ZIF template-based Fe-doped defect-rich hierarchical structure Co3S4/MoS2 as a bifunctional electrocatalyst for overall water splitting

To replace the current expensive precious metal catalysts for water electrolysis, it is important to develop inexpensive and powerful bifunctional catalysts for hydrogen production. It is an effective way to improve catalytic performance using excellent templates and elemental doping. Here, a hierarchical structure Fe-Co3S4/MoS2 was synthesized using an Fe-ZIF precursor prepared by ion exchange, followed by hydrothermal sulfuration and annealing. It required overpotentials of only 93 mV and 243 mV to achieve a current density of 10 mA cm-2 in the HER and OER, respectively. It also showed excellent catalytic performance for overall water splitting, requiring only 1.42 and 1.71 V to achieve current densities of 10 and 100 mA cm-2 in 1 M KOH. The catalyst also demonstrated excellent ultra-long-term stability. The superb catalytic performance and stability can be attributed to the Fe doping, exposing more active sites while retaining the highly stable framework of the ZIF. The component modulation of Co3S4 and MoS2 by Fe doping induced high intrinsic activity and excellent transfer coefficients. This work presents a novel approach to prepare noble metal-free catalysts with highly stable rich interfaces and defects for overall water splitting.

Synthesis and water splitting performance of FeCoNbS bifunctional electrocatalyst

Transition metal (TM) sulfides are promising catalysts for water splitting in alkaline media due to their high intrinsic activities and similar TM-S electronic structure with hydrogenase. In this work, the nanoporous FeCoNbS electrocatalyst with nanosheet morphology is synthesized through dealloying AlFeCoNb alloy followed by the steam sulphurization. The introduction of S element improves the electronic structure, further increases the active sites, regulates the mass transfer and enhances the intrinsic activity. The Nb introduction improves the electron transfer ability of the catalyst. The synergistic effect of Fe, Co and Nb improves the intrinsic activity of the active site. The FeCoNbS catalyst exhibits good catalytic performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution. The overpotentials at 10 mA cm^-2 of HER and OER are 83 and 241 mV, respectively. The Tafel slopes of HER and OER are 101.2 and 35.5 mV dec^-1, respectively. The FeCoNbS can serve as overall water splitting electrode with the decomposition voltage of 1.61 V at 10 mA cm^-2.

Enhancing the catalytic OER performance of MoS2via Fe and Co doping

Enhancing the sluggish kinetics of the electrochemical oxygen evolution reaction (OER) is crucial for many clean-energy production technologies. Although much progress has been made in recent years, developing active, stable, and cost-effective OER electrocatalysts is still challenging. The layered MoS₂, based on Earth-abundant elements, is widely explored as a promising hydrogen evolution electrocatalyst but exhibits poor OER activity. Here, we report a facile strategy to improve the sluggish OER of MoS₂ through co-doping MoS₂ nanosheets with Fe and Co atoms. The synergistic effect obtained by adjusting the Co/Fe ratio in the Fe-Co doped MoS₂ induces electronic and structural modifications and a richer active surface area morphology resulting in a relatively low OER overpotential of 380 mV (at 10 mA cm^-2). The electronic modulation upon doping was further supported by DFT calculations that show favorable interaction with the OER intermediate species, thus reducing the energy barrier for the OER. This work paves the way for future strategies for tailoring the electronic properties of transition-metal dichalcogenides (TMDCs) to activate the structure for the sluggish OER with the assistance of non-noble-metal materials.