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 °C exhibits the mixed phases of semiconducting Td‐ & 2H‐Mo0.32W0.67Te2.01 with charge carrier density of (1.20 ± 0.02) × 1019 cm−3; whereas, the nanocrystal synthesized at 820 °C shows a single phase of semi‐metallic Td‐Mo0.29W0.72Te1.99 with much higher carrier density of (1.59 ± 0.04) × 1020 cm−3. In the cyclic voltammetry (CV) analysis over 200 cycles, the MoxW1‐xTe2‐based electrodes show better stability in the I−/I3− electrolyte than a Pt electrode. In DSSC tests, a Td‐Mo0.29W0.72Te1.99‐decorated CE achieves the efficiency (η) of 8.85%, better than those CEs fabricated with Td‐ & 2H‐Mo0.32W0.67Te2.01 (7.81%) and sputtered Pt (8.01%). The electrochemical impedance spectra reveal that the Td‐Mo0.29W0.72Te1.99 electrode possesses low charge‐transfer resistance in electrocatalytic reactions. These exceptional properties make Weyl semi‐metallic Td‐MoxW1‐xTe2 a potential electrode material for a wide variety of electrocatalytic applications. Phase‐engineered Weyl semi‐metallic MoxW1‐xTe2 nanosheets, are exploited as a highly efficient counter electrode for dye‐sensitized solar cells, achieving higher efficiency of ≈10% over the conventional Pt. The Td‐MoxW1‐xTe2‐based counter electrode can robustly promote the charge transfer during the redox reaction at the counter electrode/electrolyte interface, leading to the stable electrocatalytic performance over 200 scanning cycles in the I3‐/I‐ medium.