MFC-driven H2S electro-oxidation based on Fe nanoparticles anchored on carbon aerogel-ZIF-8: a combined experimental and DFT study

Abstract

Electrocatalysts for the electrochemical oxidation of hydrogen sulfide (H₂S) to elemental sulfur and its recovery in the form of sulfur, particularly catalysts based on metal–organic-framework (MOF) supports, have been widely investigated. However, energy saving during the electrochemical oxidation of H₂S, the formation of a catalyst with superb conductivity and stability by protecting a zeolitic imidazolate framework-8 (ZIF-8) from being destroyed during synthesis, and the prevention of Fe sites from deactivation are still challenging tasks. Herein, an effective strategy to improve the crystalline structure and enhance the porosity/surface area of ZIF-8 with poor crystallinity by the induced growth of a carbon aerogel (CA)-ZIF-8 on a mixed-metal metal–organic framework (MM-MOF) template with good crystallinity and optimized Fe nanoparticle doping content (1, 3, and 5 wt%) is described. Moreover, a microbial fuel cell (MFC) with different cathode catalysts was started up and operated to provide the electrical energy to drive the electrocatalytic removal of H₂S. Through open-circuit voltage (OCV) and anodic polarization measurements at 0.2, 0.5, and 0.7 V vs. the standard hydrogen electrode (SHE), the Fe-doped CAs-ZIF-8@MM-MOF (1 wt%) exhibits excellent electro-catalytic activity (8.12 ± 0.11 h⁻¹ at 0.7 V vs. SHE) compared to a pristine carbon cloth (CC) electrode (1.13 ± 0.24 h⁻¹ at 0.7 V vs. SHE). According to surface characterization and density functional theory (DFT) calculation results, it is worth noting that the introduction of a low loading of Fe nanoparticles into a catalyst support prefers to occupy an Fe–N₄ configuration rather than an M–Fe–M (C) configuration. The Fe–N₄ active centers favor the adsorption and association/dissociation of H₂S. In contrast, the M–Fe–M (C) centers are more favorable for strengthening the bonding between the Fe nanoparticles and the support.