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The design of high‐entropy single‐atom catalysts (HESAC) with 5.2 times higher entropy compared to single‐atom catalysts (SAC) is proposed, by using four different metals (FeCoNiRu‐HESAC) for oxygen reduction reaction (ORR). Fe active sites with intermetallic distances of 6.1 Å exhibit a low ORR overpotential of 0.44 V, which originates from weakening the adsorption of OH intermediates. Based on density functional theory (DFT) findings, the FeCoNiRu‐HESAC with a nitrogen‐doped sample were synthesized. The atomic structures are confirmed with X‐ray photoelectron spectroscopy (XPS), X‐ray absorption (XAS), and scanning transmission electron microscopy (STEM). The predicted high catalytic activity is experimentally verified, finding that FeCoNiRu‐HESAC has overpotentials of 0.41 and 0.37 V with Tafel slopes of 101 and 210 mVdec−1 at the current density of 1 mA cm−2 and the kinetic current densities of 8.2 and 5.3 mA cm−2, respectively, in acidic and alkaline electrolytes. These results are comparable with Pt/C. The FeCoNiRu‐HESAC is used for Zinc–air battery applications with an open circuit potential of 1.39 V and power density of 0.16 W cm−2. Therefore, a strategy guided by DFT is provided for the rational design of HESAC which can be replaced with high‐cost Pt catalysts toward ORR and beyond. [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]

To realize economically feasible electrochemical CO2 conversion, achieving a high partial current density for value-added products is particularly vital. However, acceleration of the hydrogen evolution reaction due to cathode flooding in a high-current-density region makes this challenging. Herein, we find that partially ligand-derived Ag nanoparticles (Ag-NPs) could prevent electrolyte flooding while maintaining catalytic activity for CO2 electroreduction. This results in a high Faradaic efficiency for CO (>90%) and high partial current density (298.39 mA cm‒2), even under harsh stability test conditions (3.4 V). The suppressed splitting/detachment of Ag particles, due to the lipid ligand, enhance the uniform hydrophobicity retention of the Ag-NP electrode at high cathodic overpotentials and prevent flooding and current fluctuations. The mass transfer of gaseous CO2 is maintained in the catalytic region of several hundred nanometers, with the smooth formation of a triple phase boundary, which facilitate the occurrence of CO2RR instead of HER. We analyze catalyst degradation and cathode flooding during CO2 electrolysis through identical-location transmission electron microscopy and operando synchrotron-based X-ray computed tomography. This study develops an efficient strategy for designing active and durable electrocatalysts for CO2 electrolysis. A key factor for the electrochemical reduction of CO2 to CO is limiting the competing H2 evolution reaction. Here, authors use real-time synchrotron X-ray computed tomography to show that a silver nanoparticle-ligand catalyst structure improves water management, thereby maintaining CO production. [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]

Hydrogen energy is regarded as an auspicious future substitute to replace fossil fuels, due to its environmentally friendly characteristics and high energy density. In the pursuit of clean hydrogen production, there has been a significant focus on the advancement of effective electrocatalysts for the process of water splitting. Although noble metals like Pt, Ru, Pd and Ir are superb electrocatalysts for the hydrogen evolution reaction (HER), they have limitations for large-scale applications, mainly high cost and low abundance. As a result, non-precious transition metals have emerged as promising candidates to replace their more expensive counterparts in various applications. This review focuses on recently developed transition metal phosphides (TMPs) electrocatalysts for the HER in alkaline media due to the cooperative effect between the phosphorus and transition metals. Finally, we discuss the challenges of TMPs for HER. [ABSTRACT FROM AUTHOR]

In general, commercial ZnO owns the poor selectivity and activity toward electroreduction CO2 to formate. In contrast, the numbers of Sn‐based nanomaterials are reported as excellent electrocatalysts for formate production, however, the metallic Sn is more expensive than Zn. In this study, it is demonstrated that an atomically dispersed Sn on a tensile‐strained ZnO nanosheet (Sn SA/ZnO) shows dramatically improved activity and selectivity for formate production over a wide potential window compared with that of commercial ZnO. Especially, Sn SA/ZnO exhibits 205‐fold mass activity enhancement than the commercial Sn at −1.7 V versus reversible hydrogen electrode normalized with element Sn. The experimental measurements combined with theoretical calculations revealed that Sn SA/ZnO can effectively capture and activate CO2 by its exposed double‐active sites (Sn and O), while the tensile strain on its surface boosts the catalytic selectivity by strengthening the adsorption of the *HCOO intermediate for the electrochemical reduction of CO2 to formate. [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]

Hydrogen generation by electrolysis of water in an alkaline solution is a promising technology for clean hydrogen energy. Amorphous materials show much better performance than their crystalline counterparts. However, it is still challenging to design amorphous metal materials. Here, a series of amorphous transition metal nanoparticles (NPs) is successfully synthesized using a twisted covalent organic network (CON) that can provide twisted carbon layers as well as asymmetrically distributed nitrogen. With the fixed monomer pore, a low loading amount of RuCl3 results in amorphous‐only Ru nanoclusters (NCs, 1.5 nm), while a high content of RuCl3 leads to crystalline dominant Ru NPs (3 nm). The mixed phased Ru‐CON catalyst for the hydrogen evolution reaction (HER) shows extremely low overpotential at 10 mA cm–2 (12.8 mV in 1.0 m KOH) and superior stability (after 100 h test, current loss 5.3% at 75 mA cm–2). More importantly, amorphous‐only Ru‐CON with smaller Ru NCs shows much better mass activity and considerable stability compared to mixed‐phase Ru‐CON materials since amorphous Ru NPs can provide more active sites than in their crystalline state. With this strategy, amorphous Fe NPs and Ir NPs are successfully prepared for extended applications, and the HER activities are reported. [ABSTRACT FROM AUTHOR]

Ru nanoparticles (NPs) and single atoms (SAs)‐based materials have been investigated as alternative electrocatalysts to Pt/C for hydrogen evolution reaction (HER). Exploring the dominant role of atomic‐ and nano‐ruthenium as active sites in acidic and alkaline media is very necessary for optimizing the performance. Herein, an electrocatalyst containing both Ru SAs and NPs anchored on defective carbon (RuSA+NP/DC) has been synthesized via a Ru–alginate metal–organic supramolecules conversion method. RuSA+NP/DC exhibits low overpotentials of 16.6 and 18.8 mV at 10 mA cm−2 in acidic and alkaline electrolytes, respectively. Notably, its mass activities are dramatically improved, which are about 1.1 and 2.4 times those of Pt/C at an overpotential of 50 mV in acidic and alkaline media, respectively. Theoretical calculations reveal that Ru SAs own the most appropriate H* adsorption strength and thus, plays a dominant role for HER in acid electrolyte, while Ru NPs facilitate the dissociation of H2O that is the rate‐determining step in alkaline electrolyte, leading to a remarkable HER activity. [ABSTRACT FROM AUTHOR]

Facilitating the dissociation of water and desorption of hydrogen are both crucial challenges for improving the hydrogen evolution reaction (HER) in alkaline media. Herein, we report the synthesis of heterostructure of Ru2P/WO3@NPC (N, P co‐doped carbon) by a simple hydrothermal reaction using ruthenium and tungsten salts as precursors, followed by pyrolyzing under an Ar atmosphere. The Ru2P/WO3@NPC electrocatalyst exhibits an outstanding HER activity with an overpotential of 15 mV at a current density of 10 mA cm−2 and excellent durability in a 1.0 M KOH solution, outperforming state‐of‐the‐art Pt/C and most reported electrocatalysts. Experimental results combined with density functional calculations reveal that the electron density redistribution in Ru2P/WO3@NPC is achieved by electron transfer from NPC to Ru2P/WO3 and from Ru2P to WO3, which directly promotes the dissociation of water on W sites in WO3 and desorption of hydrogen on Ru sites in Ru2P. [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]

A nanocomposite of PC/Sb/SbPO4 (PC, phosphorus‐doped carbon) exhibits a high activity and an excellent selectivity for efficient electrocatalytic conversion of N2 to NH3 in both acidic and neutral electrolytes under ambient conditions. At a low reductive potential of −0.15 V versus the reversible hydrogen electrode (RHE), the PC/Sb/SbPO4 catalyst achieves a high Faradaic efficiency (FE) of 31 % for ammonia production in 0.1 m HCl under mild conditions. In particular, a remarkably high FE value of 34 % is achieved at a lower reductive potential of −0.1 V (vs. RHE) in a 0.1 m Na2SO4 solution, which is better than most reported electrocatalysts towards the nitrogen reduction reaction (NRR) in neutral electrolyte under mild conditions. The change in surface species and electrocatalytic performance before and after N2 reduction is explored by an ex situ method. PC and SbPO4 are both considered as the active species that enhanced the performance of NRR. [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]

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]

Highlights: [•] Various metals supported on carbon were synthesized by an impregnation method. [•] Alloying two different metals significantly decreased the overpotential for charging. [•] Pt–Ru/C catalyst exhibited the lowest charging voltage, and high cyclability for over 40 cycles with the highest round-trip efficiency and lowest cell impedance. [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]

Hydrogen gas (H2) is being intensively proposed as a next-generation clean energy owing to the depletion of fossil fuels. Electrochemical water splitting is one of the most promising processes for hydrogen production. Furthermore, many efforts focusing on electrochemical water splitting have been made to develop low-cost, electrochemically active, and stable catalysts for efficient hydrogen production. MoS2 has emerged as an attractive material for developing catalysts for the hydrogen evolution reaction (HER). Hence, in this study, we design hierarchically ordinated two-dimensional (2D) MoS2 nanosheets on three-dimensional (3D) reduced graphene oxide (rGO) (H-2D/3D-MoS2-rGO) aerogel structures as a new class of electrocatalysts for the HER. We use the one-pot hydrothermal synthesis route for developing high-performance electroactive materials for the HER. The as-prepared H-2D/3D-MoS2-rGO contains a unique 3D hierarchical structure providing large surface areas owing to the 3D porous networks of rGO and more active sites owing to the many edge sites in the MoS2 nanosheets. In addition, the H-2D/3D-MoS2-rGO structure exhibits remarkable electrochemical properties during the HER. It shows a lower overpotential than pure MoS2 and excellent electrochemical stability owing to the large number of active sites (highly exposed edge sites) and high electrical conductivity from the rGO structure. [ABSTRACT FROM AUTHOR]

For the realization of commercially viable ethanol fuel cells, despite much safer than hydrogen gas, it is necessary to develop stable high-performance catalysts for ethanol electro-oxidation reaction (EOR). Unfortunately, current EOR catalysts are far from the expectation and suffer from fast activity degradation. Here we report palladium-cobalt phosphide (Pd–Co 2 P) nanoparticles (NPs) with Pd single atoms (PdSAs) anchored on graphene oxide (GO) (denoted as Pd–Co 2 P–PdSAs@GO). Its EOR mass activity (10,520 mA/mg Pd) is remarkably larger than any reported carbon-based precious metal catalysts including the benchmark Pd/C catalyst. To achieve high activity and stability, we systematically designed the catalyst with optimized elements ratio (Pd, Co/Ni/Fe, and P) and pyrolysis temperature together with electrochemical activation. The synergistic effect of charge-transfer between Pd and Co 2 P coexisting on the PdSAs@GO surface to shift the Pd d-band center promotes the bimetallic catalyst activity. The strong binding of PdSAs@GO with metals and the phosphide ligand stabilized NPs provide long-term durability. In-situ Raman analysis reveals that Co 2 P plays major roles in eliminating poisoning CO at neighboring Pd sites and retaining the catalytic activity even after 20 h. Image 1 • Palladium–cobalt phosphide nanoparticles with palladium single atoms anchored on graphene oxide (Cat-1) are reported. • The synergistic charge-transfer between Pd and Co 2 P shifts the d -band center of Pd for enhanced EOR activity. • The EOR mass activity of Cat-1 is extremely larger than any reported carbon-based precious metal catalysts. [ABSTRACT FROM AUTHOR]

Although numerous reports on nonprecious metal catalysts for replacing expensive Pt-based catalysts have been published, few of these studies have demonstrated their practical application in fuel cells. In this work, we report graphitic carbon nitride and carbon nanofiber hybrid materials synthesized by a facile and gram-scale method via liquid-based reactions, without the use of toxic materials or a high pressure-high temperature reactor, for use as fuel cell cathodes. The resulting materials exhibited remarkable methanol tolerance, selectivity, and stability even without a metal dopant. Furthermore, these completely metal-free catalysts exhibited outstanding performance as cathode materials in an actual fuel cell device: a membrane electrode assembly with both acidic and alkaline polymer electrolytes. The fabrication method and remarkable performance of the single cell produced in this study represent progressive steps toward the realistic application of metal-free cathode electrocatalysts in fuel cells. [ABSTRACT FROM AUTHOR]

Atom-migration-trapping (AMT) is an effective and straightforward strategy for fabricating single-atom catalysts (SACs), but understanding the mechanism and effects of anchoring sites on AMT are formidable challenges. Here, we demonstrate that AMT phenomena occurs in crystalline porous nanocarbon, which allows development of highly efficient SACs via systematic investigation of atomization process and chemical state of active sites. An arc discharge-based bottom-up synthesis can generate an ideal porous nanocarbon with controllable nitrogen functionality, containing metal nanoparticles for AMT. Pre-formed N-functionalities in as-synthesized catalyst play important role in capturing single metal species, while additional ammonia treatment successfully modulates coordination geometry of active sites. The atomic cobalt catalyst exhibits superior oxygen reduction activity with remarkable power performance in single-cell experiments (752 mW cm−2), exceeding the reported Co-N atomic catalysts. Our findings provide not only new perspectives in AMT phenomena but also strategies to develop an efficient and practical SACs in energy conversion systems. [Display omitted] • We synthesized Co-N x sites on crystalline nanocarbon using atomization process. • The properties of anchoring sites played a critical role in the formation of Co-N x sites. • The combined in situ analysis revealed atomization mechanism during thermal annealing. • The high-loading improved Co-N 4 was the key factors for boosting ORR. • A power density of 752 mW cm−2 was achieved, exceeding the reported Co-SACs. [ABSTRACT FROM AUTHOR]

Designing highly efficient Pt-free electrocatalysts with low overpotential for the alkaline hydrogen evolution reaction (HER) remains a significant challenge. In this paper, we successfully construct Ru-incorporated oxygen-vacancy-enriched MoO 2 nanosheets (Ru/MoO 2−x) for the HER through a "one stone two birds" strategy. This strategy can solve two urgent problems simultaneously, the intrinsic electrochemical activity of original MoO 2 is far from satisfactory and the H 2 O adsorption/dissociation abilities of Ru are weak. Specifically, the oxygen-vacancy-enriched MoO 3 serves as an excellent platform for anchoring and trapping Ru ions. In-depth analyses indicate that the incorporation of Ru nanoclusters induces transition from MoO 3 to MoO 2 , generates oxygen vacancies, and creates Ru-O-Mo sites. The synergistic effect of Ru nanoclusters, Ru-O-Mo sites and oxygen-vacancy-enriched MoO 2 will endow the obtained catalyst excellent electrocatalytic activity. In particular, the optimal Ru/MoO 2−x electrocatalyst delivered a low overpotential of 29 mV at 10 mA cm−2 in a basic electrolyte. The incorporated Ru nanoclusters induce the transition from MoO 3 to MoO 2 , generation of oxygen vacancies, and creation of Ru-O-Mo sites simultaneously, endowing the synthesized catalyst excellent performance towards alkaline HER. [Display omitted] • A"one stone two birds" strategy is adopted. • The incorporation of Ru induces transition from MoO 3 to MoO 2. • The introduction of Ru promotes to generate oxygen vacancy and create Ru-O-Mo site. • The optimal catalyst exhibits high intrinsic activity for alkaline HER. [ABSTRACT FROM AUTHOR]

A critical role of bond competition in tailoring Mn valence state and bifunctional electrocatalyst activity of manganese oxide is evidenced by the remarkable improvement of the electrocatalyst activity of α-MnO 2 upon the partial substitution of electronegative Ru 4+ ion. The replacement of Mn 4+ ion with more electronegative Ru 4+ one is quite effective in weakening adjacent (Mn−O) bonds in terms of bond competition, leading to the stabilization of Jahn-Teller active Mn 3+ species, as well as in providing electrocatalytically active Ru sites. The resulting Ru-substituted α-Mn 1−x Ru x O 2 nanowires show much higher electrocatalyst activities for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) than does the physical mixture of α-MnO 2 and RuO 2 , indicating the main role of (Mn−O) bond covalency in the optimization of the bifunctional electrocatalyst activity of manganese oxide. The present study underscores that, like the previous strategy of structural disorder enhancement, the substitution of highly electronegative cation can provide a novel efficient way of improving the electrocatalyst performance of manganese oxide via the bond competition between adjacent (Ru−O) and (Mn−O) bonds. [ABSTRACT FROM AUTHOR]

The core-shell nanostructures are used to improve the specific activity of catalysts in electrooxidation reactions. We report a porous Cu-rich@Cu 3 Pt core-shell using a seeding method. In this method, a hetero-nucleation process is carried out in the presence of cubic Cu 2 O seeds. Cu-rich@Cu 3 Pt core-shell is used as an electrocatalyst in electrooxidation reactions. According to the data obtained using transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD), Cu-rich@Cu 3 Pt has a porous nanostructure and dominant {111} facets. It consists of a well-defined core-shell structure in which a Cu-rich phase is the core and Cu 3 Pt alloy is the shell. The porous Cu-rich@Cu 3 Pt exhibits an excellent electrocatalytic performance in methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). [ABSTRACT FROM AUTHOR]

Carbon-based nanostructures as a non-precious catalyst for oxygen reduction reaction (ORR) exhibit excellent electrocatalytic activities due to high specific surface areas and favorable active sites supported by the doped transition metals and nitrogen species. We synthesize the metal-nitrogen doped carbon nanostructures (MPc-C, M = Fe,Co) by using a template method in the presence of metal phthalocyanine including FePc, CoPc, and FeCoPc as metal and nitrogen as well as carbon sources. The as-prepared carbon nanostructures show a high specific surface area, porous structure, and metal-nitrogen dopants, as observed by field-emission scanning electron microscopy (FE-SEM), field-emission transmission electron microscopy (FE-TEM), X-ray photo-electron spectroscopy (XPS), and nitrogen sorption measurement. Especially, among the doped carbon nanostructures, FeCoPc-C exhibits superior ORR electrocatalytic properties in an alkaline medium: an electron transfer number close to 4, high half-wave potential, improved electrochemical stability, and methanol tolerance. [ABSTRACT FROM AUTHOR]

High-performance electrocatalysts have attracted growing interest because of their crucial roles in renewable energy technologies. In this study, the host, interlayer, and surface features of electrocatalytically-active 2D nanosheets (NSs) are systematically controlled with the synergetic combination of host−guest co-engineering and surface modification to develop a novel synthetic strategy for efficient electrocatalysts. Molecular-level control of interfacial electronic coupling and surface reactivity can be achieved by the self-assembly of MoS 2 /RuO 2 NS mixtures with variable-sized tetraalkylammonium cations and subsequent thermal aging. The resulting optimization of the operation mechanisms of restacked MoS 2 /RuO 2 NSs effectively improves the electrocatalyst functionality for hydrogen evolution reaction (HER). The extensive modifications of diverse structural and morphological parameters allow the elucidation of a linear correlation between electrochemical active surface area and HER overpotential. Systematic in-situ spectroscopic analyses clearly demonstrate the crucial role of enhanced Volmer−Tafel mechanism in improving the electrocatalytic activity via enhancement of proton adsorption and interfacial electron transfer. Promoted Volmer-Tafel process achieved by molecular-level control of host, interlayer, and surface features. [Display omitted] • Host–guest engineering and surface activation strategies are synergistically applied. • Interlayer coupling and surface activity of electrocatalyst nanosheets are optimized. • Volmer–Tafel process plays a crucial role in optimizing electrocatalyst performance. • Electrochemical active surface area acts as a main design factor for electrocatalyst. [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]

[Display omitted] • A novel laminar Sr 2 IrO 4 modified SrIrO 3 pervoskite was developed. • The layered Sr 2 IrO 4 helps stabilizing the Ir state during electrocatalysis. • The catalyst displays robust and stable activities for both OER and HER in acid. • For water splitting in acid, the catalyst requires 1.50 V to achieve 10 mA cm−2. Strontium iridate perovskites are attractive electrocatalysts for acidic water oxidation, but suffer from serious Sr-leaching during catalysis, which causes surface rearrangements that damage long-term applications. Herein, 6H phase SrIrO 3 modified with laminar Sr 2 IrO 4 (SrIrO) have been developed. Unlike the previous extreme chemical state changes of Ir, SrIrO maintained relatively stable surface Ir states during electrocatalysis. The layered nature of Sr 2 IrO 4 enables the interlaminar Sr easily extracted from the crystal while remaining the in-plane IrO 6 octahedral framework, thereby stabilizing the Ir state. The SrIrO displays extremely low overpotential of 245 mV for OER and 18.2 mV for HER at 10 mA cm−2, and outstanding catalytic stability. For acidic water splitting, SrIrO requires only 1.50 V to achieve 10 mA cm−2, surpassing most reported electrocatalysts. This work offers a new route for alleviating the surface rearrangements of perovskites, and exploring efficient and stable electrocalysts for hydrogen production via electrochemical water electrolysis. [ABSTRACT FROM AUTHOR]

• Highly active Co/Ru sites were designed via constructing Ru atom-modified Co 4 N-CoF 2. • The cooccurrence of F, N, Ru in Co neighborhood achieves optimized electronic state. • Ru atom-modified Co 4 N-CoF 2 exhibits superior hydrogen evolution reaction activity. D-band-center control engineering, particularly combining both cation and anion intercalations towards heterostructure formation with simultaneous usage of Ru, N as well as F species, for optimal electronic structure as efficient hydrogen evolution reaction (HER) catalysts remains a daunting challenge but critical for renewable-energy technologies. Herein, we lay emphasis on the design of active-site electronic structure based on d-band-center shift through the construction of Co 4 N-CoF 2 heterostructure coupled with Ru doping (Ru/Co 4 N-CoF 2). Solvothermal coordination reaction followed by annealing course causes cooccurrence of F, N, Ru in Co neighborhood. As-obtained Ru/Co 4 N-CoF 2 exhibits superior HER activity in alkaline electrolyte with overpotential as low as 53 mV to yield a current density of 10 mA cm−2 which is close to that of commercial Pt/C, outperforming many transition-metal-based catalysts recent-reported. Moreover, it still presents good durability with continuous operation of 22 h in 1.0 M KOH. Such excellent performance is ascribed to appropriate electron structure of Ru/Co 4 N-CoF 2 for optimized hydrogen binding abilities on Co/Ru sites as confirmed by synchrotron-based X-ray adsorption near-edge structure and X-ray photoelectron spectroscopies. This study not only establishes highly active electrocatalysts by impacting d-band center of active sites but also provides valuable insights into the synergistic-effect protocol of doping and heterostructure strategies for d-band-center shifting. [ABSTRACT FROM AUTHOR]

It is of tremendous significance to develop effective bifunctional electrocatalysts for electrochemical water-splitting to generate sustainable hydrogen energy. Herein, a facile and scalable strategy is evolved to design N doped bamboo-like carbon nanotube decorated with tri-metal nanoparticles (Fe–Ni–Cr/NC) for overall water-splitting in alkaline electrolyte. Coupling effects between different metals and intimately contact with the carbon matrix endow the obtained nanomaterial possesses splendid catalytic activity and stability for cathodic HER, anodic OER and overall water-splitting in alkaline electrolyte. The obtained Fe–Ni–Cr/NC exhibits the best catalytic performance for HER (284 mV@10 mA cm−2) relative to Fe–Cr/NC (368 mV), Ni–Cr/NC (314 mV) and Fe–Ni/NC (324 mV). For OER, a small overpotential of 210 mV is needed to drive 10 mAcm−2 which is superior to IrO 2 (330 mV). Thus, the interactions between different metals act as paramount effects on promoting the catalytic activities. Benefiting from the outstanding catalytic performances for both HER and OER, the designed Fe–Ni–Cr/NC possesses splendid catalytic activity for overall water-splitting with a small potential of 1.64 V to deliver 10 mA cm−2. Moreover, the obtained nanomaterial also owns remarkable long-term stability in the measured electrolyte. Image 1 • A facile strategy is developed to prepare N-doped bamboo like carbon nanotubes coupled with Fe–Ni–Cr nanoparticles. • The obtained nanomaterial presents excellent catalytic performance for overall water-splitting in alkaline media. • The prepared electrocatalyst exhibits outstanding long-term stability. [ABSTRACT FROM AUTHOR]