mS cm⁻¹ at 130 °C, similar to the state-of-the-art LiCB₁₁H₁₂ at these temperatures, however, obtaining high ion conductivity at room temperature is not possible with pristine alkali metal stannaborates.

Protonic ceramic fuel cells (PCFCs) are one of the promising routes to generate power efficiently from various fuels at economically viable temperatures (500-700 °C) due to the use of fast proton conducting oxides as electrolytes. However, the power density and durability of the PCFCs are still limited by their cathodes mostly made from solid metal oxides, which are challenging to address the sluggish oxygen reduction reaction and susceptibility to CO2 simultaneously. Here, we report an alternative approach to address this challenge by developing a new melt-solid interface through the in situ alkali metal surface segregation and consecutive eutectic formation at perovskite oxide surface at PCFC operating temperatures. This new approach in cathode engineering is successfully demonstrated over a lithium and sodium co-doped BaCo0.4Fe0.4Zr0.1Y0.1O3-δ perovskite as the model material. Our experimental results unveil that the unique in situ formed melt-solid surface stabilises the catalytically active phase in the bulk and promotes catalytically active site at surface. Our novel engineered melt-solid interface enhanced the stability of the cathode against poisoning in 10% CO2 by a factor of 1.5 in a symmetrical cell configuration and by a factor of more than two in PCFC single cells.

Aqueous Zn-ion batteries have attracted increasing research interest; however, the development of these batteries has been hindered by several challenges, including dendrite growth, Zn corrosion, cathode material degradation, limited temperature adaptability and electrochemical stability window, which are associated with water activity and the solvation structure of electrolytes. Here we report that water activity is suppressed by increasing the electron density of the water protons through interactions with highly polar dimethylacetamide and trimethyl phosphate molecules. Meanwhile, the Zn corrosion in the hybrid electrolyte is mitigated, and the electrochemical stability window and the operating temperature of the electrolyte are extended. The dimethylacetamide alters the surface energy of Zn, guiding the (002) plane dominated deposition of Zn. Molecular dynamics simulation evidences Zn²⁺ions are solvated with fewer water molecules, resulting in lower lattice strain in the NaV₃O₈·1.5H₂O cathode during the insertion of hydrated Zn²⁺ions, boosting the lifespan of Zn|| NaV₃O₈·1.5H₂O cell to 3000 cycles.

Renewable energy requires cost effective and reliable storage to compete with fossil fuels. This study introduces a new reactive carbonate composite (RCC) where Fe₂O₃ is used to thermodynamically destabilise BaCO₃ and reduce its decomposition temperature from 1400 °C to 850 °C, which is more suitable for thermal energy storage applications. Fe₂O₃ is consumed on heating to form BaFe₁₂O₁₉, which is a stable Fe source for promoting reversible CO₂ reactions. Two reversible reaction steps were observed that corresponded to, first, the reaction between β-BaCO₃ and BaFe₁₂O₁₉, and second, between γ-BaCO₃ and BaFe₁₂O₁₉. The thermodynamic parameters were determined to be ΔH = 199 ± 6 kJ mol⁻¹ of CO₂, ΔS = 180 ± 6 J K⁻¹ mol⁻¹ of CO₂ and ΔH = 212 ± 6 kJ mol⁻¹ of CO₂, ΔS = 185 ± 7 J K⁻¹ mol⁻¹ of CO₂, respectively, for the two reactions. Due to the low-cost and high gravimetric and volumetric energy density, the RCC is demonstrated to be a promising candidate for next generation thermal energy storage.

This study describes the capabilities and limitations of carrying out total scattering experiments on the Powder Diffraction (PD) beamline at the Australian Synchrotron, ANSTO. A maximum instrument momentum transfer of 19 Å⁻¹ can be achieved if the data are collected at 21 keV. The results detail how the pair distribution function (PDF) is affected by Q _max, absorption and counting time duration at the PD beamline, and refined structural parameters exemplify how the PDF is affected by these parameters. There are considerations when performing total scattering experiments at the PD beamline, including (1) samples need to be stable during data collection, (2) highly absorbing samples with a μR > 1 always require dilution and (3) only correlation length differences >0.35 Å may be resolved. A case study comparing the PDF atom–atom correlation lengths with EXAFS-derived radial distances of Ni and Pt nanocrystals is also presented, which shows good agreement between the two techniques. The results here can be used as a guide for researchers considering total scattering experiments at the PD beamline or similarly setup beamlines.

Hydrated and anhydrous LiB ₁₁ H ₁₄ salts are prepared through a facile approach. Liquid-like Li ⁺ conductivity (10 ⁻² S cm ⁻¹ ) is observed for a-LiB ₁₁ H ₁₄ ·(H ₂ O) _n at 60 °C. LiB ₁₁ H ₁₄ ·2H ₂ O is classified as a new class of ionic liquid as it melts near 70 °C.