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Urea oxidation reaction (UOR) has been utilized to substitute the oxygen evolution reaction (OER), to escalate the energy conversion efficiency in electrochemical hydrogen generation processes with denitrification of widespread urea in wastewater. This study reports breakthroughs in Ni‐based UOR electrocatalysts, particularly with NiFe oxalate (O‐NFF), derived from Ni3Fe alloy foam with prismatic nanostructures and elevated surface area. The O‐NFF achieves cutting‐edge performances, representing 500 mA cm−2 of current density at 1.47 V RHE and exceptionally low Tafel slope of 12.1 mV dec−1 (in 1 m KOH with 0.33 m urea). X‐ray photoelectron/absorption spectroscopy (XPS/XAS) coupled with density functional theory calculations unveil that oxalate ligands induce charge deficient Ni center, promoting stable urea‐O adsorption. Furthermore, Fe dopants enhance oxalate‐O charge density and H‐bond strength, facilitating C‐N cleavage for N2 and NO2− formation. The extraordinary UOR kinetics by the tandem effects of oxalate and Fe prevent Ni over‐oxidation, corroborated by operando XAS, minimizing OER interference. It agrees with an adaptive reconstruction to Fe‐doped β‐NiOOH on top surface in extended urea electrolysis with marginal loss in UOR kinetics. This findings shed light to bimetal‐organic‐framework as (pre)catalysts to improve industrial electrolytic H2 production. [ABSTRACT FROM AUTHOR]

Transition metal oxides are considered alternative electrocatalysts for ZAB owing to their multiple oxidation states. However, they have limitations such as low electrical conductivity and the deficiency of reactive sites. In this study, to overcome these shortcomings and improve electrocatalytic activity, oxygen vacancies and porous architectures were introduced through a partial reduction process and a porous carbon framework. Open porous carbon microspheres with uniformly loaded NiCo2O4 nanosheets and oxygen vacancies (V-NCO/OPC) displayed enhanced electrocatalytic performance with a low Tafel slope (68 mV dec-1) in the oxygen reduction reaction (ORR) and a low overpotential (402 mV) at 10 mA cm–2 in the oxygen evolution reaction (OER). The combined effect of the oxygen vacancies and porous architecture can offer sufficient active sites, modify the electronic structure of the metal oxide surface, and facilitate mass transport, enhancing the electrocatalytic properties of V-NCO/OPC. Furthermore, when applied for ZAB, V-NCO/OPC demonstrated better electrochemical performance including discharge power density (154.9 mW cm-2) at the current density of 175.9 mA cm-2, low voltage gap (0.85 V) at the initial cycle, and long-term (250 h) cycle stability at the current density of 10 mA cm−2 than those of noble-metal electrocatalysts. [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 oxygen evolution reaction (OER) suffers from sluggish kinetics even on the benchmark RuO2 catalyst, due to the complex four sequential proton‐coupled electron transfer steps. Severe electrochemical oxidation and dissolution issues also make RuO2 fail as an alternative to highly expensive iridium‐based OER catalysts applied in proton exchange membrane water electrolysis. Herein, an acid‐stable W18O49‐δ matrix‐confined Ru solid solution oxide is developed with considerably reduced Ru loadings beyond commercial RuO2, to enhance the acidic OER kinetics and extend the long‐term durability simultaneously by incorporating Brønsted acid sites. The representative Ru0.6W17.4O49‐δ with 3D urchin‐like morphology achieves an excellent catalytic stability with ultra‐slow degradation rate and a high mass activity of 27 110 A g−1Ru @ 1.53 V versus RHE in 0.1 m HClO4 electrolyte, which is ≈10.8 times higher than that of commercial RuO2. The enhanced electron transfer from W to Ru during the OER process prevents the over‐oxidation of surface Ru sites extending the long‐term stability, while the incorporated Ru‐Obri‐W Brønsted acid sites accelerate the deprotonation step by promoting the mobility of proton from the oxo‐intermediate to the neighboring Obri sites, thus boosting the acidic OER kinetics. [ABSTRACT FROM AUTHOR]

Here,nonprecious high‐entropy chalcogenide glasses (N‐HECGs) consisting of Co, Fe, Ni, Mo, W, and Te are demonstrated in a first demonstration of acidic oxygen evolution reaction (OER). N‐HECGs electrocatalysts with high activity and stability are synthesized using a hierarchical hybrid approach based on a combination of electrochemical deposition and tellurization process. The as‐prepared CoFeNiMoWTe N‐HECGs electrocatalysts exhibit an amorphous, porous structure of arrayed nanosheets with abundant active sites and the increased valence states of metal cations due to the incorporated non‐metallic Te, enabling the enhancement of glass forming ability and the valence states of metal elements. Thanks to the combination of their unique geometrical and chemical structure, as well as high configuration entropy nature and high corrosion‐resistance ability, the resultant CoFeNiMoWTe N‐HECGs exhibit excellent acidic OER catalytic performance with a superior overpotential of 373 mV and outstanding stability of 100 h at the current density of 10 mA cm−2 in 0.5 m H2SO4. Moreover, the CoFeNiMoWTe‐based proton exchange membrane water electrolyzer is demonstrated to require a cell voltage of 1.81 V at 70 °C to obtain the practically high current density of 1 A cm−2, and exhibits remarkably long‐term stability for 100 h with small potential degradation of only 30 mV. [ABSTRACT FROM AUTHOR]

The development of efficiently active and stable bifunctional noble‐metal‐based electrocatalysts toward overall water splitting is urgent and challenging. In this work, a rutile‐structured ruthenium‐zinc solid solution oxide with oxygen vacancies (Ru0.85Zn0.15O2‐δ) is developed by a simple molten salt method. With naturally abundant edges of ultrasmall nanoparticles clusters, Ru0.85Zn0.15O2‐δ requires ultralow overpotentials, 190 mV for acidic oxygen evolution reaction (OER) and 14 mV for alkaline hydrogen evolution reaction (HER), to reach 10 mA cm−2. Moreover, it shows superior activity and durability for overall water splitting in different electrolytes. Experimental characterizations and density functional theory calculations indicate that the incorporation of Zn and oxygen vacancies can optimize the electronic structure of RuO2 by charge redistribution, which dramatically suppresses the generation of soluble Rux>4 and allows optimized adsorption energies of oxygen intermediates for OER. Meanwhile, the incorporation of Zn can distort local structure to activate the dangling O atoms on the distorted Ru0.85Zn0.15O2‐δ as proton acceptors, which firmly bonds the H atom in H2O* to stabilize the H2O and considerably improves the HER activity. [ABSTRACT FROM AUTHOR]

Reducing the particle sizes of transition metals [TMs] and avoiding their aggregation are crucial for increasing the TMs atom utilization and enhancing their industrial potential. However, it is still challenging to achieve uniform distributed and density-controlled TMs nanoclusters [NCs] under high temperatures due to the strong interatomic metallic bonds and high surface energy ofNCs. Herein, a series ofTMs NCs with controllable density and nitrogen-modulated surface are prepared with the assistance of a selected covalent organic polymer [COP], which can provide continuous anchoring sites and size-limited skeletons. The prepared Ir NCs show superior hydrogen evolution reaction [HER] and oxygen evolution reaction [OER] activities than commercial Pt/C and Ir/C in both acid and alkaline media. In particular, the as-prepared Ir NCs exhibit remarkable full water splitting performance, reaching a current density of 10 mA cm-2 at ultralow overpotentials of 1.42 and 1.43 V in alkaline and acidic electrolyte, respectively. The excellent electrocatalytic activities are attributed to the increased surface atom utilization and the improved intrinsic activity ofIr NCs. More importantly, the Ir NCs catalyst shows superior long-term stability due to the strong interaction between Ir NCs and the N-doped carbon layer. [ABSTRACT FROM AUTHOR]

Promoting the activity of Ir-based nanomaterials for oxygen evolution reaction (OER) in acid media without losing their durability is crucial for reducing overpotentials in energy conversion, such as electrochemical water splitting. Here, a nanocomposite composed of a-IrOx and lanthanum salt (LaCO3OH) was constructed to further improve its OER activity by tuning the electronic structure of a-IrOx, because a-IrOx is a well-known critical material as the active layer of Ir-based anodic catalysts. The interaction between Ir and La via O atoms as a bridge in the catalyst IrOx/LaCO3OH, verified by X-ray absorption near edge structure spectroscopy, tunes the electronic structure of a-IrOx and thus obviously enhances its activity for the OER in acid media, compared with commercially available IrO2 as well as most of the reported Ir-based OER electrocatalysts. The overpotential of IrOx/LaCO3OH at a current density of 10 mA cm−2 is 255 mV with a Tafel slope of 55 mV dec−1. This work reveals that the strong electronic interaction between Ir- and La-based materials can efficiently improve activity and reduce energy consumption, as well as enlarging the family of acidic OER electrocatalysts. [ABSTRACT FROM AUTHOR]

The development of an efficient pH‐universal hydrogen evolution reaction (HER) electrocatalyst is essential for practical hydrogen production. Here, an efficient and stable pH‐universal HER electrocatalyst composed of the strongly coupled 2D NiCo2S4 and 2D ReS2 nanosheets (NiCo2S4/ReS2) is demonstrated. The NiCo2S4/ReS2 2D–2D nanocomposite is directly grown on the surface of the carbon cloth substrate, which exhibits excellent HER performance with overpotentials of 85 and 126 mV at a current density of 10 mA cm−2 and Tafel slopes of 78.3 and 67.8 mV dec−1 under both alkaline and acidic conditions, respectively. Theoretical and experimental characterizations reveal that the chemical coupling between NiCo2S4 and ReS2 layers induces electron transfer from Ni and Co to interfacial Re‐neighbored S atoms, enabling beneficial H atom adsorption and desorption for both acidic and alkaline HER. Simultaneously, an electron transfer‐induced spin‐crossover generates high‐spin interfacial Ni and Co atoms that promote water dissociation kinetics at the NiCo2S4/ReS2 interface, which is the origin of the superior alkaline HER activity. NiCo2S4/ReS2 also shows decent catalytic activity and long‐term durability for oxygen evolution reaction, and finally bifunctionality for overall water splitting. This study suggests a rational strategy to enhance water dissociation kinetics by inducing spin‐crossover via electron transfer. [ABSTRACT FROM AUTHOR]

A composite catalyst of nano-grade IrO 2 /TiO 2 powder is synthesized by Adams' fusion method for reducing overvoltage of solid polymer electrolyte (SPE) cell and cost-down of noble metal catalyst, simultaneously. The IrO 2 /TiO 2 catalysts, which has a porous composite nanostructure, are prepared according to molar ratio of Ir and Ti element with a specific surface area of 34.1–55.3 m2 g−1. It is found that crystal structure of TiO 2 is more dominated by the rutile phase than by Anatase. For a SPE system, total catalyst loading of anode which made of TiO 2 and IrO 2 is prepared as low as 0.77 mg cm−2 or less, in which the loading amount of the IrO 2 only is set to 0.6 mg cm−2 or less. The anode catalyst layer of about 10 ㎛ thickness is coated on the membrane (Nafion 212) for the membrane electrode assembly (MEA) by the decal method. The strong adhesion between the catalyst electrode the membrane is observed by Scanning electron microscopy (SEM). Linear sweep voltammetry (LSV) results shows that the nano-composite IrO 2 /TiO 2 catalysts has better oxygen evolution reaction (OER) than that of the synthesis IrO 2 only. Finally, the IrO 2 /TiO 2 catalysts is applied as anode electrode for SPE cells and it is observed that in spite of the lower loading amount of the IrO 2 less than 0.5 mg cm−2, working voltage of 1.68 V is observed at a current density of 1 A cm−2 and operating temperature of 80 °C. • Nano-composite Ir 2 /TiO 2 as anode catalyst is synthesized by Adam's Fusion method. • The loading amount of IrO 2 is reduced less than 0.5 mg cm−2 for SPE electrolysis. • The Ir 2 /TiO 2 shows enhanced durability properties for SPE electrolysis at 1 A cm−2. [ABSTRACT FROM AUTHOR]

NiFe‐based hydroxides are considered as promising nonprecious catalysts for water oxidation due to their low cost and easy preparation. However, the rational design of NiFe‐based electrocatalysts remains a great challenge to address the sluggish reaction kinetics and severe deactivation problems for oxygen evolution reaction (OER). Here, the authors report a facile approach to fabricate an amorphous Ce‐doped NiFe hydroxide catalyst, which enables high activity and outstanding stability toward OER in alkaline media. The overpotential of electrodeposited amorphous Ce‐doped NiFe is only 195 mV at 10 mA cm−2. Meanwhile, the durability of the amorphous Ce‐doped NiFe is maintained for 300 h at 100 mA cm−2. The comprehensive characterization results reveal that the improved electrochemical performance of the amorphous Ce‐doped NiFe catalyst is originated from the favorable oxidation transition of active sites enabled by Ce‐doping. It is a very good strategy to introduce highly oxidized state ions to regulate the NiFe‐based catalyst to improve the catalytic activity and stability. [ABSTRACT FROM AUTHOR]

In water splitting, anode catalysts for the oxygen evolution reaction (OER), which is the rate‐determining step, are more critical than cathode catalysts. Herein, the authors prepare Ni‐IrOx composite catalysts consisting of NiO and IrO2 for the OER by a solid‐state reaction with different ratios of NiO to IrO2 and reaction temperatures. In particular, Ni‐IrOx‐400 with a molar ratio of NiO/IrO2 = 1:1 heated at 400 °C shows the best OER performance. In the overall water splitting test using an anion exchange membrane (AEM) water electrolyzer, the single cell with Ni‐IrOx‐400 as the anode catalyst shows current densities of 1454.8 mA cm−2, respectively, measured at 1.8 V. Furthermore, the stability tests of the AEM single cells are carried out at 50 °C under a constant current density of 500 mA cm−2. The single cell with Ni‐IrOx‐400 shows only a slight increase in the overpotential (rate: 2.0 mV h−1) for 100 h owing to the enhanced stability of Ni‐IrOx‐400 compared to IrO2 (12.5 mV h−1). The improved OER performance of the Ni‐IrOx‐400 may be attributed to a composite structure that can prevent particle agglomeration and thus preserve the active sites during the OER. [ABSTRACT FROM AUTHOR]

The poor catalyst stability in acidic oxidation evolution reaction (OER) has been a long-time issue. Herein, we introduce electron-deficient metal on semiconducting metal oxides-consisting of Ir (Rh, Au, Ru)-MoO3 embedded by graphitic carbon layers (IMO) using an electrospinning method. We systematically investigate IMO's structure, electron transfer behaviors, and OER catalytic performance by combining experimental and theoretical studies. Remarkably, IMO with an electron-deficient metal surface (Irx+; x > 4) exhibit a low overpotential of only ~156 mV at 10 mA cm−2 and excellent durability in acidic media due to the high oxidation state of metal on MoO3. Furthermore, the proton dissociation pathway is suggested via surface oxygen serving as proton acceptors. This study suggests high stability with high catalytic performance in these materials by creating electron-deficient surfaces and provides a general, unique strategy for guiding the design of other metal-semiconductor nanocatalysts. The poor catalyst stability for oxygen evolution in acidic media has been a long-time issue. Here, authors demonstrate iridium on MoO3 exhibits a low overpotential for oxygen evolution and excellent durability in acidic media due to the high oxidation state of iridium metal on MoO3. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is a key reaction for many electrochemical devices. To date, many OER electrocatalysts function well in alkaline media, but exhibit poor performances in neutral and acidic media, especially the acidic stability. Herein, sodium‐decorated amorphous/crystalline RuO2 with rich oxygen vacancies (a/c‐RuO2) was developed as a pH‐universal OER electrocatalyst. The a/c‐RuO2 shows remarkable resistance to acid corrosion and oxidation during OER, which leads to an extremely high catalytic stability, as confirmed by a negligible overpotential increase after continuously catalyzing OER for 60 h at pH=1. Besides, a/c‐RuO2 also exhibits superior OER activities to commercial RuO2 and most reported OER catalysts under all pH conditions. Theoretical calculations indicated that the introduction of Na dopant and oxygen vacancy in RuO2 weakens the adsorption strength of the OER intermediates by engineering the d‐band center, thereby lowering the energy barrier for OER. [ABSTRACT FROM AUTHOR]

To develop effective electrocatalytic splitting of acidic water, which is a key reaction for renewable energy conversion, the fundamental understanding of sluggish/destructive mechanism of the oxygen evolution reaction (OER) is essential. Through investigating atom/proton/electron transfers in the OER, the distinctive acid–base (AB) and direct‐coupling (DC) lattice oxygen mechanisms (LOMs) and adsorbates evolution mechanism (AEM) are elucidated, depending on the surface‐defect engineering condition. The designed catalysts are composed of a compressed metallic Ru‐core and oxidized Ru‐shell with Ni single atoms (SAs). The catalyst synthesized with hot acid treatment selectively follows AB‐LOM, exhibiting simultaneously enhanced activity and stability. It produces a current density of 10/100 mA cm−2 at a low overpotential of 184/229 mV and sustains water oxidation at a high current density of up to 20 mA cm−2 over ≈200 h in strongly acidic media. [ABSTRACT FROM AUTHOR]

Developing highly active, durable, and cost‐effective electrocatalysts for the oxygen evolution reaction (OER) is of prime importance in proton exchange membrane (PEM) water electrolysis techniques. Herein, a surface lanthanum‐deficient (SLD) iridium oxide as a highly efficient OER electrocatalyst is reported (labeled as La3IrO7‐SLD), which is obtained by electrochemical activation, and shows better activity and durability than that of commerically available IrO2 as well as most of the reported Ir‐based OER electrocatalysts. At a current density of 10 mA cm−2, the overpotential of La3IrO7‐SLD is 296 mV, which is lower than that of IrO2 (316 mV). Impressively, the increase of potential is less than 50 mV at a voltage–time chronopotentiometry extending for 60 000 s using a glass carbon electrode that is vastly superior to IrO2. Moreover, the mass activity of the catalyst is approximately five times higher than that of IrO2 at 1.60 V versus reversible hydrogen electrode. Density functional theory calculations suggest that a lattice oxygen participating mechanism with central Ir atoms serving as active sites (LOM‐Ir) rationalizes the high activity and durability for the La3IrO7‐SLD electrocatalyst. The favorable energy level of surface active Ir 5d orbitals relative to coordinated O 2p orbitals makes the La3IrO7‐SLD more active. [ABSTRACT FROM AUTHOR]

Developing highly efficient and durable bifunctional electrocatalyst for oxygen reduction (ORR) and oxygen evolution reaction (OER) is quite important for developing rechargeable zinc‐air batteries. Herein, one kind of manganese phosphate‐based electrocatalyst (Mnx(PO4)y/NPC) with high specific surface area (1106.9 m2 g−1) is prepared via a facile and scalable avenue, which possesses remarkable catalytic performance for the both ORR and OER, indicated by a more positive half‐wave potential of 0.87 V in 0.1 M KOH for the ORR as well as an overpotential of 0.37 V to achieve the current density of 10 mA cm−2 in 1 M KOH for the OER. Furthermore, the Mnx(PO4)y/NPC assembled rechargeable zinc‐air battery shows an excellent charge‐discharge cycling performance, revealed by the smaller sum of charge‐discharge potentials, comparable to that of Pt/C+IrO2. This research adds a new kind of electrocatalyst into the family of non‐noble metal‐based bifunctional electrocatalyst for rechargeable zinc‐air batteries. Re‐charge ahead: Mnx(PO4)y/NPC exhibits excellent catalytic performance for both ORR and OER, which possesses more superior electrochemical performance than Pt/C for the application in zinc‐air battery. The specific approaches to 668 mA h gZn−1. This work provides a facile and efficient avenue to synthesize non‐precious electrocatalyst with bifunctional catalytic effects and using in rechargeable zinc‐batteries. [ABSTRACT FROM AUTHOR]

• Composite of Co(OH)Se and C was constructed through selenization process using a NaHSe solution. • Co(OH)Se-C revealed excellent bifunctional activities for catalyzing ORR and OER. • Co(OH)Se-C cathode showed excellent electrochemical properties for Zn-air batteries. Multi-anionic transition metal compounds with unique electron structures that are favorable for electron transfer are promising oxygen electrocatalysts. In this study, to synthesize a bifunctional oxygen electrocatalyst for Zn-air batteries (ZABs), unique structured composite of cobalt hydroxy selenide (Co(OH)Se) and nitrogen-doped carbon (C) was fabricated using a novel water vapor-assisted heat-treatment and an anion-exchange technique using a NaHSe solution. C@Co(OH)Se prepared under low-temperature and low-pressure condition successfully exhibited excellent electrocatalytic activities for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) via synergistic effects. Accordingly, C@Co(OH)Se-based ZAB displayed great cycle stability (discharge/charge potential gap of 1.01 V after 7,000 min cycling) and rate capability (1.25 V at 15 mA cm−2). By first demonstrating the potential use of multi-anionic Co(OH)Se as a bifunctional electrocatalyst for the ORR/OER and presenting a technique for complexing transition metal compounds and carbon matrices, our study expands the range of electrocatalyst design and synthesis. [ABSTRACT FROM AUTHOR]

In this paper, Ni‐based titanate nanosheets are used as a model system to reveal how incorporation of Fe affects their catalytic ability for the oxygen evolution reaction (OER). The Fe incorporation effects are studied without structural and morphological changes due to the rigid framework of TiO2 based nanosheets. Transition metal doped titanate nanosheets are prepared by cation‐assisted exfoliation of protonated layered potassium titanate. Fe incorporation within the lattice of Ni doped titanate nanosheets by co‐doping stabilizes nickel ions in lower oxidation state by charge transfer effect, caused increased OER activity at Ni sites by the electronic interaction. In contrast, incorporation of Fe from the electrolyte, highly‐active Fe sites at edges or corners of Ni doped titanate nanosheets are formed by electrochemical cycling in Fe‐containing electrolyte rather than electronic effects on Ni. Through this work, Fe incorporation effects are experimentally revealed without crystal structural or morphological changes, and a method to produce a highly active and stable OER catalyst is provided. [ABSTRACT FROM AUTHOR]

Anion exchange membrane water electrolysis (AEMWE) uses a zero-gap membrane-electrode-assembly (MEA) consisting of a polymer electrolyte membrane and non-precious metal-based catalysts. However, anode catalysts for the oxygen evolution reaction (OER), which is the rate-determining-step in WE, need to be intensively developed to achieve superior electrocatalytic activity and stability. Herein, we report the synthesis and characterization (experimental and simulation) of spherical Ni-doped (5–15 at%) cobalt phosphide (Ni-CoP) as the anode catalyst for the OER. Specifically, the DFT calculation exhibited that the addition of Ni in CoP might increase the energy density in the Fermi level of pristine CoP, enhance the charge transfer rate during the OER, and reduce the energy barrier for the formation of OOH* , thereby boosting the OER activity. The prepared Ni-doped CoP catalyst was directly loaded onto a foam-type Ni-based gas diffusion layer for effective application in AEMWE. It was found that the electrocatalytic activity of the AEMWE depends on the porosity of the NFs as catalyst substrates. The unit cell containing the membrane-electrode-assembly fabricated with NCP-10 delivered a high current density of 1.12 A cm−2 at 1.8 V and a low reduction rate of 0.64 mA cm−2 h−1 for 250 h. [Display omitted] • Spherical Ni-doped CoP (NCP) was prepared as the anode catalyst for the OER. • The prepared NCP catalyst was loaded onto a Ni-foam (NF) in AEMWE. • The electrocatalytic activity of the AEMWE depends on the porosity of the NFs. • CoP doped with 10 at% Ni (NCP-10) exhibited improved OER performance. • The AEMWE fabricated with NCP-10 delivered enhanced performance. [ABSTRACT FROM AUTHOR]

Perovskite oxide ceramics attracts significant attention as a strong candidate of bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalyst for the metal-air batteries. Numerous approaches to the viability of bifunctional perovskite electrocatalyst represent that the electro­chemical performance is highly correlated with defect chemistry, surface structure, and overall polycrystalline perovskite structure. By making use of the intrinsic flexibility of internal structure and high nonstoichiometry in perovskite oxide, the heat treatment effect of the complex Ba0.5Sr0.5Co xFe1- xO3-δ ( x = 0.2 and 0.8) perovskites in argon atmosphere at 950 °C (Ar-BSCF5582 and Ar-BSCF5528) on the surface structure/defect chemistry and electrocatalytic performance is intensively investigated. Upon heat-treatment in argon atmosphere, the amorphous thickness layer increases from ≈20 to 180-200 nm in BSCF5582, while there is little change in BSCF5528 with ≈20 nm. The electrocatalytic performance of BSCF5582 catalyst both in ORR and OER deteriorates seriously, while Ar-BSCF5528 demonstrates a significant increase of electro­chemical performance in ORR. This study demonstrates that the electrochemical performances of a perovskite catalyst can be significantly determined by the simultaneous modification of both surface structure and internal defect chemistry, which are explained with transmission electron microscopy and atomic-selective X-ray absorption fine structure analyses, respectively. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) along with hydrogen evolution reaction (HER) have been considered critical processes for electrochemical energy conversion and storage through metal-air battery, fuel cell, and water electrolyzer technologies. Here, a new class of multifunctional electrocatalysts consisting of dominant metallic Ni or Co with small fraction of their oxides anchored onto nitrogen-doped reduced graphene oxide (rGO) including Co-CoO/N-rGO and Ni-NiO/N-rGO are prepared via a pyrolysis of graphene oxide and cobalt or nickel salts. Ni-NiO/N-rGO shows the higher electrocatalytic activity for the OER in 0.1 m KOH with a low overpotential of 0.24 V at a current density of 10 mA cm−2, which is superior to that of the commercial IrO2. In addition, it exhibits remarkable activity for the HER, demonstrating a low overpotential of 0.16 V at a current density of 20 mA cm−2 in 1.0 m KOH. Apart from similar HER activity to the Ni-based catalyst, Co-CoO/N-rGO displays the higher activity for the ORR, comparable to Pt/C in zinc-air batteries. This work provides a new avenue for the development of multifunctional electrocatalysts with optimal catalytic activity by varying transition metals (Ni or Co) for these highly demanded electrochemical energy technologies. [ABSTRACT FROM AUTHOR]

The lack of high-efficient, low-cost, and durable bifunctional electrocatalysts that act simultaneously for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is currently one of the major obstacles to commercializing the electrical rechargeability of zinc-air batteries. A nanocomposite CoO-NiO-NiCo bifunctional electrocatalyst supported by nitrogen-doped multiwall carbon nanotubes (NCNT/CoO-NiO-NiCo) exhibits excellent activity and stability for the ORR/OER in alkaline media. More importantly, real air cathodes made from the bifunctional NCNT/CoO-NiO-NiCo catalysts further demonstrated superior performance to state-of-the-art Pt/C or Pt/C+IrO2 catalysts in primary and rechargeable zinc-air batteries. [ABSTRACT FROM AUTHOR]

La0.3(Ba0.5Sr0.5)0.7Co0.8Fe0.2O3− δ is a promising bifunctional perovskite catalyst for the oxygen reduction reaction and the oxygen evolution reaction. This catalyst has circa 10 nm-scale rhombohedral LaCoO3 cobaltite particles distributed on the surface. The dynamic microstructure phenomena are attributed to the charge imbalance from the replacement of A-site cations with La3+ and local stress on Co-site sub-lattice with the cubic perovskite structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ferric oxyhydroxides NPs (FON) was synthesized by straightforward hydrolysis route. • FON has a spindle morphology with nano-sized grains and pores. • FON exhibits a good energy storing ability and electrocatalytic activity. • Outstanding structural features of the material enhance electrochemical activity. • Thereby help it better serve as both energy storage devices and electrocatalysts. The rational design and development of novel electrode materials with a unique hierarchical nanostructure is crucial for improving their electrochemical activities, charge transfer kinetics, energy efficiency, and energy-storing ability in energy conversion and storage devices. In this study, we synthesized spindle-shaped ferric oxyhydroxide nanoparticles directly grown on carbon cloth (spindle-FON/CC) by a facile and straightforward hydrolysis method. This material is a promising candidate for the fabrication of efficient electrodes used in supercapacitors (SCs) and electrocatalytic cells for the oxygen evolution reaction (OER). The as-prepared spindle-FON/CC exhibits unique structural features with nano-sized grains and pores that provide large electrolyte contact areas (electrochemically active sites) and favorable ion diffusion pathways. These structural properties lead to efficient capacitive behavior and electrochemical catalytic activity. The as-prepared spindle-FON/CC electrode showed a high specific capacitance of 612.5 mF cm−2 and outstanding cycling stability (95.7 % capacitance retention after 4,000 cycles). When used as an OER electrocatalyst, the spindle-FON/CC exhibited improved electrocatalytic activity with a low overpotential of 216 mV at a current density of 10 mA cm−2 and a small Tafel slope of 73.4 mV dec−1. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dual functions of hot H 2 S treatment is utilized for nanostructuring of bulk Co 3 O 4. • Nanostructured Co 3 O 4 /CoO@CoS x is formed as a result of reduction and sulfurization. • Catalytic activity of Co 3 O 4 /CoO@CoS x is comparable to that of state-of-the-art IrO 2. • This thermal method is generalizable to other bulk oxides. Nanostructuring is an essential step in synthesizing highly active electrocatalysts. Unfortunately, it has not been widely adopted in the electrodes of commercial electrolyzers because of difficulties associated with scalability and process complexity. As a remedy to this long-standing problem, we demonstrate a facile thermal route to transform poor oxide electrocatalysts into highly active ones by utilizing hot H 2 S gas as a dual functional agent. Using bulk cobalt oxide as a model system, we reveal that H 2 S that would otherwise be stable up to 1000 °C can be catalytically decomposed on the surface of Co 3 O 4 into H 2 and sulfur species at a moderately high temperature. The produced H 2 and sulfur react with Co 3 O 4 and transform it into nanostructured Co 3 O 4 /CoO@CoS x particles that are highly active towards the oxygen evolution reaction. The optimum sample can be produced after only 10 min of H 2 S treatment, highlighting the simplicity and scalability of our process. [ABSTRACT FROM AUTHOR]

The water splitting for hydrogen energy is largely constrained by sluggish anodic oxygen evolution reaction (OER). Cobalt oxide, one of the most promising non‐noble metal catalysts for OER, can exhibit highly enhanced catalytic OER activity when deposited on gold substrates. However, it still remains challenging to develop efficient Au/Co3O4 catalysts that can maximize the catalytic activity with the minimum use of gold. Here is reported a simple leaching derived synthesis of atomically dispersed/clustered gold on mesoporous cobalt oxides as highly efficient catalysts for OER. With greatly lowered gold contents <1 wt%, the catalyst shows twice as much current density and Au normalized activity than mesoporous cobalt oxide at 400 mV overpotential. The present work provides a simple synthesis route toward atomically dispersed/clustered gold supported catalysts, which can be extended to the development of a wide variety of efficient nanocatalysts that can be designed for specific applications. [ABSTRACT FROM AUTHOR]

For a high-performance OER, we synthesized NiFe LDH as an anode catalyst with a high specific surface area and electrical conductivity using a solvent ratio-adjusted hydrothermal method. [Display omitted] • We synthesized NiFe LDH using a solvent ratio-adjusted hydrothermal method. • The oxygen vacancies produced by alcoholysis promote the charge transfer rate. • The interplanar distance was increased by inserting nitrate in NiFe LDH. • WE 55 synthesized at a proper ratio of water and ethanol showed the best performance. NiFe layered double hydroxides (LDH) with their high specific surface areas have been used as alternatives to noble metal catalysts for the oxygen evolution reaction (OER) in anion exchange membrane water electrolysis. However, for bulk LDH structures, relatively narrow interplanar distances can lead to the slow diffusion of OH− and the induction a local acidic atmosphere, resulting in catalyst corrosion. In this study, we synthesize solvent (water and ethanol) ratio-adjusted NiFe LDH anode catalysts to enhanced the OER. Results show that the catalyst prepared at a 5:5 ratio of water and ethanol (WE 55) delivers a low overpotential of 310 mV at 50 mA cm−2, Tafel slope of 40.5 mV dec−1, and 100 h-stability in a half-cell test, and a high current density of 744.2 mA cm−2 at 1.8 V and 70 °C in a single-cell test. WE 55 exhibits a manipulated oxygen vacancy and a substantially high specific surface area of ∼ 164.5 m2 g−1, leading to improved charge transfer and mass transport rates. [ABSTRACT FROM AUTHOR]

[Display omitted] • Facile synthesis of Ni 2 P supported on nitrogen doped-carbon (Ni 2 P@N-C). • Bifunctional activity for ammonia oxidation (AOR) and hydrogen evolution (HER). • Ni 2 P@N-C electrocatalyst exhibits about 78% decomposition of ammonia. • The hydrogen generation is estimated to be 2.144 mmol (H2) /mol (NH3) h cm2. • A low energy consumption rate of 8.611 KWH Kg (H2) −1 was achieved. Ammonia, as an efficient hydrogen carrier, is emerging as an alternative energy resource to replace fossil fuels in the carbon–neutral era. Hydrogen production by water electrolysis seeks a lower potential dependent anodic reaction to overcome its energy-inefficiency that originates from the high potential anodic oxygen evolution reaction (OER). In this work, nickel phosphide supported on nitrogen doped-carbon (Ni 2 P@N-C) was prepared by one-pot synthesis for the bifunctional activity of hydrogen evolution (HER) and ammonia oxidation (AOR) reactions. The Ni 2 P@N-C electrocatalyst exhibits about 78% decomposition of ammonia compared to the initial concentration. The amount of hydrogen generated in a 0.5 M ammonia environment for 30 min is about 2.144 mmol (H 2) / mol (N H 3) h cm2. The fabricated ammonia electrolysis cell demonstrates a comparatively low energy consumption rate of 8.611 KWHkg (H 2) −1. Thus, engineering a bifunctional electrocatalyst for a low potential anode oxidation reaction and the cathodic HER is a promising strategy to fabricate an energy efficient electrolysis cell for hydrogen production with a low cell potential requirement. [ABSTRACT FROM AUTHOR]

Doped carbon structures have been developed as non-precious metal catalysts for oxygen reduction reactions (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Among doped carbon structures, Fe- and N-doped carbon (Fe/N/C) nanostructured catalysts have received attention due to their catalytic activity, comparable to that of Pt, avoiding the use of critical raw materials. However, obviously, its durability is not yet neither fully understood nor comparable to that of traditional catalysts. In this study, we synthesized mesoporous F-doped Fe/N/C, which is a tri-doped carbon nanostructure, as a cathode catalyst for ORR. Tri-doped carbon catalysts with different amounts (x) of F (Fx-Fe/N/C) were prepared using Fe-5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine iron(III) chloride and NH 4 F as the Fe/N- and F- doping sources, respectively, and Santa Barbara amorphous-15 as the template. Fx-Fe/N/C with an optimal F content exhibited excellent electrocatalytic performance for ORRs i.e. a high half-wave potential of 809 mV in 0.1 M HClO 4 solution, a maximum power density of 280 mW cm−2, and a high stability for 4000 min at 0.5 V, owing to the high proportion of FeN x and pyridinic N as active sites, strong C–F bonds, and hydrophobic surfaces. We synthesized mesoporous F-doped Fe/N/C, which is a tri-doped carbon nanostructure, as a cathode catalyst for ORR. Fx-Fe/N/C with an optimal F content exhibited excellent electrocatalytic activity and durability for ORRs owing to the high proportion of FeNx and pyridinic N as active sites, strong C–F bonds, and hydrophobic surfaces. [Display omitted] [ABSTRACT FROM AUTHOR]

Progress in acidic water splitting has remained limited because of low oxygen evolution reaction (OER) activities, sluggish reaction kinetics, and severe catalyst degradation. Thus, a highly active and durable OER catalyst is required for the commercialization of acidic water electrolyzers. Here, we report t -phase ruthenium oxide atomic layers implanted on Mo 2 TiC 2 T x MXene (R AL -M) as a model electrocatalyst for the OER in acidic media, which exhibits a remarkable mass activity (6.2 A mg−1), excellent turnover frequency (TOF; 2.4 s−1), and negligible loss of durability after 22 h in a two-electrode cell configuration. The mass activity and TOF of R AL -M are 150 times (RuO 2 -Premetek Co.) and 540 times (RuO 2 -Sigma-Aldrich) greater than the industrially adopted electrocatalysts at pH 0.48. Computational calculations show that the ruthenium active sites of R AL -M have a strong affinity to oxygen species (e.g., OH*, O*, and OOH*), which efficiently adapts water dissociation and favors both the adsorbate evolution and lattice oxygen mechanistic pathways to accelerate the OER. [Display omitted] • A novel t -phase ruthenium oxide atomic layers implanted on Mo 2 TiC 2 T x MXene (R AL -M) was prepared. • For the first time, we reported R AL -M as a model electrocatalyst for the oxygen evolution reaction (OER) in acidic media. • The mass activity and turnover frequency of RAL-M was150/540 times greater than the industrial catalysts. • DFT reveals that the AEM and LOM pathways not only reduce the OER overpotential but also enhance the mass activity. [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]

The main challenge for the anode electrocatalyst in a polymer electrolyte membrane water electrolyzer (PEMWE) is to maintain activity and stability simultaneously under the corrosive environment. We report a highly active and durable iridium electrocatalyst supported on boron carbide for the oxygen evolution reaction. The physical and electrochemical properties of the catalyst are controlled by changing the synthetic reduction temperature from 30 °C to 100 °C. The prepared Ir/B 4 C-100 °C catalyst shows two times higher mass activity than Ir/B 4 C-30 °C, even outperforming two commercial catalysts. The improved activity can be correlated to the high concentration of Ir (III) and OH species on the surface and the well-dispersed iridium nanoparticles on the support. Controlling the reduction temperature is also found to enhance iridium stability by developing the interactions between iridium and B 4 C. These metal-support interactions inhibit the oxidative dissolution of Ir (III) and the aggregation of iridium species. Ir/B 4 C-100 °C also shows better single cell performance than those of two commercial catalysts when tested in a PEMWE. The cell with the synthesized catalyst of Ir/B 4 C-100 °C shows a current density of 1.98 A/cm2 at 1.8 V, whereas those with two commercial catalysts exhibit values of 1.36 and 0.692 A/cm2 at 1.8 V, respectively. [Display omitted] • A series of boron carbide-supported iridium catalysts were synthesized. • The physical and electrochemical properties of the iridium catalyst were controlled. • OER activity and durability of Ir/B 4 C-100 °C outperformed two commercial catalysts. • High amount of Ir(III) and OH species and high dispersion provided better activity. • Metal-support interaction of Ir/B 4 C-100 °C enhanced the durability of Ir. [ABSTRACT FROM AUTHOR]

Water electrolysis (WE) is an attractive advanced technology for the production of H 2. A key issue in the WE is to develop suitable catalysts for the oxygen evolution reaction (OER), where a relatively large energy loss occurs. The Ir-doped NiCo 2 O 4 catalysts exhibit the formation of a solid solution and a porous nanostructure. The oxygen vacancies formed by Ir doping can enhance the electrocatalytic activity for the OER owing to increased electrical conductivity and tunable adsorption energies of OH- and H 2 O. In comparison to IrO 2 as a representative OER catalyst, the Ir(10 at%) doped NiCo 2 O 4 catalyst (10-Ir-NCO) exhibits the better OER performance (overpotential of 303 mV at 10 mA cm−2) and its stability for 20,000 s. In addition, in the overall water splitting test, the 10-Ir-NCO || Pt/C exhibits the excellent OER activity (a low overpotential of 0.5 V at 100 mA cm−2) and stability (20 h at 50 mA cm−2). [Display omitted] • Ir-doped NiCo 2 O 4 catalysts were synthesized with various amounts of Ir dopant. • The catalysts exhibited a spinel structure consisting of NiCo 2 O 4 host and Ir dopant. • The catalyst exhibited the enhanced activity and stability for the OER compared to IrO 2. • The enhanced activity may result from the replacement of Ni and Co with Ir in octahedral sites. • The enhanced activity may be attributed to the oxygen vacancies. [ABSTRACT FROM AUTHOR]

• Iridium nanoclusters supported on boron carbide are proposed as a catalyst for the oxygen evolution reaction. • A simple chemical reduction method was used to synthesize grape-like iridium nanoclusters supported on B 4 C. • Iridium nanoclusters supported on B 4 C showed better oxygen evolution activity than a commercial iridium oxide catalyst. Reducing the iridium loading for the oxygen evolution reaction (OER) is one of the main challenges of polymer electrolyte membrane water electrolysis (PEMWE). This study introduces grape-like iridium nanoclusters supported on boron carbide (B 4 C) which increase iridium utilization compared to a non-supported iridium catalyst. A simple chemical reduction method with NaBH 4 as a reducing agent was used to synthesize iridium nanoclusters on B 4 C. TEM images indicated that grape-like iridium nanoclusters were successfully dispersed on the B 4 C support. The catalytic performance of Ir/B 4 C was better than that of a commercial catalyst. To reach a current density of 10 mA/cm2, the overpotential of Ir/B 4 C was less than that of the commercial catalyst by 32 mV. Ir/B 4 C also has a mass activity 2.55 times higher than that of the commercial catalyst at 1.55 V. These improvements are attributed to the high electrochemical active surface area, the weak adsorption strength of oxygen, and the presence of Ir(OH) 4 on the surface. The durability of Ir/B 4 C is comparable to that of the commercial catalyst at 1 mA/cm2 for 15 h and higher at 10 mA/cm2 for 3 h. B 4 C may weaken the oxidative dissolution of iridium by transferring electrons even though the high electrochemical surface area of iridium in Ir/B 4 C may reduce its durability. [ABSTRACT FROM AUTHOR]

• Bimetal TMO supported carbon (CNT/Graphene) based electrocatalyst (NCGC) is synthesized via dry synthesis. • NCGC exhibited high electrochemical activity and good stability for both OER & HER. • NCGC provide low overpotentials of 290 and 214 mV at 10 mA cm−2 to drive the OER & HER, respectively. • NCGC offers reasonable electrochemical stable electrolysis performance over 60 h. The rational design of highly efficient bifunctional electrocatalysts for the oxygen and hydrogen evolution reactions is still an ongoing challenge. Herein, bimetallic transition metal oxide incorporated three-dimensional (3D) nitrogen-doped graphene/carbon nanotube (CNT) conductive matrix has been developed via dry synthesis and applied as a potential catalyst for the oxygen and hydrogen evolution reactions. The key features of the structure as well as its 3D network, nitrogen doping, and metal oxide formation were confirmed using various characterization techniques such as scanning electron and transmission electron microscopies, X-ray diffraction, and X-ray photoelectron spectroscopy. A nickel cobalt oxide-incorporated 3D nitrogen-doped graphene/CNT conductive matrix (NCGC) exhibits low overpotentials of 290 and 214 mV at 10 mA cm−2 to drive the oxygen and hydrogen evolution reactions, respectively. Furthermore, the NCGC electrocatalyst maintains a reasonably long-term water electrolysis performance over 20 h, thought to be as a result of an improvement in the activity and stability of NCGC through the synergetic effects of the bimetallic transition oxide and 3D nitrogen-doped graphene/CNT. The overall electrochemical activity and stability of the prepared NCGC make it a good economical substitute for commercial noble metal-based catalysts for use in renewable energy production. [ABSTRACT FROM AUTHOR]