Kuei-Hsien Chen

Abstract Double-atom site catalysts (DASs) have emerged as a recent trend in the oxygen reduction reaction (ORR), thereby modifying the intermediate adsorption energies and increasing the activity. However, the lack of an efficient dual atom site to improve activity and durability has limited these catalysts from widespread application. Herein, the nitrogen-coordinated iron and tin-based DASs (Fe-Sn-N/C) catalyst are synthesized for ORR. This catalyst has a high activity with ORR half-wave potentials (E1/2) of 0.92 V in alkaline, which is higher than those of the state-of-the-art Pt/C (E1/2 = 0.83 V), Fe-N/C (E1/2 = 0.83 V), and Sn-N/C (E1/2 = 0.77 V). Scanning electron transmission microscopy analysis confirmed the atomically distributed Fe and Sn sites on the N-doped carbon network. X-ray absorption spectroscopy analysis revealed the charge transfer between Fe and Sn. Both experimental and theoretical results indicate that the Sn with Fe-NC (Fe-Sn-N/C) induces charge redistribution, weakening the binding strength of oxygenated intermediates and leading to improved ORR activity. This study provides the synergistic effects of DASs catalysts and addresses the impacts of P-block elements on d-block transition metals in ORR.

Direct Z-scheme heterojunctions are widely used for photocatalytic water splitting and CO2 reduction due to facilitating well-separated photogenerated charge carriers and spatial isolation of redox reactions. Here, using a facile two-step hydrothermal and ion-exchange method, we uniformly decorate silver orthophosphate (i.e., Ag3PO4) quantum dots with an average characteristic size of ∼10 nm over tin(iv) sulphide (i.e., SnS2) nanosheets to form a 0D/2D heterojunction. The direct Z-scheme mechanism, i.e. charge transport for efficient electron (from SnS2) and hole (from Ag3PO4) recombination, is confirmed by the following experiments: (i) ultraviolet and X-ray photoelectron spectroscopies; (ii) photodeposition of Pt and PbO2 nanoparticles on reduction and oxidation sites, respectively; (iii) in situ X-ray photoelectron spectroscopy; and (iv) electron paramagnetic resonance spectroscopy. Owing to the photoreduction properties of Ag3PO4 with orthophosphate vacancies, Z-scheme charge carrier transfer, and efficient exciton dissociation, an optimized heterojunction shows a high CO2-to-CO reduction yield of 18.3 μmol g−1 h−1 with an illustrious selectivity of ∼95% under light illumination, which is about 3.0 and 47.8 times larger than that of Ag3PO4 and SnS2, respectively. The carbon source for the CO product is verified using a 13CO2 isotopic experiment. Moreover, by tracing the peak at ∼1190 cm−1 in the dark and under light irradiation, in situ diffuse reflectance infrared Fourier transform spectroscopy demonstrates that the CO2 reduction pathway goes through the COOH* intermediate.

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Multielement alloying is an appealing approach for suppressing thermal conductivity of thermoelectric materials. In this study, we synthesized GeTe-based high-entropy alloys with notable (S, Se) substitution at Te sites and (Ag, Sb) at Ge sites. The Ge0.82Ag0.08Sb0.1S0.5Se0.1Te0.4 exhibits an extremely low thermal conductivity of ∼ 0.66 W/m⋅K and a high Seebeck coefficient (>250 μV/K) over a temperature range of 150 – 400 °C. The influence of lattice distortion on phase transformation and transport properties of Ge0.9-2xAg2xSb0.1S0.5Se0.1Te0.4 (x = 0 – 0.06) was investigated.

Tin-based composites are promising anode materials for high-performance lithium-ion batteries (LIBs); however, insufficient conductivity, as well as fatal volume expansion during cycling lead to poor electrochemical reversibility and cycling stability. In this work, we demonstrate the lithium-ion storage behaviors of SnS2 anode material deposited on different electrode supports. The SnS2 grown on 3D hierarchical carbon nanotube-carbon cloth composites (SnS2-CNT-CC) shows superior capacity retention and cycle stability, compared to that on planar Mo sheets and carbon cloth. The specific capacity of SnS2 on Mo, CC, and CNT-CC is around 240, 840, and 1250 g−1, respectively. The SnS2-CNT-CC electrode outperforms in the cyclic performance and rate capability compared to other electrode configurations due to the multi-electron pathway and high surface area derived from 3D hierarchical CNT-CC electrode support. Furthermore, a significant decrease in the charge transfer resistance is observed by utilizing 3D hierarchical CNT-CC electrode support. The use of 3D hierarchical structures as electrode support could be the best alternative to enhance the electrochemical performances for the next generation LIBs.

Abstract A heterobimetallic corrole complex, comprising oxygen reduction reaction (ORR) active non-precious metals Co and Fe with a corrole-N4 center (PhFCC), is successfully synthesized and used to prepare a dual-atom molecular catalyst (DAMC) through subsequent low-temperature pyrolysis. This low-temperature pyrolyzed electrocatalyst exhibited impressive ORR performance, with onset potentials of 0.86 and 0.94 V, and half-wave potentials of 0.75 and 0.85 V, under acidic and basic conditions, respectively. During potential cycling, this DAMC displayed half-wave potential losses of only 25 and 5 mV under acidic and alkaline conditions after 3000 cycles, respectively, demonstrating its excellent stability. Single-cell Nafion-based proton exchange membrane fuel cell performance using this DAMC as the cathode catalyst showed a maximum power density of 225 mW cm−2, almost close to that of most metal–N4 macrocycle-based catalysts. The present study showed that preservation of the defined CoN4 structure along with the cocatalytic Fe–Cx site synergistically acted as a dual ORR active center to boost overall ORR performance. The development of DAMC from a heterobimetallic CoN4-macrocyclic system using low-temperature pyrolysis is also advantageous for practical applications.

In addition to the Ge-vacancy control of GeTe, the antimony (Sb) substitution of GeTe for the improvement of thermoelectric performance is explored for Ge1−xSbxTe with x = 0.08–0.12. The concomitant carrier concentration (n) and the aliovalent Sb ion substitution led to an optimal doping level of x = 0.10 to show ZT ∼ 2.35 near ∼800 K, which is significantly higher than those single- and multi-element substitution studies of the GeTe system reported in the literature. In addition, Ge0.9Sb0.1Te demonstrates an impressively high power factor of ∼36 μW cm−1 K−2 and a low thermal conductivity of ∼1.1 W m−1 K−1 at 800 K. The enhanced ZT level for Ge0.9Sb0.1Te is explained through a systematic investigation of micro-structural change and strain analysis from room temperature to 800 K. A significant reduction of lattice thermal conductivity (κlat) is identified and explained by the Sb substitution-introduced strained and widened domain boundaries for the herringbone domain structure of Ge0.9Sb0.1Te. The Sb substitution created multiple forms of strain near the defect centre, the herringbone domain structure, and widened tensile/compressive domain boundaries to support phonon scattering that covers a wide frequency range of the phonon spectrum to reduce lattice thermal conductivity effectively.