Photochemical Hydrogen Production Research Articles

Hydrogen-Mediated Photoelectrocatalysis with Nickel-Modified Poly(Heptazine Imides)

Polymeric carbon nitrides (C3N4) are photochemically active organic semiconductors that can be produced in a wide range of structural types. Here, a poly-(heptazine imide) containing nickel single atoms (Ni-PHI) is employed for photochemical hydrogen production and is compared to the non-nickel-doped semiconductor. Film deposits are formed on a platinum disk electrode (to detect hydrogen) and a coating of the molecularly rigid polymer of intrinsic microporosity PIM-1 is applied to (i) mechanically stabilize the photo-catalyst film without impeding photocatalysis and (ii) assist in the interfacial hydrogen capture/oxygen suppression process. In the presence of hole quenchers such as methanol or ethanol, anodic photocurrents linked to hydrogen production/oxidation are observed. A comparison with an experiment on glassy carbon confirms the formation of interfacial hydrogen as a mediator. The effects of hole quencher concentration are evaluated. The system Pt/Ni-PHI/PIM-1 is employed in a single-compartment photo-fuel cell.Graphical

Exploring the potential of calcined nanolayered manganese oxides for water-oxidation reaction

Large-scale electrochemical and photochemical hydrogen production methods from water splitting are limited by the water-oxidation reaction (WOR). This study investigates the influence of calcination temperatures on the WOR efficiency of layered Mn oxides, which are known for their stability and high catalytic activity. The Mn oxides were synthesized via thermal decomposition of KMnO4 and characterized using various techniques including scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, thermal gravimetric analysis, and Raman spectroscopy. The results indicate that even after calcination at high temperatures (≥400 °C), layered Mn oxides remain effective catalysts for WOR. Notably, the calcined sample at 800 °C in cerium (IV) ammonium nitrate at concentrations of 0.30 M shows maximum turnover frequency and turnover number of 6.7 × 10−6/s and 8.6 × 10−3 mol (O2)/mol (Mn) (for 1300 s), respectively.

A multi-model assessment of the Global Warming Potential of hydrogen

With increasing global interest in molecular hydrogen to replace fossil fuels, more attention is being paid to potential leakages of hydrogen into the atmosphere and its environmental consequences. Hydrogen is not directly a greenhouse gas, but its chemical reactions change the abundances of the greenhouse gases methane, ozone, and stratospheric water vapor, as well as aerosols. Here, we use a model ensemble of five global atmospheric chemistry models to estimate the 100-year time-horizon Global Warming Potential (GWP100) of hydrogen. We estimate a hydrogen GWP100 of 11.6 ± 2.8 (one standard deviation). The uncertainty range covers soil uptake, photochemical production of hydrogen, the lifetimes of hydrogen and methane, and the hydroxyl radical feedback on methane and hydrogen. The hydrogen-induced changes are robust across the different models. It will be important to keep hydrogen leakages at a minimum to accomplish the benefits of switching to a hydrogen economy.

Deep learning for the encounter of inorganic nanomaterial for efficient photochemical hydrogen production

A strong photosynthetic multifaceted called photosystem I (PS I) successfully catches photons to produce a charge detached phase through a quantum yield. The low latent reductant that is created is dignified at a redox potential that is conducive to H2 development, and this charge detached phase is constant for around 100 ms. By using dithiol as a molecular wire to link Photo System I to the particles and transport electrons as of the incurable electron transport cofactor of Photo System I, towards the nanoparticle, PS I consumes been covalently connected to the surfaces of like as Pt and also Au nanoparticles. The Photosystem I or molecular wire or nanoparticle bio conjugates are capable of catalysing the reaction 2H+ + 2e H2 when illuminated. H2 development is not slowed down by the transference of electrons from PS I in the direction of the nanoparticle via the molecular wire. The speed of H2 evolution is increased fivefold when the system is supplied by means of more effective donor sideways electron-donating kinds. When evaluating hydrogen production based on predicted energy from the sun with observed values falling on unstable slopes, the root mean square error called as RMSE as well as coefficient of determination called R2 are utilised as performance metrics. The most effective model among those taken into consideration, the Deep Learning model performs well and is quite compatible with the observational data.

Photochemical production of molecular hydrogen in the presence of substituted acridine salts

The photocatalytic properties of new representatives of the family of metal-free catalysts, 10-hydro-9-phenylacridine, 10-methyl-9-phenylacridinium chloride, and 10-phenyl-9-phenylacridinium chloride, were studied with respect to the reaction of molecular hydrogen generation in the presence of acids of different strength (HClO4, CH3SO3H, and CF3COOH) and reducing agents ([Bu4N]Cl, [Bu4N]Br, and [Bu4N]I). It was found that the strength of acids (p K a) and the nature of the reducing agent ( E 0) significantly affect the efficiency, i.e. turnover frequency (TOF), of the process under study. The amount of formed molecular hydrogen reaches its maximum in the case of the combination HClO4 and [Bu4N]I, characterized by minimal p K a and E0 values, respectively. The influence of the nature of substituents at the nitrogen atom in 9-phenylacridine on the efficiency of the molecular hydrogen production was analyzed. It was shown that the limiting stage of the process is the protonation of the formed radical.

A Theoretical Study of Tris-(<i>o</i>-benzoquinonediimine)-First-Row Divalent Transition Metal Complexes

The ligand o-phenylenediamine (opda) and its oxidized form, o-benzoquinonediimine (bqdi), act as a fascinating candidate coordinating toward transition metal ions leading to the photochemical hydrogen production in absence of photosensitizers. Herein, we report the systematic study of the interaction between the oxidized form bqdi ligand, tris-(o-benzoquinonediimine) with divalent first-row transition metal series using DFT calculations. The lowest energy structures, bond length, binding energies, frontier molecular orbital analysis, natural bond orbitals, and global reactivity descriptor were calculated using B3LYP/6-311G(d,P) level of theory. The time dependent-DFT at the CAM-B3LYP/6-311+G(d,p) level of theory was applied to determine the electronic structures and the optical spectra. The theoretical binding trend of the divalent first-row transition metal series is decreasing as follows: Cu >Ti > V > Co > Ni > Fe > Cr > Zn >Mn. Among them, the binding potency of iron (II) by the bqdi ligand was not predominantly sturdy as compared to other first-row divalent transition metal ions. The origin of strong coordination with Fe(II) is attributed to its extra capability to induce covalent coordination of bqdi ligands. The complex exhibited two strong peaks at 370 nm and 452 nm, due to the HOMO-3 to LUMO+1 and HOMO-1 to LUMO transitions, respectively. Natural bond orbital analysis showed that the major interaction happens between the N lone pair electrons of the ligand with an anti-bonding orbital of metal ions, in which Ti showed the highest interaction energy than other metal ions. The present systemic DFT study of bqdi ligands with the first-row transition metals strongly encourages the future establishment of photochemical hydrogen production in absence of photosensitizers.

Solar-light-driven photocatalytic hydrogen evolution by push-pull thiophenoxy-substituted zinc phthalocyanines

Two zinc phthalocyanine derivatives (ZnPc 1 and 2) carrying bulky 2,6-diisopro-pylthiophenoxy peripheral substituents have been synthesized and their performances as photosensitizers in photochemical hydrogen production evaluated. To examine the influence of the spacer on the performance of ZnPc 1 and 2, the carboxyl group has been linked to the macrocycle ring either directly or via the phenyl ring, respectively. The photocatalytic activities of ZnPcs (ZnPc 1 and ZnPc 2) as sensitizers of TiO2 for hydrogen production were investigated in the presence of Pt. ZnPc 1 and ZnPc 2 sensitized TiO2 produced 0.687 mmolg[Formula: see text]h[Formula: see text] and 0.436 mmol g[Formula: see text]h[Formula: see text] hydrogens, which also reached 3.986 and 2.091 mmolg[Formula: see text] after 8h illumination, respectively, under visible light ([Formula: see text] 420 nm) irradiation. In addition, STH efficiencies of ZnPc 1/TiO2 and ZnPc 2/TiO2 were determined as 1.77% and 1.12%, respectively. ZnPc 1/TiO2 exhibited 1.9-fold more photocatalytic hydrogen amount than ZnPc 2/TiO2, and the hydrogen evolution performance of the photocatalyst in the presence of Pt enhanced to 3.021 mmol g[Formula: see text]h[Formula: see text] and 0.911mmol g[Formula: see text]h[Formula: see text] for ZnPc 1 and ZnPc 2, respectively.

Photochemical Production of Molecular Hydrogen in the Presence of Substituted Acridine Salts

Photochemical Production of Molecular Hydrogen in the Presence of Substituted Acridine Salts

Hydrogen production by the layer-by-layer assembled films of PAni-TiO2-AuNPs

The production of high-performance and low-cost nanomaterials enables scale-up within the production sector for green hydrogen. In this regard, polymer films, such as composite films that consist of polyaniline (PAni), titanium dioxide (TiO2), and gold (AuNP) nanoparticles assembled by a layer-by-layer (LbL) technique, have been applied for hydrogen production as efficient photocatalysts. These composite films have been shown to be suitable materials for photochemical and photoelectrochemical hydrogen production, wherein the film morphology and thickness control photocatalytic performance. In addition, reflectance diffuse spectroscopy (UV–vis) was used to establish the synthesis conditions by verifying the plasmon resonance surface of PAni (emeraldine salt - ES) and AuNPs. The presence of PAni-ES increases film crystallinity (XRD) and avoids electron-hole recombination, providing a high recombination time of 9.38 s (3.93 s and 4.2 s for lesser crystalline sample). Thus, the hydrogen photochemical production also increases up to 2 times due to fewer trap states. Furthermore, the composite films can be used as photoanodes in photoelectrochemical hydrogen production due to their current stability. The bands position were calculated through Mott-Schottky and showed increased overpotential for the hydrogen evolution reaction from −0.46 V for bare TiO2 to ∼1.9 V for the best thin film. These results have interesting implications for the synthesis of photocatalytic materials because they identify the crucial parameters necessary for obtaining high-performance and low-cost materials for hydrogen production.

Planet‐Wide Ozone Destruction in the Middle Atmosphere on Mars During Global Dust Storm

AbstractThe Nadir and Occultation for MArs Discovery (NOMAD)/UV‐visible (UVIS) spectrometer on the ExoMars Trace Gas Orbiter provided observations of ozone (O3) and water vapor in the global dust storm of 2018. Here we show in detail, using advanced data filtering and chemical modeling, how Martian O3 in the middle atmosphere was destroyed during the dust storm. In data taken exactly 1 year later when no dust storm occurred, the normal situation had been reestablished. The model simulates how water vapor is transported to high altitudes and latitudes in the storm, where it photolyzes to form odd hydrogen species that catalyze O3. O3 destruction is simulated at all latitudes and up to 100 km, except near the surface where it increases. The simulations also predict a strong increase in the photochemical production of atomic hydrogen in the middle atmosphere, consistent with the enhanced hydrogen escape observed in the upper atmosphere during global dust storms.

Hole utilization in solar hydrogen production.

In photochemical production of hydrogen from water, the hole-mediated oxidation reaction is the rate-determining step. A poor solar-to-hydrogen efficiency is usually related to a mismatch between the internal quantum efficiency of photon-induced hole generation and the apparent quantum yield of hydrogen. This waste of photogenerated holes is unwanted yet unavoidable. Although great progress has been made, we are still far away from the required level of dexterity to deal with the associated challenges of wasted holes and its consequential chemical effects that have placed one of the greatest bottlenecks in attaining high solar-to-hydrogen efficiency. A critical assessment of the hole and its related phenomena in solar hydrogen production would, therefore, pave the way moving forward. In this regard, we focus on the contextual and conceptual understanding of the dynamics and kinetics of photogenerated holes and its critical role in driving redox reactions, with the objective of guiding future research. The main reasons behind and consequences of unused holes are examined and different approaches to improve overall efficiency are outlined. We also highlight yet unsolved research questions related to holes in solar fuel production.

Photochemical hydrogen production based on the HCOOH/CO2 cycle promoted by a pentanuclear cobalt complex.

The first catalytic cycle for hydrogen production based on the photochemical two-electron reduction of carbon dioxide (CO2) and the dehydrogenation of formic acid at ambient temperature was demonstrated using a pentanuclear cobalt complex (Co5). A series of mechanistic studies were performed to elucidate the mechanism responsible for the promotion of the photocatalytic cycle by Co5.

One-Dimensional (1D) Nanostructured Materials for Energy Applications.

At present, the world is at the peak of production of traditional fossil fuels. Much of the resources that humanity has been consuming (oil, coal, and natural gas) are coming to an end. The human being faces a future that must necessarily go through a paradigm shift, which includes a progressive movement towards increasingly less polluting and energetically viable resources. In this sense, nanotechnology has a transcendental role in this change. For decades, new materials capable of being used in energy processes have been synthesized, which undoubtedly will be the cornerstone of the future development of the planet. In this review, we report on the current progress in the synthesis and use of one-dimensional (1D) nanostructured materials (specifically nanowires, nanofibers, nanotubes, and nanorods), with compositions based on oxides, nitrides, or metals, for applications related to energy. Due to its extraordinary surface–volume relationship, tunable thermal and transport properties, and its high surface area, these 1D nanostructures have become fundamental elements for the development of energy processes. The most relevant 1D nanomaterials, their different synthesis procedures, and useful methods for assembling 1D nanostructures in functional devices will be presented. Applications in relevant topics such as optoelectronic and photochemical devices, hydrogen production, or energy storage, among others, will be discussed. The present review concludes with a forecast on the directions towards which future research could be directed on this class of nanostructured materials.

Novel facet-engineered multi-doped TiO2 mesocrystals with unprecedented visible light photocatalytic hydrogen production

We report on the facile synthesis of anatase multi-doped TiO2 mesocrystals with highly energetic {001} facets and their outstanding photocatalytic activity. The structural and compositional properties were investigated via different techniques such as XRD, XPS, Raman photoluminescence, and electron paramagnetic resonance, which confirmed the fabrication of C, Co, and Ti3+-doped anatase single crystal-like mesocrystals. The Mott-Schottky analysis showed a drastic increase in the carrier density upon cobalt doping, resulting in a 6-fold increase in the photoelectrochemical performance compared to the undoped sample. Besides, the photocatalytic efficiency of the as-fabricated mesocrystals in the photochemical production of hydrogen was estimated under AM1.5 conditions without using any hole scavengers. The Co-doped C/Ti3+ TiO2 mesocrystals showed an unprecedented hydrogen production rate when compared to the other similar titanium-based mesocrystals. Finally, the unprecedented enhancement of Co-doped C/Ti3+ TiO2 mesocrystals in water splitting makes them promising candidates for various photocatalytic applications.

A facile strategy for fabricating C@Cu2O/CuO composite for efficient photochemical hydrogen production with high external quantum efficiency

Hydrogen production from photocatalytic water splitting by non-noble-metal photocatalysts is considered to be the most promising solution to the world energy crisis issues. Herein, a chrysanthemum-like crystalline C@Cu2O/CuO composite with remarkable photochemical water reduction activity has been successfully fabricated via conditioned calcinations of the Cu(II) based MOF. Under visible light irradiation, Cu2O/CuO/C-350 gives a remarkable H2 evolution rate of 26.7 mmol g−1h−1 with high external quantum efficiency of 52.4% at 425 nm. The unique morphology, significantly improved charge carrier separation and synergistic effects of the composite system should be responsible for the excellent photocatalytic activity. To get further evidence about the origin of the improved photoactivity of the Cu2O/CuO/C-350, a series of characterization has been carried out. These findings propose a new unexplored avenue for the fabrication of highly active and low cost photocatalyst for practical H2 generation via photochemical water reduction.

High-throughput measurement of the influence of pH on hydrogen production from BaTiO3/TiO2 core/shell photocatalysts

The rates of hydrogen production from four different BaTiO3/TiO2 core/shell photocatalysts and their components were measured as a function of pH using a parallelized and automated photochemical reactor (PAPCR) to determine the optimized structure and pH condition for photochemical hydrogen production. The amount of hydrogen produced by each reactor in a 96-reactor array was quantified by the color change of a hydrogen-sensitive material. For the core/shell photocatalysts annealed at 600 °C, the increase in hydrogen production rate with pH at pH 3–9 is ascribed to the adsorption of more negatively charged species that bend the bands upward, promoting hole transport to the surface and the oxidation half reaction. At intermediate pH, the core/shell catalyst annealed at 600 °C had the highest reactivity, indicating that the generation and transport of charge carriers were improved by the BaTiO3/TiO2 core/shell structure. The results demonstrate that PAPCR is an effective way to compare the performance of hydrogen-producing catalysts with different structures and in different operating conditions.

Recent advances in earth-abundant photocatalyst materials for solar H2 production

Harvesting solar energy attracts great attention due to its abundant, clean, and permanent characteristics. Thus, photocatalysts have emerged as promising candidates for converting the solar energy to practically useful hydrogen molecules. Tremendous efforts have been devoted in developments of efficient photocatalysts for water splitting, but most of photocatalysts utilize noble metals to improve photocatalytic performance. Progress in photocatalyst materials for the hydrogen production coupled with a better understanding of the basic catalytic mechanisms has enabled better selection of catalytic nanomaterials with improved performance. In this review, we analyze the current state of the art in photocatalyst materials for photochemical hydrogen production through water splitting using earth-abundant materials. We also explore two main factors involved in both material morphology and sacrificial agent to further improve the activity, efficiency and stability of photocatalysts.

The photocatalytic hydrogen formation and NO2− oxidation on the hetero-junction Ag/NiFe2O4 prepared by chemical route

The photoelectrochemical ability of Ag(5%)/NiFe2O4 for H2 evolution under visible light irradiation was studied. The hetero-junction prepared by sol gel method shows a much higher activity than the physical mixture (hetero-system: Ag + NiFe2O4). The electrons of NiFe2O4 activated by visible light are focalized toward Ag clusters, intimately contacted to the spinel. The bifunctional crystallite is generated by incorporation of ultrafine Ag crystallites, thereby avoiding high over-voltages. The spinel was characterized by thermal analysis, X-ray diffraction and scanning electron microscopy. The optical gap of NiFe2O4 (1.59 eV) is due to the crystal field splitting of d-d transition of Fe3+: 3d orbital in octahedral site. p-type conductivity of NiFe2O4 was demonstrated from the capacitance measurement in alkaline KOH solution (0.1 M). The conduction band (−0.87 V) is more cathodic than the H2 evolution and the hetero-junction was successfully used for the photochemical hydrogen production under visible light irradiation. The photo-activity is dependent on the nature of the hole scavenger (NO2−, Fe(CN)64− and I−). NO2− is a hazardous ion and gave the best activity, due to its optimal band bending of 0.5 V and is converted to nitrate. An evolution rate of {0.17 cm3 H2 (g catalyst)−1 mn−1} was obtained at pH ∼ 7 with an apparent quantum yield of 1.3%.

Charge transfer dynamics and catalytic performance of a covalently linked hybrid assembly comprising a functionalized cobalt tetraazamacrocyclic catalyst and CuInS2/ZnS quantum dots for photochemical hydrogen production

Covalently attaching the cobalt tetraazamacrocyclic complex to the surface of CuInS2/ZnS quantum dots enhanced the charge-separation efficiency and photocatalytic activity of the hybrid system.

A cobalt complex, a highly efficient catalyst for electro- and photochemical driven hydrogen generation in purely aqueous media

The reaction of 2,2-bipyridine (bpy), Co(NO3)2·6H2O and KCN produces a new cobalt complex, [(bpy)2Co(CN)2]·NO31. Under photoirradiation with blue light (λmax = 469 nm) in air, together with [Ru(bpy)3]Cl2 and ascorbic acid in a pH 5.0 aqueous solution, this cobalt complex possesses extremely high activity for photocatalytic hydrogen generation with a remarkable initial turnover rate of 1.56 × 105 mol H2/mol catalyst/h. This photocatalytic activity can be sustained for at least 18 h with a turnover number (TON) of 7.3 × 105 moles of H2 per mole of catalyst. This performance is significantly better than any molecular catalysts reported in the literature for photochemical hydrogen production. The result can be attributed to the fact that the reductive quenching to [Ru(bpy)3]Cl2 by ascorbic acid (kq = 1.55 × 1010 M−1 s−1) dominates over the oxidative quenching by 1 (kq = 1.027 × 1010 M−1 s−1). Additionally, 1 can electrocatalyze hydrogen generation from a neutral water with a turnover frequency (TOF) of 462 mol of hydrogen per mole of catalyst per hour at an overpotential of 638 mV. This finding affords a new method for water reduction by using transition metal complexes as molecular catalysts in purely aqueous media.