High entropy 2D metals sulfides: Fast synthesis, exfoliation and electrochemical activity in overall water splitting at alkaline pH

[Display omitted] •A novel method for synthesizing 2D flakes of high entropy sulfides (HES) is proposed.•Created material was tested as an electrocatalyst for water splitting at different pH.•The as-prepared HES flakes show good catalytic activity towards OER under alkaline conditions.•As prepared 2D HES showed moderate catalytic activity towards HER.•Electrochemical self-activation, results in significant increase of HER catalytic activity in alkaline conditions. Novel simple and efficient method for synthesis of 2D high entropy sulfides of iron group metals is described. The method utilizes inorganic salts as precursors and CS2 as a sulfurizing agent, which makes it possible to achieve high entropy composition through combination of freezing of the precursor solution, subsequent freeze-drying step, sulfurization, and exfoliation in liquid nitrogen. The created material was investigated as a catalyst for electrochemical water splitting at different pH. Measured overpotentials at 10 and 100 mA*cm−2 current densities for hydrogen evolution reaction (HER) were found to be 49 and 315 mV respectively, while for oxygen evolution reaction (OER) theoverpotentials required for reaching 10 and 100 mA*cm−2 current densities were 370 and 591 mV respectively, both in 1 M KOH solution. The Tafel slopes for HER were found to be 235, 105, and 111 mV/dec in basic, neutral, and acidic conditions, respectively, while only 63 mV/dec for OER in basic conditions. The calculated values of the turnover frequency were 0.62 s−1 for HER and 0.10 s−1 for OER. We also confirmed the key role of high entropy in the catalytic activity of the material by excluding individual elements from the composition of the HES.