H2 Production Activity Research Articles

Dual co-catalysts Ag/Ti3C2/TiO2 hierarchical flower-like microspheres with enhanced photocatalytic H2-production activity

Solar-powered semiconductor photocatalysis is considered a powerful strategy for addressing environmental pollution and energy crisis. Nevertheless, the separation and transfer abilities of photogenerated photocatalysts remain unsatisfactory. Herein, dual Ti3C2 nanosheets/Ag co-catalysts synergistically decorated hierarchical flower-like TiO2 microspheres for boosting photocatalytic H2 production were fabricated by electrostatic self-assembly and subsequent photoreduction procedures. The optimal Ag/Ti3C2/TiO2 composite demonstrated an excellent photocatalytic H2-production rate of 1024.72 μmol g−1 h−1 under simulated solar irradiation, achieving nearly 40, 2.3, and 1.8 folds with respect to that obtained on pristine TiO2, optimized Ti3C2/TiO2 composite, and Ag/TiO2 composite, respectively. The considerably improved photocatalytic H2-production activity is associated with the synergistic effect of the hierarchical flower-like structure of TiO2, excellent electrical conductivity of Ti3C2, and surface plasmon resonance effect of Ag, which enhances the light absorption capacity and promotes the separation and transfer of photogenerated carriers. This study provides insight into the design of high-efficiency photocatalysts with dual co-catalysts for solar H2 production.

C2H2 Semi-hydrogenation over S-modified PdM IMCs: Tuning catalytic performance by surface S Atom, and metal M type and ratio

The space region of metal active site and metal types and ratios plays a crucial role in tuning product selectivity based on the molecule size of target product and by-product. This work employs DFT calculations and microkinetic modeling to perform C2H2 semi-hydrogenation over a series of S-modified PdM IMCs with different M types (Cu, Ag and Au) and ratios (1: 1, 3: 1 and 1: 3). The results show that the catalytic performance of C2H2 semi-hydrogenation strongly depends on the space region of metal active site and the electronic properties induced by S atoms and the M type and ratio. Only S/Pd1Ag1 and S/Pd1Au1 are screened out to show higher H2 dissociation activity, C2H4(g) selectivity and production activity, moreover, green oil can be well inhibited. Compared to Pd1Ag1 and Pd1Au1, the d-band center over S/Pd1Ag1 and S/Pd1Au1 farther away from the Fermi level increased C2H4(g) selectivity and production activity. More importantly, the greatly decreased space region of active site over S/Pd1Ag1 and S/Pd1Au1 caused by S atoms inhibited green oil production. This finding in this work provides the valuable theoretically structural information for designing and screening PdM catalysts by S modification in alkyne semi-hydrogenation.

Sun-light driven hydrogen generation by Pd/Rb2O cocatalysts: Escalate the utility of rutile TiO2 for photocatalytic water splitting

Rising consumption and cost of fossil fuels invite the researchers to discover the renewable energy sources. Herein, a novel approach to enhance the photocatalytic performances of rutile-TiO2 has been revealed. To boost the hydrogen generation reactions, Pd/Rb2O cocatalysts have been deposited over TiO2 via chemical reduction. The morphology and optical characteristics of catalysts were demonstrated by XRD, Raman, UV-Vis/DRS, SEM and TEM analysis. Surface properties, particle sizes, and chemical composition were examined via AFM and XPS techniques. The H2 production activities were monitored by GC-TCD (Shimadzu-2010/Japan). Comparatively, Pd1.8/RbO0.2@TiO2 was found most active catalysts that can deliver hydrogen 22.74 mmolg−1h−1. Higher H2 generation activities were attributed to the presence of Pd and Rb2O cocatalysts. Rb2O promoted electrons from TiO2 to Pd active sites by elevation in fermi energy levels to attain the equilibrium during photoreactions. The mechanistic approach for higher electron transportation and better charge separation has been demonstrated and discussed over here. On the basis of results, it can be concluded that the work reported here in is reliable for sustainable energy applications.

Scale-up of Co–Ni cathodes produced from spent Ni–Cd batteries for hydrogen production in an oxy-hydrogen gas cell

Ni(II) and Co(II) ions are recovered from real leached positive electrodes of spent Ni–Cd batteries, and subsequently co-deposited on A36 carbon steel using direct and pulsed currents. The idea is to evaluate how variations in texture and composition of recycled coatings affect their catalytic activities for H2 production at microelectrolysis levels, and using an oxy-hydrogen gas (HHO) cell. The most active Ni–Co electrocatalyst in 0.1 M HClO4 or KOH towards hydrogen evolution reaction (HER) is formed using pulsed current at −50 mA cm−2, according to electrochemical measurements and gas chromatography (GC). This plating mode favors grain size refinement and pH rise during metal deposition, to prevent the formation of oxides/hydroxides with low catalytic activity arising in direct current. In the HHO cell, the most active Co–Ni coating produces 21.63 mL min−1 H2, while A36 carbon and 304 stainless steels present lower generations of 7.30 and 7.55 mL min−1, respectively.

Transient Metal Centers at the Covalent Heterointerface Favor Photocatalytic Hydrogen Evolution.

Semiconductor heterostructures effectively promote the transfer and separation of interfacial photoinduced charges for the photocatalytic process. Herein, we constructed a direct Z-scheme SnSe2/CdS heterojunction photocatalyst. N-type SnSe2 semiconductors are suitable candidate materials for oxidation half-reactions in Z-scheme heterojunctions. The intimate atomic-level interfacial contact through Cd-Se bonds provides a better interfacial charge transport channel for the photoinduced charges. Moreover, the transient Sn4+/Sn0 centers caused by the photoredox process boost the interfacial charge transport/separation at the interface. Besides, the presence of S vacancies acting as electron enrichment centers further enhances the redox ability for hydrogen production. Therefore, the SnSe2/CdS heterostructure showed a superior visible-light photocatalytic H2-production activity of 13.6 mmol·g-1·h-1 using ascorbic acid as a sacrificial agent, which is 9.7 times higher than that of pristine CdS. The apparent quantum yield reaches 10.5% at λ = 420 nm. This work provides a useful way to improve charge transfer in the Z-scheme heterojunction photocatalyst for hydrogen production.

Carbon fiber cloth@BiOBr/CuO as immobilized membrane-shaped photocatalysts with enhanced photocatalytic H2 production activity

BackgroundHydrogen plays an important role in developing an environment-friendly, low-emission, and sustainable energy system. Carbon fiber (CF) cloth is a useful porous and conductive substrate. Loading appropriate semiconductor nanomaterials on CF cloth is an effective method to fabricate flexible and high-performance photocatalysts. MethodsCarbon fiber (CF) cloth@BiOBr/CuO were synthesized as immobilized membrane-shaped photocatalysts by the growth of BiOBr using successive ionic layer adsorption and reaction (SILAR), followed by calcination and forming the CuO cocatalyst. Significant findingsThe loading of optimized amounts of BiOBr (three immersion cycles in the SILAR process) and the CuO shell leads to enhanced H2 production activity. The CF cloth@BiOBr/CuO photocatalyst (S3BOB3C) is a flexible, membrane-shaped, and immobilized photocatalyst with high activity (1863 μmol h−1g−1), which is 4.4 times active when compared to the CF cloth@BiOBr photocatalyst (S1BOB) (423 μmol h−1g−1). The p-n heterojunctions in BiOBr/CuO composites with type-II band alignment can improve photocatalytic H2 production performance.

Enhanced Photocatalytic H2-production Activity of CdS Nanoflower using Single Atom Pt and Graphene Quantum Dot as Dual Cocatalysts

Enhanced Photocatalytic H2-production Activity of CdS Nanoflower using Single Atom Pt and Graphene Quantum Dot as Dual Cocatalysts

In Operando Photoswitching of Cu Oxidation States in Cu-Based Plasmonic Heterogeneous Photocatalysis for Efficient H2 Evolution.

Metal nanoparticles (NP) supported on TiO2 are known to be efficient photocatalysts for solar-to-chemical energy conversion. While TiO2 decorated with copper NPs has the potential to become an attractive system, the poor oxidative stability of Cu severely limits its applicability. In this work, we demonstrate that, when Cu NPs supported on TiO2 nanobelts (NBs) are engaged in the photocatalytic generation of H2 from water under light illumination, Cu is not only oxidized in CuO but also dissolved under the form of Cu+/Cu2+ ions, leading to a continuous reconstruction of nanoparticles via Ostwald ripening. By nanoencapsulating the CuOx (Cu/CuO/Cu2O) NPs by a few layers of carbon supported on TiO2 (TC@C), Ostwald ripening can be suppressed. Simultaneously, the resulting CuOx@C NPs are photoreduced under light illumination to generate Cu@C NPs. This photoswitching strategy allows the preparation of a Cu plasmonic photocatalyst with enhanced activity for H2 production. Remarkably, the photocatalyst is even active when illuminated with visible light, indicating a clear plasmonic enhancement of photocatalytic activity from the surface plasmonic resonance (SPR) effect of Cu NPs. Three-dimensional electromagnetic wave-frequency domain (3D-EWFD) simulations were conducted to confirm the SPR enhancement. This advance bodes for the development of scalable multifunctional Cu-based plasmonic photocatalysts for solar energy transfer.

Superexchange-induced Pt-O-Ti3+ site on single photocatalyst for efficient H2 production with organics degradation in wastewater

Efficient photocatalytic H2 production from wastewater instead of pure water is a dual solution to the environmental and energy crisis, but due to the rapid recombination of photoinduced charge in the photocatalyst and inevitable electron depletion caused by organic pollutants, a significant challenge of dual-functional photocatalysis (simultaneous oxidative and reductive reactions) in single catalyst is designing spatial separation path for photogenerated charges at atomic level. Here, we designed a Pt-doped BaTiO3 single catalyst with oxygen vacancies (BTPOv) that features Pt-O-Ti3+ short charge separation site, which enables excellent H2 production performance (1519 μmol·g-1·h-1) while oxidizing moxifloxacin (k = 0.048 min-1), almost 43 and 98 times than that of pristine BaTiO3 (35 μmol·g-1·h-1 and k = 0.00049 min-1). The efficient charge separation path is demonstrated that the oxygen vacancies extract photoinduced charge from photocatalyst to catalytic surface, and the adjacent Ti3+ defects allow rapid migration of electrons to Pt atoms through the superexchange effect for H* adsorption and reduction, while the holes will be confined in Ti3+ defects for oxidation of moxifloxacin. Impressively, the BTPOv shows an exceptional atomic economy and potential for practical applications, a best H2 production TOF (370.4 h-1) among the recent reported dual-functional photocatalysts and exhibiting excellent H2 production activity in multiple types of wastewaters.

Computation-based regulation of excitonic effects in donor-acceptor covalent organic frameworks for enhanced photocatalysis

The strong excitonic effects widely exist in polymer-semiconductors and the large exciton binding energy (Eb) seriously limits their photocatalysis. Herein, density functional theory (DFT) calculations are conducted to assess band alignment and charge transfer feature of potential donor-acceptor (D-A) covalent organic frameworks (COFs), using 1,3,5-tris(4-aminophenyl)triazine (TAPT) or 1,3,5-tris(4-aminophenyl)benzene (TAPB) as acceptors and tereph-thaldehydes functionalized diverse groups as donors. Given the discernable D-A interaction strengths in the D-A pairs, their Eb can be systematically regulated with minimum Eb in TAPT-OMe. Guided by these results, the corresponding D-A COFs are synthesized, where TAPT-OMe-COF possesses the best activity in photocatalytic H2 production and the activity trend of other COFs is associated with that of calculated Eb for the D-A pairs. In addition, further alkyne cycloaddition for the imine linkage in the COFs greatly improves the stability and the resulting TAPT-OMe-alkyne-COF with a substantially smaller Eb exhibits ~20 times higher activity than the parent COF.

Hydrogen Production from Hydrophobic Ruthenium Dye-Sensitized TiO2 Photocatalyst Assisted by Vesicle Formation.

Dye-sensitized H2 evolution photocatalysts have attracted considerable attention as promising systems for the photochemical generation of H2 from water. In this study, to mimic the reaction field of natural photosynthesis artificially, we synthesized a hydrophobic Ru(II) dye-sensitized Pt-TiO2 nanoparticle photocatalyst, RuC9@Pt-TiO2 (RuC9 = [Ru(dC9bpy)2(H4dmpbpy)]2+; dC9bpy = 4,4'-dinonyl-2,2'-bipyridine, H4dmpbpy = 4,4'-dimethyl phosphonic acid-2,2'-bipyridine), and integrated it into 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer vesicle membranes. The photocatalytic H2 production activity in 0.5 M l-ascorbic acid aqueous solution enhanced by more than three times in the presence of DPPC vesicles (apparent quantum yield = 2.11%), whereas such a significant enhancement was hardly observed when the vesicle formation was omitted. These results indicate that the highly dispersed state of the hydrophobic RuC9@Pt-TiO2 nanoparticles in the DPPC bilayer vesicles is a key factor in achieving enhanced photocatalytic H2 production activity in aqueous solution.

Construction of multi-interfacial charge transfer paths in the NiS/CdS@CuS composite for efficient and broadband visible light photocatalytic H2 production

Broad-spectrum response and high charge separation are two important prerequisites and also challenges for a photocatalyst to achieve excellent activity. Herein, we developed a closely-contacted NiS/CdS@CuS hybrid photocatalyst to construct multi-interfacial charge transfer paths to address these two challenges. Different from previously reported, limited charge transfer for the CdS system, the synergy between photoinduced interfacial charge transfer (IFCT) at the intimate CdS/CuS interface and the superior H2 production cocatalyst (NiS) enables a multi-interfacial charge transfer, which greatly accelerates charge separation and achieves broadband H2 production. The optimal NiS/CdS@CuS composite exhibits the high H2 production activity of 25.02 mmol g−1 h−1 with an apparent quantum efficiency of 27.21% at 420 nm. This activity is even higher than that of the optimized Pt/CdS system. The creation of photoinduced IFCT allows the photocatalytic H2 production of CdS extended to 610 nm. Multiple comparison systems are constructed to understand the reaction mechanisms and highlight the importance of synergy between the three components. This work supplies a paradigm for fabricating efficient H2 production photocatalyst with both enhanced charge transfer dynamics and expanded light response range.

Exceptional Photocatalytic Performance of the LaFeO3/g-C3N4 Z-Scheme Heterojunction for Water Splitting and Organic Dyes Degradation

To simulate natural photosynthesis, scientists have developed an artificial Z-scheme system that splits water into hydrogen and oxygen using two different semiconductors. Researchers are striving to improve the performance of Z-scheme systems by improving light absorption, developing redox couples with high stability, and finding new cocatalysts. Here, we report the synthesis and utilization of LaFeO3/g-C3N4 as a Z-scheme system for water reduction to produce hydrogen and organic dye degradation under visible light irradiation. The as-fabricated photocatalyst revealed exceptional activity for H2 production (i.e., 351 µmol h−1g−1), which is 14.6 times higher compared to that of the single-component g-C3N4 (i.e., 24 µmol h−1g−1). In addition, the composite photocatalyst degraded 87% of Methylene Blue (MB) and 94% of Rhodamine B (RhB) in 2 h. Various experimental analyses confirmed that the exceptional performance of the LaFeO3/g-C3N4 Z-scheme catalyst is due to remarkably enhanced charge carrier separation and improved light absorption. The development of this highly effective Z-scheme heterostructure photocatalyst will pave the way for the sustainable development of newly designed Z-scheme scheme systems that will tackle energy and environmental crises.

In Situ Growth Facilitating the Piezo-Photocatalytic Effect of Zn1-xCdxS/ZnO Nanorods for Highly Efficient H2 Production.

Photocatalytic H2 production holds promise for alleviating energy and environmental issues. The separation of photoinduced charge carriers plays vital roles in enhancing the activity of photocatalytic H2 production. The piezoelectric effect has been proposed to be effective in facilitating the separation of charge carriers. However, the piezoelectric effect is usually restricted by the noncompact contact between the polarized materials and semiconductors. In this study, Zn1-xCdxS/ZnO nanorod arrays on stainless steel for piezo-photocatalytic H2 production are fabricated by an in situ growth method, achieving an electronic-level contact between Zn1-xCdxS and ZnO. The separation and migration of photogenerated charge carriers in Zn1-xCdxS are significantly improved by the piezoelectric effect induced by ZnO under mechanical vibration. Consequently, under solar and ultrasonic irradiation, the H2 production rate of Zn1-xCdxS/ZnO nanorod arrays achieves 20.96 μmol h-1 cm-2, which is 4 times higher than that under solar irradiation. Such a performance can be attributed to the synergies of the piezoelectric field of bent ZnO nanorods and the built-in electric field of the Zn1-xCdxS/ZnO heterostructure, which efficiently separate the photoinduced charge carriers. This study provides a new strategy to couple polarized materials and semiconductors for highly efficient piezo-photocatalytic H2 production.

Application of a Functionalized K1–xNixNbO3 Structure: Enhancing the Photocatalytic Activity of a CdS/K1–xNixNbO3 Composite

Herein we report a K1–xNixNbO3 composite undergoing a phase transition from orthorhombic to rhombohedral, resulting in a Ni particle and a short Nb–Oδ- on the surface caused by a structural distortion. The Ni particles are dispersed on the overall surface of the structure, and the short bonded Nb–Oδ- sticks out to the structure interstices on the surface. The properties of the structure and surface of K1–xNixNbO3 are defined by spectroscopic analysis of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman, nuclear magnetic resonance (1H NMR), and X-ray photoelectron spectroscopy (XPS). This unique surface property enables the formation of two hybrid composites that deposit CdS on either site of the Ni/Ni–H particle or short Nb–Oδ-, resulting in a different interface between CdS and K1–xNixNbO3. The one that deposits CdS on the Ni/Ni–H particles is denoted as SCdS/K1–xNixNbO3, and the other that deposits CdS on the short Nb–Oδ- is denoted as CdS/K0.9Ni0.1NbO3. SCdS/K1–xNixNbO3 exhibits a delayed kinetics for CdS photoinduced electrons compared to that of CdS/K1–xNixNbO3 as decayed fluorescence at ca. 311 ps, while indicating ca. 238 ps for CdS/K1–xNixNbO3. As a result, SCdS/K1–xNixNbO3 exhibits a superior photocatalytic activity for H2 production of ca. 3.1 mmol g–1 h–1 compared to CdS/K1–xNixNbO3 with ca. 2.7 mmol g–1 h–1.

Highly efficient twinned MnxCd1-xS homojunction photocatalyst modified by noble metal-free Ni12P5 for H2 evolution under visible light

A series of twin-phase MnxCd1-xS solid solutions with zinc blende (ZB) and wurtzite (WZ) structures were prepared by an alkaline hydrothermal method in this work. When using 0.35 M Na2SO3/0.25 M Na2S solution as a sacrificial agent under visible light (λ ≥ 420 nm), the H2 production activity of T-Mn0.5Cd0.5S is 33.4 mmol h−1 g−1, significantly higher than that of ZB-Mn0.5Cd0.5S (15.4 mmol h−1 g−1) or WZ-Mn0.5Cd0.5S (18.2 mmol h−1 g−1). The photocatalytic activity of T-Mn0.5Cd0.5S is further enhanced by introducing Ni12P5 as a cocatalyst, in which the H2 evolution rate of 0.2% Ni12P5/T-Mn0.5Cd0.5S can reach 96.5 mmol h−1 g−1, 2.89 and 1.77 times than that of pure T-Mn0.5Cd0.5S and 0.5% Pt/T-Mn0.5Cd0.5S (54.6 mmol h−1 g−1), respectively. The crystalline phase, microstructure, elemental composition, optical and optoelectronic properties of the samples were characterized by XRD, SEM, TEM, HRTEM, XPS, UV–vis, PL and electrochemical workstation. The results show that the formation of a homojunction with interlaced energy band inhibits carrier recombination in the bulk phase of T-Mn0.5Cd0.5S. In addition, Ni12P5 can substitute for the noble metal as a cocatalyst to reduce the overpotential and improve the separation rate of electrons and holes to enhance H2 evolution. This work provides reference for building homojunction photocatalysts and loading inexpensive transition metal phosphides instead of noble metals.

Boosting the photocatalytic activity for H2 production of Bi2O2Se/CdS heterojunction

To overcome the drawback of CdS applied in photocatalytic process, Bi2O2Se with narrow band gap and unique optical and electrochemical properties was prepared and used for fabricating Bi2O2Se/CdS heterojunctions by a facile in-situ self-assembly hydrothermal method. The synthesized Bi2O2Se/CdS heterojunctions exhibited significant stronger visible-light adsorption compared with that of CdS. Bi2O2Se/CdS with a mass ratio of 2% showed the best H2 production performance (λ ≥ 420 nm), the H2 revolution rate was 424 μmol g−1 h−1 which was 24 times higher than that of CdS. This work provided fresh insights into designing heterojunction interface based on CdS to synthesize novel photocatalysts with high efficiency.

Bimetallic Sulfide MCdS Modified with TiO2 Nanoneedle Cocatalyst for Enhancing Photocatalytic H2‐evolution

AbstractMetal ion doping and composite materials preparation are the effective means to improve the activity of CdS photocatalysts. In this work, TiO2/MCdS (M=Zn, Ni) were synthetized by two steps hydrothermal method. The morphology, elemental composition and optical properties of TiO2/MCdS photocatalysts were characterized via XRD, SEM, TEM, XPS and UV‐Vis. Interestingly, TiO2 nanoneedles were able to grow inside ZnCdS particles, which caused a strong interaction between TiO2 and ZnCdS was formed. However, TiO2 nanoneedle and NiCdS were not closely combined. As a result, the TiO2/ZnCdS (581.8 μmol ⋅ g−1 ⋅ h−1) possessed the optimal H2 production rate and showed a 1.5‐fold improvement compared to TiO2/NiCdS. This improvement of photocatalytic activity was mainly attributed to the effective separation of photogenerated electron hole pairs and the synergistic catalysis of water decomposition into hydrogen by TiO2 nanneedle‐assisted catalyst. Thus, metal ion doping and TiO2 nanoneedle as co‐catalyst could improve the photocatalytic H2 production activity of CdS more effectively.

The enhanced photocatalytic activity of Zn0.5Cd0.5S with Co3S4 cocatalyst as electron trapper

The conversion of solar energy into H2 energy by photocatalytic biomass decomposition has become a research hotspot in recent years. In this work, Co3S4/Zn0.5Cd0.5S (CS/ZCS) composites with a series of mass ratio were prepared by loading ZCS nanoparticles on the surface of Co3S4 polyhedron, and characterized by many advanced tests. Moreover, their photocatalytic activity of H2 production were explored by biomass decomposition, like lactic acid (LA) and benzyl alcohol (PhCH2OH). When the amount of Co3S4 cocatalyst is 4 wt%, the H2 production of the composite photocatalyst reaches the highest, which is 17.86 mmol·g−1·h−1 for LA and 20.07 mmol·g−1·h−1 for PhCH2OH, much higher than ZCS nanoparticles. Co3S4 cocatalyst as the electrons (e−) trapper of ZCS, enhances the absorption of visible light and improves the migration efficiency of the photogenerated charge carriers (PCCs), thus greatly increasing the photocatalytic H2 production. This work may play an important role in improving H2 production from biomass decomposition for metal sulfide.

Highly selective PtCo bimetallic nanoparticles on silica for continuous production of hydrogen from aqueous phase reforming of xylose

Hydrogen (H2) is a promising energy vector for mitigating greenhouse gas emissions. Lignocellulosic biomass waste has been introduced as one of the abundant and carbon-neutral H2 sources. Among those, xylose with its short carbon chain has emerged attractive, where H2 can be catalytically released in an aqueous reactor. In this study, a composite catalyst system consisting of silica (SiO2)-supported platinum (Pt)-cobalt (Co) bimetallic nanoparticles was developed for aqueous phase reforming of xylose conducted at 225 °C and 29.3 bar. The PtCo/SiO2 catalyst showed a significantly higher H2 production rate and selectivity than that of Pt/SiO2, whereas Co/SiO2 shows no activity in H2 production. The highest selectivity for useful liquid byproducts was obtained with PtCo/SiO2. Moreover, CO2 emissions throughout the reaction were reduced compared to those of monometallic Pt/SiO2. The PtCo bimetallic nanocatalyst offers an inexpensive, sustainable, and durable solution with high chemical selectivity for scalable reforming of hard-to-ferment pentose sugars.