Axial Chlorine Induced Electron Delocalization in Atomically Dispersed FeN4 Electrocatalyst for Oxygen Reduction Reaction with Improved Hydrogen Peroxide Tolerance.

Atomically dispersed iron sites on nitrogen-doped carbon (Fe-NC) are the most active Pt-group-metal-free catalysts for oxygen reduction reaction (ORR). However, due to oxidative corrosion and the Fenton reaction, Fe-NC catalysts are insufficiently active and stable. Herein, w e demonstrated that the axial Cl-modified Fe-NC (Cl-Fe-NC) electrocatalyst is active and stable for the ORR in acidic conditions with high H2 O2 tolerance. The Cl-Fe-NC exhibits excellent ORR activity, with a high half-wave potential (E1/2 ) of 0.82 V versus a reversible hydrogen electrode (RHE), comparable to Pt/C (E1/2 = 0.85 V versus RHE) and better than Fe-NC (E1/2 = 0.79 V versus RHE). X-ray absorption spectroscopy analysis confirms that chlorine is axially integrated into the FeN4. More interestingly, compared to Fe-NC, the Fenton reaction is markedly suppressed in Cl-Fe-NC. In situ electrochemical impedance spectroscopy reveals that Cl-Fe-NC provides efficient electron transfer and faster reaction kinetics than Fe-NC. Density functional theory calculations reveal that incorporating Cl into FeN4 can drive the electron density delocalization of the FeN4 site, leading to a moderate adsorption free energy of OH* (∆GOH* ), d-band center, and a high onset potential, and promotes the direct four-electron-transfer ORR with weak H2 O2 binding ability compared to Cl-free FeN4, indicating superior intrinsic ORR activity.

Triangular Magnet Emergent from Noncentrosymmetric Sr0.94Mn0.86Te1.14O6 Single Crystals.

We report the successful growth of high-quality single crystals of Sr0.94Mn0.86Te1.14O6 (SMTO) using a self-flux method. The structural, electronic, and magnetic properties of SMTO are investigated by neutron powder diffraction (NPD), single-crystal X-ray diffraction (SCXRD), thermodynamic, and nuclear magnetic resonance techniques in conjunction with density functional theory calculations. NPD unambiguously determined octahedral (trigonal antiprismatic) coordination for all cations with the chiral space group P312 (no. 149), which is further confirmed by SCXRD data. The Mn and Te elements occupy distinct Wyckoff sites, and minor anti-site defects were observed in both sites. X-ray photoelectron spectroscopy reveals the existence of mixed valence states of Mn in SMTO. The magnetic susceptibility and specific heat data evidence a weak antiferromagnetic order at TN = 6.6 K. The estimated Curie-Weiss temperature θCW = -21 K indicates antiferromagnetic interaction between Mn ions. Furthermore, both the magnetic entropy and the 125Te nuclear spin-lattice relaxation rate showcase that short-range spin correlations persist well above the Néel temperature. Our work demonstrates that Sr0.94(2)Mn0.86(3)Te1.14(3)O6 single crystals realize a noncentrosymmetric triangular antiferromagnet.

Laser Scribing for Electrode Patterning of Perovskite Spectrometer-Grade CsPbBr3 Gamma-ray Detectors.

Making semiconductor radiation detectors that work at room temperature relies heavily on the deposition and pixelation of electrodes. Electrode patterning of perovskite solar cells widely implements laser scribing techniques, which is a convenient, scalable, and inexpensive technique. However, this method has not found its application in radiation detector patterning yet, and the question whether laser scribing can achieve high-quality patterns with minimum damage to a detector crystal and low interpixel cross-talk remains largely unanswered. To prove that laser scribing is a practical method for electrode patterning on perovskite CsPbBr3 detectors, we use the material to create a variety of patterns. A very low lateral leakage current (60 nA at 10 V) and high mobility-lifetime product (9.7(3) × 10-4 cm2/V) were observed between the pixel and the guard ring in tests of single-pixel devices with a separation of 200 or 100 µm between the central electrode and the guard ring. The 122 and 136 keV photopeaks in 57Co gamma-ray spectra were very well resolved with an energy resolution of up to 6.1% at 122 keV. A further reduction in gap size to 50 µm is conceivable, but more process optimization is needed.

Extreme γ-Ray Radiation Tolerance of Spectrometer-Grade CsPbBr3 Perovskite Detectors.

The perovskite compound CsPbBr3 has recently been discovered as a promising room-temperature semiconductor radiation detector, offering an inexpensive and easy-to-manufacture alternative to the current benchmark material Cd1-x Znx Te (CZT). The performance of CsPbBr3 sensors is evaluated under harsh conditions, such as high radiation doses often found in industrial settings and extreme radiation in space. Results show minimal degradation in detector performance after exposure to 1 Mrad of Co-60 gamma radiation, with no significant change to energy resolution or hole mobility and lifetime. Additionally, many of the devices are still functional after being exposed to a 10 Mrad dose over 3 days, and those that do not survive can still be refabricated into working detectors. These results suggest that the failure mode in these devices is likely related to the interface between the electrode and material and their reaction, or the electrode itself and not the material itself. Overall, the study suggests that CsPbBr3 has high potential as a reliable and efficient radiation detector in various applications, including those involving extreme fluxes and energies of gamma-ray radiation.

Regimented Charge Transport Phenomena in Semiconductive Self-Assembled Rhenium Nanotubes.

Photoconductivity, a crucial property, determines the potential of semiconductor materials for use in optoelectronic and photocatalytic device applications. The one-dimensional metal-organic nanotube semiconducting material [{Re(CO)3}6(bho)(phpy)6]n (MBT 1, where bho is benzene-1,2,3,4,5,6-hexaoate and phpy is 4-phenylpyridine) reported herein exhibits record photocurrent responses at a broad spectral range. MBT 1 is comprised of a unique nanotube structure that is composed of six rhenium sites, six 4-phenylpyridine ligands, and a benzene-1,2,3,4,5,6-hexaoate unit. The highly organized self-assembled molecular bamboo tube MBT 1 displays semiconducting characteristics with a low activation energy of 1.63 meV. The alternating current (AC) and direct current (DC) conductivities of pellet devices are approximately 10-4 S/cm. For a single-crystal device, DC conductivity was found to be 1.5 S/cm, an unprecedented 10 000 times higher. The bandgap of MBT 1 was determined to be 1.03 eV, consistent with the theoretically estimated value of 1.2 eV. Theoretical calculations suggest that the unique structural architecture of MBT 1 allows for effective charge transport, which is facilitated by the spatial separation of electrons and holes that MBT 1 contains. This also eliminates fast charge recombination. The findings are not only chemically and fundamentally important but also have great potential for applications in innovative nano-optoelectronics.

Tailoring the Co4+/Co3+ active sites in a single perovskite as a bifunctional catalyst for the oxygen electrode reactions.

Developing a non-precious metal electrocatalyst for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is desirable for low-cost energy conversion devices. Herein, we designed and developed a new class of layered cation ordered single perovskite oxides (Pr0.9Ca0.1Co0.8Fe0.2O3-δ) with an optimum ratio of the Co4+/Co3+ oxidation state and oxygen vacancy for oxygen electrode reactions. Catalytic activities are investigated as a function of electronic structure and surface composition. A moderate amount of Ca and Fe dopants keeps the B-site Co cations at a higher oxidation state (Co4+) and generates a vast amount of an oxygen defect rich structure. The improved performance in the ORR and OER is explained by the increase in the sites of Co4+ cations, a state responsible for enhanced catalytic activity. A hypothesis for how doped Ca fraction affects the adsorbed oxygen species and contributes to catalytic activity is discussed. This work sheds light on the influence of crystal structure on the catalytic property and reports that ORR and OER activities are affected not only by oxygen vacancy concentration but also by the oxidation state of the transition metal in the perovskite oxide.

Water-assisted spin-flop antiferromagnetic behaviour of hydrophobic Cu-based metal-organic frameworks.

Solvent-dependent magnetism in Cu-based metal-organic frameworks (MOFs) is reported. Spin-flop magnetic behaviour occurs at different dehydrated states of MOFs. The oxygens of guest and coordinated water molecules are responsible as water removal tunes the coordination geometry around the Cu centre and the electronic structure of the framework.