Developing efficient and stable electrocatalysts is crucial for the electrochemical production of pure and clean hydrogen. For practical applications, an economical and facile method of producing catalysts for the hydrogen evolution reaction (HER) is essential. Here, we report ruthenium (Ru) nanoparticles uniformly deposited on multi-walled carbon nanotubes (MWCNTs) as an efficient HER catalyst. The catalyst exhibits the small overpotentials of 13 and 17 mV at a current density of 10 mA cm-2 in 0.5 M aq. H 2 SO 4 and 1.0 M aq. KOH, respectively, surpassing the commercial Pt/C (16 mV and 33 mV). Moreover, the catalyst has excellent stability in both media, showing almost "zeroloss" during cycling. In a real device, the catalyst produces 15.4% more hydrogen per power consumed, and shows a higher Faradaic efficiency (92.28%) than the benchmark Pt/C (85.97%). Density functional theory calculations suggest that Ru-C bonding is the most plausible active site for the HER.

charge separation and intrinsic efficiency, which are limited by the material's wide bandgap (≈3 eV). To overcome these issues, countless studies have focused on modifying the properties of TiO 2 , such as controlling its crystal structures, morphologies, vacancies, and doping. Existing natural TiO 2 polymorphs, the anatase and rutile phases, are generally considered representative photocatalytic materials. However, brookite has not been actively studied because in the past it has been difficult to synthesize. Anatase is known to more efficiently separate photoexcited charge carriers than rutile, but its thermodynamic stability has the reverse tendency. [14,15] While studying the different properties of various TiO 2 crystal structures, morphology-dependent characteristics have also been investigated, including efficient charge carrier dynamics, which include longer charge carrier diffusion length than the particle size to separate charges suppressing charge recombination. In addition to these high-crystalline-controlled studies, defect engineering approaches have also been vigorously investigated, to extend the material's light absorption range from the ultraviolet (UV) region to visible light. The general method used to enhance photocatalytic performance has been to introduce defects into TiO 2 structures, by chemical and physical doping, and induce vacancies in titanium (Ti) or oxygen (O) positions. These defect engineering strategies create new energy states, which act as charge trapping sites or narrowing bandgap to extend light absorption region. The formation of new energy states and defect sites is dependent on synthesis methods and conditions, indicating that predicting property and mechanism of synthesized TiO 2 materials is difficult before testing catalytic reactions. This uncertainty is one of the main problems to design new high-performance catalysts. Up to now, numerous researches have been reported to enhance photocatalytic activities and to reveal the mechanism. Even though it has not been confirmed the mechanism and activity for all situations, we can get insight for comprehensive understanding to predict and to design new catalysts. This work reviews modifying strategies of TiO 2 materials to enhance their photocatalytic activity with categorizing in the several systems. First, the basic principles of photocatalytic reactions on TiO 2 are described. Second, the characteristics of surface modification with other elements and doped systems in the lattice of photocatalysts are discussed. Finally, multicomponent heterostructure systems and current photocatalyst To address energy and environmental problems, innumerable titanium dioxide (TiO 2)-based photocatalysts have been reported over the last four decades. TiO 2 has attracted immense interest because it is low-cost, abundant, and photoresponsive. Sunlight-driven fuel production is one of the ideal photocatalytic approaches in terms of economics and the environment. However, performance issues with TiO 2 photocatalysts remain, including insuffici...

The physical and photochemical properties of covalent organic frameworks (COFs) can be tuned by their structural features such as the chemical composition and conjugation of building units. The combination of building units with different intrinsic properties can also influence their intrinsic electronic, adsorption, and optical properties. For the study on the symmetrical feature of COF and its physical/photochemical properties, we prepared benzothiazole-based COFs (TTzTp and BTzTp) with two different combinations, composed of tris-benzothiazole triamine (TTz) or bis-benzothiazole diamine (BTz) with triformylphloroglucinol (Tp), respectively. For their C3+C3 and C3+C2 symmetries, the COFs, synthesized from benzothiazole core units with approximately twice the difference in their pore dimensions, showed good affinity with CO2 and light-harvesting properties depending on the conjugation state of building units. The COFs were then applied as photosensitizers in a photocatalytic CO2 conversion system. The larger-pore-sized BTzTp showed a higher CO2-to-CO conversion rate than TTzTp, which stemmed from enhanced photocatalytic driving force by suitable band alignment, wider band gap with longer separated charge lifetime, and higher charge carrier mobility with a higher crystalline fraction in the structure.

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A scalable and low‐cost production of graphene nanoplatelets (GnPs) is one of the most important challenges for their commercialization. A simple mechanochemical reaction has been developed and applied to prepare various edge‐functionalized GnPs (EFGnPs). EFGnPs can be produced in a simple and ecofriendly manner by ball milling of graphite with target substances (X = nonmetals, halogens, semimetals, or metalloids). The unique feature of this method is its use of kinetic energy, which can generate active carbon species by unzipping of graphitic CC bonds in dry conditions (no solvent). The active carbon species efficiently pick up X substance(s), leading to the formation of graphitic CX bonds along the broken edges and the delamination of graphitic layers into EFGnPs. Unlike graphene oxide (GO) and reduced GO (rGO), the preparation of EFGnPs does not involve toxic chemicals, such as corrosive acids and toxic reducing agents. Furthermore, the prepared EFGnPs preserve high crystallinity in the basal area due to their edge‐selective functionalization. Considering the available edge X groups that can be selectively employed, the potential applications of EFGnPs are unlimited. In this context, the synthesis, characterizations, and applications of EFGnPs, specifically, as metal‐free carbon‐based electrocatalysts for dye‐sensitized solar cells (DSSCs) in both cobalt and iodine electrolytes are reviewed.