HER characterization at pH 0 and 14. We first investigated the electrochemical HER performance of L-CoS in different pH conditions, namely 0.5 M H2SO4 and 1 M KOH (Figure and). To assess the intrinsic catalytic activities of the investigated catalysts, electrochemical surface area (ECSA) calculations were performed based on double-layer capacitance and were used for the normalization of the geometric current density (Figure ). From the results (Figure and Figure ), L-CoS exhibits the best HER performance in 0.5 M H2SO4. To achieve a geometric current density of -10 mA/cmgeo. , a minimum overpotential of 150 mV is essential for L-CoS, still higher than that of commercial 20 wt.% Pt/C (29 mV). In comparison, when the electrolyte was changed to 1 M KOH, the observed HER overpotential (-10 m/cmgeo. 2 ) of L-CoS increased dramatically. Additionally, L-CoS displays a similar HER performance (427 mV at -0.5 mA/cmECSA 2 and 332 mV at -10 mA/cmgeo. 2 ,) compared to reference Co3O4-ZIF (422 mV at -0.5 mA/cmECSA 2 and 332 mV at -10 mA/cm geo.