Improved HER Catalysis through Facile, Aqueous Electrochemical Activation of Nanoscale WSe₂

In the search for nonprecious metal catalysts for the hydrogen evolution reaction (HER), transition metal dichalcogenides (TMDCs) have been proposed as promising candidates. Here, we present a facile method for significantly decreasing the overpotential required for catalyzing the HER with colloidally synthesized WSe₂. Solution phase deposition of 2H WSe₂ nanoflowers (NFs) onto carbon fiber electrodes results in low catalytic activity in 0.5 M H₂SO₄ with an overpotential at -10 mA/cm² of greater than 600 mV. However, two postdeposition electrode processing steps significantly reduce the overpotential. First, a room-temperature treatment of the prepared electrodes with a dilute solution of the alkylating agent Meerwein's salt ([Et₃O][BF₄]) results in a reduction in overpotential by approximately 130 mV at -10 mA/cm². Second, we observe a decrease in overpotential of approximately 200-300 mV when the TMDC electrode is exposed to H⁺, Li⁺, Na⁺, or K⁺ ions under a reducing potential. The combined effect of ligand removal and electrochemical activation results in an improvement in overpotential by as much as 400 mV. Notably, the Li⁺ activated WSe₂ NF deposited carbon fiber electrode requires an overpotential of only 243 mV to generate a current density of -10 mA/cm². Measurement of changes in the material work function and charge transfer resistance ultimately provide rationale for the catalytic improvement.