Electrochemical water splitting has emerged as a pivotal technology for green hydrogen production, offering a viable pathway toward a sustainable energy future. Among various electrolysis systems, Anion exchange membrane water electrolysis is particularly noteworthy as a cost-effective solution capable of operating under the fluctuating power inputs typical of renewable energy sources. However, the overall efficiency of water splitting is fundamentally limited by the oxygen evolution reaction, which exhibits sluggish kinetics compared to the hydrogen evolution reaction. While IrO₂ and RuO₂ serve as current benchmarks, their scarcity and high cost necessitate the development of earth-abundant alternatives. This review provides a comprehensive overview of fundamental OER mechanisms including the adsorbate evolution mechanism, lattice oxygen mechanism, and oxide path mechanism while highlighting how new pathways can circumvent traditional scaling relations. We discuss recent advancements in transition metal-based electrocatalysts, encompassing oxides, hydroxides, chalcogenides, phosphides, nitrides, and carbides, with a focus on innovative design strategies such as defect engineering, heteroatom doping, and heterostructure construction. This paper concludes by addressing current challenges and offering perspectives on future directions for the development of highly efficient and economically viable oxygen evolution electrocatalysts for large-scale applications.

This review systematically examines the structural characteristics, compositional design strategies, and recent research trends of layered double hydroxides (LDHs), which are recognized as promising electrocatalyst materials in electrochemical nitrate-to-ammonia conversion. Despite the rapid growth in related research, achieving simultaneous high selectivity and efficiency remains a significant technical challenge due to the complex mechanisms of the nitrate reduction reaction (NitRR) and its inherent competition with the hydrogen evolution reaction (HER). In this study, we analyzed the structural contributions of LDH catalysts for maximizing nitrate reduction efficiency and systematically established key catalyst design indicators required to ensure optimal performance. Specifically, we provide a detailed investigation of the physicochemical mechanisms for enhancing NH₃ production by precisely regulating the adsorption energies of reaction intermediates and maximizing charge transfer efficiency through compositional control and defect engineering. Furthermore, we discuss advanced structural design strategies, such as core-shell tandem structures, MOF-derived architectures, and interlayer anion control, as effective methods for enhancing catalytic performance and optimizing mass transport processes. These insights offer a strategic roadmap for designing high-performance LDH catalysts and represent a critical step toward the practical implementation of sustainable green ammonia production systems, particularly for integration into high-efficiency membrane electrode assembly (MEA) technologies.

As the importance of eco-friendly technologies increases, hydrogen vehicles are gaining significant attention as a key component of future mobility. However, the sensor technology required to accurately measure the concentration of high-purity hydrogen gas, which serves as the fuel for hydrogen vehicles, currently lacks the sensitivity needed for commercialization and remains at a demonstrative stage. This study aims to enhance the detection performance of hydrogen sensors by optimizing the fabrication process of a membrane electrode assembly (MEA) with a Pt-based electrode-electrolyte-electrode structure, where the proton-conducting electrolyte is sandwiched between upper and lower Pt electrodes. The MEA was fabricated using a hot press method, and the process was optimized by adjusting pressure, temperature, and time parameters to improve both the physical and electrical properties of the MEA. The hydrogen sensor produced using the optimized MEA showed improved sensitivity. This enhancement enables the effective monitoring of high-purity hydrogen gas used in hydrogen vehicles, thereby improving the fuel efficiency of these vehicles.

Titanium oxide (TiO₂), a representative photocatalyst, reacts to ultraviolet ray energy and has antibacterial, deodorizing, and antifouling properties using superhydrophilic properties, so it is widely used in various industrial fields such as environmental purification, building exterior walls, and road facilities. However, due to the nature of the photocatalyst, it reacts to ultraviolet rays known to be harmful to the human body, and is designed to react to natural light outdoors and to ultraviolet light sources inside a sealed device indoors, so indoor space is extremely limited. This study aims to develop spatial antibacterial technology for everyday living spaces by researching methods for antibacterial and deodorization by reacting titanium oxide (TiO₂)-based photocatalysts with the visible light range emitted from lighting devices in everyday spaces. Through the results of this study, it was verified through experiments that the photocatalyst exhibits antibacterial and deodorizing properties in response to lighting devices (LED, fluorescent lights, etc.) used in daily life. Based on the research results, we hope that various studies will be conducted to create a safer living environment by applying this technology to various fields such as large-scale complex facilities where an unspecified number of floating populations gather, airports, port waiting rooms, and public transportation.

Oxygen evolution reaction is a critical bottleneck for the development of efficient electrochemical hydrogen production because of its sluggish reaction. Among various catalysts, transition metal-based layered double hydroxide has drawn significant attention due to their excellent catalytic properties and cost-effectiveness. This paper begins with basic crystal structures, and then conventional adsorbate evolution mechanism of layered double hydroxide. Strategies for enhancing catalytic properties based on adsorbate evolution mechanism and lattice oxygen mechanism that could surpass theoretical limit of adsorbate evolution mechanism are discussed. This paper ends with a brief discussion on the challenges and future directions of layered double hydroxide-based oxygen evolution reaction catalysts.

Nano Pt particles were dispersed on carbon-based supports by a polyol process for a catalyst application in a polymer electrolyte fuel cell. We tried to optimize the effect of pH on the electrostatic forces between the support and the Pt colloids. We investigated the relationship among the surface charges on the carbon support, the solution pH, and the concentration of a glycolate, and the Pt particle size. The produced catalyst with nano Pt particles on the support was evaluated by the long-term cyclic voltammetry (CV) performance test and compared with the results from a commercial catalyst. Our experimental results reveal that the pH-control can modify the particle size distribution and the dispersion of the nano Pt particles. This resulted in a cost-effective method for the synthesis of highly Pt loaded Pt/C catalysts for fuel cells better than a commercial catalyst system.

Ultrawide bandgap gallium oxide (Ga₂O₃) semiconductors are known to have excellent photocatalytic properties due to their high redox potential. In this study, CO₂ reduction is demonstrated using nanostructured Ga₂O₃ photocatalyst under ultraviolet (254 nm) light source conditions. After the CO₂ reduction, C₂H₄ remained as a by-product in this work. Nanostructured Ga₂O₃ photocatalyst also showed an excellent endurance characteristic. Photogenerated electron-hole pairs boosted the CO₂ reduction to C₂H₄ via nanostructured Ga₂O₃ photocatalyst, which is attributed to the ultrawide and almost direct bandgap characteristics of the gallium oxide semiconductor. The findings in this work could expedite the realization of CO₂ reduction and a simultaneous C₂H₄ production using a low cost and high performance photocatalyst.

Direct exposure to toxic and hazardous gases has always been considered as the most pervasive problem worldwide, leading to a gradual increase in the number of asthma patients due to NO_x/SO_x gases inhaling and exposure to 50 ppm formaldehyde gases. Therefore, the development of accurate gas sensors is a key issue for resolving these problems. To address such issues, the development of membranes for selective filtering of target molecules as well as nanocatalyst for enhancing the sensing selectivity is highly crucial. In this review, the research progress for porous membrane materials (e.g. MOFs, and graphene) and nanocatalyst technology for the development of selective and accurate gas sensors will be discussed.

As the recent climate problems are getting worse year after year, the demands for clean energy materials have highly increased in modern society. However, the candidate material classes for clean energy expand rapidly and the outcomes are too complex to be interpreted at laboratory scale (e.g., multicomponent materials). In order to overcome these issues, the firstprinciples calculations are becoming attractive in the field of material science. The calculations can be performed rapidly using virtual environments without physical limitations in a vast candidate pool, and theory can address the origin of activity through the calculations of electronic structure of materials, even if the structure of material is too complex. Therefore, in terms of the latest trends, we report academic progress related to the first-principles calculations for design of efficient electrocatalysts. The basic background for theory and specific research examples are reported together with the perspective on the design of novel materials using first-principles calculations.

In this study, we created a DBD plasma device and a MnO₂ catalyst mesh filter for evaluating ozone reduction of devices via the catalyst method. The DBD plasma device was manufactured by applying MnO₂ paste to soda lime glass via the screen-printing method. The MnO₂ catalyst mesh filter was manufactured by mixing MnO₂ powder with binder with a 10% difference in concentration from 10% to 50% and then applying it using the dip-coating method. Finally, we sintered a MnO₂ catalyst mesh filter in an electric furnace. We evaluated the characteristics of ozone generation according to the MnO₂ gas flow of DBD plasma devices, the opening ratio, and ozone reduction performance of the MnO₂ catalyst filters. Ozone reduction performance was approximately 20.4% at MnO₂10 wt%, 37.8% at MnO₂ 30 wt% and 50% at MnO₂ 50 wt%.

This study describes the development of graphene-TiO₂ conjugates for the enhancement of the photocatalytic efficiency of TiO₂. Graphene-based hybrid nanomaterials have attracted considerable attention because of the unique and advantageous properties of graphene. In the proposed hybrid nanomaterial, graphene serves as an electron acceptor to ensure fast charge transfer. Effective charge separation can, therefore, be achieved to slow down electron-hole recombination. This results in an enhancement of the photocatalytic activity of TiO₂. In addition, increased adsorption and interactions with the adsorbed reagents also lead to an improvement in the photocatalytic activity of graphene-TiO₂ hybrid nanomaterials. The acquired result is encouraging in that the photocatalytic activity of TiO₂ was initiated using visible light (630 nm) instead of the typical UV light.

TiO₂ has excellent photocatalytic properties and several studies have reported the increase in its specific surface area. The structure of TiO₂ nanofibers indicates promising improved photocatalytic properties and these nanofibers can thus potentially be applied in air pollution sensors and pollutant removal filters. In this study, a TiO₂ nanofiber was fabricated by the electrospinning method. The fabrication processing factors such as the applied voltage, the distance between nozzle and collector, and the inflow rate of solution were controlled. The precursor was titanium (Ⅳ) isopropoxide and as-spun TiO₂ nanofibers were heated at 450℃ for 2 h to obtain an anatase crystalline structure. The microstructure was analyzed using field emission scanning electron microscope (FE-SEM) and X-ray diffraction analysis (XRD). The anatase phase was observed in the TiO₂ nanofibers after heat treatment. The diameter of TiO₂ nanofibers increased with the flow rate, but decreased with decreasing applied voltage and nozzle to collector distance. The diameter of TiO₂ nanofibers was controlled in the range of 364 nm to 660 nm. These nanofibers are expected to be very useful in photocatalytic applications.

Recently, various type of nanomaterials such as nanorod, nanowire, nanotube and their core/shell nanostructures have attracted much attention in photocatalyst due to their unique properties. Among them, Type-II core/shell heterostructures have extensively studied because it has exhibited improved electrical and optical properties against their single-component nanostructure. Such structures are expected to offer high absorption efficiency and fast charge transport due to their stepwised energetic combination and large internal surface area. Thus, it has been considered as potential candidates for high efficient photocatalytic activity. In this work, we introduce a novel chemical conversion process to synthesize Type-II ZnO/ZnSe core/shell heterostructures. A plausible conversion mechanism to ZnO/ZnS ecore/shell heterostructres was proposed based on SEM, XRD, TEM and XPS analysis. The ZnO/ZnSe heterostructures exhibited excellent photocatalytic activity toward the decomposition of RhB dye compared to the ZnO nanorod arrays due to enhanced light absorption and the type-II cascade band structure.

In this study, the influence of electrochemical properties by mixing Tetrabutylammonium hydroxide (TBAOH) and ammonium hydroxide (NH4OH) electrode on the dssc. The titanias were prepared using a sol-gel method by mixing Tetrabutylammonium hydroxide and Ammonium hydroxide. The TiO2nanopowder prepared by sol-gel methode, and to improve the distributed properties of TiO2 nanopowder,the TBAOH and NH4OH was added. The I-V values of cells show that the Tetrabutylammonium has 6.51%efficiency.

The prepartion of various metal oxide nanostructures via hydrothermal method, hydrolysis, thermal evaporation and electrospinning and their applications to chemoresistive sensors have been investigated. Hierarchical and hollow nanostructures prepared by hydrothermal method and hydrolysis showed the high response and fast responding kinetics on account of their high gas accessibility. Thermal evaporation and electrospinning provide the facile routes to prepare catalyst-loaded oxide nanowires and nanofibers, respectively. The loading of noble metal and metal oxide catalyst were effective to achieve rapid response/recovery and selective gas detection.

Abstract: Cu doped SnO(2) thick films for gas sensors were fabricated by screen printing method on alumina substrates and annealed at 500℃ in air, respectively. Structural properties of SnO(2) by X-ray diffraction showed (110), (101) and (211) dominant tetragonal phase. The effects of catalyst Cu in SnO(2)-based gas sensors were investigated. Sensitivity of SnO(2):Cu sensors to 2,000 ppm CO(2) gas and 50 ppm H(2)S gas was investigated for various Cu concentration. The highest sensitivity to CO(2) gas and H(2)S gas of Cu doped SnO(2) gas sensors was observed at the 8 wt% and 12 wt% Cu concentration, respectively. The improved sensitivity in the Cu doped SnO(2) gas sensors was explained by decrease of electron depletion region in Cu and SnO(2) junction, and increase of reactive oxygen and surface area in the SnO(2).