Co-catalyst For Hydrogen Production Research Articles

Infiltration of C-ring into crystalline carbon nitride S-scheme homojunction for photocatalytic hydrogen evolution

Enhancing the carrier separation in graphitized carbon nitride (g-C3N4) is advantageous for improving its photocatalytic activity. Herein, we propose a feasible method for preparing CN-C by thermal polymerization to gradually infiltrate carbon rings (C-rings) into the surface of crystalline carbon nitride (CN), enabling photogenerated electrons to be transferred rapidly between the CN inner layers and the CN/C outer layer. Successful penetration and distribution of carbon rings into carbon nitride were confirmed by secondary ion mass spectroscopy using ratio analysis of C and N elements at various depths of the prepared photocatalyst. Theoretical calculations indicated that CN and CN/C in the molecule generated different Fermi levels to form an S-scheme homojunction, establishing appropriate built-in electric fields and thus enabling interlayer charge migration. Moreover, the overlap of the conjugate plane of C-rings with carbon nitride led to the formation of photogenerated in-plane charge transfer tunnels. The two-electron transfer tunnels greatly improved the dissociation efficiency of photogenerated electrons. The prepared sample loaded with 3 wt% Pt as a co-catalyst for hydrogen production under visible light irradiation, and the prepared optimal sample CN-C showed a maximum quantum efficiency of 15.56% for photocatalytic H2 evolution at 385 nm. This research introduces a new idea for constructing a directional transfer path for charge carriers in-plane and intralayer.

Mo2C MXene Nanosheets Made in Different Etching Solutions as Co-catalysts for Hydrogen Production

Mo2C MXene is a two-dimensional material, which can be applied as a co-catalyst to significantly enhance the photocatalytic performance of CdS for H2 production. To understand the effect of the synthesis process of Mo2C MXene nanosheets on the catalytic performance, in this paper, Mo2C MXene was made from Mo2Ga2C by hydrothermal etching in different etchants. Diverse cations (Li+, Na+, K+, or NH4+) in etchants resided on the surface of Mo2C MXene nanosheets. Then, the samples were used to construct CdS/Mo2C-MXene composites for photocatalytic H2 evolution. Among them, Mo2C MXene with Li+ shows the best photocatalytic H2 production rate of 22,048 μmol g–1 h–1 under visible light. The remarkable performance arises from the modification at the nanoscale of Mo2C MXene with Li+, thereby resulting in better photoabsorption behavior, high separation efficiency of photogenerated carriers, and fast charge transfer at the heterointerface. Moreover, the energy band structures explain that the changes of band gap and the position of the conductive band in the photocatalyst tuned by cations are also key to affect photocatalytic activities.

Fabrication of CdLa2S4@La(OH)3@Co3S4 Z-scheme heterojunctions with dense La, S-dual defects for robust photothermal assisted photocatalytic performance

Optimize the separation and transport mechanism of photogenerated carriers in heterojunction composites, and make full use of the active sites of each material are key factors to enhance photocatalytic activity. Herein, we successfully synthesize defective CdLa2S4@La(OH)3@Co3S4 (CLS@LOH@CS) Z-scheme heterojunction photocatalysts through a facile solvothermal method, which show broad-spectrum absorption and excellent photocatalytic activity. La(OH)3 nanosheets not only greatly increase the specific surface area of photocatalyst, but also can be coupled with CdLa2S4 (CLS) and form Z-scheme heterojunction by converting irradiation light. In addition, Co3S4 with photothermal properties is obtained by in-situ sulfurization method, which can release heat to improve the mobility of photogenerated carriers, and also be used as a cocatalyst for hydrogen production. Most importantly, the formation of Co3S4 leads to a large number of sulfur vacancy defects in CLS, and thus improving the separation efficiency of photogenerated electrons and holes, and increasing the catalytic active sites. Consequently, the maximum hydrogen production rate of CLS@LOH@CS heterojunctions can reach 26.4 mmol g-1h−1, which is 293 times than pristine CLS (0.09 mmol g-1h−1). This work will provide a new horizon for synthesizing high efficiency heterojunction photocatalysts through switching the separation and transport modes of photogenerated carrier.

A new and highly efficient co-catalyst Zn-Ni5P4 for photocatalytic H2 evolution with the reduced capacitance via Zn doping

Non-noble metal co-catalysts for hydrogen production have capacitance characterization, which can store photo-excited electrons from semiconductor and show capacitance catalysis. However, the overlarge capacitance of co-catalysts constrains prompt release of electrons. Here, we reported a new and highly efficient co-catalyst Zn-Ni5P4 via evenly doping Zn in Ni5P4. Loading Zn-Ni5P4 on CdS, the photocatalyst Zn-Ni5P4/CdS shows an ultrahigh activity of 8969 μmol/g/h, which is 2.4 times of Ni5P4/CdS (3668 μmol/g/h). More interestingly, by the Pt loading on the surface of Ni5P4, the (Pt/Ni5P4)/CdS shows only 1.3 times of Ni5P4/CdS. Zn doping in Ni5P4 reduces the capacitance by 140 mF/g and electrochemical impedance, which benefits the release of photo-excited electrons. Moreover, the reduced overpotential and the increased specific surface area also account for the enhanced co-catalytic performance of Zn-Ni5P4. This paper presents an effective and low-cost method to inhibit negative effect of capacitance catalysis of non noble co-catalysts.

H2O2 Exfoliation of TiO2 for Enhanced Hydrogen Production from Photocatalytic Reforming of Methanol

Hydrogen is considered a future energy carrier for clean and sustainable technology. Photocatalytic reforming of methanol produced hydrogen using water and energy from sunlight. This study reported enhanced activity of TiO2 without metal co-catalyst for hydrogen production following H2O2 exfoliation. TiO2 was transformed into peroxo-titania species on the outer layer of the particles, resulting in surface exfoliation. The exfoliation reduced TiO2 crystallite sizes enhanced the surface hydroxyl group and reduced the band gap to 3.0 eV. Hydrogen production from methanol-water mixtures on the TiO2 after four consecutive exfoliations was measured at 300 µmol, significantly higher than the fresh TiO2 (50 µmol). H2O2 exfoliated TiO2 reduced the pathway for charge migration to the surface. A high concentration of surface hydroxyl group trapped the charge carriers for efficient hydrogen production. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Cucurbit[6]uril as a co-catalyst for hydrogen production from formic acid

Cucurbiturils are organic macrocycles, which are only rarely used for catalytic reactions. We studied a composite comprising of single-walled carbon nanotubes (SWCNTs), cucurbit[6]uril (CB6) and Au species and demonstrated that CB6 is a co-catalyst for hydrogen production from formic acid. Thus, insertion of CB6 into SWCNTs with open tips provides a decrease of the reaction temperatures by 60 K as compared to those over pure SWCNTs. This indicates that CB6 is a metal-free catalyst for this reaction. The use of CB6 during the synthesis of Au catalysts supported on SWCNTs leads to even a stronger decrease of the reaction temperature by 110 K as compared to the Au/SWCNTs catalyst. Density functional theory (DFT) calculations show that these effects could be explained by abstraction of the hydrogen atom from the hydroxyl group of the formic acid molecule on the basic carbonyl portal of the CB6 molecule with the formation of the formate containing adduct. Unusual sandwich-like structures of Au were formed inside the SWCNTs channels due to the interaction of Au with CB6. The results create a base for the development of catalysts containing cucurbiturils for the energy related reactions taking place through the hydrogen abstraction from reactant molecules.

Surface phosphorization for the enhanced photoelectrochemical performance of an Fe2O3/Si photocathode.

Transition metal phosphates (TMPs) are regarded as efficient co-catalysts for photoanodes, but they are rarely applied in hydrogen production reactions. In this work, iron phosphate (FePi), a co-catalyst for hydrogen production, is introduced onto the Fe2O3 surface by facile surface phosphorization under low-temperature conditions. The surface FePi leads to a shift of the onset potential by +201 mV and an increase in the photocurrent density by more than 10 mA cm-2 at 0 VRHE for the Fe2O3/p-Si photocathode in a strong alkaline electrolyte. The role of FePi stems from the smaller transfer resistance, efficient photogenerated carrier separation and electron injection, and preferable H* adsorption energy, as suggested by Kelvin probe force microscopy and density functional theory (DFT) calculation. The surface phosphorization presents a facile and attractive strategy for the treatment of transition metal oxide catalyzed photocathodes for green hydrogen production.

Semiconductor Photocatalysts for Solar-to-Hydrogen Energy Conversion: Recent Advances of CdS

Background: Photocatalytic hydrogen evolution from water splitting using photocatalyst semiconductors is one of the most promising solutions to satisfy the increasing demands of a rapidly developing society. CdS has emerged as a representative semiconductor photocatalyst due to its suitable band gap and band position. However, the poor stability and rapid charge recombination of CdS restrict its application for hydrogen production. The strategy of using a cocatalyst is typically recognized as an effective approach for improving the activity, stability, and selectivity of photocatalysts. Introduction: Solar-driven photocatalytic hydrogen production from water splitting is one of the most promising solutions to satisfy the increasing demands of a rapidly developing society. CdS has emerged as a representative semiconductor photocatalyst due to its suitable band gap and band position. However, the poor stability and rapid charge recombination of CdS restrict its application for hydrogen production. The strategy of using a cocatalyst is typically recognized as an effective approach for improving the activity, stability, and selectivity of photocatalysts. In this review, recent developments in CdS cocatalysts for hydrogen production from water splitting under visible-light irradiation are summarized. In particular, the factors affecting the photocatalytic performance and new cocatalyst design, as well as the general classification of cocatalysts, are discussed, which includes a single cocatalyst containing noble-metal cocatalysts, non-noble metals, metal-complex cocatalysts, metal-free cocatalysts, and multi-cocatalysts. Finally, future opportunities and challenges with respect to the optimization and theoretical design of cocatalysts toward the CdS photocatalytic hydrogen evolution are described. Methods: This review summarizes the recent developments in CdS cocatalysts for hydrogen production from water splitting under visible-light irradiation. Results: Recent developments in CdS cocatalysts for hydrogen production from water splitting under visible-light irradiation are summarized. The factors affecting the photocatalytic performance and new cocatalyst design, as well as the general classification of cocatalysts, are discussed, which includes a single cocatalyst containing noble-metal cocatalysts, non-noble metals, metal-complex cocatalysts, metal-free cocatalysts, and multi-cocatalysts. Finally, future opportunities and challenges with respect to the optimization and theoretical design of cocatalysts toward the CdS photocatalytic hydrogen evolution are described. Conclusion: The state-of-the-art CdS for producing hydrogen from photocatalytic water splitting under visible light is discussed. The future opportunities and challenges with respect to the optimization and theoretical design of cocatalysts toward the CdS photocatalytic hydrogen evolution are also described.

Can Half-a-Monolayer of Pt Simulate Activity Like That of Bulk Pt? Solar Hydrogen Activity Demonstration with Quasi-artificial Leaf Device.

Pt is the best cocatalyst for hydrogen production. It is also well-known that the surface atomic layer is critical for catalysis. To minimize the Pt content as cocatalyst, herein we report on half-a-monolayer of Pt (0.5θPt) decorated on earth-abundant Ni-Cu cocatalyst, which is integrated with a quasi-artificial leaf (QuAL) device (TiO2/ZnS/CdS) and demonstrated for efficient solar hydrogen production. For the QuAL, TiO2 is sensitized with ZnS and CdS quantum dots by the SILAR method. The 0.5θPt-decorated Ni-Cu shows an onset potential of 0.05 V vs reversible hydrogen electrode for the hydrogen evolution reaction, which is almost similar to that of commercial Pt/C. Photoactivity of the present QuAL device with either bulk Pt or 0.5θPt-coated Ni-Cu cocatalyst is, surprisingly, equal. Our findings underscore that a fraction of a monolayer of Pt can enhance the activity of the cocatalyst, and it is worth exploring further for the high activity associated with atomic Pt and other noble metals.

Tin diselinide a stable co-catalyst coupled with branched TiO2 fiber and g-C3N4 quantum dots for photocatalytic hydrogen evolution

Transitional metal dichalcogenide two-dimensional materials have revealed many astonishing properties including the substitution of noble metals as a co-catalyst for hydrogen evolution reaction. Tin diselenide (SnSe2) is the one who also received substantial consideration in many fields due to low cost, earth-abundant and environment-friendly. However, the great challenge to make heterojunction with other semiconductor material to improve its efficiency for photocatalytic water splitting. For this purpose, we have prepared a 1D nanofiber of TiO2 by electrospinning and produced a needle-like structure on the fiber by following the alkali hydrothermal method. The chemical vapor deposition method (CVD) was adopted, first to load g-C3N4 QDs then nanoflakes of SnSe2 on the branched fiber of TiO2 and make a strong heterojunction. The composite interpreted excellent photocatalytic performance by producing hydrogen about 2375 μmol. g−1.h-1 having a quantum efficiency of HER more than 16 % at 420 nm. The photoluminescence, time decay fluorescent spectra and photoelectrochemical results ratified that SnSe2 not only reduces the charge recombination by increasing the transfer of electron but also provides an active site for hydrogen production as a cocatalyst. This study presents an inexpensive and environmentally friendly cocatalyst for hydrogen production as a substitution of noble metals.

A photocatalytic system with a bis(thiosemicarbazonato)‑nickel over CdS nanorods for hydrogen evolution from water under visible light

Diacetyl‑2‑(4‑N‑methyl‑3‑thiosemicarbazone)‑3‑(4‑N‑amino‑3‑thiosemicarbazone) (H2ATSM) reacts with NiCl2 to form a new nickel(II) complex, Ni-ATSM, a new co-catalyst for hydrogen production. Under photoirradiation with blue light (λ = 469 nm), together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H2A) as a sacrificial electron donor, the nickel complex can photocatalyze hydrogen evolution with a turnover number (TON) of 11,500 mol H2 per mol of catalyst (mol of cat−1) during 80 h irradiation in a heterogeneous environment.

Noble metal-free NiS2 with rich active sites loaded g-C3N4 for highly efficient photocatalytic H2 evolution under visible light irradiation

A series of noble-metal-free NiS2-loaded g-C3N4 hybrid composites were prepared via simple hydrothermal method. Benefited from the wider spectral response range and the effective separation of photoelectron-holes of g-C3N4-NiS2 heterojunction catalysts, as well as the rich unsaturated active S atoms on the NiS2 with S22−, the composite catalysts has prominent photocatalytic performance for H2 evolution. Remarkably, the optimal composite photocatalysts achieved an average hydrogen production rate as high as 715.83 μmol/h/g in 3 h under visible-light irradiation, which is 2.75 times as high as that of precious metal Pt (259.5 μmol/h/g) as a co-catalyst. Besides, the composite catalyst still shows prominent photocatalytic performance for H2 evolution after three continuous photocatalytic reaction cycles for 9 h. This study provided a facile method to build a low-cost but effective metal sulfide co-catalyst for hydrogen production under visible light irradiation.

Rational Design and Fabrication of Noble‐metal‐free NixP Cocatalyst Embedded 3D N‐TiO2/g‐C3N4 Heterojunctions with Enhanced Photocatalytic Hydrogen Evolution

AbstractDeveloping low‐cost and efficient noble‐metal‐free photocatalytic materials is crucial for the hydrogen production through water splitting. Herein, N‐TiO2/g‐C3N4 heterostructure loaded with a noble‐metal‐free NixP cocatalyst was prepared by the combination of ammonia etching and photo‐reduction deposition method. The results demonstrated that N‐doped TiO2 (N‐TiO2) nanosheets were formed and stood upright on the surfaces of g‐C3N4 nanosheets, forming a 3D structure. The ternary hybridization of N‐TiO2/g‐C3N4@NixP hierarchical nanostructure was a promising strategy to achieve highly efficient photocatalytic H2 evolution, showing an optimized hydrogen evolution rate of 5438 μmol g−1⋅h−1 using 300 W Xe lamp as irradiation source, which was 7.5 times higher than that of N‐TiO2/g‐C3N4. The enhanced photocatalytic activity was ascribed to the combined effects of NixP cocatalyst loading and the formation of the intimate nanoheterojunctions between TiO2 nanosheets and g‐C3N4 nanosheets, which were favorable for promoting charge transfer. The present work would provide a novel facile preparation and practical application of many other noble‐metal‐free metal phosphides as a highly efficient cocatalyst for hydrogen production through water splitting.

Multicomponent transition metal phosphides derived from layered double hydroxide double-shelled nanocages as an efficient non-precious co-catalyst for hydrogen production

This work demonstrates a novel design strategy for MCTMPs with applications as sunlight-driven photocatalysts for hydrogen production through water splitting.

Enhancing the photocatalytic efficiency of TiO2 nanotube arrays for H2 production by using non-noble metal cobalt as co-catalyst

Non-noble metals are attractive alternatives to Pt co-catalysts for hydrogen production. Herein, Co nanoparticles were designed to uniformly deposit on the surface of TiO2 nanotube arrays (Co/TNAs) via photo-deposition and reduction method. The structure and optical property of the Co/TNAs were characterized. Compared with pure TNAs, Co/TNAs showed a highly photocatalytic activity for hydrogen production without the Pt co-catalyst under UV–vis light irradiation. The study presents a promising practical way using non-noble metal as co-catalyst for photocatalytic splitting of water into hydrogen.

Catalytic performance of CeO2 and ZrO2 supported Co catalysts for hydrogen production via dry reforming of methane

Increasing attention has been devoted to hydrogen production as a source of clean energy that is friendly to the atmosphere. Dry reforming process provides an excellent means for producing hydrogen as well as mitigating CO2 and CH4, greenhouse gases that cause global warming. Catalyst activity and stability depend on the support, active metal and methods of pretreatment. In the present work, the effect of calcination temperature on hydrogen production using cobalt supported over nano-sized ceria and zirconia catalysts was investigated. The catalysts were prepared by the wet impregnation method at different calcination temperatures (i.e., 500, 600, 700, 800 and 900 °C). BET, TGA, XRD, TPO, TPR and TEM techniques were used to characterize the prepared catalysts. The results revealed that the catalysts calcined at 500 and 600 °C exhibited better activity and higher hydrogen production than those calcined at higher temperatures. The hydrogen yields, for Co/ZrO2 and Co/CeO2 catalysts, calcined at 500 °C and 600 °C, were 75.8% & 71.4% and 59.4% & 57.5% respectively.

Promoting effect of Ce and Pr in Co catalysts for hydrogen production via oxidative steam reforming of ethanol

Co catalysts derived from hydrotalcite precursors (HT) were prepared by the conventional co-precipitation method. Additionally, Ce and/or Pr were incorporated as redox promoters employing the reconstruction method in the presence of aqueous complexes with EDTA. The solids obtained were characterized by X-ray diffraction (XRD), surface area (BET), scanning electron microscopy with energy disperse X-ray spectrometry (SEM-EDX), temperature programmed reduction (TPR), CO2-temperature programmed desorption (CO2-TPD) and the catalytic activity for hydrogen production by oxidative steam reforming of ethanol (OSRE). The results indicate that the thermal decomposition of the HT precursors generated mixed oxides composed of a periclase type solid solution and Co spinel like phases. The effect caused by the incorporation of 3wt% Ce or Pr and, 2.5wt% Ce and 2.5wt% Pr in the Co oxide was studied. The beneficial effect of these promoters was evidenced by the increase of the reducibility and the basicity of the catalyst. Even though the Co catalyst shows good catalytic behavior for OSRE, the introduction of Ce, Pr or both metals significantly improves the H2 yield, reduces the CO and carbon production, and increases the selectivity to CO2.

Fused Fe[sbnd]Co catalysts for hydrogen production by means of the ammonia decomposition reaction

Fused FeCo catalysts, with various cobalt contents, were obtained by melting of oxides of these metals and oxides of promoters at the temperature of 1600°C. The determination of the chemical composition was based on the ICP-OES method. It followed from the XRD phase analysis that cobalt had been built-in in the iron oxides lattice. Catalysts’ activities in the ammonia decomposition reaction, in temperatures within 475–600°C, for ammonia concentration at the reactor inlet between 0.5 and 100%vol, and under atmospheric pressure, were investigated. Almost full ammonia decomposition was reached at 600°C for ammonia mole fraction in the range from 0.1 to 0.25 at GHSV=24,000cm3g−1h−1. The rate of the ammonia decomposition depends on a nitriding potential. The maximal value of the ammonia decomposition rate was reached at lnP=−6.5 for FeCo(18.3) catalyst, and at lnP=−5.8 for the FeCo(4.8) catalyst. The catalyst with higher content of promoters showed higher activity in the ammonia decomposition reaction.

Preparation and characterization of porous Nb2O5 photocatalysts with CuO, NiO and Pt cocatalyst for hydrogen production by light-induced water splitting

In this study, porous Nb2O5 photocatalyst materials are prepared through thermal oxidation. According to X-ray photoelectron spectroscopy (XPS), at a temperature of 500 °C, an optimum porous Nb2O5 photocatalyst is obtained with an O/Nb ratio close to the theoretical value of 2.5. The X-ray powder diffractometer (XRD) result shows that at the main diffraction angles of 22.63° and 28.33°, crystalline diffraction signals of Nb2O5 appear with corresponding diffraction planes of (001) and (180). When CuO, NiO and Pt catalysts are added to Nb2O5 as the cocatalyst for comparison, the maximum hydrogen production efficiency for a CuO/Nb2O5 photocatalyst is achieved (1405 μmol h−1 g−1). However, when NiO and Pt are added as cocatalysts, the hydrogen production efficiencies are decreased to 800 μmol h−1 g−1 and 510 μmol h−1 g−1, respectively. Through the photoelectrochemical analysis, it finds that the CO signal peak with incomplete oxidation significantly increases as the reaction time increases, thus causing CO to adsorb on the catalyst surface (such as NiO or Pt) leading to catalyst poisoning. This results in reduced catalyst performance and hydrogen production rates.