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Seawater is the most abundant source of molecular hydrogen. Utilizing the hydrogen reserves present in the seawater may inaugurate innovative strategies aimed at advancing sustainable energy and environmental preservation endeavors in the future. Recently, there has been a surge in study in the field addressing the production of hydrogen through the electrochemical seawater splitting. However, the performance and durability of the electrode have limitations due to the fact that there are a few challenges that need to be addressed in order to make the technology suitable for the industrial purpose. The active site blockage caused by chloride ions that are prevalent in seawater and chloride corrosion is the most significant issue; it has a negative impact on both the activity and the durability of the anode component. Addressing this particular issue is of upmost importance in the seawater splitting area. This review concentrates on the newly developed materials and techniques for inhibiting chloride ions by blocking the active sites, simultaneously preventing the chloride corrosion. It is anticipated that the concept will be advantageous for a large audience and will inspire researchers to study on this particular area of concern. [ABSTRACT FROM AUTHOR]

Over the past decades, tremendous effort has been made to enhance the water‐splitting via fabricating eco‐friendly electrocatalyst with increased conductivity, and large number of accessible active sites in lab scale. However, the development of earth abundant efficient electrocatalyst with superior activity for ‐seawater‐splitting remains a great challenge for the researchers. In this regard, self‐supported catalysts are found to be the most promising candidates, they have the features of increased loading, superior adhesion, rapid mass and charge transfer, and easy wettability for large scale hydrogen production via electrochemical seawater splitting. This review investigates different fabrication processes for the self‐supported catalyst, emphasizing their distinct characteristics that contribute to improved activity. Furthermore, we provided a detailed elucidation of the procedure and characteristics of seawater splitting, emphasizing the most recent progress in the creation of self‐supportive catalyst for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and bifunctional activity. We have also examined the current barriers and potential prospects for advancing the utilization of self‐supported catalysts in the process of seawater splitting. [ABSTRACT FROM AUTHOR]

Direct seawater splitting has attracted considerable attention as an alternative to conventional alkaline water electrolysis because the former avoids the use of limited freshwater resources. However, several challenges must be overcome to realize direct seawater electrolysis. Most importantly, electrocatalysts for the anodic oxygen evolution reaction (OER) should exhibit high activity, stability, and selectivity in highly corrosive environments with abundant chloride ions. In this study, we developed high-entropy carbonate (HEC) as a promising electrocatalyst for seawater oxidation. In HECs, physicochemical interactions among different elements can effectively suppress the corrosion of OER active sites, while polyanionic CO32- can act as a corrosion-protective species by repelling negatively charged chloride ions during electrolysis. Consequently, HECs demonstrate outstanding catalytic activity, stability, and selectivity for seawater oxidation, surpassing those of ternary, quaternary, and quinary carbonates and even benchmark IrO2 catalysts. [ABSTRACT FROM AUTHOR]

The proton exchange membrane water electrolysis (PEMWE) powered by renewable electricity offers a facile route for clean hydrogen production. The oxygen evolution reaction (OER) at the anode plays a major role in affecting the overall device efficiency due to its sluggish OER kinetics. Thus, it remains a challenge to develop robust and active catalysts for OER in acid media for efficient PEMWE. Currently, iridium (Ir)‐based materials, such as mono‐ and multimetallic Ir, Ir‐based oxides, pyrochlore iridate oxides, and Ir‐based perovskites, are the most promising OER catalysts in acid media for PEMWEs. Extensive research has been conducted to enhance the specific activity of Ir species to make cost‐effective. The present review aims to provide the recent progress on addressing the long‐term durability issue of Ir‐based catalyst for OER in acidic conditions, aspiring to inspire the researchers to design highly efficient and stable Ir‐based catalysts. Moreover, the detailed OER mechanism along with the dissolution nature of Ir species is discussed and summarized. Finally, the status, challenges, and prospects for the development of Ir‐based OER catalysts are discussed. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) under acidic conditions becomes of significant importance for the practical use of a proton exchange membrane (PEM) water electrolyzer. In particular, maximizing the mass activity of iridium (Ir) is one of the maiden issues. Herein, the authors discover that the Ir‐doped calcium copper titanate (CaCu₃Ti₄O₁₂, CCTO) perovskite exhibits ultrahigh mass activity up to 1000 A gIr−1 for the acidic OER, which is 66 times higher than that of the benchmark catalyst, IrO2. By substituting Ti with Ir in CCTO, metal‐oxygen (M‐O) covalency can be significantly increased leading to the reduced energy barrier for charge transfer. Further, highly polarizable CCTO perovskite referred to as "colossal dielectric", possesses low defect formation energy for oxygen vacancy inducing a high number of oxygen vacancies in Ir‐doped CCTO (Ir‐CCTO). Electron transfer occurs from the oxygen vacancies and Ti to the substituted Ir consequentially resulting in the electron‐rich Ir and ‐deficient Ti sites. Thus, favorable adsorptions of oxygen intermediates can take place at Ti sites while the Ir ensures efficient charge supplies during OER, taking a top position of the volcano plot. Simultaneously, the introduced Ir dopants form nanoclusters at the surface of Ir‐CCTO, which can boost catalytic activity for the acidic OER. [ABSTRACT FROM AUTHOR]

Summary: Electrochemical water splitting is one of the most efficient techniques to produce hydrogen in an environmentally friendly way. However, a sluggish anodic reaction, namely oxygen evolution reaction (OER), requires the use of an efficient electrocatalyst for achieving economic hydrogen production. Transition‐metal‐based layered double hydroxides (LDHs) are promising electrocatalysts for reducing the overpotential of OER in alkaline electrolyte, which is essential for efficient water electrolysis. Nickel‐iron‐based LDHs (Ni‐Fe LDH) have been regarded as the best OER electrocatalysts under alkaline conditions. Hence, a number of research studies have been conducted on further improving the electrocatalytic performance of Ni‐Fe LDH. Although the chemical blending of other transition metals with Ni‐Fe‐LDH is a simple and reliable strategy to enhance the OER activity of Ni‐Fe‐LDH, a systematic investigation on designing Ni‐Fe‐LDH with different additional elements is still lacking. In addition, the design of multi‐metallic LDH compound via only experimental method is very costly and time‐consuming process. In this study, atomic‐scale computational and experimental studies are performed to design OER electrocatalysts including unary, binary, and ternary LDH compounds consisting of Ni, Fe, Al, and Co. Density functional theory calculations predict that Ni‐Fe‐Co ternary LDH can lead to the lowest overpotential for alkaline OER among various computationally modeled LDH systems. Further, experimental verifications successfully demonstrate the computational prediction wherein Ni‐Fe‐Co‐LDH exhibits superior catalytic performance compared with Ni‐Fe‐LDH and benchmark IrO2 catalysts. [ABSTRACT FROM AUTHOR]

Exploring bifunctional electrocatalysts to lower the activation energy barriers for sluggish electrochemical reactions for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great importance in achieving lower energy consumption and higher conversion efficiency for future energy conversion and storage system. Despite the excellent performance of precious metal-based electrocatalysts for OER and ORR, their high cost and scarcity hamper their large-scale industrial application. As alternatives to precious metal-based electrocatalysts, the development of earth-abundant and efficient catalysts with excellent electrocatalytic performance in both the OER and the ORR is urgently required. Herein, we report a core–shell CoFeS2@CoS2 heterostructure entangled with carbon nanotubes as an efficient bifunctional electrocatalyst for both the OER and the ORR. The CoFeS2@CoS2 nanocubes entangled with carbon nanotubes show superior electrochemical performance for both the OER and the ORR: a potential of 1.5 V (vs. RHE) at a current density of 10 mA cm−2 for the OER in alkaline medium and an onset potential of 0.976 V for the ORR. This work suggests a processing methodology for the development of the core–shell heterostructures with enhanced bifunctional performance for both the OER and the ORR. [ABSTRACT FROM AUTHOR]

Summary: The roles of amorphous phases in photochemical water splitting of semiconductors are still in debate, as the effects of the amorphous phase are largely irregular even in a single material. We presumed that the photochemistry of crystal‐amorphous mixed semiconductor systems would be governed by the interface characteristics, and conducted a systematic study to understand the origins of the largely varying photochemical reaction of semiconductors having an amorphous phase. First‐principles calculations on crystalline anatase and amorphous TiO2 showed that the coexistence of crystalline and amorphous TiO2 and the exposure of the phase boundary are advantageous due to the accelerated charge separation by interface dipole moment and the parallelizable oxygen evolution reaction at the boundary. Our computation‐based strategies were demonstrated in our experiments: only the TiO2 nanoparticle and nanotube having partial amorphization on surfaces have highly enhanced photocatalytic water splitting performances (approximately 700%) compared to the pristine and completely amorphized TiO2 systems. [ABSTRACT FROM AUTHOR]

Summary: Alkaline oxygen evolution reaction (OER) electrocatalysts have been widely studied for improving the efficiency and green hydrogen production through electrochemical water splitting. Currently, iron‐doped nickel‐LDHs (NF‐LDHs) are regarded as the benchmark electrocatalyst for alkaline OER, primarily owing to the physicochemical synergetic effects between Ni and Fe. Here, the third element addition into NF‐LDHs is designed to further enhance the electrocatalytic performance through the modulation of electronic property. Cu‐doped NF‐LDHs (NFC‐LDHs) are developed with the self‐supported structure on porous supports. NFC‐LDHs can be grown on carbon cloth (CC) in an intriguing 2D nanosheet structure, wherein the surface electronic configuration is suitably modulated by interactions among Ni‐Fe‐Cu. Importantly, activation energy for OER can be lowered by adding Cu into NF‐LDHs. Thereby, the NFC‐LDHs exhibited enhanced OER activity and improved stability than those of nickel‐LDHs (Ni‐LDHs) and NF‐LDHs. For NFC‐LDHs, small overpotentials of only 230 and 250 mV yield current densities of 50 and 100 mA cm−2, respectively. In addition, excellent electrochemical stability is demonstrated during long‐term OER tests without any degradation demonstrating no dissolution of active metals water electrolysis due to synergetic effects among Ni‐Fe‐Cu. [ABSTRACT FROM AUTHOR]

Borophosphate materials are promising electrocatalysts for water splitting. Their structural flexibility enable self‐adjusting of electronic structure depending on potential. The rich chemistry of borophosphate provides a huge engineering space to tune composition and structure. Herein, amorphized LiNiFe borophosphate (a‐LNFBPO) for an efficient and durable oxygen evolution reaction (OER) is first reported. Facile adsorption of oxygen intermediates on the vacancies generated by spontaneous Li dissolution during the OER and regulated electronic structure resulting from the Ni and Fe interaction can boost the OER. The amorphization of LiNiFe borophosphate modifies the electronic structure with metal‐oxygen (MO) bond contraction and the high valence state of the metal cations, which reduces the charge transfer energy between the catalyst and electrolyte. In addition, abundant defects, dangling bonds, and a disordered arrangement induced by amorphization enable an improvement in structural flexibility, facilitating a facile and entire transformation of originally inert species into the active phase during the OER process. The a‐LNFBPO@Ni foam shows excellent OER properties requiring only a 215 mV overpotential for generating 10 mA cm−2 and long‐term stability over 300 h. [ABSTRACT FROM AUTHOR]

Summary: There is a need to develop highly efficient electrocatalysts based on non‐noble metals which can be used for water splitting. Thus, to realize an acceptable oxygen evolution reaction (OER) performance, a combination of non‐noble metals was used to improve the architecture and conducive to a facile OER. For this purpose, a binder‐free and non‐noble metal‐based trimetallic (CuZnAg) composite OER a electrocatalyst was grown at the surface of fluorine‐doped tin oxide by a facile one step in‐situ electrodeposition method using chronoamperometry. The formation and performance of the catalyst were ensured from XRD, SEM, EDX, chronoamperometry, and linear scan voltammetry. The trimetallic composite showed good results toward OER in 1 M KOH electrolyte at pH 13 at a current density of 1 mA/cm2 with an overpotential of 303 mV at a scan rate of 10 mV/sec. The results revealed robust electrochemical durability under alkaline conditions and the electrocatalyst holds great promise for OER. [ABSTRACT FROM AUTHOR]

The development of earth‐abundant and efficient oxygen evolution reaction (OER) electrocatalysts is necessary for green hydrogen production. The preparation of efficient OER electrocatalysts requires both the adsorption sites and charge transfer on the catalyst surface to be suitably engineered. Herein, the design of an electrocatalyst is reported with significantly enhanced water oxidation performance via dual‐phase engineering, which displays a high number of adsorption sites and facile charge transfer. More importantly, a simple chemical etching process enables the formation of a highly metallic transition boride phase in conjunction with the transition metal hydroxide phase with abundant adsorption sites available for the intermediates formed in the OER. In addition, computational simulations are carried out to demonstrate the water oxidation mechanism and the real active sites in this engineered material. This research provides a new material design strategy for the preparation of high‐performance OER electrocatalysts. [ABSTRACT FROM AUTHOR]

The development of cost effective and high‐performance electrocatalyst is challenging but essential for realizing industrial hydrogen production by electolyzer. Electrocatalysts for water splitting must have active catalytic performance as well as high stability in strong alkaline or acidic media to be used in commercial elecrolyzer. Transition metal based electrocatalysts are considered as highly promising candidates due to their excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance and stability with low materials cost. Recently, binder free self‐supported electrocatalysts based on transition metals have emerged as state‐of‐the‐art catalytic electrodes due to their high activity and robustness. These properties are attributed to lack of catalyst powder aggregation and a strong synergetic effect between the electrode surface and catalyst. In this mini review, recent development in self‐supported electrocatalysts for OER, HER and also bifunctional OER & HER are reviewed in terms of superior activity and robust stability. Material design strategies, structural and compositional properties, and catalytic performance of recently reported self‐supported electrocatalysts are summarized. Finally, overview of recent studies, challenges and prospects related to self‐supported electrocatalysts are discussed. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis (PEMWE) represents a promising avenue for producing hydrogen sustainably. Nonetheless, its widespread adoption encounters hurdles owing to the sluggishness of the oxygen evolution reaction (OER) and the expensive noble metal catalysts, particularly iridium (Ir). Our investigation addresses these challenges by examining pyrolusite β-MnO 2 as a robust substrate for noble metal catalysts, including iridium (Ir) and ruthenium (Ru), within PEMWE systems. We illustrate that nanostructured β-MnO 2 effectively supports Ir and Ru catalysts, resulting in significantly improved catalytic activity for acidic OER compared to conventional IrO 2 catalysts. The morphology shows nanorod structures with thicknesses ranging of 30–60 nm. The catalytic activity exhibits a lower overpotential of 215 mV and a higher Ir mass activity of 2268.7 A·g Ir −1. The catalyst also exhibits lower Tafel slope value (37.82 mV/dec) and higher reaction kinetics. The catalyst also shows durability for the 12h under corrosive acidic OER conditions. The enhancements in performance can be attributed to the distinctive nanostructure of the Mn 1-x Ti x O 2 (MTO) support, which facilitates the even distribution of Ir and Ru catalysts. Additionally, the incorporation of titanium in pyrolusite β-MnO 2 enhances the electrochemical durability of the MTO support under challenging acidic OER conditions. • Nanostructured β-MnO 2 has a superior intrinsic catalytic activity for PEMWE system. • Incorporation of titanium improved the electrochemical stability of β-MnO 2. • Ir–Ru-doped Mn 1-x Ti x O 2 has an excellent OER performance under acidic conditions. [ABSTRACT FROM AUTHOR]

Transition metal doping and structural modification of MWCNT via PLA process show the significant enhancement of OER properties. [Display omitted] • The pulsed laser ablation process can effectively incorporate transition metal. • The partially collapsed MWCNT enhanced active site for electrocatalysts. • Ni-doped MWCNTs presented excellent electrocatalysts properties. Transition–metal-doped carbon-based electrocatalysts have attracted attention as alternatives to noble metal electrocatalysts (e.g. IrO 2 and RuO 2) for oxygen evolution reaction (OER) because they are inexpensive and highly efficient. However, their poor catalytic activity and time-consuming synthesis remain a challenge. Herein, we report a facile and green technique using pulsed laser ablation for preparing Ni-doped multi-walled carbon nanotubes (Ni-MWCNTs) as OER catalysts. Ni-MWCNTs exhibit high surface area, oxygen-rich functional groups (e.g., hydroxyl and carboxyl), and successful doping of Ni in the carbon framework. The as-prepared Ni-MWCNTs exhibited excellent OER catalytic performance, with an overpotential of 320 mV at the current density of 10 mA cm−2 in an alkaline medium, which is lower than that of the commercial RuO 2 catalyst. Furthermore, Ni-MWCNTs displayed the initial electrocatalytic activity after 10-h stability tests, demonstrating good electrochemical durability. We believe that this work provides a simple protocol for fabricating heteroatom-doped carbon nanotubes as high-performance OER electrocatalysts. [ABSTRACT FROM AUTHOR]

The development of bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has recently attracted significant attention. Transition metal-based electrocatalysts have demonstrated a highly promising catalytic performance in electrochemical HER or OER. Moreover, their electrocatalytic performance can be further improved using a self-supported structure of the electrocatalyst, owing to strong physicochemical contact between the catalyst and current collector. In this context, we propose vanadium-incorporated cobalt phosphide (CoVP) self-supported catalysts on carbon cloth (CoVP@CC) as highly efficient bifunctional electrocatalysts for alkaline HER and OER. In CoVP@CC, V plays a crucial role in modulating the surface electronic structure of the self-supported CoP nanosheets, leading to excellent catalytic activity in both HER and OER. The self-supported CoVP@CC demonstrates a promising overall water-splitting performance, requiring only 1.61 V to afford a current density of 10 mA cm−2. • V-incorporated CoP on carbon cloth (CoVP@CC) with a robust self-supported structure is prepared via wet chemistry. • V modulates the surface electronic structure of CoP nanosheets using a high electronic flexibility. • Self-supported CoVP@CC catalysts exhibits excellent catalytic performance for overall water splitting in alkaline media. [ABSTRACT FROM AUTHOR]

High-performance oxygen evolution reaction (OER) electrocatalysts are needed to produce hydrogen for energy generation through a carbon-free route. In this work, the solution combustion synthesis (SCS) method was employed to synthesize mixed phases of Co- and Mn-based oxides, and the relationships between the crystalline structure and the catalytic properties in the mixed phases were established. The mixed phases of Co- and Mn-based oxides shows promising OER properties, such as acceptable overpotential (450 mV for 10 mA∙cm−2) and Tafel slope (35.8 mV∙dec−1), highlighting the use of the mixed phases of Co- and Mn-based oxides as a new efficient catalysts for water splitting. Electronic structure of the mixed phases of Co- and Mn based oxides is studied in detail to give insight for the origin of high catalytic activities. In addition, excellent long-term stability for OER in alkaline media is achieved for the mixed phase of Co- and Mn based oxides. [ABSTRACT FROM AUTHOR]

As traditional non-renewable energy sources become scarcer, researchers are exploring effective strategies for producing sustainable and renewable energy. Oxygen evolution reaction through electrocatalytic water splitting (EC-OER) on the surface of a semiconductor has drawn much more attention in the worldwide as it has the principal role towards the several kind of energy applications viz. fuel cell, metal-ion rechargeable batteries and water oxidation. It is extremely difficult to develop eco-friendly, plentiful, and cost-effective nanomaterials as catalysts in order to achieve high efficiency of hydrogen production through water splitting. Furthermore, hierarchical nanostructures will become more valuable in future energy conversion applications due to their excellent physicochemical properties. Herein, we have synthesized total six different kinds of multi-metal-doped porous silica nanomaterials by utilizing the combination of nickel, iridium, and ruthenium metal slats in order to explore them as potential catalysts for electrochemical water oxidation process. We present a simple strategy to synthesize multi-metal-doped silica materials with spherical morphology, deploying a cation surfactant template (CTAB) as a structure directing agent in water-ethanol solvent mixtures. These materials are thoroughly characterized with the help of powder X-ray diffraction (PXRD), UV–Vis, FT-IR, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy (FE-SEM), nitrogen-sorption isotherm, thermogravimetric (TGA) analysis. The particles are 550–600 nm in size with a fine-looking spherical morphology and surface area in the range of 111–419 m2/g. Among all of these metal-silica, Ni–Ir–Ru-doped mesoporous silica particles (NIRS) exhibit excellent electrocatalytic activity towards oxygen evolution reaction (100 mA/cm2 current density@0.5V) with long-term durability up to 10 h, and the Tafel slope is also very low (∼68 mV/dec) in 1 M KOH medium. The excellent electrical conductivity of Ni–Ir–Ru-doped silica makes it a superior electrocatalyst due to its spherical morphology, synergistic effects of the multi metallic components, and its hierarchical nanoporous structure. [Display omitted] • A facile method for multi-metal-doped mesoporous silica was developed. • The particle sizes were 550–600 nm and surface area were up to 419 m2/g. • Multi-metal-doped mesoporous silica particles were spherical particles. • NIRS generated 100 mA/cm2 and current density@0.5V during OER in pH=14. • NIRS exhibited high durability up to 10 h with Tafel slope of 68 mV/dec in pH=14. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfur-doped multi-metal borophosphates are synthesized for enhanced alkaline seawater oxidation. • The negatively charged polyanionic surface layers improve the corrosion resistance. • The optimized catalyst demonstrates excellent electrocatalytic activity and durability. • The catalyst demonstrates high selectivity for the OER over the chloride evolution reaction (CER). Direct seawater splitting is a promising strategy for the production of green hydrogen to address water shortage and environmental concerns. However, the primary obstacle in direct seawater splitting is directly related to the high selectivity and durability of oxygen evolution reaction (OER) electrocatalysts. In this study, we developed sulfur-doped multimetal (Ni, Fe, and Co) borophosphates (BPOs) as high-performance OER catalysts for alkalized seawater electrolytes. The incorporated sulfur atoms act as precursors to enhance the corrosion resistance, as they form negatively charged polyanionic surface layers that block the chloride ions. The best catalyst demonstrates an overpotential of 278 mV in alkaline freshwater and 292 mV in alkalized seawater electrolytes when subjected to a current density of 100 mA cm−2. The overpotential disparity between the two media was only 14 mV, suggesting that the material has substantial resistance to chloride corrosion. Furthermore, excellent electrochemical durability was attained for the sulfurized and amorphized multi-metal BPOs, highlighting their high potential as promising catalysts for seawater oxidation. [ABSTRACT FROM AUTHOR]

• Developed a new tri-metallic catalyst (CNF) with a nanoprism structure. • CNF demonstrates exceptional catalytic activity and durability for alkaline and seawater oxidations. • Doping CNF with Cr (Cr-doped CNF) further enhances the catalytic performance. Electrochemical water splitting is one of the most promising methods for sustainable production of green hydrogen. The oxygen evolution reaction (OER) is a crucial step in the process of water splitting. However, it exhibits sluggish kinetics and requires a significant overpotential for functioning at reasonable reaction rates. The efficiency of the reaction can be enhanced by reducing the overpotential, lowering the energy barrier, and using an effective electrocatalyst. Transition metal-based catalysts are well studied for this purpose. Specially, nickel–cobalt (Ni-Co) based catalysts have been regarded as the best OER electrocatalysts. Therefore, several studies have been carried out to enhance the electrocatalytic efficiency of Ni-Co catalysts. While mixing other transition metals with Ni-Co is a straightforward and reliable method to improve the OER activity of Ni-Co catalysts, there is still a need for a thorough examination of the design of Ni-Co catalysts with various additional elements. Seawater electrolysis, which utilizes abundant water resources that constitute over 97% of the world's water, is highly appealing for sustainable energy production. To achieve commercial feasibility, scientists are striving to solve challenges, such as corrosion resistance, high overpotential, and the need for efficient and durable electrocatalysts. In this study, we fabricated a transition metal-based trimetallic catalyst (CNF), consisting of cobalt (Co), nickel (Ni), and iron (Fe). Furthermore, CNF was doped with chromium (Cr-doped CNF) and tested for the OER in alkaline freshwater and alkaline seawater. Our Cr-doped trimetallic CNF catalyst demonstrates exceptional performance in both seawater and freshwater, with overpotential of 320 mV and 280 mV at 10 mA cm−2 current density, making it a promising candidate for large-scale, sustainable hydrogen production. [ABSTRACT FROM AUTHOR]

Transition metal-based alloy nanostructures have emerged as promising catalysts for electrochemical water splitting, offering a potential solution to the growing demand for clean and renewable energy. Also, research on encapsulation engineering of alloy nanostructures using carbon matrices has recently advanced, presenting a new approach that combines the conductive properties of carbon matrices with an alloy structure to enhance electrochemical performance in water splitting. However, the specific roles of the alloy core, carbon shell, and their synergistic effect in improving electrochemical performance are still not well understood. In this paper, we report on the encapsulation of a ternary Co–Fe–Al alloy nanostructure using a carbon matrix and investigate its electrochemical oxygen evolution reaction (OER). The optimized carbon matrix-encapsulated Co 0.3 Fe 0.2 Al 0.5 alloy catalyst demonstrated superior electrocatalytic activity for OER (achieving 250 mV at 10 mA cm−2) and long-term stability. Through density functional theory calculations, we also elucidate the crucial role of Al in enhancing the OER catalytic performance of the proposed carbon-encapsulated Co–Fe alloy catalyst. By comparing the free electron concentration and required applied potentials to trigger OER, we provide insights into the beneficial effects of incorporating Al into the Co–Fe alloy catalyst. [Display omitted] • CoFeAl alloy nanostructures within conductive carbon matrices, enhancing both stability and electrochemical performance for the oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • First report on metal nitride-oxynitride nanohybrid for water splitting. • Fabrication of transition metal nitride without direct use of ammonia gas. • Only 263 and 118 mV overpotential at 10 mA cm−2 current density for OER and HER, respectively for the nanohybrid. • Superior performance and stability than commercial RuO 2 and Pt-C couple in two-electrode alkaline water splitting reaction. Abstract Excellent Electrochemical water splitting with remarkable durability can provide a solution for the increasing global energy demand. Herein, we report an efficient and stable overall water splitting system; cobalt nitride-vanadium oxynitride nanohybrid, prepared from the polyaniline (PANI) mediated synthetic protocol. This nanohybrid produces significantly higher water oxidation, proton reduction as well as overall water splitting performances compared to the cobalt nitride, vanadium oxynitride or even noble metal catalyst systems. Only 263 mV overpotential is required to reach 10 mA cm−2 current density for oxygen evolution reaction (OER) and 118 mV for the same in case of hydrogen evolution reaction (HER). Finally, the bifunctional nanohybrid has been explored for the alkaline overall water splitting at cell voltage of 1.64 V to attain 10 mA cm−2 current density with long term stability for 100 h. Post-catalytic analyses have revealed the formation of defect rich amorphous CoO x sites leading to high OER activity, whereas crystalline Co(OH) 2 -Co δ +-N (0 < δ < 2) centres are generated after HER. To the best of our knowledge, this is the first example of a nitride-oxynitride nanohybrid system employed for the overall water splitting, and its superior activity and durability recommend its potential for practical utilization. [ABSTRACT FROM AUTHOR]

Development of efficient and stable electrocatalysts for oxygen evolution reaction (OER) under acidic conditions is desirable goal for commercializing proton exchange membrane (PEM) water electroyzer. Herein, we report iridium-doped hydrogenated titanate (Ir–HTO) nanobelts as a promising catalyst with a low-Ir content for the acidic OER. Addition of low-Ir (∼ 3.36 at%) into the single-crystalline HTO nanobelts with large exposed {100} facets significantly boost catalytic activity and stability for OER under acidic conditions. The Ir-HTO outperforms the commercial benchmark IrO 2 catalyst; an overpotential for delivering 10 mA cm−2 current density was reduced to about 25% for the Ir-HTO. Moreover, the catalytic performance of Ir-HTO is positioned as the most efficient electrocatalyst for the acidic OER. An improved intrinsic catalytic activity and stability are also confirmed for the Ir-HTO through in-depth electrochemical characterizations. Therefore, our results suggest that low-Ir doped single-crystalline HTO nanobelts can be a promising catalyst for efficient and durable OER under acidic conditions. • We developed an Ir-doped catalyst for the acidic oxygen evolution reaction (OER). • Ir was incorporated into a H 2 Ti 3 O 7 nanobelts (Ir–HTO) with large exposed {100} facets. • The single-crystalline nature of HTO increased the active sites for the OER. • The Ir-HTO nanobelts have a low Ir content (about 3–4 wt%) at the atomic scale. • The Ir-HTO nanobelts have high catalytic activity and durability for acidic OER. [ABSTRACT FROM AUTHOR]

[Display omitted] • Te and Cl co-doped NiFe MOF electrocatalyst was derived from NiFe MOF. • Te metalloid incorporation on MOFs facilitates electron transfer. • Incorporated halogen Cl could induce defects on MOF during OER. • The proposed co-doping process can improve performances of various MOF catalyst. Metal-organic frameworks (MOFs) are promising electrocatalysts for oxygen evolution reaction (OER) due to their large amounts of active sites reacting with water molecules and desired adsorption/desorption characteristics with oxygen intermediate. However, the intrinsically low electrical conductivity of MOFs hinders their commercialization for the highly efficient OER catalyst. Here, we report 2D morphological NiFe MOF electrocatalyst co-doped with metalloid and non-metal elements for the enhanced OER performances. Te metalloid incorporation on MOFs facilitates electron transfer from transition metals of MOFs to embedded metalloids, which improves OER kinetics enabling favorable adsorption of oxygen intermediate on the surface of the electrocatalyst. Incorporated halogen Cl element could effectively induce defects on MOF as leach out from the surface of electrocatalyst during OER, allowing more active sites exposed to reactants. With the synergistic effect of metalloid (Te) and halogen (Cl) doping on NiFe MOF, the Te and Cl co-doped NiFe MOF growth on Ni foam (NF) present an excellent OER property requiring low overpotential for 224 mV at 30 mA cm−2 in alkaline condition and long-term stability over 120 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fabrication of [Fe(CN) 6 ]3− coordination sphere vacancies in NiFe PBA. • [Fe(CN) 6 ]3− vacancies increase the oxidation state of Ni active species. • Reduced graphene oxide maximize the concentration of [Fe(CN) 6 ]3− vacancies. • [Fe(CN) 6 ]3− vacancies could prevent the dissolution of Fe. • Only 251 mV at 10 mA cm−2 and the long-term stability for 200 h in 1 M KOH. Development of efficient and durable electrocatalysts for the oxygen evolution reaction (OER) is essential for sustainable hydrogen production by water splitting. The physicochemical properties of the electrocatalyst can be tailored by defect engineering. Herein, we report the fabrication of [Fe(CN) 6 ]3− coordination sphere vacancies via the rapid coprecipitation in Ni 3 Ⅱ[FeIII (CN) 6 ] 2-x (x ≤ 0.12) electrocatalyst anchored on reduced graphene oxide (v-NiFe PBA@rGO) for OER. The formation of [Fe(CN) 6 ]3− coordination sphere vacancies (V FeCN) via the rapid coprecipitation during the synthesis under the absence of chelating agents enables the regulation of electronic states of Ni active site, leading to the improvement in OER. Reduced graphene oxide (rGO) is employed as a substrate to maximize the concentration of V FeCN and exposed active sites by the uniform formation of nano-sized Ni 3 Ⅱ[FeIII (CN) 6 ] 2-x. The presence of V FeCN and hybridization with rGO effectively suppress Fe leaching behavior. The v-NiFe PBA@rGO shows a low overpotential of 251 mV at 10 mA cm−2 in alkaline condition and the long-term stability for 200 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • HER and ORR electrocatalyst derived from Ni MOF was synthesized. • N-doped carbon layer was implemented to protect the HER catalyst. • ORR catalytic carbon layer coating increases HER stability. • The proposed method can enhance the stability of various Ni-based catalysts. Alkaline electrolysis is one of the most powerful technologies to produce hydrogen energy, where the electrocatalysts play an important role. The cathode electrocatalysts often suffer from undesirable oxidation due to the oxygen gas crossover through the porous separator during electrolysis. This leads to oxygen reduction reaction (ORR) on the cathode electrocatalysts, resulting in the loss of activity for hydrogen evolution reaction (HER). Here, we report a highly efficient and durable HER and ORR bifunctional electrocatalyst derived from Ni metal-organic frameworks to address the above problem. Decoupled active sites for ORR and HER are induced in a hybrid material, NiFeP@Ni_NC, where an ORR catalytic N-doped nanocarbon layer can protect a HER catalytic Niδ+ from the undesired ORR. Therefore, excellent bifunctional stability is secured for NiFeP@Ni_NC. The strategy to enhance HER stability presented herein can be widely extended to design bifunctional electrocatalysts with improved stability in alkaline electrolysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfidation performed on these homogeneously grown nanosheets (NiFe-LDH-S) via a facile CVD process. • Optimal NiFe-LDH-S sample demonstrated excellent catalytic activity. • NiFe-LDH-S showed high corrosion resistance for seawater oxidation. • Synthesized NiFe-LDH-S350 exhibited enhanced intrinsic catalytic activity metrics. Given the abundance of water on the surface of the Earth, water splitting using seawater may be an effective solution to the future energy crisis. However, oxygen evolution reaction (OER) electrocatalysts require several specific characteristics to be used in seawater electrolysis, such as high catalytic activity, selectivity, and resistivity against chlorine corrosion. This paper reports that sulfur incorporation into nickel–iron layered double hydroxide (NiFe-LDH-S) can fulfill the abovementioned requirements for seawater oxidation. Sulfidation was performed on NiFe-LDH nanosheets homogeneously grown on a porous carbon scaffold via a facile chemical vapor deposition (CVD) process. The best NiFe-LDH-S sample demonstrated excellent catalytic activity with a high corrosion resistance for seawater oxidation. [ABSTRACT FROM AUTHOR]

• CMO based nanorods have been synthesized through an oxalate precipitation method. • The overpotential decreases from 425 mV at 10 mA cm−2 to 365 mV after the lower the annealing temperature. • The OER activity is improved due to the synergistic effect of large surface area and surface defects as catalytic active sites. Development of a cost-effective oxygen evolution reaction (OER) catalyst for hydrogen production from water has attracted the attention of scientists due to its potential to solve current environmental and energy issues, such as CO 2 emissions and depletion of fossil fuels. In this paper, we report a facile synthesis to develop cobalt-manganese-oxide (Mn x Co 3−x O 4 , CMO) nanorods via an oxalate precipitation method followed by annealing at different temperatures. Importantly, morphology and surface area of the CMO nanorods, which are directly related to the OER activity, can be precisely controlled by changing annealing temperatures. The CMO nanorods engineered by oxalate precipitation and subsequent heat treatment show promising OER catalytic performance, such as a small overpotential of 365 mV for generating a current density of 10 mA cm−2, a low Tafel slope of 50.6 mV dec−1, and excellent long-term stability in alkaline media. Electrochemical properties combined with materials characterization provide insightful information on the OER mechanism of the CMO nanorods. [ABSTRACT FROM AUTHOR]