Morphological families of self-assembled porphyrin structures and their photosensitization of hydrogen generation

We have developed a new model to investigate the complete lattice dynamics of cesium chloride at 78 K and at room temperature (298 K).The new model, van der Waals three body force shell model (VTSM) incorporates the effect of van der Waals interactions and three-body interactions in the frame work of rigid shell model where short range interactions are effective up to the second neighbour.A good agreement has been obtained between theory and experiment for dependant properties also.

Heterogeneous dinuclear rhodium(II) coordination polymer, [Rh2(p-BDC)2]n (p-BDC = 1,4-benzenedicarboxylate), which formed self-assembly infinite two-dimentional slit sheets structure was performed as hydrogen production catalyst for photochemical reduction of water under visible light irradiation in the presence of a multicomponent system containing Ru(bpy)32+, MV2+, and EDTA–2Na.

Wide-bandgap gallium nitride (GaN) quantum dot (QD) structure is attractive because it is a zero-dimensional (0-D) confinement structure and has many unique physical characteristics. We have successfully grown self-assembled InGaN QDs structure by metal organic chemical vapor deposition. A high quality GaN/sapphire template with a flat surface and the suitable growth condition including low growth temperature and low V/III ratio were used to grow InGaN QDs structure. The density of InGaN QDs is about 4.5 × 1010 cm-2 with an average lateral size of 11.5 nm and an average height of 1.6 nm. The effect of the interruption growth for InGaN QDs structure was systematic studied with the growth temperature of 660°C. The surface morphology and optical property was measured by atomic forced microscopy and various temperature PL, respectively. The results indicated that as increasing interruption time from 30s to 120s, QDs area occupied on the surface above the wetting layer increases from 5.2% to 7.2%, and the In composition decreases from 25% to 21%. The results were discussed by considering the influences of ad-atom desorption and diffusion effect between wetting layer and InGaN QDs structure. Our results suggest that the interruption growth during an optimum time can modify the size of InGaN QDs and extend the emission wavelength to short wavelength, and at the same time improve the QD optical quality. Using this technique was feasible for formation of multi layer InGaN QDs structures and applicable for the fabrication of GaN-based light emitting devices.

We describe the growth of InP quantum structures on In0.5Al0.5P lattice-matched matrices deposited on (001) GaAs substrates using metalorganic chemical vapor deposition. We find that the deposited InP initially forms quantum wires, about 50 nm in width and a few nanometers in height. Further deposition of InP leads to the formation of quantum dots (QDs) on top of these wires. By varying the matrix growth conditions, the morphology of the InP quantum structures can be tuned. We demonstrate that the density of the wires and the QDs can be tuned by controlling the diffusion kinetics, i.e., changing the growth rate or growth temperature, during the growth of the In0.5Al0.5P matrix. Linear chains of self-assembled InP QDs can be achieved using optimized matrix layers.

Hydrogen storage and production via electrochemistry using advanced amorphous metal catalysts with enhanced performance, cost, and durability may offer dynamic and intermittent power generation opportunities. As a new sub-class of materials, Pd-based metallic-glasses (MGs) have drawn intense attention because of their grain-free, randomly packed atomic structure with intrinsic chemical heterogeneity, bestowing unique physical, structural and chemical properties for energy applications. The first section of this review gives a general introduction to crystalline Pd and Pd-based MGs, including the fabrication techniques of MGs and their hydrogen applications. The second section is devoted to hydrogen sorption of Pd-based MGs examined under ribbons, nanowires/microrods, and thin-films subsections. Hydrogen evolution via Pd-based MGs is analyzed in the third section under the bulk rod, ribbons and thin-films subsections. The fourth section consists of hydrogenation kinetics and sensing, pseudocapacitance, and electron transfer kinetics subsections. The final section provides a broad summary of Pd-based metallic glasses and future prospects. Altogether, this review provides a thorough and inspirational overview of hydrogen sorption and evolution of Pd-based MGs targeted for future large-scale hydrogen energy storage and production systems.

Hydrogen (H2) evolution from ‘Grasslands Huia’ white clover (Trifolium repens L.) nodulated by Rhizobium trifolu TA1, was suppressed by 6% acetylene-inair during acetylene reduction (AR) assays of nitrogen (N) fixation. Field measurements showed significant H2 evolution and reduced nodule relative efficiency over summer in a laxly mown pasture, but virtually no H2 was evolved from a closely grazed pasture. Plants transferred in winter from outdoors to a controlled cabinet with good growth conditions, showed increased AR rates and a decrease in nodule relative efficiency from 1 to 0.52 in 5 weeks. Defoliation of plants in a growth cabinet greatly reduced H2 evolution, confirming that conditions of growth have large effects on H2 evolution in white clover. No diurnal patterns of H2 evolution or AR were observed in plants growing outdoors. The significance of H2 evolution to AR assays of N fixation by white clover is discussed.

Polymeric melon shows real promise to be a next generation photocatalyst material for solar hydrogen production. Because it is earth abundant, and highly stable in photoredox reactions. However, a long-standing problem with polymeric melon is that it is inactive for photocatalytic hydrogen evolution without a metal cocatalyst, such as Pt. Sluggish charge transfer kinetics and a high activation energy for proton reduction makes pristine melon overly dependent on a high loading of precious Pt-cocatalyst for hydrogen evolution. While Pt-assisted hydrogen evolution is not considered economic for scale-up, a modulation of intrinsic photophysical and physicochemical properties of melon is therefore crucial to overcome the Pt dependency. However, to our knowledge, no systematic study has been reported to date to make melon independent of Pt for solar hydrogen evolution. Here we show that the limiting factors of Pt-dependent hydrogen production can be overcome by amorphization. The amorphization lowers the band gap, shifts the proton reduction potential close to the origin, and enhances the light harvesting and charge transport. Therefore, it results in a Pt-free hydrogen evolution under visible light irradiation. We here also present a mechanistic understanding of the origin of this cocatalyst-free hydrogen evolution.

Many state-of-the-art photocatalyst systems suffer from high charge recombination rates that limit the number of charge carriers available for photocatalytic reactions on the surface. Additionally, the overpotential for the desired conversion reactions is often relatively high, likewise having an impeding effect on the activity. To overcome these limitations, the catalyst surface can be decorated with a cocatalyst that improves charge separation and lowers the overpotential. Noble metals have been especially promising in this regard.[1] However, the use of noble metals significantly increases the material costs and requires rare resources, thus compromising their sustainability. Molecular cocatalysts can be used alternatively, but suffer from stability issues, especially in aqueous media.[2] Recently, earth-abundant cocatalyst systems have emerged as alternative materials to improve photocatalytic hydrogen or oxygen generation.[3] Among the elements used, iron is one of the most abundant elements in the earth crust, and non-toxic. The use of iron-based cocatalysts can therefore significantly decrease photocatalyst production costs and minimize the creation of hazardous waste. Furthermore, iron is a core constituent of many active centers in enzymes, such as hydrogenase, nitrogenase or CO dehydrogenase, that are active in natural reduction and oxidation reactions.[4] This implies, that the development of efficient iron-based cocatalysts should generally be achievable. Interestingly, iron-based materials have only rarely been used as cocatalysts in photocatalysis. However, very prominent examples for photoelectrochemistry are FeOOH or Fe-based layered double hydroxides (LDH).[5] [6] On the other hand, ternary iron oxides and sulphides are promising electrocatalysts for water splitting and CO2 reduction, exhibiting low overpotentials for the respective reaction.[7] [8] E.g. we recently showed the first microwave-synthesis of phase-pure violarite Ni2FeS4 in only 30 minutes, and its application for electrocatalytic CO2 reduction and hydrogen generation.[8] The observed activity underlines the potential of these materials for the application in photocatalysis as well. Additionally, some of the known iron-based chalcogenides possess near metallic conductivity that should facilitate charge transfer. However, apart from the reduction of the overpotential, an efficient charge transfer from photocatalyst to cocatalyst is required, which necessitates a suitable band alignment, something, that is frequently overlooked in literature.In this contribution, novel ternary iron-based chalcogenides will be presented as efficient cocatalysts on TiO2 and C3N4, leading to a significant activity increase in hydrogen evolution, oxygen evolution and nitrogen reduction for both absorbers, even upon addition of relatively low amounts of 1 wt.-%. The influence of cocatalyst loading will be presented, and the activity will be compared to noble metal cocatalysts such as platinum. Additionally, electronic interactions between absorber and cocatalyst have been explored.[1] J. Yang, D. Wang, H. Han, C. Li, Acc. Chem. Res. 2013, 46, 1900–1909.[2] X. T. Xu, L. Pan, X. Zhang, L. Wang, J. J. Zou, Adv. Sci. 2019, 6, DOI 10.1002/advs.201801505.[3] D. Li, J. Shi, C. Li, Small 2018, 14, 1–22.[4] D. C. Rees, Annu. Rev. Biochem. 2002, 71, 221–246.[5] F. A. L. Laskowski, M. R. Nellist, J. Qiu, S. W. Boettcher, J. Am. Chem. Soc. 2019, 141, 1394–1405.[6] L. Wang, F. Dionigi, N. T. Nguyen, R. Kirchgeorg, M. Gliech, S. Grigorescu, P. Strasser, P. Schmuki, Chem. Mater. 2015, 27, 2360–2366.[7] C. Simon, J. Timm, D. Tetzlaff, J. Jungmann, U. P. Apfel, R. Marschall, ChemElectroChem 2021, 8, 227–239.[8] C. Simon, J. Zander, T. Kottakkat, M. Weiss, J. Timm, C. Roth, R. Marschall, ACS Appl. Energy Mater. 2021, acsaem.1c01341.

Sunlight-driven water splitting is studied actively for production of renewable solar hydrogen as a storable and transportable energy carrier. Both the efficiency and scalability of water- splitting systems are essential factors for practical application of renewable solar hydrogen because of the low areal density of solar energy [1]. It is desirable to develop particulate photocatalysts and their reaction systems that efficiently split water, because such systems can be spread over wide areas by inexpensive processes potentially. The author’s group has studied various oxide and oxynitride semiconductors as photocatalysts for water splitting. In my talk, recent progress in photocatalytic materials and reactors will be presented with focus on perovskite-type materials.SrTiO3 loaded with proper cocatalysts has been known to be active in overall water splitting under ultraviolet light irradiation since 1980s. Recently, the apparent quantum yield (AQY) of this photocatalyst in overall water splitting has been improved drastically [2]. The author's group has found that doping Al3+ into the titanium site of SrTiO3 boosts the water splitting activity by two orders of magnitude [3]. By refining the preparation conditions of the Al-doped SrTiO3 (SrTiO3:Al) photocatalyst and the loading conditions of cocatalysts working as hydrogen and oxygen evolution sites, the AQY of overall water splitting has reached more than 90% at 365 nm [2], equivalent to an internal quantum efficiency of almost unity. This quantum efficiency is the highest yet reported and indicate that a particulate photocatalyst can drive the greatly endergonic overall water splitting reaction at a quantum efficiency comparable to values obtained from photon-to-chemical or photon-to-current conversion in photosynthesis or photovoltaic systems, respectively.Photocatalyst sheets based on SrTiO3:Al contained in a panel-type reactor split water into hydrogen and oxygen and release gas bubbles at a rate corresponding to a solar-to-hydrogen energy conversion efficiency of 10% under intense ultrviolet illumination even when the water depth is merely 1 mm [4]. Moreover, the photocatalyst can maintain 80% of its initial activity during 1300 h of constant simulated sunlight irradiation at ambient pressure with appropriate surface modifications [5]. A prototype 1-m2-sized panel reactor containing SrTiO3:Al photocatalyst sheets splits water under natural sunlight irradiation without a significant loss of the intrinsic activity of the photocatalyst sheets. A solar hydrogen production system with a greater size (100 m2) was recently built, and its performance and system characteristics are under investigation.SrTiO3:Al harvests only the ultraviolet light of the sunlight. It is essential to develop photocatalysts active under visible light irradiation. BaTaO2N is a visible light that can evolve hydrogen and oxygen from aqueous solutions containing sacrificial electron donors and acceptors, respectively. Recently, the AQYs of BaTaO2N in these sacrificial reactions have been improved significantly. Highly-crystalline BaTaO2N can be synthesized by directly nitriding a mixture of BaCO3 in the presence of RbCl flux [6]. The resultant BaTaO2N shows decent hydrogen evolution activity when a platinum cocatalyst is loaded by impregnation. By optimizing the cocatalyst loading conditions, the electron transfer from the BaTaO2N photocatalyst to the platinum cocatalyst, and thus the hydrogen evolution activity, was enhanced. The AQY of the resultant Pt-loaded BaTaO2N reached 6.8% at 420 nm in the sacrificial hydrogen evolution reaction. This is exceptionally high among nitride-type photocatalysts with visible light absorption of up to 650 nm.In conventional synthesis, BaTaO2N is nitrided from a mixture of BaCO3, Ta2O5, Ba- and Ta-containing complex oxides, often in the presence of flux. However, these starting materials have different crystal structures from the product BaTaO2N, and so the crystal structures have to be change during the nitridation. This is thought to induce defects in the product material. Therefore, a perovskite-type oxide with a Ba/Ta molar ratio of unity was designed, namely a complex oxide nominally denoted as Na1/4Ba3/4Zn1/4Ta3/4O3 [7]. This oxide can be nitrided into BaTaO2N because Na and Zn components are volatile at high temperature. The resultant BaTaO2N exhibited an AQY of 11.9% at 420 nm in the sacrificial oxygen evolution reaction after loading of a cobalt oxide cocatalyst. Hisatomi et al. Catal. 2019, 2, 387.Takata et al., Nature 2020, 581, 411.Ham et al., Mater. Chem. A 2016, 4, 3027.Goto et al., Joule 2018, 2, 509.Lyu et al. Sci. 2019, 10, 3196.Luo et al., Growth Des. 2020, 20, 255.Jadhav et al. J. Mater. Chem. A. 2020, 8, 1127.

Highly efficient visible-light photocatalytic H2 evolution over 2D–2D CdS/Cu7S4 layered heterojunctions

Developing robust nonprecious metal‐based electrocatalysts toward hydrogen evolution reaction is crucial for large‐scale hydrogen production via electrochemical water splitting. Herein, surface high‐entropy NiFeCoCuTi alloy on column‐nanostructured nanoporous Ni skeleton is reported as multisite electrocatalyst for highly efficient hydrogen evolution in nonacidic environments by making use of surface heterogeneous atoms with distinct hydrogen and hydroxyl adsorption behaviors to accelerate water dissociation and mediate adsorption of hydrogen intermediates for combination into molecules. Associated with the column‐nanostructured nanoporous Ni skeleton that facilitates electron transfer/mass transportation and enables highly accessible and abundant electroactive sites, self‐supported monolithic nanoporous high‐entropy NiFeCoCuTi alloy electrode exhibits superior nonacidic hydrogen evolution reaction (HER) electrocatalysis, with low onset overpotentials and Tafel slopes. It only takes overpotential of as low as ≈209 mV to deliver ultrahigh current density of 2 A cm−2, along with exceptional stability for more than 240 h, in 1 m KOH electrolyte. These outstanding properties make nanoporous NiFeCoCuTi high‐entropy alloy (HEA) electrode attractive candidate as cathode material in the water electrolysis for large‐scale hydrogen production and suggest HEAs as ideal platform to develop multisite electrocatalysts.

Hollow tubular Co9S8 grown on In2O3 to form S-scheme heterojunction for efficient and stable hydrogen evolution

Photocatalytic hydrogen evolution is a promising method to convert solar energy. Here, the heterojunction structure of g‐C3N4/CdS was modified by NiCoP prepared by one‐step method for the first time, and the photocatalyst NiCoP‐g‐C3N4/CdS was successfully designed and prepared, which can effectively separate and transfer photogenerated electrons and efficient hydrogen evolution under visible light. Moreover, NiCoP‐g‐C3N4/CdS photocatalyst has abundant surface‐active sites, and its photocatalytic hydrogen evolution performance has been greatly improved. When NiCoP content was 5 % in NiCoP‐g‐C3N4/CdS, the catalytic activity was the highest, and the hydrogen production rate reached an astonishing 55.63 mmol h−1 g−1, which was 23.35 times that of CdS (2.38 mmol h−1 g−1) and 11.51 times that of g‐C3N4/CdS (4.84 mmol h−1 g−1). In addition, NiCoP‐g‐C3N4/CdS photocatalyst has excellent stability for hydrogen production. The materials were characterized and analyzed by XRD, SEM, TEM, XPS, UV‐Vis DRS, FTIR, UPS, N2 adsorption‐desorption process and electrochemical test etc. At the same time, the possible mechanism of NiCoP‐g‐C3N4/CdS photocatalytic hydrogen production reaction is proposed. This study provides a new idea for the rational design of heterojunction photocatalyst and transition metal phosphide cocatalyst.

Micro-patterned graphite electrodes: An analysis and optimization of process parameters on hydrogen evolution in water electrolysis

Present day energy demands require greener, cleaner, scalable and high-rate hydrogen production by employing abundant solar energy-driven catalysis. Amongst emerging low cost photocatalysts, graphitic carbon nitrides (gC 3 N 4 ) have emerged as exciting platforms for hydrogen production using sunlight due to their interesting semiconducting properties with the unique band structure. However, the fast electron-hole recombination in g-C 3 N 4 restricts their high performance in producing hydrogen which limits its wider applicability for large scale H 2 production. Synergistic hybridization of gC 3 N 4 with two-dimensional (2D) transition metal organo-phosphates can potentially ensure swift charge transfer, which however has never been realized. Keeping in mind the urgency, we herein report the first demonstration of the synthesis of gC 3 N 4 -2D cobalt di-tert-butyl phosphate bipyridine (gC 3 N 4 -CDTBP) hybrids for facile and enhanced H 2 production under visible light. Further analysis with the transmission electron microscopic imaging (HRTEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) reveal the inter-layer coupling and bond alignment, confirming the synergistic hybridization between the component layers. This novel hybrid nanosystem achieves a hydrogen evolution rate of 682.4 μmol h -1 g -1 , outperforming state-of-the-art g-C 3 N 4 –based photocatalysts such as CoPi/ g-C 3 N 4 (234 μmol h -1 g -1 ) and cobalt phosphate hydroxide/ g-C 3 N 4 (254 μmol h -1 g -1 ), demonstrating the strong synergistic effect of the 2D–2D CDTBP-g-C 3 N 4 interface. Suppression of exciton recombination in gCDTBP- gC 3 N 4 as compared to pristine gC 3 N 4, and consequent 25-fold enhancement in photoelectric current upon hybridization reveals the swift charge transfer. The findings of the present study highlight the importance of developing advanced hybrid nanocatalysts for scalable hydrogen production. With the push for green energy, scalable hydrogen production using solar-driven catalysis is crucial. Graphitic carbon nitride (gC 3 N 4 ) is a top contender, but fast carrier recombination limits its efficiency. We report the first ambient-condition synthesis of gC 3 N 4 -CDTBP hybrids which exhibited superior visible light photocatalytic activity, with the hydrogen production rate of ∼682.4 μmol/h.g and enhanced photocurrent, outperforming pristine gC 3 N 4 significantly.