Electrolyte-dependent HER activity of mesoporous iron-based ZIF-67 leaf-like nanosheets†

Abstract

Several methodologies have been employed to boost the HER activity of metal–organic frameworks. Herein, iron-based ZIF-67 structures were synthesized with different iron contents, and their HER activity was evaluated in 1.0 M KOH, 0.5 M H₂SO₄ and seawater. Metal contents effectively enhanced the physical characteristics of the Fe@ZIF-67-2 structure, and electrolytic impacts were found to be significant. Structure of the Fe@ZIF-67-2 electrocatalyst exhibited a high specific surface area of 72.21 m² g⁻¹ and electrical conductivity of 14.29 μS cm⁻¹. Fe@ZIF-67-2 also displayed an overpotential of 45 mV and a Tafel slope of 32 mV dec⁻¹ in 1 M KOH electrolyte. Enhancement in the electrical conductivity, mesoporous nature, specific and electrochemical surface area promoted the flow of active charge carriers, facilitated the adsorption and desorption process at the active sites and led to a good electrocatalytic activity of the Fe@ZIF-67-2 structure. It also exhibited a greater turnover frequency of 129.35 ms⁻¹ at a fixed V_RHE of 0.8 V. Suitable intercalation of the electrolyte ions on the surface of the electrocatalyst is another significant factor in the production of H₂ molecule and led to an enhancement in the HER efficiency of Fe@ZIF-67-2. Hence, the electrocatalyst Fe@ZIF-67-2 showed a good electrocatalytic HER activity in 1 M KOH.