Hydrogen evolution using first-row transition metal complexes has gained growing attention as a promising route to clean energy generation. This review focuses on recent progress in the molecular design of catalysts based on abundant metals such as iron, cobalt, and nickel, with emphasis given to electrocatalytic systems. We explore how ligand modification strategies have enhanced catalytic performance by influencing key properties such as electron and proton transfer, and active site reactivity. Drawing on major advances over the last decade, this review aims to guide future efforts in optimising ligand frameworks, improving electrochemical performance, and advancing molecular electrocatalysts toward real-world hydrogen production technologies.

In the pursuit of developping efficient and green methods for hydrogen production, a key focus is the development of the most energy-efficient catalysts. The analysis of various proton sources primarily aims at eliminating rate-limiting steps associated with protonation events and ensuring the stability of the catalyst. In this work, we report how two distinct proton sources can cause a mechanistic shift in the hydrogen evolution reaction. Specifically, we explore this reactivity change in the presence of triethylammonium and trifluoroacetic acid with two thiosemicarbazone-based complexes, using cobalt and nickel metal centers. Our combined experimental and theoretical results reveal that the complete sequence of steps leading to hydrogen release strongly depends on the proton source. This demonstrates the importance of thoroughly investigating the interactions between a catalyst and a proton source to optimize hydrogen evolution systems.

The search for alternative non-noble transition metal catalysts able to evolve hydrogen has been the focus of intense research. Molecular complexes bearing redox-active ligands have been reported as efficient electrocatalysts for hydrogen evolution reaction (HER). This study showcases a new family of nickel-thiosemicarbazone complexes displaying significant activity for HER in DMF solvent using trifluoracetic acid as proton source. Following previous works in our group, the ligand was stereochemically tailored, placing methoxy groups at different locations and considering various combinations of positions. Three complexes within the series were shown to outperform the parent catalyst bearing the methoxy group in para position. Overall, the nickel catalyst having the chemical substituent in meta position displays the best catalytic performances while having the lowest overpotential. These results support that ligand stereochemical tailoring in metal complexes improves electrocatalytic HER and suggest that ligand tuning is a promising direction to enhance catalyst performances. A new series of nickel-thiosemicarbazone complexes was synthesized with the methoxy group placed in different positions on the phenyl ring. Their ability to promote electrocatalytic proton reduction into hydrogen was investigated. The meta-substituted complex, NiTSC-(m)-OCH3, outperformed all other tested complexes with a greatly increased TOF of 676.9 s-1 compared to the reference catalyst, NiTSC-(p)-OCH3, with a TOF of 90 s-1. image

Thiocarbohydrazone-based catalysts feature ligands that are potentially electrochemically active. From the synthesis point of view, these ligands can be easily tailored, opening multiple strategies for optimization, such as using different substituent groups or metal substitution. In this work, we show the possibility of a new strategy, involving the nuclearity of the system, meaning the number of metal centers. We report the synthesis and characterization of a trinuclear nickel-thiocarbohydrazone complex displaying an improved turnover rate compared with its mononuclear counterpart. We use DFT calculations to show that the mechanism involved is metal-centered, unlike the metal-assisted ligand-centered mechanism found in the mononuclear complex. Finally, we show that two possible mechanisms can be assigned to this catalyst, both involving an initial double reduction of the system.

In order to diminish environmental issues such as global warming due to increased carbo dioxide (CO2) emissions, considerable efforts have been made in the research community. Photocatalytic hydrogen (H2) production is a very important way towards this goal, since sunlight is an abundant source of energy and H2 is a clean fuel, producing no greenhouse gases. Inexpensive, stable and non-toxic carbon dots were easily synthesized and used as photosensitizers in water in the presence of a series of molecular cobalt catalysts (CoTSC). The catalysts were thiosemicarbazone-based complexes able to transfer electrons for hydrogen evolution reaction. Under visible light irradiation, the nitrogen-doped carbon dots (NCdots) transfer the photoexcited electrons to the catalyst, producing an activity of 358 & mu;mol gNCdot-1 h-1 (TONCo=570) for CoTSC-N(CH3)2CN after 24 h of irradiation. These types of molecular catalysts display great activity and stability in combination with the easily synthesized and modified carbon dot materials. An efficient photocatalytic system with earth abundant carbon dots and a series of cobalt thiosemicarbazone catalysts was designed and studied. All prepared photocatalysts produced hydrogen, reaching a rate of 358 & mu;mol gNCdot-1 h-1 upon light irradiation in water.+image

Solar cells based on metal halide perovskite and polymer donor:nonfullerene acceptor blend absorbers have recently witnessed a significant rise in their photovoltaic performance. However, they still suffer from some instability issues originating from the inferior interface quality and poor nanomorphology of the absorber layer. In this work, a series of functionalized boron‐dipyrromethene, BODIPY, molecules are introduced as ultrathin interlayers at the absorber/electron transport layer interface. This study indicates that BODIPY compounds with a high molecular dipole moment can enhance the device performance mainly due to better interface energy level alignment. They also induce passivation of defect traps and improvement in the charge transport properties of the absorber layer coated on top of them. Among the various compounds used, amino‐functionalized BODIPY, owing to the synergetic effect of the abovementioned factors, enables the highest power conversion efficiency in organic (15.69%) as well as in perovskite solar cells (20.12%). Amino‐functionalized BODIPY also demonstrates an enhanced stability under continuous illumination (in nitrogen) without and with heating (at 65 °C) for 1000 h. These results pave the way for the implementation of molecules with tailor‐made functionalities in high efficiency and stable solution‐based photovoltaic devices of the future.

Nitrogen-doped carbon dots were used as photosensitizers for H-2 evolution in the presence of a series of mononuclear thiosemicarbazone nickel complexes. The catalysts were designed to display different substituents at the para position of the phenyl rings. These chemical modifications tune the electron-donating abilities of the complexes and influence their capability to reduce protons into hydrogen. All photocatalytic experiments were performed in aqueous solution, using as sacrificial electron donor TCEP/Asc (1 : 1), 0.1 M each, at pH=5. The complex bearing the most electron-donating ligand with the dimethylamino (N(CH3)(2)) substituent behaves as the best catalyst in our series of photocatalytic systems with TONCAT=148, under white led radiation for 30 h. Therefore, this noble metal-free system can effectively produce hydrogen in water and further chemical modification of the ligand will likely improve its production.

An interfacial engineering approach was adopted in order to optimize the photovoltaic parameters and the stability of n-i-p planar perovskite solar cells (PSCs). A thin manganese (Mn) porphyrin [(TMePyP)I4Mn(AcO)] layer was introduced between the titania (TiO2) electron transport layer (ETL) and the perovskite absorber. The introduction of porphyrin onto the TiO2 substrate provoked a significant decrease in the work function (W-F), which arose from the large local dipole moment. The modification also provided a more hydrophobic environment that favored the growth of homogeneous and large perovskite crystals. Moreover, the electron charge transport to the ETL was facilitated via the highly paramagnetic character of the Mn porphyrin, whereas the negative impact of humidity and oxygen on the PSC performance was hindered. Density functional theory analysis justified the observed large decrease of the W-F and the strong electronic coupling of porphyrin with the TiO2 compact layer (following the porphyrin deposition), which are beneficial for electron extraction. By combining the Mn porphyrin and the CH3NH3PbI3 perovskite, significant enhancement of the stabilized power conversion efficiency by 22% was recorded. The shelf-shield stability was also improved after more than 600 h of storage in the dark under ambient conditions.

This work reports on the synthesis and characterization of a series of mononuclear thiosemicarbazone nickel complexes that display significant catalytic activity for hydrogen production in DMF using trifluoroacetic acid as the proton source. The ligand framework was chemically modified by varying the electron-donating abilities of the para substituents on the phenyl rings, which was expected to impact the capability of the resulting complexes to reduce protons into hydrogen. Over the four nickel complexes that were obtained, the one with the thiomethyl substituent, NiSCH3, was found to overtake the catalytic performances of the parent complex NiOCH3 featuring lower overpotential values and similar maximum turnover frequencies. These results confirm the electronic effects of the ligand on HER when using thiosemicarbazone nickel complexes and support that chemical modifications can tune the catalytic performances of such systems.

Semiconductor colloidal quantum dots (CQDs) offer size- and composition-tunable luminescence of high colour purity. Importantly, their emission can be tuned deep into the second biological near-infrared (NIR-II) window (1,000–1,700 nm). However, applications are hindered by the low efficiencies achieved to date. Here, we report NIR-II CQD light-emitting diodes with an external quantum efficiency of 16.98% and a power conversion efficiency of 11.28% at wavelength 1,397 nm. This performance arises from device engineering that delivers a high photoluminescence quantum yield and charge balance close to unity. More specifically, we employed a binary emissive layer consisting of silica-encapsulated silver sulfide (Ag 2 S@SiO 2 ) CQDs dispersed in a caesium-containing triple cation perovskite matrix that serves as an additional passivation medium and a carrier supplier to the emitting CQDs. The hole-injection contact also features a thin porphyrin interlayer to balance the device current and enhance carrier radiative recombination.

Photovoltaic devices based on organic semiconductors and organo-metal halide perovskites have not yet reached the theoretically predicted power conversion efficiencies while they still exhibit poor environmental stability. Interfacial engineering using suitable materials has been recognized as an attractive approach to tackle the above issues. We introduce here a zinc porphyrin-triazine-bodipy donor-π bridge-acceptor dye as a universal electron transfer mediator in both organic and perovskite solar cells. Thanks to its "push-pull" character, this dye enhances electron transfer from the absorber layer toward the electron-selective contact, thus improving the device's photocurrent and efficiency. The direct result is more than 10% average power conversion efficiency enhancement in both fullerene-based (from 8.65 to 9.80%) and non-fullerene-based (from 7.71 to 8.73%) organic solar cells as well as in perovskite ones (from 14.56 to 15.67%), proving the universality of our approach. Concurrently, by forming a hydrophobic network on the surface of metal oxide substrates, it improves the nanomorphology of the photoactive overlayer and contributes to efficiency stabilization. The fabricated devices of both kinds preserved more than 85% of their efficiency upon exposure to ambient conditions for more than 600 h without any encapsulation.

Motivated by the excellent electron-transfer capability of porphyrin molecules in natural photosynthesis, we introduce here the first application of a porphyrin compound to improve the performance of planar perovskite solar cells. The insertion of a thin layer consisting of a triazine-substituted Zn porphyrin between the TiO2 electron transport layer and the CH3NH3PbI3 perovskite film significantly augmented electron transfer toward TiO2 while also sufficiently improved the morphology of the perovskite film. The devices employing porphyrin-modified TiO2 exhibited a significant increase in the short-circuit current densities and a small increase in the fill factor. As a result, they delivered maximum power conversion efficiency (PCE) of 16.87% (average 14.33%), which represents a 12% enhancement compared to 15.01% (average 12.53%) of the reference cell. Moreover, the porphyrin-modified cells exhibited improved hysteretic behavior and a higher stabilized power output of 14.40% compared to 10.70% of the reference devices. Importantly, nonencapsulated perovskite solar cells embedding a thin porphyrin interlayer showed an elongated lifetime retaining 86% of the initial PCE after 200 h, while the reference devices exhibited higher efficiency loss due to faster decomposition of CH3NH3PbI3 to PbI2.

In the present work, we effectively modify the TiO2 electron transport layer of organic solar cells with an inverted architecture using appropriately engineered porphyrin molecules. The results show that the optimized porphyrin modifier bearing two carboxylic acids as the anchoring groups and a triazine electron-withdrawing spacer significantly reduces the work function of TiO2, thereby reducing the electron extraction barrier. Moreover, the lower surface energy of the porphyrin-modified substrate results in better physical compatibility between the latter and the photoactive blend. Upon employing porphyrin-modified TiO2 electron transport layers in PTB7:PC71BM-based organic solar cells we obtained an improved average power conversion efficiency up to 8.73%. Importantly, porphyrin modification significantly increased the lifetime of the devices, which retained 80% of their initial efficiency after 500 h of storage in the dark. Because of its simplicity and efficacy, this approach should give tantalizing glimpses and generate an impact into the potential of porphyrins to facilitate electron transfer in organic solar cells and related devices.

Here, we use a simple and effective method to accomplish energy level alignment and thus electron injection barrier control in organic light emitting diodes (OLEDs) with a conventional architecture based on a green emissive copolymer. In particular, a series of functionalized zinc porphyrin compounds bearing π-delocalized triazine electron withdrawing spacers for efficient intramolecular electron transfer and different terminal groups such as glycine moieties in their peripheral substitutes are employed as thin interlayers at the emissive layer/Al (cathode) interface to realize efficient electron injection/transport. The effects of spatial (i.e., assembly) configuration, molecular dipole moment and type of peripheral group termination on the optical properties and energy level tuning are investigated by steady-state and time-resolved photoluminescence spectroscopy in F8BT/porphyrin films, by photovoltage measurements in OLED devices and by surface work function measurements in Al electrodes modified with the functionalized zinc porphyrins. The performance of OLEDs is significantly improved upon using the functionalized porphyrin interlayers with the recorded luminance of the devices to reach values 1 order of magnitude higher than that of the reference diode without any electron injection/transport interlayer.

The effect of Gurney naps on two-dimensional airfoils, three-dimensional wings, and a reflection plane model were investigated. There have been a number of studies on Gurney flaps in recent years, but these studies have been limited to two-dimensional airfoil sections. A comprehensive investigation on the effect of Gurney flaps for a wide range of configurations and test conditions was conducted at Wichita State University. A symmetric NACA 0011 and a cambered GA(W)-2 airfoil were used during the single-element airfoil part of this investigation. The GA(W)-2 airfoil was also used during the two-element airfoil study with a 25% chord slotted flap deflected at 10, 20, and 30 deg, Straight and tapered reflection plane wings ,vith natural laminar flow (NLF) airfoil sections were tested for the three-dimensional wing part of this investigation. A fuselage and engine were attached to the tapered NLF wing for the reflection plane model investigation. In an cases the Gurney flap improved the maximum lift coefficient compared to the baseline clean configuration. However, there was a drag penalty associated with this lift increase.