Kuei-Hsien Chen

The electrocatalytic carbon dioxide reduction reaction (eCO2RR) in an acidic environment is crucial for mitigating carbonate and bicarbonate formation while enhancing CO2 conversion efficiency. However, the hydrogen evolution reaction (HER) often outcompetes eCO2RR in a proton-rich microenvironment, posing a significant challenge. This study introduces an in-situ phosphatizing method to alter the electronic structure of a Ni–N4 single-atom catalyst (Ni–N3PC), thereby suppressing HER and promoting eCO2RR performance in acidic environments. The Ni–N3PC catalyst achieves a CO Faradaic efficiency (FE) exceeding 90 % over a wide potential range, high carbon conversion efficiency, a CO partial current density of –357.7 mA cm−2, and long-term stability for 100 h at –100 mA cm−2 with a FE of 85 %. Electrochemical impedance spectroscopy and turnover frequency analysis reveal that Ni–N3PC exhibits lower charge-transfer resistance and higher intrinsic activity, respectively. The structural characterization using X-ray absorption spectroscopy confirms the formation of Ni–P and Ni–N bonds while scanning transmission electron microscopy shows atomically dispersed Ni atoms on carbon networks. Density functional theory calculations further support the experimental results, showing that Ni–N3PC significantly lowers the energy barrier for the key *COOH intermediate, resulting in outstanding eCO2RR performance. This research provides valuable insights into the design of highly efficient Ni single-atom catalysts for industrial eCO2RR applications.

Tin monosulfide (SnS), an affordable group IV-VI binary compound, has emerged as a promising semiconductor due to its abundance and low toxicity. The exceptionally low thermal conductivity from the strong lattice anharmonicity makes this material suitable for thermoelectric applications. However, the poor thermoelectric properties of polycrystalline, compared to its single-crystal counterpart, remain the challenge. Furthermore, the anisotropic performance based on the sintering process complicates the preparation of this polycrystalline material. In this study, we successfully improved the electrical transport properties of polycrystalline SnS by employing the in-plane transport properties with texture modulation from hot-pressing at 973 K. This enhancement led to the high electrical conductivity of ≈ 55 S cm−1 in polycrystalline Na-doped SnS observed at room temperature. Additionally, the hole carrier concentration of p-type SnS was further optimized by co-doping of Na and Ag. Our co-doped SnS exhibits a relatively high power factor peak of ≈ 4.49 μWcm−1K−2 at 473 K. With the significant improvement of the electrical conductivities, the thermal conductivities remained unaltered. This work successfully demonstrated a substantial enhancement by ∼66.7 % in the thermoelectric figure of merit (zT) from 0.18 to 0.3 at a relatively low temperature of 573 K in polycrystalline SnS via the microstructural modification from texturing and the optimization of carrier concentration from co-doping.

Tin monosulfide (SnS) is a promising light-harvesting material for solar cell applications, owing to its potential for large-scale production, cost-effectiveness, eco-friendly source materials, and long-term stability. However, SnS crystallizes in an orthorhombic structure, which results in a highly anisotropic charge transport behavior. Tailoring the crystallographic orientation of the SnS absorber layer plays a critical role in the enhancement of the transfer of charge carriers and the power conversion efficiency (PCE). By controlling the substrate tilting angle and temperature ramp rate in vapor transport deposition, the crystal growth orientation was tuned to a preferred direction which significantly suppressed the unfavorable (040) crystallographic plane. Through the combination of these two approaches, the PCE could be increased from 0.11% to 2%. The effect of the tilting angle was numerically simulated to investigate its role in controlling the film uniformity and directing the film growth. In addition, the correlation between the texture coefficient of the (040) plane and the charge transport properties was determined by a combination of analytical methods such as device performance studies, electrochemical impedance spectroscopy, along with transient photovoltage, space-charge-limited current, and dark current measurements. These techniques were blended together to prove that the marked improvement in PCE can be ascribed to a reduced charge recombination (in both SnS bulk and interfaces) and an enhanced hole mobility.