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Surface reconstruction or elemental leaching is generally involved in the oxygen evolution reaction (OER) process on transition metal-based oxides during alkaline water electrolysis, which gives rise to both opportunities and challenges for the development of OER electrocatalysts. Reaction-derived metal (oxy)hydroxides have been proven to be the actual active species for many metal oxides but have suffered from the dissolution of active elements. Here, the construction of a dynamically stable CoFe (oxy)hydroxide OER nanocatalyst is proposed, which delivers a low overpotential of 253 mV at 10 mA cm−2 and high mass activity (3.78 A mg−1 at an overpotential of 300 mV), among the highest of all the hydroxides reported previously. The in situ synthesized nanocatalyst acts as a stable CoOxHy host for Fe adsorption and facilitates active Co–O–Fe motif formation. The weak metal–O coordination environment and hydrophilic surface morphology lead to superficial mass transfer. The drawbacks of Fe depletion for conventional CoFe (oxy)hydroxides are overcome, attributed to tardy lattice oxygen ion diffusion and dynamic Fe-saturated dual metal active sites, which lead to a stable performance for over 100 h. This study provides a design strategy for OER electrocatalysts with both high mass activity and durability, which shows application prospects for large-scale electrochemical water splitting. [ABSTRACT FROM AUTHOR]

Reversible solid oxide cells (rSOCs) have significant potential as efficient energy conversion and storage systems. Nevertheless, the practical application of their conventional air electrodes, such as La0.8Sr0.2MnO3−δ (LSM), Ba0.5Sr0.5Co0.8Fe0.2O3‐δ (BSCF), and PrBa0.8Ca0.2Co2O5+δ (PBCC), remains unsatisfactory due to interface delamination during prolonged electrochemical operation. Using micro‐focusing X‐ray absorption spectroscopy (µ‐XAS), a decrease (increase) in the co‐valence state from the electrode surface to the electrode/electrolyte interface is observed, leading to the above delamination. Utilizing the one‐pot method to incorporate an oxygen‐vacancy‐enriched CeO2 electrode into these air electrodes, the uniform distribution of the Co valence state is observed, alleviating the structural delamination. PBCC–CeO2 electrodes exhibited a degradation rate of 0.095 mV h−1 at 650 °C during a nearly 500‐h test as compared with 0.907 mV h−1 observed during the 135‐h test for PBCC. Additionally, a remarkable increase in electrolysis current density from 636 to 934 mA cm−2 under 1.3 V and a maximum power density from 912 to 989 mW cm−2 upon incorporating CeO2 into PBCC is also observed. BSCF–CeO2 and LSM–CeO2 also show enhanced electrochemical performance and prolonged stability as compared to BSCF and LSM. This work offers a strategy to mitigate the structural delamination of conventional electrodes to boost the performance of rSOCs. [ABSTRACT FROM AUTHOR]

The rich physical properties unveiled in a plethora of transition and rare-earth metal oxides have been attributed to the intricate interplays between the orbital, charge, and spin degrees of freedom. Among them, rare-earth manganites (RMnO3) have been attracting tremendous attention owing to the ionic size-induced lattice distortion dictated by the Goldschmidt tolerance factor and the substantial Jahn–Teller distortion unique to Mn3+ ions, which evidently have resulted in a variety of emergent characteristics in electronic, magnetic, and orbital ordering. In this work, we deliberately engineered the orientation of a series of orthorhombic YMnO3 (o-YMO) films grown on SrTiO3(100) [STO(100)] and SrTiO3(110) [STO(110)] substrates by means of pulsed laser deposition. The x-ray diffraction (XRD) and reciprocal space mapping revealed that o-YMO/STO(100) is c-axis-oriented and o-YMO/STO(110) is a-axis-oriented, respectively. The XRD ϕ-scans further indicate that both films have excellent in-plane crystallinity, allowing the exploration of anisotropies along the respective crystallographic orientations. Indeed, the x-ray absorption linear dichroism spectroscopy taken along the respective crystallographic orientations evidently exhibited substantial anisotropy. Theoretical fitting with configuration interaction cluster calculations suggests that the d 3 z 2 − r 2 orbitals are parallel to YMO[001]/(100), leading to stronger electron scattering along the c-axis. Independent polarization-dependent Δ R/R spectra obtained using the femtosecond pump–probe method exhibited substantial anisotropic behaviors in carrier relaxation dynamics when probing along different crystallographic orientations, presumably due to orbital ordering anisotropies. [ABSTRACT FROM AUTHOR]

Anionic redox chemistry can surpass theoretical limits of conventional layered oxide cathodes in energy density. A recent model system of sodium-ion batteries, O3-NaLi 1/3 Mn 2/3 O 2 , demonstrated full anionic redox capacity but is limited in reversibility and kinetics due to irreversible structural rearrangement and oxygen loss. Solutions to these issues are missing due to the challenging synthesis. Here, we harness the unique structural richness of sodium layered oxides and realize a controlled ratio of P2 structural intergrowth in this model compound with the overall composition maintained. The resulted O3 with 27 % P2 intergrowth structure delivers an excellent initial Coulombic efficiency of 87 %, comparable to the state-of-the-art Li-rich NMCs. This improvement is attributed to the effective suppression of irreversible oxygen release and structural changes, evidenced by operando Differential Electrochemical Mass Spectroscopy and X-ray Diffraction. The as-prepared intergrowth material, based on the environmentally benign Mn, exhibits a reversible capacity of 226 mAh g -1 at C/20 rate with excellent cycling stability stemming from the redox reactions of oxygen and manganese. Our work isolates the role of P2 structural intergrowth and thereby introduces a novel strategy to enhance the reversibility and kinetics of anionic redox reactions in sodium layered cathodes without compromising capacity., (© 2024 Wiley-VCH GmbH.)

Anionic redox allows the direct formation of O─O bonds from lattice oxygens and provides higher catalytic in the oxygen evolution reaction (OER) than does the conventional metal ion mechanism. While previous theories have predicted and experiments have suggested the possible O─O bond, it has not yet been directly observed in the OER process. In this study, operando soft X-ray absorption spectroscopy (sXAS) at the O K-edge and the operando Raman spectra is performed on layered double CoFe hydroxides (LDHs) after intercalation with [Cr(C 2 O 4 ) 3 ] 3- , and revealed a three-step oxidation process, staring from Co 2+ to Co 3+ , further to Co 4+ (3d6L), and ultimately leading to the formation of O─O bonds and O 2 evolution above a threshold voltage (1.4 V). In contrast, a gradual oxidation of Fe is observed in CoFe LDHs. The OER activity exhibits a significant enhancement, with the overpotential decreasing from 300 to 248 mV at 10 mA cm -2 , following the intercalation of [Cr(C 2 O 4 ) 3 ] 3- into CoFe LDHs, underscoring a crucial role of anionic redox in facilitating water splitting., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Hydrogen obtained from electrochemical water splitting is the most promising clean energy carrier, which is hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Thus, the development of an efficient OER electrocatalyst using nonprecious 3d transition elements is desirable. Multielement synergistic effect and lattice oxygen oxidation are two well-known mechanisms to enhance the OER activity of catalysts. The latter is generally related to the high valence state of 3d transition elements leading to structural destabilization under the OER condition. We have found that Al doping in nanosheet Ni-Fe hydroxide exhibits 2-fold advantage: (1) a strong enhanced OER activity from 277 mV to 238 mV at 10 mA cm -2 as the Ni valence state increases from Ni 3.58+ to Ni 3.79+ observed from in situ X-ray absorption spectra. (2) Operational stability is strengthened, while weakness is expected since the increased Ni IV content with 3d 8 L 2 (L denotes O 2p hole) would lead to structural instability. This contradiction is attributed to a reduced lattice oxygen contribution to the OER upon Al doping, as verified through in situ Raman spectroscopy, while the enhanced OER activity is interpreted as an enormous gain in exchange energy of Fe IV -Ni IV , facilitated by their intersite hopping. This study reveals a mechanism of Fe-Ni synergy effect to enhance OER activity and simultaneously to strengthen operational stability by suppressing the contribution of lattice oxygen.

A transition-metal oxide of PbCu 3 Mn 4 O 12 was prepared at 1523 K and 10 GPa. An A-site-ordered quadruple perovskite structure with the space group Im 3̅ is assigned for this compound. Based on bond-valence-sum calculations and X-ray absorption spectroscopy, the charge combination is determined to be PbCu 3 2+ Mn 4 4+ O 12 . Due to Cu 2+ (↑)-Mn 4+ (↓) antiferromagnetic coupling, a near-room-temperature ferrimagnetic phase transition is observed at approximately 287 K. PbCu 3 Mn 4 O 12 exhibits a semiconducting electric transport property with the energy band gap E g ≈ 0.2 eV. In addition, considerable low-field magnetoresistance effects are observed at lower temperatures. This study provides an intrinsic near-room-temperature ferrimagnetic semiconductor that exhibits potential applications in next-generation spintronic devices.

An AA' 3 B 2 B' 2 O 12 -type quadruple perovskite oxide of CaCu 3 Cr 2 Re 2 O 12 was synthesized at 18 GPa and 1373 K. Both an A- and B-site ordered quadruple perovskite crystal structure was observed, with the space group Pn -3. The valence states are verified to be CaCu 3 2+ Cr 2 3+ Re 2 5+ O 12 by bond valence sum calculations and synchrotron X-ray absorption spectroscopy. The spin interaction among Cu 2+ , Cr 3+ , and Re 5+ generates a ferrimagnetic transition with the Curie temperature ( T C ) at about 360 K. Moreover, electric transport properties and specific heat data suggest the presence of a half-metallic feature for this compound. The present study provides a promising quadruple perovskite oxide with above-room-temperature ferrimagnetism and possible half-metallic properties, which shows potential in the usage of spintronic devices.

Electrochemical nitrate reduction to ammonia offers an attractive solution to environmental sustainability and clean energy production but suffers from the sluggish *NO hydrogenation with the spin-state transitions. Herein, we report that the manipulation of oxygen vacancies can contrive spin-polarized Fe 1 -Ti pairs on monolithic titanium electrode that exhibits an attractive NH 3 yield rate of 272,000 μg h -1 mg Fe -1 and a high NH 3 Faradic efficiency of 95.2% at -0.4 V vs. RHE, far superior to the counterpart with spin-depressed Fe 1 -Ti pairs (51000 μg h -1 mg Fe -1 ) and the mostly reported electrocatalysts. The unpaired spin electrons of Fe and Ti atoms can effectively interact with the key intermediates, facilitating the *NO hydrogenation. Coupling a flow-through electrolyzer with a membrane-based NH 3 recovery unit, the simultaneous nitrate reduction and NH 3 recovery was realized. This work offers a pioneering strategy for manipulating spin polarization of electrocatalysts within pair sites for nitrate wastewater treatment., (© 2024. The Author(s).)

Materials with negative thermal expansion (NTE) attract significant research attention owing to their unique physical properties and promising applications. Although ferroelectric phase transitions leading to NTE are widely investigated, information on antiferroelectricity-induced NTE remains limited. In this study, single-crystal and polycrystalline Pb 2 CoMoO 6 samples are prepared at high pressure and temperature conditions. The compound crystallizes into an antiferroelectric Pnma orthorhombic double perovskite structure at room temperature owing to the opposite displacements dominated by Pb 2+ ions. With increasing temperature to 400 K, a structural phase transition to cubic Fm-3m paraelectric phase occurs, accompanied by a sharp volume contraction of 0.41%. This is the first report of an antiferroelectric-to-paraelectric transition-induced NTE in Pb 2 CoMoO 6 . Moreover, the compound also exhibits remarkable NTE with an average volumetric coefficient of thermal expansion α V = -1.33 × 10 -5 K -1 in a wide temperature range of 30-420 K. The as-prepared Pb 2 CoMoO 6 thus serves as a prototype material system for studying antiferroelectricity-induced NTE., (© 2023 Wiley-VCH GmbH.)