ABSTRACT
A single step deposition technique of Pt/C films for electrocatalytic applications is presented. The hollow cathode gas flow sputtering (GFS) method allows a catalyst production within few minutes without further steps. The herein presented films consist of small Pt nanocrystals (2-5â nm) deposited in a matrix of nanocrystalline carbon. The films show a low and stable overpotential under acidic conditions in the hydrogen evolution reaction (HER). Relatively low Pt-mass activity (<1â mA/µgPt ) is attributed to the yet too high Pt-content in the films. Another issue discovered in this work is a non-graphitic state of carbon resulting in its high resistivity. Still, the GFS deposition technique providing by nature high deposition rates and a substance-to-material yield of 80-90 % is advantageous than other sputtering techniques and especially chemical methods in that sense. This technique is scalable to areas in the range of square meters and thus represents an attractive way to efficiently produce large-scale cathode coatings for industrial electrolysers.
ABSTRACT
We report a systematic investigation on the influence of two-step post-deposition treatments (PDTs) on TiO2 buffer layers deposited by ultrasonic spray pyrolysis (USP) for emerging Sb2Se3 photovoltaics. Air annealing is a typical method for recrystallizing chemically deposited TiO2 films. However, organic residues (such as carbon species) from a precursor solution based on titanium tetraisopropoxide and acetylacetone may still remain on the TiO2 surface, therefore requiring an additional annealing step. We demonstrate that vacuum annealing can be a suitable technological approach to decrease the concentration of carbon species in TiO2 films. Vacuum annealing was performed at temperatures at 160-450 °C prior to the 450 °C air annealing step. It was found that vacuum annealing at 160 °C followed by subsequent air annealing led to better device performance. This was explained by achieving an optimal balance between the removal of carbon content during vacuum annealing and the active recrystallization of TiO2 during air annealing. The decrease of carbon concentration by employing the two-step approach was supported by changes in the lattice parameters of TiO2 and proven by X-ray photoelectron spectroscopy (XPS). The given study provides experimental evidence on how nanoscale carbon species in the TiO2 heterojunction partner layer of a Sb2Se3 solar cell can affect the device's performance. By this approach, we generate complementary insights on how the quality of the main interface has an impact and can take a key role despite the optimized Sb2Se3 grain structure and orientation.
ABSTRACT
We present an efficient non-enzymatic hydrogen peroxide sensor composed of flower-like silver microstructures. The silver microstructures´ morphology is controlled by adding minute amounts of either succinic or malonic acid as directing agents. Morphologically, silver particles showed ball-like structures in the absence of both directing agents, while the presence of 50 ppm of succinic acid and malonic acid lead to monodisperse chrysanthemum and water-lily flower-like structure, respectively. A higher concentration of succinic acid resulted in a rose flower-like structures. Electrochemically, the rose flower-like silver microstructures exhibited the best performance for H2O2 detection as evaluated by their outstanding electrocatalytic activity (12 times higher) and sensitivity (2.4 mM-1 cm-2, 24 times higher) with lower detection limit (0.4 µM, 5 times smaller) together with their excellent H2O2 selectivity compared to that of the ball-shaped structures. Additionally, rose-flower microstructures exhibited excellent long-term stability; 11 and 3 times higher compared to ball- and water-lily structures, respectively. This substantial performance enhancement is attributed to their unique flower-like structure providing a higher number of active surface sites (at least 8 times higher) and a faster detachment rate of in-situ generated oxygen bubbles from their surface.
