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Abstract: Cryptomelane is a hollandite-like material consisting of K+ cations in an α-MnO2 tunnel-like crystallographic motif. Cryptomelane with stoichiometry KxMn8O16 (x ≈ 1.45) has been synthesized and its magnetic properties investigated using variable-temperature magnetic susceptibility, heat capacity, and neutron powder diffraction. Three distinct transitions at T1 = 184 K, T2 = 54.5 K, and T3 = 24 K are observed. At T1 there is a subtle tetragonal → monoclinic transition associated with emergence of a set of nonmagnetic superstructure peaks indexable to a incommensurate modulation parallel to the α-MnO2 tunnels. Our findings are consistent with a relation previously reported in titanate hollandites, that ⁠. Magnetic Bragg peaks emerge below T2 = 54.5 K, and their positions indicate an incommensurate modulated magnetic structure. The model consistent with the data is a dual- structure with a ferromagnetic component and an incommensurate ⁠, with the latter most likely to be helical. The period of oscillation of the incommensurate magnetic component is in line with predictions based on a Heisenberg spin Hamiltonian [Mandal et al. Phys. Rev. B 2014, 90, 104420]. Below T3 = 24 K, there is a magnetic transition, which gives rise to a different set of magnetic Bragg peaks indicative of a highly complex magnetic structure.

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Abstract: Layered NaMO2 oxides are attractive cathode materials for Na-ion batteries due to their exceptional tunability of redox chemistry, voltage, and structural stability via transition-metal composition and layer ordering. Here, we demonstrate that microwave synthesis provides a rapid and efficient route to the preparation of NaMO2 materials. Six oxide compositions in the Na–Mn–Fe–Ni–Cu–O phase space were synthesized on 7–10 min timescales. Synchrotron X-ray diffraction, Raman spectroscopy, and electron microscopy confirm well-ordered layered frameworks composed of micrometer-scale particles. Compositional analysis using inductively coupled plasma optical emission spectroscopy and X-ray fluorescence shows that near-target stoichiometries are obtained without the excess sacrificial Na precursors typically required in conventional solid-state routes, consistent with suppressed Na volatilization during the short reaction. The rapid reaction thereby provides access to highly sodiated O3 phases that can be difficult to obtain under equilibrium conditions. The high mobility of Na+, combined with the large size mismatch between Na and M, promotes the formation of well-ordered frameworks with no evidence of antisite disorder between Na and the transition metal ions. Electrochemical measurements reveal composition-dependent Na-ion (de)insertion behavior: Mn/Fe-rich compositions deliver high capacity but exhibit pronounced hysteresis, while Ni substitution increases operating potential and suppresses abrupt phase transitions. Dopant levels of Cu, previously reported to stabilize the structure, are readily incorporated and further smooth the potential profiles, albeit at the expense of capacity. These results demonstrate that microwave synthesis enables rapid and reliable access to O3–NaMO2 phases, emphasizing its suitability as a platform for the rapid exploration of compositions.

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Abstract: The thermal catalytic hydrogenolysis of polyolefins offers a pathway to convert plastic waste to value-added hydrocarbons. However, the reliance on noble metals such as Ru or Pt remains a significant barrier to large-scale implementation. In this work, we demonstrate that the Zr-containing mixed metal oxides (MMOs), Co0.7Al0.3–xZrx (CAZ), Ni0.7Al0.3–xZrx (NAZ), and Ni0.7Co0.3–xZrx (NCZ), with x = 0, 0.1, 0.2, and 0.3, are highly effective at 250 °C under 20 bar of H2 for virgin isotactic polypropylene (PP) (Mw = 240 kDa) hydrogenolysis to give liquid hydrocarbon products. The catalysts were produced by calcination of the Zr-containing layered double hydroxide (LDH) precursors; [Co0.7Al0.3–xZrx(OH)2][CO3](0.3–x)/2, [Ni0.7Al0.3–xZrx(OH)2][CO3](0.3–x)/2, [Ni0.7Co0.3–xZrx(OH)2][CO3](0.3–x)/2; x = 0, 0.1, 0.2, and 0.3. This approach allowed us to exploit the compositional tunability of the LDH framework to control the homogeneous distribution of the active metal centers. We find that Zr incorporation in these MMOs can significantly enhance catalytic PP hydrogenolysis. Our best-performing catalysts, Co2.1Al0.3Zr0.6Oy, delivers, after 1 h at 275 °C and 20 bar of H2, liquid hydrocarbon yields above 75% at a total PP conversion of over 90%, while keeping methane yields below 3%. Mechanistic studies show that these catalysts favor backbone C–C cleavage, delivering C3, C6, and C9 hydrocarbon selectivity. These scalable, highly efficient, and cost-effective catalysts are also efficient for the hydrogenolysis of a mix of commercial PP products. Hydrogenolysis of mixed pipette tips using Co2.1Al0.3Zr0.6Oy (275 °C, 1.5 h, 20 bar H2) produced a liquid hydrocarbon yield of 74%.

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Abstract: Cycling stability remains a critical challenge in the development of high-nickel positive electrode materials for lithium-ion batteries. Although existing strategies such as delaying the formation of the H3 phase or operating below a cut-off voltage have shown promise, they limit the exploitation of the full energy density. In this study, we introduce nanorod high-nickel materials, including LiNiO2, which demonstrate high-voltage cycling stability up to 4.95 V, more stable than traditional microcrystal counterparts. Our comparative analysis reveals that enhanced structural reversibility in the bulk structure is the key factor contributing to this improved cycling performance. The nanorod structure demonstrates an ability to endure the substantial lattice mismatch present in the Li layer at the H2-H3 interphase, thereby facilitating a comprehensive recovery from H3 to the H2 phase during discharge. This work offers insights into optimizing high-nickel positive electrode materials, improving cycling stability in high-energy battery applications.

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Abstract: Barocaloric (BC) effects at liquid–vapor transitions in hydrofluorocarbons drive most commercial technologies used for heating and cooling in the heating, ventilation and air-conditioning sector. However, these fluids suffer from huge global warming potential and alternative gases are less efficient, toxic or flammable. Solid–solid and solid–liquid BC materials have zero global warming potential and could even improve on current device efficiencies. Whilst solid–liquid BCs typically outperform solid–solid BCs, the latter are advantageous as they avoid leaks and present easier handling and recyclability thus facilitating waste management. Here we confine the solid–liquid BC stearic acid inside the nanopores of a functionalized metal-organic framework (MOF) and demonstrate that the colossal BC properties are retained in a solid-state material. Moreover, the enhanced interactions between the pore surface and the BC material allow a level of active control over the thermal response, as opposed to passive encapsulation. Our results open novel avenues to exploit and tune colossal BC effects in a wide range of combinations of solid–liquid BC materials embedded within functionalized MOFs, without the associated engineering drawbacks.