In situElectrochemical Transformation of Ni3S2and Ni3S2-Ni from Sheets to Nanodisks: Towards Efficient Electrocatalysis for Hydrogen Evolution Reaction (HER) (original) (raw)
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Electrodeposited nickel-sulfide films as competent hydrogen evolution catalysts in neutral water
The development of low-cost, efficient, and robust electrocatalysts of the hydrogen evolution reaction (HER) is a crucial step toward the conversion and storage of sustainable and carbon-neutral energy resources, such as solar energy. Not only the HER catalysts need to be composed of inexpensive elements, they are also desirable to be prepared at low energy cost. In this work, we report that nickelsulfide (Ni-S) films prepared by facile potentiodynamic deposition are active HER catalysts in aqueous media. Notably, the Ni-S films showed catalytic activity in water with a wide range of pH values (0 to 14), as well as in natural water. In pH 7 phosphate buffer, a current density of 60 mA cm À2 could be achieved with a Tafel slope of 77 mV dec À1 and a Faradaic efficiency of 100%. A long-term bulk electrolysis of the Ni-S film exhibited steady current over 100 h with no deactivation, demonstrating its superior stability in neutral water. Further, an initial activation process was observed, which is likely due to the increase in the effective surface area of the Ni-S film under electrocatalytic conditions. A suite of characterization techniques, including X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, were conducted to probe the composition and structure of the Ni-S film, revealing that its major component is Ni 3 S 2 which was preserved under electrocatalytic conditions.
Interface engineering has been demonstrated to be effective in promoting hydrogen evolution reaction (HER) in an alkaline solution. Herein, we report that the HER activity of a NiS 2 nanoarray on a titanium mesh (NiS 2 /TM) in alkaline media is greatly boosted by the electrodeposition of Ni(OH) 2 onto NiS 2 [Ni(OH) 2 − NiS 2 /TM]. Ni(OH) 2 −NiS 2 /TM only needs an overpotential of 90 mV to deliver 10 mA cm −2 in 1.0 M KOH. Density functional theory calculations confirm that Ni(OH) 2 −NiS 2 has a lower water dissociation free energy and a more optimal hydrogen adsorption free energy than NiS 2 .
Nano Convergence, 2017
Catalysts for oxygen evolution reactions (OER) are at the heart of key renewable energy technologies, and development of non-precious metal catalysts with high activity and stability remain a great challenge in this field. Among various material candidates, metal sulfides are receiving increasing attention. While morphology-dependent catalytic performances are well established in noble metal-based catalysts, relatively little is known for the morphology-catalytic performance relationship in metal sulfide catalysts. In this study, uniform spider web-like Ni nanosheets-Ni 3 S 2 and honeycomb-like Ni 3 S 2 structures are deposited on nickel foam (Ni 3 S 2 /NF) by a facile one-step hydrothermal synthetic route. When used as an oxygen evolution electrode, the spider web-like Ni-Ni 3 S 2 /NF with the large exposed surface area shown excellent catalytic activity and stability with an overpotential of ~310 mV to achieve at 10 mA/ cm 2 and a Tafel slope of 63 mV/dec in alkaline media, which is superior to the honeycomb-like structure without Ni nanosheet. The low Tafel slope of the spider web-like Ni-Ni 3 S 2 /NF represents one of the best OER kinetics among nickel sulfide-based OER catalysts. The results point to the fact that performance of the metal sulfide electrocatalysts might be fine-tuned and optimized with morphological controls.
Advanced Functional Materials, 2019
2D molybdenum disulfide (MoS 2) displays a modest hydrogen evolution reaction (HER) activity in acidic media because the active sites are limited to a small number of edge sites with broader basal planes remaining mostly inert. Here, it is reported that the MoS 2 basal planes could be activated by growing nickel phosphide (Ni 2 P) nanoparticles on them. Thus a Ni 2 P/MoS 2 heterostructure is constructed via in situ phosphidation of an indigenously synthesized NiMoS 4 salt as a single precursor to form a widely cross-doped and chemically connected heterostructure. The conductivity and stability of the Ni 2 P/MoS 2 heterostructure are further enhanced by hybridization with conductive N-doped carbon supports. As a result, the Ni 2 P/MoS 2 /N:RGO or Ni 2 P/MoS 2 /N:CNT electrocatalyst displays Pt-like HER performance in acidic media, outperforming the incumbent best HER electrocatalyst, Pt/C, in a more meaningful high current density region (>200 mA cm −2) making them a promising candidate for practical water electrolysis applications. Since nonprecious metal catalysts showing Pt-like HER performance in acidic media are rare, the Ni 2 P/MoS 2 heterostructure catalyst is a promising candidate for practical hydrogen production via water electrolysis.
RSC Advances, 2018
The depletion of fossil fuels and associated environmental problems have drawn our attention to renewable energy resources in order to meet the global energy demand. Electrocatalytic hydrogen evolution has been considered a potential energy solution due of its high energy density and environment friendly technology. Herein, we have successfully synthesized a noble-metal-free Co-Ni/MoS 2 nanocomposite for enhanced electrocatalytic hydrogen evolution. The nanocomposite has been well characterized using HRTEM, elemental mapping, XRD, and XPS analysis. The as-synthesized nanocomposite exhibits a much smaller onset potential and better current density than those of Co-MoS 2 , Ni-MoS 2 and MoS 2 , with a Tafel value of 49 mV dec À1 , which is comparable to that of a commercial Pt/C catalyst. The synergistic effect and interfacial interaction of Co-Ni bimetallic nanoparticles enhances the intrinsic modulation in the electronic structure resulting in an improved HER performance. Moreover, the electrochemical impedance spectroscopic results suggest smaller resistance values for the Co-Ni/MoS 2 nanocomposite, compared to those for the charge transfer of bare nanosheets, which increase the faradaic process and in turn enhance the HER kinetics for a better performance. Our as-synthesized Co-Ni/MoS 2 nanocomposite holds great potential for the future synthesis of noble-metal-free catalysts.
The production of Hydrogen (H 2) gas for fuel cell application using electrochemical methods is attracting the attention of the researchers in recent years owing to its high calorific value. Current researchers are enthused to prepare cost effective catalysts from abundant elements in earth crust for the huge production of H 2. Recently electrochemical studies are reported based on Metal sulfides and oxides such as MoS 2 , CoS, WO 3 as best catalyst for H 2 generation under diverse pH conditions. We focused on preparing nanoporous Nickel Sul-fide (NiS) films from Nickel Hexacyanoferrate (NiHCF) nanocubes using electrochemical cycling of the precursor films in Sulfide medium and characterized those using spectroscopy and Microscopy techniques such as FT-IR, Raman spectroscopy, XPS, EDS, XRD, FESEM, AFM, and TEM. The cubic structure of NiHCF gets transformed into NiS cubic skeleton by etching in presence of sulfide ions (S 2À). The nanoporous NiS give best results for Hydrogen Evolution Reaction (HER) in the alkali medium. The catalysts were electrochemically modified on glassy carbon surface for electrochemical characterization including Tafel polarization. For comparison, the same procedure was used to prepare other metal sulfides including MnS, FeS, and CoS to compare their catalytic activity towards Hydrogen evolution. Among them, the NiS was shown to be the most efficient electrocatalyst for hydrogen evolution and has shown promise as an alternative to platinum.