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.     

Metal-free hybrid composite particles with phosphorus and oxygen-doped graphitic carbon nitride dispersed on kaolin for catalytic activity toward efficient hydrogen release

Here, hybrid kaolin-g-C₃N₄ heterostructure particles were fabricated by calcination in the first step, followed by hydrothermal phosphoric acid activation in the second step, and phosphorus (P) and oxygen (O) doped kaolin-g-C₃N₄ metal-free catalyst was synthesized. This hybrid metal-free catalyst was used for the first time for the production of effective hydrogen (H₂) from sodium borohydride (NaBH₄) methanolysis. The hydrogen generation rate (HGR) value of 5500 ml min⁻¹g⁻¹ was obtained with the P and O doped kaolin-g-C₃N₄ catalyst. The activation energy (Ea) of 31.90 kJ mol⁻¹ by P and O doped kaolin-g-C₃N₄ for the production of H₂ was obtained. The kaolin-g-C₃N₄ and P and O doped kaolin-g-C₃N₄ metal-free catalysts were systematically characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). Based on the results obtained, the mechanism of P and O-doped kaolin-g-C₃N₄ catalyst on H₂ production from NaBH₄ methanolysis was also proposed.     

Sulphur and nitrogen-doped metal-free microalgal carbon catalysts for very active dehydrogenation of sodium borohydride in methanol

Micro algae based on Spirulina platensis is successfully used for the synthesis of S and N-doped metal-free carbon materials. The procedure consists of three stages; (i) Activated carbon production by KOH activation in CO₂ atmosphere (S-AC), (ii) S atom doping to the obtained S-AC using sulphuric acid by hydrothermal activation (S-AC-S), (iii) N atom doping by hydrothermal activation to S-AC obtained using nitric acid (S-AC-S-N). The S and N doped metal-free catalysts are used for H₂ release in NaBH₄ methanolysis reaction (NaBH₄-MR) for the first time. The metal-free carbon catalysts are characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM-EDS), X-ray diffractometer spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR), nitrogen adsorption and elemental analysis (CHNS) methods. When the HGR values obtained for S-AC-S-N (26,000 mL min^?1 g^?1) and S-AC (2641 mL min^?1 g^?1) are compared, there is a 9.84-fold increase. Activation energy (Ea) value for S-AC-S-N was 10.59 kJ mol^?1.     

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.     

Steam reforming of CH4 at low temperature on Ni/ZrO2 catalyst: Effect of H2O/CH4 ratio on carbon deposition

In present work, the H₂O/CH₄ on carbon deposition in SRM reaction over Ni/ZrO₂ was studied. Prepared by impregnation, the catalysts were characterized by TEM, XPS, H₂-TPR, TG-DSC-MS, Raman, and XRD. The results showed that when H₂O/CH₄ = 2 with GHSV of 14460 h⁻¹, the highest CH₄ conversion (46.8%) was achieved on the Ni/ZrO₂ catalyst at 550 °C. This was due to the relatively high surface content of Ni⁰ (27%) species and the formation of easy removal polymer carbon (C₁). When the H₂O/CH₄ was 1, a large amount of difficult to remove fiber carbon (C₂) formed and polymer carbon would wrap around the catalyst to reduce its activity. However, excess water might promote surface reconstruction by converting Ni⁰ to Ni(OH)₂, which reduced the surface Ni⁰ content and then inhibited the catalytic activity, while the amount of carbon deposited, especially C₂, reduced significantly.     

Chlorine-mediated synthesis of self-exfoliated and wavy-structured graphitic carbon nitride nanosheets for enhanced photocatalytic hydrogen evolution

Graphitic carbon nitride (GCN) has drawn widespread interests in solar hydrogen production. However, the difficult exfoliation and the intrinsic shortcomings greatly restrict the hydrogen production efficiency. Herein, we report a chlorine-mediated strategy to synthesize ultrathin wavy-structured GCN nanosheets for enhancing photocatalytic activity. Chlorine is firstly doped into the melem-based oligomer; in subsequent polymerization process, self-exfoliated wavy-structured GCN are obtained owing to the effect from chlorine removal. The obtained wavy-GCN presents superior H₂ evolution rate at 3372 μmol·g^?1 h^?1, which is 25 times higher than pristine GCN. Comprehensive characterizations reveal two main reasons for the enhanced photocatalytic activity. 1) The GCN is in-situ self-exfoliated owing to removal of doped chlorine, increasing accessible active sites. 2) The introduction of nitrogen-defects into GCN gives rise to enhanced light absorption capacity and reduced charge carriers recombination rate. This work provides a new bottom-up two-step strategy for structural regulation of GCN towards enhanced photocatalytic performance.     

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.     

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.     

Phosphorus and oxygen doped carbon-based on Spirulina microalgae as efficient metal-free catalysts to obtain H2 from methanolysis of NaBH4

Metal-free catalysts (SP–KOH–P) doped phosphorus and oxygen as a result of modification with H₃PO₄ to the surface of the activated carbon sample (SP–KOH) obtained by activation of KOH with Spirulina microalgae were used to obtain hydrogen (H₂) from methanolysis of NaBH₄. The characteristic structure of SP-KOH-P and SP-KOH metal-free catalysts were examined by XRD, TEM, elemental analysis, FTIR, and ICP-MS. The effects of the amount of catalyst, NaBH₄ concentration, reusability, and temperature on H₂ production rate from NaBH₄ methanolysis reaction were investigated. The hydrogen production rate (HGR) obtained with 25 mg SP-KOH-P was found to be 19,500 mL min^?1 g^?1. The activation energy (Ea) value of SP-KOH-P metal-free catalyst sample was calculated as 38.79 kJ mol^?1.     

B (boron), O (oxygen) dual-doped carbon spheres as a high-efficiency electrocatalyst for nitrogen reduction

Recently, electrochemical nitrogen reduction (NRR) has attracted significant interest due to its green synthesis process. However, the slow kinetics caused by the difficulty of NN bond activation and the competitive hydrogen evolution reaction hinder the development and application of electrochemical nitrogen reduction. Herein, we synthesized a metal-free electrocatalyst of B, O-decorated carbon microspheres (B,O-CMS) by a hydrothermal method using nitrogen-free raw materials. The doping of B increases the specific surface area, induces abundant microporous structure and adjusts the electronic structure of the materials. As a result, in 0.1 M HCl, B,O-CMS achieves a high V_NH3 of 19.2 μg h^?1 mg^?1_cat. and a high FE of 5.57% at ?0.25 V vs. RHE, along with outstanding selectivity for NH₃ production and stability. This work provides an effective approach to rationally design high-performance metal-free catalysts for NRR by doping heteroatoms into carbon materials.     

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.     

Comparative study between supported and doped MgO catalysts in supercritical water gasification for hydrogen production

Different catalyst structures may influence the catalytic performance of catalysts in supercritical water gasification (SCWG). This study reports the catalytic activity of supported (SP) and doped (DP) MgO catalysts in catalyzing the gasification of oil palm frond (OPF) biomass in supercritical water to produce hydrogen. Two types of supported catalysts, labelled as Ni-SP (nickel supported MgO) and Zn-SP (zinc supported MgO), were synthesized via impregnation method. Another two types of doped catalysts, labelled as Ni-DP (nickel doped MgO) and Zn-DP (zinc doped MgO), were synthesized by using the self-propagating combustion method. All the synthesized catalysts were found to be pure with the doped catalysts exhibited small crystallites, in comparison to that produced by the supported catalysts. The specific surface area increased in the order of Ni-DP (67.9 m² g⁻¹) > Zn-DP (36.3 m² g⁻¹) > Ni-SP (30.1 m² g⁻¹) > Zn-SP (13.1 m² g⁻¹). Regardless of supported or doped, the Ni-based catalysts always had larger specific surface area than that in the Zn-based catalysts. Unexpectedly, the Zn-based catalysts with smaller surface area for SCWG produced higher hydrogen (H₂) yield from the OPF biomass. When compared to the non-catalytic reaction, the H₂ yield increased by 187.2% for Ni-SP, 269.0% for Zn-SP, 361.7% for Ni-DP, and 438.1% for Zn-DP. Among the studied catalysts, the Zn-DP displayed the highest H₂ yield because it had the highest number of basic sites; approximately twenty-fold higher than that of the Zn-SP catalyst. The Zn-DP also proved to be the most stable catalyst, as verified from the X-Ray photoelectron spectroscopy (XPS) results. As such, this study concludes that the catalytic performances of the synthesized catalysts do not only depend on the specific surface area, but they are also influenced by the number of basic sites and the catalyst stability. It is trustworthy to note that this is the initial study that associated SCWG with doped catalysts. The doped catalysts, hence, may serve as a new catalyst system to generate SCWG reactions.     

Well-dispersed CoSx nanoparticles modified tubular sulfur doped carbon nitride for enhanced photocatalytic H2 production activity

Appropriate dispersion of cocatalyst on semiconductor for improving photocatalytic H₂ production efficiency is a challenging work in semiconductor photocatalysis. Herein, we constructed the noble-metal-free CoS_x modified tubular sulfur doped carbon nitride (SCN) photocatalysts by chemical precipitation process. The amorphous CoS_x well dispersed on SCN served as H₂ production sites, which reduced the overpotential and inhibited the recombination of photogenerated carriers by interfacial charge transfer. Maximized H₂ production rate of 573.06 μmol g⁻¹ h⁻¹ under visible light irradiation was obtained by optimizing the CoS_x loading proportion to 2.4%, which was higher than that of 0.75 wt% Pt/SCN. In addition, a possible mechanism for improved H₂ production activity was proposed based on the experiments and discussion. This work provides a new strategy to design rational structure of non-noble metal cocatalyst modified photocatalyst to further improve H₂ production performance.     

Ru nanoclusters coupling with hierarchical phosphorus and oxygen dual-doped carbon nanotube architectures for effective hydrogen evolution reaction

The construction of an effective catalyst for hydrogen evolution reaction (HER) is a top priority. Herein, we demonstrate ruthenium (Ru) nanoclusters coupled with phosphorus and oxygen dual-doped carbon nanotube (CNT) architecture (Ru-POCA). The increased hydrophilicity and negatively charged surface of CNTs can strongly trap Ru ions. The hierarchical structure is favorable of providing abundant pathways and exposing more active sites for HER. Due to the synergistic effect of the hierarchical structure and modified surface chemistry, Ru-POCA exhibits excellent catalytic HER activity. The overpotential is 22 and 40 mV with a Tafel slope of 28.0 and 27.1 mV dec⁻¹ in 1 M KOH and 0.5 M H₂SO₄ at 10 mA cm⁻². Moreover, Ru-POCA processes good catalytic stability in both acidic and alkaline electrolytes, while the boosted catalytic HER activity is fundamentally studied by density functional theory calculation. This work provides a rational approach to constructing hierarchically structured Ru-CNTs-based catalysts for hydrogen evolution reaction.     

An optimized nickel phosphate/carbon composite electrocatalyst for the oxidation of formaldehyde

The electrocatalytic performance of highly conducting Nickel phosphate (NiPh)/carbon composite catalyst is investigated for the oxidation of formaldehyde in alkaline solution. The NiPh nanoparticles are synthesized by a cost-effective one-pot method, which is based on refluxing nickel and phosphate precursors at 90 °C. Inks of the composite catalyst are produced by mixing NiPh nanoparticles with carbon conductive additives (CCA) and Nafion oil. Then, the ink is cast then dried on the glassy carbon electrode. Systematic study is performed to investigate the effect of varying the CCA loading on the electrochemical oxidation of formaldehyde. The best catalytic performance is obtained for NiPh/CCA composite catalyst containing 20 wt% of CCA (NiPh/CCA-20 wt%). The physicochemical properties of the composite catalysts are investigated and analyzed by field-emission scanning electron microscopy (FE-SEM), Energy Dispersive x-ray Spectroscopy (EDX) and X-ray diffraction (XRD). Also, the N₂ adsorption/desorption isotherms are recorded and the Brunauer–Emmett–Teller (BET) and Barrett-Joyner-Halenda (BJH) methods are used to calculate the specific surface area and pore size distribution. The electrocatalytic performance of the NiPh/CCA composite was compared to the pristine NiPh for the oxidation of formaldehyde in alkaline solution. Electrochemical impedance spectroscopy technique is used to study the electrical conductivity of the composite catalysts. Additionally, cyclic voltammetry and chronoamperometry techniques are used to calculate key parameters such as surface coverage (Γ) of Ni²⁺/Ni³⁺ species, the diffusion coefficient of the formaldehyde (D) and the catalytic rate constant (k_cat). Ã, D and k_cat values for the NiPh/CCA-20 wt% catalyst are 5.95 × 10⁻⁵ mmol cm⁻², 1.08 × 10⁻⁴ cm² s⁻¹ and 2.59 × 10⁷ cm³ mol⁻¹ s⁻¹ respectively. Both Γ and k_cat parameters are used to identify the optimum composition of the catalyst.     

Fine-tuning catalytic performance of ultrafine bimetallic nickel-platinum on metal-organic framework derived nanoporous carbon/metal oxide toward hydrous hydrazine decomposition

Heterogeneous catalysts with a high performance as well as low cost is pivotal but still challenging for hydrous hydrazine (N₂H₄·H₂O) as a hydrogen storage material. Herein, bimetallic PtNi nanoparticles are well dispersed on nitrogen doped porous carbon/zirconia support (PtNi/NC-ZrO₂). PtNi/NC-ZrO₂ nanocatalysts could be responsive and completely for catalyzing hydrous hydrazine decomposition with a H₂ selectivity of 100% as well as a turnover frequency of 1716 h⁻¹ measured at 323 K, outperforming most heterogeneous metal catalysts. This is mainly attributed that bi-support NC-ZrO₂ can efficiently expedite the electron transfer to metallic NPs and re-construct the electronic structure bimetallic active sites for selectively catalyzing hydrous hydrazine decomposition.     

Highly efficient electrochemical generation of H2O2 on N/O co-modified defective carbon

The electrochemical oxygen reduction reaction (ORR) via two-electron pathway is a sustainable way of producing hydrogen peroxide. Nanostructured carbon materials are proved to be effective catalysts for 2e^? ORR. Herein, a series of mesoporous carbon with tunable nitrogen species and oxygen functional groups were synthesized by varying the added amount of dopamine hydrochloride as nitrogen and oxygen source. The modified catalysts exhibited higher content of pyrrolic-N and ether C–O groups which are confirmed by a series of characterization. Raman spectra and correlation analysis revealed that the increased proportion of defect sites in carbon materials are closely related to the introduced pyrrolic-N and ether C–O groups. And the rotating ring-disk electrode (RRDE) measurement carried out in 0.1 M KOH electrolyte showed the H₂O₂ selectivity increased with the content of defect sites. Among them, the optimized catalyst (NOC-6M) exhibited a selectivity of 95.2% and a potential of 0.71 V vs. RHE at ?1 mA cm^?2. Moreover, NOC-6M possessed the high H₂O₂ production rate of 548.8 mmol g_cat^?1 h^?1 with faradaic efficiency of 92.4% in a two-chamber H-cell. Further mechanistic analysis revealed that the introduction of pyrrolic-N and ether C–O are likely to improve the binding energy of the defect sites toward 1OOH intermediate, resulting in a more favorable 2e^? ORR pathway for H₂O₂ production.     

Phosphorus doped carbon nanodots particles based on pomegranate peels for highly active dehydrogenation of sodium borohydride in methanol

Here, the carbon nanodots were successfully synthesized from pomegranate peels (PPCD). This obtained PPCD was treated by a hydrothermal process with phosphoric acid for P doping (P doped PPCD) and used as a metal-free catalyst to obtain hydrogen(H₂) from sodium borohydride (NaBH₄) methanolysis for the first time. The characteristics of the samples obtained by ultraviolet, fluorescence, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and Inductively coupled plasma mass spectrometry (ICP-MS) analyses were examined. NaBH₄ concentration effect, temperature effect and catalyst reusability experiments were carried out. Using 10 mg of the catalyst with 2.5% NaBH₄, an HGR value of 13000 mL min^?1g^?1 was obtained. The activation energy (Ea) for the P-doped PPCD catalyst was 30.96 kJ mol^?1.     

Rich carbon vacancies facilitated solar light-driven photocatalytic hydrogen generation over g-C3N4 treated in H2 atmosphere

Graphite carbon nitride (g-C₃N₄) has caught far-ranging concern for its masses of advantages, for instance, the unique graphite-like two-dimensional lamellar structure, low cost, nontoxic, suitable bandgap of 2.7 eV and favorable stability. Whereas owing to the shortcomings of low solar absorptivity and fast recombination of photo-induced charge pairs, the overall quantum efficiency of photocatalysis for g-C₃N₄ is suboptimal, resulting in limited practicality of g-C₃N₄ (GCN). In our study, modified g-C₃N₄ materials (HCN) with ample carbon vacancies (CVs) were obtained through calcinating of g-C₃N₄ in H₂ atmosphere. Higher specific surface area and more active sites of HCN were induced by roasting of g-C₃N₄ in H₂. CVs that occurred in the N-(C₃) bond lead to the reduction of electron density around N, thus narrowing the bandgap of HCN-3h and enlarging corresponding light response capability. Under the synergistic function of abundant pore construction and CVs on HCN, the photo-excited e^?/h⁺ pairs can be memorably separated and transferred, which is favorable to photocatalytic efficiency. Among HCN, the HCN-3h sample has the highest H₂ generation rate of 4297.9 μmol h^?1 g^?1, which achieves 2.3-fold higher than that of GCN (1291.7 μmol h^?1 g^?1). This paper brings forward a meaningful method of boosting the photocatalytic performance of photocatalysts by constructing abundant CVs.     

Carbon nanotubes-promoted Co–B catalysts for rapid hydrogen generation via NaBH4 hydrolysis

In this work, multiwalled carbon nanotubes (MWCNTs) promoted Co–B catalysts for NaBH₄ hydrolysis have been designed and synthesized. The structural features of as-prepared catalysts have been investigated and discussed as a function of MWCNTs contents by X-ray diffraction, X-ray photoelectron spectra, N₂ adsorption/desorption isotherms, scanning electron microscope. The results show that the catalysts still maintain an amorphous structure with the addition of carbon nanotubes promoter. However, the appropriate amount of MWCNTs promoter in Co–B catalysts leads to large specific surface area, fine dispersion of active components, increased active sites and high electron density at active sites. Moreover, hydrogen spillover on the catalyst is promoted, which contributes to regeneration of active sites and accelerating catalytic cycle. Among all the experimental samples, it is found that the Co–B catalyst promoted by 10 wt% carbon nanotubes exhibits optimal catalytic activity with remarkably high hydrogen generation rate of 12.00 L min⁻¹·g_catalyst⁻¹ and relatively good stability.