Facile synthesis of carbon encapsulated RuO2 nanorods for supercapacitor and electrocatalytic hydrogen evolution reaction

In this work, carbon encapsulated RuO₂ nanorods (RuO₂ NRs/C) has been synthesized by thermolysis of ruthenium chloride and Punica granatum (P. granatum) peel under N₂ atmosphere. The synthesized RuO₂ NRs/C was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction method (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) analyses. The FT-IR results suggested that the organic constituents of P. granatum have been carbonized and encapsulated over RuO₂ nanorods (RuO₂ NRs). The XRD pattern of RuO₂ NRs/C revealed its crystalline nature and carbon encapsulation. The synthesized RuO₂ NRs/C has been well dispersed with the average width of 20 nm, exposed from the FE-SEM and HR-TEM images. The EDS results of RuO₂ NRs/C showed the existence of three elements viz., Ru, O and C. Further, the supercapacitor and electrocatalytic hydrogen evolution reaction (HER) activities of RuO₂ NRs/C were studied using standard electrochemical methods. The synthesized RuO₂ NRs/C offered a maximum specific capacitance of 151.3 F g⁻¹ at a scan rate of 5 mV s⁻¹, obtained from the cyclic voltammetry results. The onset over potential and Tafel slope of synthesized RuO₂ NRs/C for HER were −0.099 V_RHE and −99.4 mV dec⁻¹, respectively. The present study revealed that RuO₂ NRs/C as a better candidate for supercapacitor and HER.     

Thin-film iron-oxide nanobeads as bifunctional electrocatalyst for high activity overall water splitting

Developing only Fe derived bifunctional overall water splitting electrocatalyst both for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) while performing at low onset overpotential and with high catalytic stability is a rare instance. We present here the first demonstration of unique iron-oxide nanobeads (FeO_x-NBs) based electrocatalyst executing both OER and HER with high activity. Thin-film electrocatalytic FeO_x-NBs assembly is surface grown via simple spray coating (SC). The unique SC/FeO_x-NBs propels OER initiating water oxidation just at 1.49 V_RHE (η = 260 mV) that is the lowest observable onset potential for OER on simple Fe-oxide based catalytic films reported so far. Catalyst also reveals decently high HER activity and competent overall water splitting performance in the FeO_x-NBs two-electrode system as well. Catalyst also presents stable kinetics, with promising high electrochemically active surface area (ECSA) of 1765 cm², notable Tafel slopes of just 54 mV dec^1? (OER) and 85 mV dec^1? (HER), high exchange current density of 1.10 mA cm^2? (OER), 0.58 mA cm^2? (HER) and TOF of 74.29s^1?@1.58V_RHE, 262s^1?@1.62V_RHE (OER) and 82.5s^1?@-0.45V_RHE, 681s^1?@-0.56V_RHE (HER).     

Electrocatalytic performance of carbon dots/palladium nanoparticles composite towards hydrogen evolution reaction in acid medium

In this work, nitrogen doped carbon dots (NDCDs) and nitrogen doped carbon dots supported palladium nanoparticles composite (n-Pd@NDCDs) were synthesized through hydrothermal carbonization and thermolytic reduction using Morinda citrifolia (M. citrifolia) fruit and palladium chloride as carbon and Pd precursors, respectively. The synthesized materials viz., n-Pd@NDCDs and NDCDs were duly characterized by high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The optical properties of NDCDs were studied by ultraviolet visible (UV–Vis), and fluorescence spectroscopy techniques. Further, the electrocatalytic hydrogen evolution reaction (HER) performance of n-Pd@NDCDs was evaluated by linear sweep voltammetry (LSV), Tafel, and electrochemical impedance spectroscopy (EIS) measurements in 0.5 M aqueous H₂SO₄. The onset potential of n-Pd@NDCDs was about −0.195 V_RHE, which was lower than NDCDS (−0.392 V_RHE) and bare glassy carbon (−0.603 V_RHE). The calculated Tafel slope values of n-Pd@NDCDs were 135 and 141.8 mV/dec, from the voltammetric and EIS methods, respectively. Moreover, the n-Pd@NDCDs exhibited small overpotential of 0.291 V to attain a current density of 10 mA/cm². The EIS studies revealed that the HER charge transfer resistance was dropped from 84.3 to 18.3 Ω/cm² while increasing of potential, which revealed good conductivity and electrocatalytic activity of n-Pd@NDCDs. Thus the present work vouched for the candidature of n-Pd@NDCDs as an effective electrocatalyst for the HER in acidic medium.     

Direct synthesis of nitrogen-rich carbon sheets via polybenzoxazine as highly active electrocatalyst for water splitting

In this work, we propose a novel nitrogen-rich carbon sheets (N-CSs), with conceivable use as efficient catalysts for hydrogen evolution reaction (HER). N-CSs are directly synthesized from polybenzoxazine (PBz) by carbonization followed by KOH activation. PBz was prepared from eugenol, melamine, and paraformaldehyde through ring-opening polymerization. FT-IR and NMR spectroscopy confirmed the corresponding chemical structures of the new benzoxazine monomer. The morphology, structure and surface properties of the N-CSs are investigated by Raman spectroscopy, wide-angle X-ray diffraction, and X-ray photoelectron spectroscopy. The catalytic activity of N-CSs towards HER is thoroughly investigated by electrochemical techniques. In N-CSs, it is established that nitrogen gratified electrocatalytic activity, and hence nitrogen atoms should enhance the electrocatalytic properties by increasing the active sites. As the kinetic current is stabilized by the outer nitrogen atom as such, HER is proposed to proceed on these active sites by the Volmer-Heyrovsky mechanism. The N-CSs show outstanding catalytic activity towards HER with lowest onset-potential (?10 mV_RHE) and Tafel slope (45 mV dec^?1) in 0.5 M H₂SO₄ aqueous electrolyte.     

Hierarchical MoS2 nanoflowers on carbon cloth as an efficient cathode electrode for hydrogen evolution under all pH values

In this paper, a facile hydrothermal synthetic strategy was developed for MoS₂ nanoflowers with enlarged interlayer spacing on the carbon cloth (CC) as a high efficiency cathode electrode for hydrogen evolution reaction (HER) under wide pH condition. It was observed that the loading amount of MoS₂ has a major impact on the HER performance, where the optimized MoS₂/CC exhibited a low onset potential of 94 mV and a small Tafel slope of 50 mV dec^?1 in strong acid solution (pH = 0). The improved HER performance can be contributed to the enlarged interlayer spacing, abundant defects and more exposed active sites in the small size MoS₂ nanosheets as revealed by XRD and HRTEM. Meanwhile, it also exhibited relatively good performance for HER under basic and neutral conditions with the overpotentials of 188 (pH = 14) and 230 (pH = 7) mV to achieve current density of 10 mA cm^?2 and the Tafel slopes of 52 and 84 mV dec^?1, respectively.     

Novel 13X Zeolite/PANI electrocatalyst for hydrogen and oxygen evolution reaction

In this work, first 13X zeolite was prepared by the hydrothermal method. Then, the composite electrode was fabricated by using 13X zeolite and aniline monomer in nickel foam by electropolymerization technique in an acidic medium (13X/PANI). The synthesized 13X zeolite was characterized by physicochemical characterization techniques such as Fourier transform infra-red (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) pattern and nitrogen sorption isotherm. 13X/PANI composite was further analyzed by XRD, XPS and FE-SEM techniques. Furthermore, the catalyst activity of the synthesized 13X, PANI and 13X/PANI composite electrodes was evaluated in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by using linear square voltammetry (LSV) and Tafel slope method. The Tafel slopes of HER were found to be 203 mV dec⁻¹, 440 mV dec⁻¹ and 282 mV dec⁻¹ for 13X, PANI and 13X/PANI-15 electrodes respectively. While the OER Tafel slopes were found to be 423 mV dec⁻¹, 310 mV dec⁻¹ and 168 mV dec⁻¹ for 13X, PANI and 13X/PANI-15, respectively. 13X/PANI-15 electrodes show excellent catalytic performance about the overpotential at 10 mA cm⁻² for HER and the overpotential at 20 mA cm⁻² for OER. The obtained results suggest fabricated novel electrodes are a potential candidate for HER and OER reaction and can be open new avenue for other electrochemical reactions.     

Electrocatalytic hydrogen production on GCE/RGO/Au hybrid electrode

We have prepared a nanocomposite hybrid film to produce a collaborative network of gold (Au) nanoparticles that are highly dispersed on reduced graphene oxide (RGO) sheets, and tested it for electrocatalytic hydrogen production. The RGO/Au nanocomposite film synthesized on glassy carbon electrode (GCE) allows significant improvements to the electron-transfer process. The Au nanoparticles decorated on the surface of graphene increases the electron density, which synergistically promote the adsorption of hydrogen atoms on the graphene sheets and consequently enhance the hydrogen evolution reaction (HER) activity. The surface properties of the composite was characterized by field-emission scanning electron microscopy (FE-SEM) and the electrocatalytical performances evaluated as-prepared electrocatalyst toward (HER) by linear sweep voltammetry (LSV), Tafel polarization curves and electrochemical impedance spectroscopy (EIS) analyses. The GCE/RGO/Au nanohybrid electrode exhibited good catalytic activity for HER with an onset potential of ?0.3 V and a Tafel slope of 136 mV dec^?1, achieving a current density of 10 mA cm^?2 at an overpotential of ?0.43 V.     

Cytosine assisted aqueous synthesis of AgPt hollow alloyed nanostructures as highly active electrocatalyst for ethylene glycol oxidation and hydrogen evolution

Herein, a simple one-pot aqueous method was developed for synthesis of AgPt hollow alloyed nanostructures (AgPt HANS) with polyvinylpyrrolidone (PVP) and cytosine as the dispersing agent and eco-friendly growth-director, respectively. The synthesized architectures displayed the improved catalytic performance toward ethylene glycol oxidation reaction (EGOR) relative to commercial Pt black in alkaline media. Meanwhile, the catalyst exhibited the enhanced catalytic activity for hydrogen evolution reaction (HER) with the positive onset potential (E_onset, ?39 mV) and a small Tafel slope (40 mV dec^?1) relative to commercial Pt/C (20 wt%, ?31 mV, 33 mV dec^?1) in 0.5 M H₂SO₄, along with the more positive E_onset (?34 mV) and a smaller Tafel slope (59 mV dec^?1) in 0.5 M KOH compared with Pt/C (?35 mV, 85 mV dec^?1).     

Novel strongly coupled tungsten-carbon-nitrogen complex for efficient hydrogen evolution reaction

Alternatives to noble metal based electrocatalysts are vitally necessary to produce hydrogen from water at low overpotentials. Earlier research on tungsten based electrocatalyst has been mainly concentrated towards tungsten carbide (WC) and tungsten nitride (WN) as the potential electrocatalysts for hydrogen evolution reaction (HER), whereas tungsten carbide (W₂C) has been least focused upon. Herein, we report a highly active novel strongly coupled tungsten-carbon-nitrogen complex (W₂C-NC-WN complex) prepared by in situ carbonization method. This W₂C-NC-WN complex exhibits a remarkable electrochemical performance for HER with a small onset potential of 33 mV vs. RHE and requires an overpotential (η) of 145 mV vs. RHE to render ?10 mA cm^?2 current density. The Tafel analysis demonstrates a slope of 96 mV dec^?1 which is much better than WN (109.6 mV dec^?1) and WC (142.4 mV dec^?1). The strong coupling of W₂C and WN within N-doped carbon (NC) framework brings about a significant enhancement in HER kinetics and faster electron transport due to the remarkable reduction in charge transfer resistance. The facile synthetic approach reported here, provides a powerful tool for the structurally controlled modification of the catalyst while simultaneously introducing active species.     

CoSe2 nanoparticles grown on carbon nanofibers derived from bacterial cellulose as an efficient electrocatalyst for hydrogen evolution reaction

Exploration of high-efficiency and inexpensive Pt-free electrochemical catalysts for hydrogen evolution reaction (HER) is highly significative for carbon dioxide free energy conversion systems. In this work, we described the development of CoSe₂ nanoparticles grown on the carbon nanofibers (CNFs) derived from bacterial cellulose (CNFs/CoSe₂) through a facile one-step hydrothermal preparation, which not only showed a three-dimensional (3D) porous network structure, but also possessed large surface area. This rationally designed architecture realizes the uniform distribution of CoSe₂ nanoparticles to provide with fully exposed active edges and the unique conductive interwoven carbon nanofibers facilitates the charge transportation in HER process, thus leading to remarkable HER activity. As expected, the CNFs/CoSe₂ shows a low onset overpotential of ?85 mV, low overpotential (η₁₀ = 119 mV) for reaching a current density of ?10 mA cm^?2 and smaller Tafel slope of 54 mV dec^?1 as well as good cycling stability in acidic electrolyte.     

A high active hydrogen evolution reaction electrocatalyst from ionic liquids-originated cobalt phosphide/carbon nanotubes

Ionic liquid/carbon nanotubes (IL/CNTs) composite was applied as the precursor to prepare CNTs-supported cobalt phosphide via low-temperature phosphidation. CoP_(MBMG)/CNTs, generated from N,N-bis(4-(methoxycarbonyl)benzyl)-N-methyl-d-glucaminium dibromodichlorocobaltate(II) (MBMG)₂-CoCl₂Br₂), exhibits the best catalytic activity toward hydrogen evolution reaction with an onset overpotential of 55 mV, a Tafel slope of 58 mV dec^?1, 95% Faradaic efficiency (FE), current densities of 10 and 20 mA cm^?2 at overpotentials of 135 and 160 mV, and it can maintain the catalytic activity for at least 27 h. FT-IR, Raman spectroscopy, XPS and XRD were utilized to investigate the phosphidation process. All experimental results confirmed that anion from (MBMG)₂-CoCl₂Br₂ can form CoP and glucaminium-based cation can become amorphous carbon after phosphidation to obtain the high HER activity of CoP_(MBMG)/CNTs.     

In-situ synthesis of carbon-coated β-NiS nanocrystals for hydrogen evolution reaction in both acidic and alkaline solution

The electrocatalytic hydrogen evolution reaction (HER) performance of carbon-coated β-NiS (NiS@C) nanocrystals has been investigated for the first time. The NiS@C nanocrystals were synthesized via a facile solvothermal method followed by in-situ carbonization process with the solvent (ethylene glycol) as the carbon source. Benefited from the well-dispersed NiS nanocrystals and the formation of carbon layer on NiS nanocrystals, the NiS@C nanocrystals displayed a high HER activity in 0.5 M H₂SO₄, which needed an overpotential of 85 mV to achieve current density of 10 mA cm^?1 with a Tafel slope of 46 mV dec^?1, as well as long term stability for HER. Additionally, the NiS@C nanocrystals also showed efficient electrocatalytic activity under alkaline media.     

Defect-rich MoSx/carbon nanofiber arrays on carbon cloth for highly efficient electrocatalytic hydrogen evolution

Engineering MoS₂ catalysts with more active sites and higher conductivity is an effective way to improve its electrochemical activity. Herein, defect-rich amorphous MoS_x/carbon nanofiber (CF) arrays on carbon cloth (CC) support (denoted as MoS_x/CF/CC) was designed and fabricated, which served as an efficient free-standing electrocatalyst for hydrogen evolution reaction (HER) in acid media. This architecture was beneficial to expose more active catalytic sites and improve the electron/ion transport. In addition, abundant defects altered preferred growth direction of MoS_x, resulting in the formation of irregular MoS_x particles at the surface of CF arrays. The as-synthesized MoS_x/CF/CC-2 exhibited excellent stability and superior HER activity, with a small onset overpotential (107 mV) and low Tafel slope (51 mV dec^?1). Such excellent electrochemical performance was attributed to the enriched active sites and shortened charge diffusion distance. This work would pave a new way for rational design and fabrication of defect-rich MoS_x-based composite electrode for renewable energy applications.     

Platinum nanoparticles deposited nitrogen-doped carbon nanofiber derived from bacterial cellulose for hydrogen evolution reaction

The nitrogen-doped carbon nanofiber derived from low and high proportion polyaniline doped bacterial cellulose (BC) was obtained via polymerization followed by pyrolysis. The resulting products were named LN-BC and HN-BC accordingly. Platinum nanoparticles modified LN-BC and HN-BC was then prepared (Pt@LN-BC and Pt@HN-BC) via electrochemical deposition. The morphologies of LN-BC and HN-BC indicated that the BC lost its nanowire structure after polyaniline modification and pyrolysis under nitrogen atmosphere. Platinum nanoparticles with diameters ranging from 3 to 5 nm can be well dispersed in the HN-BC support. The HER performance of Pt@LN-BC and Pt@HN-BC was fully investigated. Electrochemical results showed that the Pt-based catalysts had better HER activity than the Pt free catalysts in acid, indicating the HER activity was mainly from Pt. Besides, Pt@HN-BC had better HER activity than Pt@LN-BC in acid, suggesting N-doping rate was an important factor in enhancing HER activity. And the 10Pt@HN-BC (deposition for 10 s) with 4.38 wt% Pt loading was the best HER catalyst among the Pt@HN-BC. The onset potential (@ ?1 mA cm^?2) and overpotential (@ ?10 mA cm^?2) of the 10Pt@HN-BC in 0.5 M H₂SO₄ is ?18 and ?47 mV, respectively. The corresponding Tafel slope was ?35 mV dec^?1, which is quite comparable to that of Pt/C (10 wt%). The electrochemical double layer capacitance (C_dl) and turnover frequency (TOF) were estimated and presented in the work. Long-term stability test confirmed that the 10Pt@HN-BC had excellent stability, which was important for practical application.     

Urchin-like Co0.8-Mn0.2-P/CC nanowires array: a high-performance and cost-effective hydrogen evolution electrocatalyst

Using cost-effective materials to replace precious Pt-based hydrogen evolution reaction (HER) catalysts holds great foreground for energy saving and environmental protection. In this work, we successfully prepared an urchin-like Co_0.8-Mn_0.2-P nanowires array supported on carbon cloth (CC) through a hydrothermal-phosphatization strategy and we also systematically studied its electrocatalytic HER performance. Electrochemical tests demonstrate that our urchin-like Co_0.8-Mn_0.2-P/CC possesses outstanding HER activity in acidic and alkaline media. In 0.5 M H₂SO₄, this urchin-like Co_0.8-Mn_0.2-P/CC only requires an overpotential of 55 mV to drive a current density of 10 mA cm⁻², with the Tafel slope of 55.9 mV dec⁻¹. Similarly, when reaching the same current density, just a particularly low overpotential of 61 mV is required with a corresponding Tafel slope of 41.7 mV dec⁻¹ in 1 M KOH. Furthermore, this electrocatalyst exhibits superior stability with 1000 cycles of cyclic voltammetry and 24 h in the I-T test. Such excellent HER catalytic performance can be attributed to the synergistic effect between Co and Mn atoms and high electrochemical active surface area (ECSA). Our work provides a valuable synthesis strategy of non-precious and high HER performance catalytic material.     

Bio-derived nanoporous activated carbon sheets as electrocatalyst for enhanced electrochemical water splitting

Designing highly efficient and durable metal-free electro-catalysts replacing the precious (non)noble metals is crucial to the future hydrogen economy and various renewable energy conversion and storage devices. Herein, we report an efficient low-cost nanoporous activated carbon sheets (NACS) with hierarchical pore architecture from Indian Ooty Varkey (IOV) food waste for oxygen evolution (OER) and hydrogen evolution reactions (HER) by following “waste to wealth creation” strategy. Characterization of NACS carbo-catalyst reveals the presence of pyridinic-nitrogen inherited by self-doping of N from the biomass with high BET surface area (1478.0 m² g^-1). As an electrocatalyst in alkaline medium, it exhibits low-onset potential (1.36 V vs. RHE), an overpotential (η₁₀) of 0.34 V at 10.0 mA cm⁻² with a small Tafel value (43 mV dec⁻¹), and good stability towards OER compared to Pt or Ir commercial catalysts. Tested as HER catalyst, it displays an impressive HER activity with a low-onset potential of −0.085 V (vs. RHE), and overpotential (η₁₀) of 0.38 V at 10.0 mA cm⁻² with a small Tafel slope of 85 mV dec⁻¹.     

MoS2 supported on MOF-derived carbon with core-shell structure as efficient electrocatalysts for hydrogen evolution reaction

In this work, the porous carbon polyhedra were firstly obtained by carbonizing the zeolite imidazole framework (ZIF-8). Then the carbon polyhedra and precursors of MoS₂ were successfully combined by a hydrothermal reaction, forming the C-MoS₂ composites with different carbon contents. The well-tuned C-MoS₂ sample possesses a core-shell morphology, in which the carbon substrate is well decorated by vertically aligned MoS₂ ultrathin nanosheets. The resulting composites can be used as electrocatalysts of hydrogen evolution reaction (HER), displaying significantly superior activities to pure MoS₂ and carbon. It's found that the carbon content largely affects the architectures and HER behaviors of catalysts. In particular, the optimized catalyst yields the best catalytic activity with the lowest onset potential (35 mV), smallest Tafel slope (53 mv dec^?1), lowest overpotential (200 mV at 10 mA cm^?2), as well as extraordinary long-term stability in H₂SO₄. The enhanced HER activity can be attributed to the unique core-shell structure, where abundant active edge sites of MoS₂ are exposed and the underlying carbon substrate effectively improves the conductivity of the electrode.     

Incorporation of pyridinic and graphitic N to Ni@CNTs: As a competent electrocatalyst for hydrogen evolution reaction

Cheap production of hydrogen (H₂) from eco-friendly routes is preeminent for solving future energy challenges. This study explores the hydrogen evolution reaction (HER) activity of nickel (Ni) nanoparticles and nitrogen doped carbon nanotubes (NiNCNTs), which are fabricated by a cheap and one-step pyrolysis method. The most active catalyst synthesized at 800°C exhibits an overpotential of 0.244 V to reach a current density of 10 mA cm⁻², Tafel slope of 93.3 mV dec⁻¹ and a satisfactory 10 hours stability. Low resistance and large ECSA value of the sample also favor the competent response for HER in alkaline media. The robust HER activity of the catalyst is as a result of the nickel nanoparticles which are the active spots of reaction; while the presence of well-developed nitrogen containing carbon nanotubes with large content of pyridinic and graphitic nitrogen may provide high-electron density and feasible routes for its transportation to deliver an outstanding HER performance.     

MOF-derived Zn,S, and P co-doped nitrogen-enriched carbon as an efficient electrocatalyst for hydrogen evolution reaction

In this study, Zn, S, and P co-doped nitrogen N-enriched carbon (ZnSP/NC) was successfully fabricated as an efficient electrocatalyst for the hydrogen evolution reaction (HER) process via pyrolysis, sulfurization, and phosphorization. The metal Zn derived from zeolitic imidazolate framework-8 (ZIF-8) was combined with the S element to form ZnS nanoparticles, and then embedded in N-enriched carbon during the sulfurization process. Following this, the P element was well-dispersed in the catalyst via phosphorization. It was found that ZnSP/NC exhibits excellent electrocatalytic activity when used as a catalyst for the HER process. ZnSP/NC, with an overpotential of 171 mV and a Tafel slope of 54.78 mV dec⁻¹, demonstrates superior electrocatalytic activity as compared to Zn/NC (277 mV, 92.34 mV dec⁻¹) and ZnS/NC (241 mV, 76.41 mV dec⁻¹). During the HER process, ZnS and P serve as active sites, while the N-enriched carbon provides reliable electronic transmission. The synergistic effects among the ZnS, P, and N-enriched carbon result in an excellent electrocatalytic activity of ZnSP/NC for the HER process.     

Synthesis of nitrogen-doped MoSe2 nanosheets with enhanced electrocatalytic activity for hydrogen evolution reaction

Benefiting from improved electrical conductivity, the N-doped MoSe₂ nanosheets show substantially enhanced HER activity with a lower onset overpotential of approximately ?135 mV and a smaller Tafel slope of 62 mV dec^?1, which exhibiting enhanced catalytic performance compared with that of pure MoSe₂. The success of improving the HER performance via the introduction of N dopant offers a new opportunity in the development of high performance MoSe₂-based electrocatalyst.