Fabrication of high-performance noble-metal-free bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water is a promising strategy toward future carbon-neutral economy. Herein, a one-pot hydrothermal synthesis of cobalt sulfide/nickel sulfide heterostructure supported by nickel foam (CoS /NiS@NF) was performed. The Ni foam acted as the three-dimensional conducting substrate as well as the source of nickel for NiS. The formation of CoS /NiS@NF was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The formation of CoS /NiS@NF facilitated easy charge transport and showed synergistic electrocatalytic effect toward HER, OER, and overall water splitting in alkaline medium. Remarkably, CoS /NiS@NF showed catalytic activity comparable with that of benchmarking electrocatalysts Pt/C and RuO. For CoS /NiS@NF, overpotentials of 204 and 280 mV were required to achieve current densities of 10 and 20 mA cm for HER and OER, respectively, in 1.0 M KOH solution. A two-electrode system was formulated for overall water splitting reaction, which showed current densities of 10 and 50 mA cm at 1.572 and 1.684 V, respectively. The prepared catalyst exhibited excellent durability in HER and OER catalyzing conditions and also in overall water splitting operation. Therefore, CoS /NiS@NF could be a promising noble-metal-free electrocatalyst for overall water splitting application.

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Doping engineering emerges as a contemporary technique to investigate the catalytic performance of MoS 2 . Cation and anion co-doping appears as an advanced route toward electrocatalytic hydrogen evolution reaction (HER). V and N as dopants in MoS 2 (VNMS) build up a strain inside the crystal structure and narrow down the optical band gaps manifesting the shifting of the absorbance band toward lower energy and improved catalytic performance. FE-SEM, HR-TEM, and XRD analysis confirmed that V and N doping decreases agglomeration possibility, particle size, developed strain, and crystal defects during crystal growth. Frequency shift and peak broadening in Raman spectra confirmed the doping induced strain generation in MoS 2 leading to the modification of acidic and alkaline HER (51 and 110 mV @ 10 mAcm −2 , respectively) performance. The improved donor density in VNMS was confirmed by the Mott− Schottky analysis. Enhanced electrical conductivity and optimized electronic structures facilities H* adsorption/desorption in the catalytically active (001) plane of cation and anion co-doped MoS 2 .

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The electrocatalyst comprising two different metal atoms is found suitable for overall water splitting in alkaline medium. Hydrothermal synthesis is an extensively used technique for the synthesis of various metal sulfides. Time-dependent diffusion of the constituting ions during hydrothermal synthesis can affect the crystal and electronic structure of the product, which in turn would modulate its electrocatalytic activity. Herein, cobalt molybdenum bimetallic sulfide was prepared via hydrothermal method after varying the duration of reaction. The change in crystal structure, amount of Co−S−Mo moiety, and electronic structure of the synthesized materials were thoroughly investigated using different analytical techniques. These changes modulated the charge transfer at the electrode−electrolyte interface, as evidenced by electrochemical impedance spectroscopy. The Tafel plots for the prepared materials were investigated considering a less explored approach and it was found that different materials facilitated different electrocatalytic pathways. The product obtained after 12 h reaction showed superior catalytic activity in comparison to the products obtained from 4, 8, and 16 h reaction, and it surpassed the overall water splitting activity of the RuO 2 −Pt/C couple. This study demonstrated the ion diffusion within the bimetallic sulfide during hydrothermal synthesis and change in its electrocatalytic activity due to ion diffusion.

The development of non‐noble metal based electrocatalysts for overall water splitting is a potent strategy towards a carbon‐neutral and clean energy economy. Herein, hierarchical CoSx@MoS2 was synthesized via a one‐pot solvothermal process. Formation of the heterostructure was confirmed by electron microscopy and spectroscopic techniques. CoSx@MoS2 showed competent electrocatalytic activity towards both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline medium. Superior electrocatalytic activity was attributed to the increase in number of active sites, betterment in charge transfer and facilitation of H‐ and O‐ containing active species adsorption‐desorption at the active sites. Overall water splitting efficiency of CoSx@MoS2 was found to be superior in comparison to the state‐of‐the‐art RuO2‐Pt/C couple. Along with efficiency the heterostructure also exhibited long‐term operational durability. Thus, hierarchical CoSx@MoS2 is a potential non‐noble metal based bifunctional electrocatalyst towards overall water splitting.

Hydrogen evolution reaction (HER) was improved through nitrogen (N) doping in molybdenum disulfide (MoS2) due to the formation of 1T‐metallic phase as compared to the thermodynamically stable 2H‐semiconducting phase. Generally, the phase transition of MoS2 from semiconducting 2H to metallic 1T was carried out by chemical intercalation method. A facile solvothermal synthetic procedure is used to organize 1T@2H MoS2 nanoflower by incorporating N in MoS2 crystal lattice which improved the catalytic activity with the generation of metallic property of MoS2. Optimized N doping is an effective strategy for the development of mixed phase MoS2. Physicochemical characterization techniques confirmed the formation of hybrid phase (1T@2H) MoS2 by N incorporation. A tuned dopant concentration in MoS2 crystal lattice effectively enhanced the catalytic performance by modifying the physical and chemical properties. Moreover, optimal N doped MoS2 offered a very low overpotential of ∼108 and ∼141 mV to reach the benchmarking current density of 10 mA cm−2 for HER in acidic and basic medium, respectively. This work elucidated a rational implantation of phase engineering, which is an efficient strategy to develop efficient electrocatalysts, shedding light on the improvement of transition metal‐based electrocatalyst in renewable energy technologies.

Iron–sulfur-based materials are advantageous for electrocatalytic activity owing to their high natural abundance and lesser toxicity. A few investigations on the hydrogen evolution reaction (HER) catalyzing activity of Fe–S materials were performed. However, the oxygen evolution reaction (OER) catalyzing activity or overall water splitting activity of Fe–S materials has not been studied extensively till date. Another technical aspect that suppresses the activity of the electrocatalyst is related to the usage of polymeric binders for electrode fabrication. Keeping these aspects in mind, iron sulfide was directly electrodeposited on nickel foam by varying the deposition potentials and duration of deposition. Ni-doped O-incorporated iron sulfide having the FeS2 lattice domains was obtained as the deposition product. The morphology, electronic structure, and charge carrier density in the valence band of the electrodeposits changed with the change in duration of electrodeposition, which in turn modulated the electrocatalytic activity. The electrode fabricated at −0.9 V potential after 30 min was found to be superior toward HER and OER. The electrodeposit obtained after 45 min showed comparable HER catalyzing activity. An asymmetric electrolyzer constructed with these electrodes showed a comparable water splitting activity to that of the RuO2(+)||Pt/C­(−) electrolyzer and also surpassed its activity at higher potential.