Self-Assembled, Stabilizer-Free ZnS Nanodot Films Using Spray-Based Approaches

A direct self-assembly of high-quality, uncoated ZnS nanodots on a given substrate was obtained using two techniques: the sequential and cyclic spray ion layer gas reaction (spray-ILGAR) as well as the simultaneous and continuous spray chemical vapor deposition (spray-CVD). The spray-ILGAR nanodots are homogeneous in size (3–6 nm), regular in shape, and uniform in composition, while the spray-CVD nanodots are larger and irregular in shape with inclusions of ZnO. By employing these two spray-based techniques, the synthesis of nanodots directly assembled on the substrate surface can be realized in a controlled manner, covering a certain range of compositions, tunable sizes, and controllable interparticle distances. <i>In situ</i> mass spectrometry was implemented in the real-time process in order to achieve better understanding of the intrinsic chemistry involved. We systematically study the influence of the process parameters on the formation of the nanodots and compare the morphology, composition, and property of the obtained nanodots. Based on these investigations, the underlying mechanism that controls the special growth of the nanodots in spray-ILGAR and spray-CVD processes is proposed. It can account for the similarities and differences of these two kinds of nanodots. A passivation/point contact bilayer, composed of the spray-based ZnS nanodots covered by a homogeneous ILGAR In₂S₃ layer, is used as the buffer in the chalcopyrite solar cells, resulting in the cell performance improvement compared to the pure ILGAR In₂S₃ buffer

Elucidating the Complex Oxidation Behavior of Aqueous H₃PO₃ on Pt Electrodes via <i>In Situ</i> Tender X‑ray Absorption Near-Edge Structure Spectroscopy at the P <i>K</i>‑Edge

In situ tender X-ray absorption near-edge structure (XANES) spectroscopy at the P K-edge was utilized to investigate the oxidation mechanism of aqueous H3PO3 on Pt electrodes under various conditions relevant to high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) applications. XANES and electrochemical analysis were conducted under different tender X-ray irradiation doses, revealing that intense radiation induces the oxidation of aqueous H3PO3 via H2O yielding H3PO4 and H2. A broadly applicable experimental procedure was successfully developed to suppress these undesirable radiation-induced effects, enabling a more accurate determination of the aqueous H3PO3 oxidation mechanism. In situ XANES studies of aqueous 5 mol dm–3 H3PO3 on electrodes with varying Pt availability and surface roughness reveal that Pt catalyzes the oxidation of aqueous H3PO3 to H3PO4. This oxidation is enhanced upon applying a positive potential to the Pt electrode or raising the electrolyte temperature, the latter being corroborated by complementary ion-exchange chromatography measurements. Notably, all of these oxidation processes involve reactions with H2O, as further supported by XANES measurements of aqueous H3PO3 of different concentrations, showing a more pronounced oxidation in electrolytes with a higher H2O content. The significant role of water in the oxidation of H3PO3 to H3PO4 supports the reaction mechanisms proposed for various chemical processes observed in this work and provides valuable insights into potential strategies to mitigate Pt catalyst poisoning by H3PO3 during HT-PEMFC operation