Phase-Engineered Weyl Semi-Metallic MoxW1-xTe2 Nanosheets as a Highly Efficient Electrocatalyst for Dye-Sensitized Solar Cells

The emerging Weyl semi-metals with robust topological surface states are very promising candidates to rationally develop new-generation electrocatalysts for dye-sensitized solar cells (DSSCs). In this study, a chemical vapor deposition (CVD) method to synthesize highly crystalline Weyl semi-metallic MoxW1-xTe2 nanocrystals, which are applied for the counter electrode (CE) of DSSCs for the first time, are employed. By controlling the temperature-dependent phase-engineered synthesis, the nanocrystal grown at 760 degrees C exhibits the mixed phases of semiconducting T-d- & 2H-Mo0.32W0.67Te2.01 with charge carrier density of (1.20 +/- 0.02) x 10(19) cm(-3); whereas, the nanocrystal synthesized at 820 degrees C shows a single phase of semi-metallic T-d-Mo0.29W0.72Te1.99 with much higher carrier density of (1.59 +/- 0.04) x 10(20) cm(-3). In the cyclic voltammetry (CV) analysis over 200 cycles, the MoxW1-xTe2-based electrodes show better stability in the I-/I-3(-) electrolyte than a Pt electrode. In DSSC tests, a T-d-Mo0.29W0.72Te1.99-decorated CE achieves the efficiency (eta) of 8.85%, better than those CEs fabricated with T-d- & 2H-Mo0.32W0.67Te2.01 (7.81%) and sputtered Pt (8.01%). The electrochemical impedance spectra reveal that the T-d-Mo0.29W0.72Te1.99 electrode possesses low charge-transfer resistance in electrocatalytic reactions. These exceptional properties make Weyl semi-metallic T-d-MoxW1-xTe2 a potential electrode material for a wide variety of electrocatalytic applications.