Electrochemical data for molybdenum diselenide-borophene (B/MoSe2) composite

Molybdenum diselenide (MoSe2) and boron powders were purchased from Sigma Aldrich. All reagents were used without further purification.
Both bulk MoSe2 and boron have been introduced to the planetary zirconia ball mill (Fritsch Pulverisette). A series of composites with different MoSe2 to boron ratios MoSe2/B_1:10, MoSe2/B_1:1, MoSe2/B_10:1, MoSe2/B_100:1, and MoSe2/B_1000:1 with a total mass loading of 500 mg have been fabricated. Each of the prepared composites was milled using the same operating parameters with the exact number of zirconia balls (18). These processes were carried out for a total grinding time of 6 hours (to avoid overheating, the processes were conducted in a cyclic manner – 30 minutes of operation with 15-minute breaks), at a rotational speed of 450 rpm. The sample composed by MoSe2/B_1:1 manifested the best electrochemical behavior (it will be labeled as B/MoSe2), thus only this sample underwent detailed analyses.
The electrochemical analyses were performed using a BioLogic VMP-3 potentiostat in a three-electrode setup, with the reactor equipped with a temperature-controlled bath at 25 ℃. A mercury sulfate electrode (MSE, HgǀHg2SO4 in 1 M H2SO4, RE-2CP) served as the reference electrode (RE), while a platinum wire was used as the counter electrode (CE). The working electrode (WE) consisted of a 10 x 40 mm graphitic foil with a thickness of 125 µm (Goodfellow) coated with an active material. The active material dispersion was prepared at a concentration of 10 mg/mL in a solution of isopropanol/water (1:3 by volume) containing 0.05 % Nafion (Sigma-Aldrich) as a binder. The electrodes were fabricated by drop-casting 200 µL of the active material dispersion onto both sides of the graphitic foil, followed by drying at 90 ℃ under vacuum for 12 hours. All electrochemical measurements were conducted under acidic conditions using 0.5M H2SO4. To evaluate the stability of the most active material, current densities of 10, 20, and 50 mA/cm2 were applied for 20 hours. All potentials were referenced to the reversible hydrogen electrode (RHE), calculated using the equation ERHE=0.059 x pH + EWE + E0, where ERHE, EWE, and E0 represent the potential of reversible hydrogen electrode (RHE), working electrode (WE), and standard potential of reference electrode vs. RHE (E0 = 0.657 V), respectively. Before electrochemical testing, the mercury sulfate electrode (MSE) was calibrated in 0.1 M HCl solution relative to the RHE.