Metal-free catalysts with phosphorus and oxygen doped on carbon-based on Chlorella Vulgaris microalgae for hydrogen generation via sodium borohydride methanolysis reaction

Metal-free catalysts (C–KOH–P) containing phosphorus (P) and oxygen (O) prepared by the modification with phosphoric acid (H₃PO₄) of activated carbon (C–KOH) obtained by activation of Chlorella Vulgaris microalgae with potassium hydroxide (KOH) were investigated for the hydrogen (H₂) generation reaction from methanolysis of sodium borohydride (NaBH₄). Elemental analysis, XRD, FTIR, ICP-MS, and nitrogen adsorption were used to analyze the characteristics of metal-free catalysts. The results showed that groups containing O and P were attached to the carbon sample. In the study, the hydrogen production rates (HGR) obtained with metal-free C–KOH and C–KOH–P catalysts were 3250 and 10,263 mL/min/g, respectively. These HGR values are better than most values obtained for many catalysts presented in the literature. Besides, relatively low activation energy (Ea) of 27.9 kJ/mol was obtained for this metal-free catalyst. The C–KOH–P metal-free catalyst showed ideal reusability with 100% conversion and a partial reduction in the H₂ production studies of NaBH₄ methanolysis after five consecutive uses.     

Very efficient dehydrogenation of methanolysis reaction with nitrogen doped Chlorella Vulgaris microalgae carbon as metal-free catalysts

In this study, nitrogen (N) doped metal-free catalysts were obtained as a result of nitric acid (HNO₃) activation of carbon sample (C–KOH–N), which was obtained based on Chlorella Vulgaris microalgae by KOH activation (C–KOH). These catalysts have been effectively used to produce hydrogen (H₂) from the sodium borohydride (NaBH₄) methanolysis reaction. Compared to the C–KOH catalyst, the catalytic activity for C–KOH–N showed a seven-fold improvement. Hydrogen generation rate (HGR) values obtained for the NaBH₄ methanolysis reaction for C–KOH and C–KOH–N metal-free catalysts were 3250 and 20,100 mL min^?1 g^?1. The catalysts were characterized using various analytical techniques such as XPS, XRD, SEM, FTIR, BET, and elemental analysis. This work can provide a new alternative strategy to produce specific heteroatom-doped metal-free carbon catalysts for environmentally friendly conversion to produce H₂ efficiently.     

Oxygen and nitrogen-doped metal-free microalgae carbon nanoparticles for efficient hydrogen production from sodium borohydride in methanol

Here, the oxygen(O) and nitrogen(N) doped metal-free carbon synthesis including potassium hydroxide (KOH) activation of Spirulina Platensis microalgae, followed by nitric acid (HNO₃) activation is reported for the first time. Oxygen and nitrogen-doped metal-free catalysts were investigated for efficient hydrogen (H₂) production from methanolysis of sodium borohydride (NaBH₄). Compared to the catalyst obtained with the KOH activation, the catalytic activity for O and N doped metal-free showed about a four-fold improvement. The catalysts were analysed by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffractometer (XRD), nitrogen adsorption, elemental analysis and Fourier-transform infrared spectroscopy (FTIR). The effects of temperature, NaBH₄ amounts, catalyst loading and reusability experiments on the catalytic performance of obtained metal-free catalysts by H₂ release from NaBH₄ methanolysis were performed. This study can provide a new alternative strategy to produce specific metal-free carbon catalysts doped heteroatom for environmentally friendly conversion to produce H₂ efficiently.     

Metal-free catalyst fabrication by incorporating oxygen groups on the surface of the carbonaceous sample and efficient hydrogen production from NaBH4 methanolysis

In the present study, metal-free catalysts for efficient H₂ generation from NaBH₄ methanolysis was produced for the first time from apricot kernel shells with two-step activation. The first stage of the two-stage activation includes the production of activated carbon with the KOH agent (AKOH), and the second stage includes hydrothermally HNO₃ activation with oxygen doping (O doped AKOH + N). The hydrogen production rate (HGR) and the activation energy (Ea) of the reaction with the obtained metal-free catalyst (10 mg) were determined as 14,444 ml min^?1 g^?1 and 7.86 kJ mol^?1, respectively. The structural and physical-chemical properties of these catalysts were characterized by XRD (X-ray diffraction), SEM (scanning electron microscopy), elemental CHNS analysis, FT-IR (Fourier transform infrared spectroscopy), and nitrogen adsorption analysis. Also, the reusability results of this metal-free catalyst for H₂ production are promising.     

g-C3N4 particles with boron and oxygen dopants/carbon vacancies for efficient dehydrogenation in sodium borohydride methanolysis

In the study, metal-free boron and oxygen incorporated graphitic carbon nitride (B and O doped g-C₃N₄) with carbon vacancy was successfully prepared and applied as a catalyst to the dehydrogenation of sodium borohydride (NaBH₄) in methanol for the first time. The hydrogen generation rate (HGR) value was found to be 11,600 mL min^?1g^?1 by NaBH₄ of 2.5%. This is 2.53 times higher than the g-C₃N₄ catalyst without the addition of B and O. The obtained activation energy was 25.46 kJ mol^?1. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), energy dispersive X-Ray analyser (EDX), Transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR) analyses for characterization were performed. A possible mechanism of H₂ production from the reaction using metal-free B and O doped g-C₃N₄ catalyst with carbon vacancy has been proposed. This study showed that g-C₃N₄ and its composites with doping atoms can be used effectively in H₂ production by NaBH₄ methanolysis.     

Spirulina microalgal strain as efficient a metal-free catalyst to generate hydrogen via methanolysis of sodium borohydride

Metal-free catalyst based on Spirulina platensis microalgae (SPM) is protonated by phosphoric acid (H₃PO₄) treatment (SPM-H₃PO₄). The microalgae sample is then exposed to heating with different temperatures including 200, 300, and 400 °C (SPM-H₃PO₄-H). The modified microalgae sample based on Spirulina platensis as a catalyst is directly used to generate hydrogen via the methanolysis of sodium borohydride (MSB). The activation temperature, activation time, NaBH4 concentration, catalyst amounts, temperature and reusability tests were carried out. The maximum hydrogen production rates (HGR) obtained for SPM-H₃PO₄-H at temperatures of 30 °C and 60 °C were 3975 and 9600 mLmin⁻¹gcat⁻¹, respectively. At the same time, the activation energy(Ea) of 17.78 kJ mol⁻¹ was obtained. Reusability experiments were performed for this microalgae-based metal-free catalyst. XRD, SEM, FTIR, BET, and TEM analyzes were performed for characterization of these metal-free catalyst samples.     

Nitrogen doped carbon fibers derived from carbonization of electrospun polyacrylonitrile as efficient metal-free HER electrocatalyst

Development of durable and efficient electrocatalyst for hydrogen evolution reaction (HER) is significantly important for forwarding the commercialization of water splitting technology. In this work, we report a facile synthesis of nitrogen doped carbon fibers derived from the carbonization of the electron-spun polyacrylonitrile (PAN) membrane at 800 °C (NCFs-800) as efficient and stable metal-free electrocatalyst for HER catalysis in both acidic and alkaline mediums. Ascribing to the homogenous nitrogen dopants in electrocatalyst, NCFs-800 requires only 114.3 mV and 198.6 mV vs. RHE to achieve current density of 10 mA cm⁻² in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively. Moreover, the HER activity is well maintained after 2000 potential cycles indicating that NCFs-800 possesses high durability in both acidic and alkaline conditions due to the fibrous structure with high corrosion resistance. Our study offers new strategy to synthesize stable and efficient metal-free electrocatalyst, which could be extended to other heteroatom doped carbon electrocatalyst.     

Metal nanoparticles supported on polyacrylamide water beads as catalyst for efficient generation of H2 from NaBH4 methanolysis

Water beads made from polyacrylamide polymer p-(AAm) were decorated with high efficient metal nanoparticles by inexpensive, fast, simple, and environmental friendly method. These water beads balls were kept in the metal salt solutions for 4 h; to adsorb the metals ions from these aqueous solutions. The metal ions decorated on the p-(AAm) water beads were converted to metal nanoparticles by its reduction with aqueous solution of NaBH₄. The prepared materials p-(AAm) loaded with MNPs (M@p-(AAm)) were characterized by ATR-FTIR, XRD, XPS, FESEM, and EDS which show the successful preparation of MNPs over the surface and within p-(AAm). Afterwards the M@p-(AAm) were investigated as a catalyst for the generation of hydrogen from the methanolysis of NaBH₄. The Ag@p-(AAm) show good catalytic activity for NaBH₄ methanolysis reaction as compared to the other loaded MNPs. In addition, different parameters which effecting H₂ generation were also investigated such as; MNPs types, catalyst amount and temperature of the reaction. Low activation energy (Ea) of 21.37 ± 0.67 kJ mol⁻¹, was calculated for NaBH₄ methanolysis reaction at temperature ranging from 5.0 °C to 35 °C. Moreover, the catalyst reusability was also studied and found no decrease in percent conversion, however percent efficiency was decreases about 37% after completion of four cycles.     

Chlorella vulgaris microalgae strain modified with zinc chloride as a new support material for hydrogen production from NaBH4 methanolysis using CuB,NiB, and FeB metal catalysts

This study aims to produce hydrogen (HG) from sodium borohydride (NaBH₄) methanolysis using CuB, NiB or FeB catalysts prepared with a different support material including C. vulgaris microalgae strain modified using zinc chloride (CMS-ZnCl₂). The NaBH₄ concentration, metal percentage in the supported-catalyst, the optimal ZnCl₂ percentage, and temperature effect on the NaBH₄ methanolysis were investigated. X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and Scanning electron microscopy (SEM) analysis were performed for the CMS-ZnCl₂-CuB characterization. Also, the low activation energy (Ea) of 22.71 kJ mol⁻¹ was found with the supported catalyst obtained. Under the same conditions, nearly 100% conversion was achieved in the reusability experiments repeated five times, but a gradual decrease in catalytic activity was observed after each use.     

Transition metal carbides coupled with nitrogen-doped carbon as efficient and stable Bi-functional catalysts for oxygen reduction reaction and hydrogen evolution reaction

Developing non-precious metal catalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for proton exchange membrane fuel cell (PEMFC), metal-air batteries and water splitting. Here, we report a in-situ simple approach to synthesize ultra-small sized transition metal carbides (TMCs) nanoparticles coupled with nitrogen-doped carbon hybrids (TMCs/NC, including WC/NC, V₈C₇/NC and Mo₂C/NC). The TMCs/NC exhibit excellent ORR and HER performances in acidic electrolyte as bi-functional catalysts. The potential of WC/NC at the current density of 3.0 mA cm^?2 for ORR is 0.814 V (vs. reversible hydrogen electrode (RHE)), which is very close to Pt/C (0.827 V), making it one of the best TMCs based ORR catalysts in acidic electrolyte. Besides, the TMCs/NC exhibit excellent performances toward HER, the Mo₂C/NC only need an overpotential of 80 mV to drive the current density of 10 mA cm^?2, which is very close to Pt/C (37 mV), making it the competitive alternative candidate among the reported non-precious metal HER catalysts.     

Very fast H2 production from the methanolysis of NaBH4 by metal‐free poly(ethylene imine) microgel catalysts

The polyethyleneimine (PEI) microgels prepared via microemulsion polymerization are protonated by hydrochloric acid treatment (p‐PEI) and quaternized (q‐PEI) via modification reaction with methyl iodide and with bromo alkanes of different alkyl chain lengths such as 1‐bromoethane, 1‐bromobutane, 1‐bromohexane, and 1‐bromooctane. The bare p‐PEI and q‐PEI microgels are used as catalysts directly without any metal nanoparticles for the methanolysis reaction of sodium borohydride (NaBH₄). Various parameters such as the protonation/quaternization reaction on PEI microgels, the amount of catalyst, the amount of NaBH₄, and temperature are investigated for their effects on the hydrogen (H₂) production rate. The reaction of self‐methanolysis of NaBH₄ finishes in about 32.5 min, whereas the bare PEI microgel as catalyst finishes the methanolysis of NaBH₄ in 22 min. Surprisingly, it is found that when the protonated PEI microgels are used as catalyst, the same methanolysis of NaBH₄ is finished in 1.5 min. The highest H₂ generation rate value is observed for protonated PEI microgels (10 mg) with 8013 mL of H₂/(g of catalyst.min) for the methanolysis of NaBH₄. Moreover, activation parameters are also calculated with activation energy value of 23.7 kJ/mol, enthalpy 20.9 kJ/mol, and entropy ?158 J/K.mol. Copyright © 2016 John Wiley & Sons, Ltd.     

Protection and confinement effect of carbon on Co/CoxOy nano-catalyst for efficient NaBH4 hydrolysis

The hydrolysis of sodium borohydride (NaBH₄) over catalysts is a promising method to produce hydrogen. Although Co-based catalysts exhibit high activity for NaBH₄ hydrolysis, they are still far from satisfying practical applications, especially their poor durability in alkaline media. Herein, a carbon shell structure was designed and synthesized to improve the stability of the mixture of Co⁰ and Co_xO_y nanofilms (Co/Co_xO_y@C) during NaBH₄ hydrolysis via a facile polymerization-pyrolysis strategy with Co/Co_xO_y nanofilms as the precursor. As a result, the Co/Co_xO_y@C catalyst can achieve a remarkable H₂ generation rate of 4348.6 mL min^?1 g_Co^?1 with a low activation energy of 43.6 kJ mol^?1, which is superior to most previously reported catalysts. Moreover, the catalyst shows high stability with an H₂ generation-specific rate of 79% after five cycles. The excellent performance of carbon substrate can well prevent the agglomeration of Co-based nanoparticle and improve the corrosion resistance of the active Co to BO₂^? and OH^?. This work would widen the road for the preparation of nanoconfined catalysts, which has prospective application potentials for H₂ production from NaBH₄ hydrolysis.     

Design of efficient noble metal single-atom and cluster catalysts toward low-temperature preferential oxidation of CO in H2

The preferential oxidation of CO in H₂ is attractive for the removal of trace amounts of CO to meet the requirement of proton-exchange membrane fuel cells (PEMFCs) application. The key is to design highly effective catalysts that work well in a wide range of low temperatures. Here, the recent progress in Au and Pt group metal catalysts for the PROX reaction is summarized, covering those with single-atom and cluster dispersed metal species with remarkable performance. Firstly, the progress of some representative catalysts is overviewed, with an emphasis on the strategies for improving low-temperature activity, selectivity, and stability. Then, special attention is focused on the key parameters affecting performance in the PROX reaction. Moreover, the reaction mechanisms in terms of adsorption and activation of reactants are discussed. Finally, the challenges and opportunities are offered for guiding the design of advanced noble metal catalysts toward the PROX process.     

Development of shape-engineered α-MnO2 materials as bi-functional catalysts for oxygen evolution reaction and oxygen reduction reaction in alkaline medium

In this work, three kinds of α-MnO₂ nano shapes, namely, nano-wires, nano-tubes and nano-particles have been prepared with a fine control over α-crystallographic form by employing hydrothermal procedure. The materials have been thoroughly characterized by X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) spectrometry, field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The MnO₂ nano shapes are used as a model system for examining the shape-influenced bi-functional electrocatalytic activity towards oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline medium. The bi-functional role has been investigated by cyclic voltammetry and linear sweep voltammetry with rotating ring disc electrode (RRDE) techniques. It is found that α-MnO₂ nano-wires possess enhanced electrocatalytic activity compared to other two shapes namely nano-tubes and nano-particles despite the nano-tubes having a much higher specific surface area. The insight of bi-functional electrocatalytic activity is analysed in terms of catalyst surface with the help of first principles density functional theory (DFT) calculations based on the fact of surface energies and adsorption of water on the surface for a facile reaction.     

CeO2 supported multimetallic nano materials as an efficient catalyst for hydrogen generation from the hydrolysis of NaBH4

Nowadays, there is still no suitable method to store large amounts of energy. Hydrogen can be stored physically in carbon nanotubes or chemically in the form of hydride. In this study, sodium borohydride (NaBH₄) was used as the source of hydrogen. However, an inexpensive and useful catalyst (Co–Cr–B/CeO₂) was synthesized using the NaBH₄ reduction method and its property was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), x-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) measurements. The optimized Co–Cr–B/CeO₂ catalyst exhibited an excellent hydrogen generation rate (9182 mLg_metal⁻¹min⁻¹) and low activation energy (35.52 kJ mol⁻¹). The strong catalytic performance of the Co–Cr–B/CeO₂ catalyst is thought to be based on the synergistic effect between multimetallic nanoparticles and the effective charge transfer interactions between the metal and the support material.     

Performance improvement of oxygen on the carbon substrate surface for dispersion of cobalt nanoparticles and its effect on hydrogen generation rate via NaBH4 hydrolysis

Carbon substrates, as previously reported, are colloidal carbon spheres (CCS) that contain oxygen-rich functional groups on the surface could that provide a suitable support for Co catalysts used for the hydrolysis of NaBH₄. Our results show that the unmodified CCS substrate does not adequately interact with the Co²⁺ precursor to decrease the cobalt ion concentration in solution. However, after successful modification of the oxygen groups on the CCS substrate's surface, the Co ion concentration in solution decreased by 30% indicating interaction of the Co ions with the substrate surface. Also the cobalt dispersion and the hydrogen generation rate (HGR) for the catalysts supported on the modified substrate is much better than for the Co catalyst supported on the unmodified substrate. Therefore, the presence of oxygen on the substrate surface is not sufficient to provide a suitable dispersion and performance for nanocatalysts and modification of the surface leads to an improved catalyst.     

ZnFe2O4@ZnFe2S4 core-shell nanosheet on Ni foam as efficient and novel electrocatalyst for oxygen generation

Due to the augmentation of societies and the need for more energy, attention to clean and renewable energy has increased. One of these alternative energies was the use of water splitting. Since the oxidation reaction of water suffers from a delayed reaction, it is important to use efficient and low-cost electrocatalysts in the process. In this work we report the synthesis of ZnFe₂O₄@ZnFe₂S₄ by the hydrothermal method. Here, we successfully synthesize the ZnFe₂O₄@ZnFe₂S₄ core-shell nanosheet on Ni Foam via a novel and facile process for oxygen evolution reactions (OER). The metal-based electrode made of ZnFe₂O₄@ZnFe₂S₄ is efficient for the electrochemical reaction of water oxidation due to its electrical strength and high catalytic activity. The catalyst is calcined at 400 °C and characterized by XRD, FESEM, TEM, EDS, MAP and RAMAN techniques. The electrolysis of water using ZnFe₂O₄@ZnFe₂S₄/NF a current density of 5 mA cm^?2 can be achieved by cell voltage of 1.45 V (vs. RHE) volts in a solution of 1 M KOH. The catalyst synthesized to reach 5 mA cm^?2 in oxygen evolution reaction only has 222 mV overpotentials.     

Hollow ZnxCo1-xSe2 microcubes derived from Metal–Organic framework as efficient bifunctional electrocatalysts for hydrogen evolution and oxygen evolution reactions

Herein, we designed a simple and universal method to prepare cobalt-based bimetallic Zn_xCo_1-x-MOFs precursors, which were used as templates to synthesize effective bifunctional electrocatalyst hollow porous Zn_xCo_1-xSe₂ microcubes by one-step hydrothermal method. The cubic morphology of the Zn_xCo_1-x-MOFs precursors was well inherited. Particularly, the Zn_0.1Co_0.9Se₂ exhibited superior HER and OER performance in acidic solution and alkaline solution, respectively. Benefiting from the hollow porous structure, the synergistic effect of Zn–Co–Se and the incorporation of a small number of zinc atoms.

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MoS2||CoP heterostructure loaded on N,P-doped carbon as an efficient trifunctional catalyst for oxygen reduction,oxygen evolution,and hydrogen evolution reaction

Exploring multifunctional electrocatalysts is crucial for the development of energy conversion and storage equipments, such as fuel cells, water splitting devices and zinc-air batteries. Herein, we provide a rational design whereby the cobalt phosphide particles are introduced into molybdenum sulfide nanosheets to form a heterostructure (MoS₂||CoP) through the ultrasonic method and calcination. Subsequently, N, P-doped carbon (NPC) is obtained synchronously. The as-prepared MoS₂||CoP/NPC demonstrates highly effective multifunctional catalytic performance for oxygen evolution and hydrogen evolution reaction at lower overpotential, as well as oxygen reduction reaction at high half-wave potential. What this reveals is higher power density and superior stability in zinc-air battery. The excellent electrocatalytic activity of MoS₂||CoP/NPC may be attributed to the presence of the MoS₂||CoP heterostructure, as well as N, P-doped carbon coupled with a high percentage of pyridinic-N. This work proposes a novel and facile strategy to prepare the heterostructure compound and serves as a good reference for constructing efficient and low-cost electrocatalysts.     

3D hierarchical network NiCo2S4 nanoflakes grown on Ni foam as efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reaction in alkaline solution

The development of cost-effective and high-efficiency electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) still remains highly challenging. Exposing as many active sites as possible is the key method to improve activity of HER and OER performance. In this communication, we demonstrate a novel 3D hierarchical network NiCo₂S₄ nanoflake grown on Ni foam (NiCo₂S₄-NF) as a highly efficient and stable electrochemical catalyst. The NiCo₂S₄-NF exhibits overpotentials as low as 289 and 409 mV at 100 mA cm^?2, superior long-term durability during a 20 h measurement, and a low Tafel slope of 89 and 91 mV dec^?1 for HER and OER in 1.0 M NaOH solution. The outstanding performance is owe to the inherent activity of ultrathin NiCo₂S₄ nanoflakes and the special structure of NiCo₂S₄-NF that can provide a huge number of exposed active sites, accelerate the transfer of electrons, and facilitate the diffusion of electrolyte simultaneously.