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 Mo x W 1‐x Te 2 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 °C exhibits the mixed phases of semiconducting T d ‐ & 2H ‐Mo 0.32 W 0.67 Te 2.01 with charge carrier density of (1.20 ± 0.02) × 10 19 cm −3 ; whereas, the nanocrystal synthesized at 820 °C shows a single phase of semi‐metallic T d ‐Mo 0.29 W 0.72 Te 1.99 with much higher carrier density of (1.59 ± 0.04) × 10 20 cm −3 . In the cyclic voltammetry (CV) analysis over 200 cycles, the Mo x W 1‐x Te 2 ‐based electrodes show better stability in the I − /I 3 − electrolyte than a Pt electrode. In DSSC tests, a T d ‐Mo 0.29 W 0.72 Te 1.99 ‐decorated CE achieves the efficiency ( η ) of 8.85%, better than those CEs fabricated with T d ‐ & 2H ‐Mo 0.32 W 0.67 Te 2.01 (7.81%) and sputtered Pt (8.01%). The electrochemical impedance spectra reveal that the T d ‐Mo 0.29 W 0.72 Te 1.99 electrode possesses low charge‐transfer resistance in electrocatalytic reactions. These exceptional properties make Weyl semi‐metallic T d ‐Mo x W 1‐x Te 2 a potential electrode material for a wide variety of electrocatalytic applications.