Introduction of MoS2–FeS2 with an S-Vacancy Defect as an Efficient Bifunctional Electrocatalyst for Hydrogen Evolution Reaction and Ferrocyanide and Iodide Oxidation Reactions

A composite of MoS2–FeS2 was synthesized and applied as a bifunctional electrocatalyst to fabricate a modified glassy carbon electrode capable of facilitating the hydrogen evolution reaction (HER), iodide oxidation reaction (IOR), and ferrocyanide oxidation reaction (FOR). The investigation delved into the influence of chemical composition and experimental variables on the electrocatalytic performance of MoS2–FeS2 toward HER. The observed electrocatalytic metrics, including Tafel slope, onset potential, turnover frequency, and stability toward HER, demonstrated comparability with those achieved using Pt/C. This comparison underscores the potential of MoS2–FeS2 as an attractive alternative to Pt/C for electrocatalytic applications, offering similar performance while potentially addressing cost and environmental concerns linked to platinum-based catalysts. Furthermore, the versatility of the MoS2–FeS2 composite was evident in its catalytic activity not only for HER but also for IOR and FOR, indicating its suitability across various electrochemical processes. Subsequent exploration focused on the electrocatalytic behavior of MoS2–FeS2 in the iodide oxidation reaction (IOR) and ferrocyanide oxidation reaction (FOR), which could potentially replace the oxygen evolution reaction (OER). The findings highlighted MoS2–FeS2's significantly superior electrocatalytic performance compared to RuO2 in these reactions. Additionally, the required potentials for HER at the cathode and IOR at the anode in a HER-IOR configuration, as well as HER at the cathode and FOR at the anode in a HER-FOR setup, were notably lower, measured at 0.82 and 0.65 V, respectively, than those obtained in a HER-OER setup (2.08 V) using the MoS2–FeS2 modified electrode under similar experimental conditions. This exceptional electrocatalytic performance of MoS2–FeS2 was attributed to enhanced conductivity, a substantial electroactive surface area with numerous active sites, synergistic interactions between FeS2 and MoS2 sites, a high density of shared and bridging disulfide sites, a prevalence of sulfur vacancies within MoS2–FeS2, and minimal structural degradation.