Novel 2D-AuSe nanostructures as effective platinum replacement counter electrodes in dye-sensitized solar cells.

Studies to improve the efficiency of dye-sensitized solar cells (DSSCs) include, but are not limited to, finding alternatives such as 2D layered materials as replacement counter electrodes (CEs) to the commonly used Pt. Herein, we report for the first time, the use of AuSe as a counter electrode for the reduction of triiodide ions (I3 -) to iodide ions (I-). The colloidal synthesis of gold selenide nanostructures produced α-AuSe and ß-AuSe dominated products as determined by XRD. Electron microscopy showed α-AuSe having belt-like structures while ß-AuSe had a plate-like morphology. EDS mapping confirmed the elemental composition and homogeneity of the AuSe CEs. Cyclic voltammetry curves of the AuSe CEs displayed the double set of reduction-oxidation peaks associated with the reactions in the I3 -/I- electrolyte and therefore were comparable to the Pt CV curve. The α-AuSe CE showed better electrocatalytic activity with a reduction current of 6.1 mA than that of ß-AuSe and Pt CEs, which were 4.2 mA and 4.8 mA, respectively. The peak-to-peak separation (ΔE pp) for the α-AuSe CE was also more favourable with a value of 532 mV over that of the ß-AuSe CE of 739 mV however, both values were larger than that of the Pt CE, which was found to be 468 mV. The EIS and Tafel plot data showed that α-AuSe had the best catalytic activity compared to ß-AuSe and was comparable to Pt. The DSSC using α-AuSe as a CE had the highest PCE (6.94%) as compared to Pt (4.89%) and ß-AuSe (3.47%). The lower efficiency for Pt was attributed to the poorer fill factor. With these novel results, α-AuSe is an excellent candidate to be used as an alternative CE to Pt in DSSCs.

Evaluating the Effect of Varying the Metal Precursor in the Colloidal Synthesis of MoSe2 Nanomaterials and Their Application as Electrodes in the Hydrogen Evolution Reaction.

Herein we report on the use of different metal precursors in the synthesis of MoSe2 nanomaterials in order to control their morphology. The use of Mo(CO)6 as the metal precursor resulted in the formation of wrinkled few-layer nanosheets, while the use of H2MoO4 as the metal precursor resulted in the formation of nanoflowers. To investigate the effect of the morphologies on their performance as catalysts in the hydrogen evolution reaction, electrochemical characterization was done using linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrical impedance spectroscopy (EIS). The MoSe2 nanoflowers were found to have superior electrochemical performance towards the hydrogen evolution reaction with a lower Tafel slope, on-set potential, and overpotential at 10 mA/cm2 compared to the wrinkled few-layer nanosheets. This was found to be due to the higher effective electrochemical surface area of the nanoflowers compared to the nanosheets which suggests a higher number of exposed edge sites in the nanoflowers.