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.