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Hydrogen peroxide (H2O2) is widely used as a green oxidant for varying applications. Electrosynthesis is an economical and environmentally-friendly strategy to directly produce H2O2. Its practical production is hindered, however, by the lack of highly efficient and selective as well as low-cost electrocatalysts. Transition metal chalcogenide materials have been proved to be good catalysts for the oxygen evolution reaction, but their selectivity towards conversion of O2 to H2O2 remains unsatisfactory. In this work, 3 atomic-layer defect-rich CoSe2 nanosheets have been successfully grown on carbon cloth as a high performance electrocatalyst. The morphology of CoSe2 can be tuned by regulating the wettability of the growth substrate. The atomic-layer CoSe2 nanosheets showed unprecedented 92% selectivity towards H2O2 production in alkaline solutions, and the yields of H2O2 in alkaline and acidic solutions were 1227.7 mg L−1 h−1 and 894 mg L−1 h−1, respectively. The high efficiency and selectivity originate from the rich defects in the atomic-layer CoSe2 nanosheets, which can accelerate the adsorption of OOH by the exposed Co defect sites.

Metal–organic frameworks (MOFs) are increasingly being investigated as electrocatalysts for the oxygen evolution reaction (OER). Despite their promising catalytic activity, many fundamental questions concerning their structure−performance relationships—especially those regarding the roles of active species—remain to be answered. Here we show the structural transformation of a Ni0.5Co0.5-MOF-74 during the OER by operando X-ray absorption spectroscopy analysis and high-resolution transmission electron microscopy imaging. We suggest that Ni0.5Co0.5OOH0.75, with abundant oxygen vacancies and high oxidation states, forms in situ and is responsible for the high OER activity observed. The ratio of Ni to Co in the bimetallic centres alters the geometric and electronic structure of as-formed active species and in turn the catalytic activity. Based on our understanding of this system, we fabricate a Ni0.9Fe0.1-MOF that delivers low overpotentials of 198 mV and 231 mV at 10 mA cm−2 and 20 mA cm−2, respectively. Metal–organic frameworks (MOFs) are increasingly being explored for electrocatalytic oxygen evolution, which is half of the water splitting reaction. Here the authors show that, under reaction conditions, mixed metal oxyhydroxides form at the nodes of bimetallic MOFs, which are highly catalytically active.

To reach a closed-loop material system and meet the urgent requirement of sustainable energy storage technologies, it is essential to incorporate efficient waste management into designing new energy storage materials. Here, a “two birds with one stone” strategy to transform rusty iron products into Prussian blue as high-performance cathode materials, and recover the rusty iron products to their original status, is reported. Owing to the high crystalline and Na+ content, the rusty iron derived Prussian blue shows a high specific capacity of 145 mAh g−1 and excellent cycling stability over 3500 cycles. Through the in situ X-ray diffraction and in situ Raman spectra, it is found that the impressive ion storage capability and stability are strongly related to the suppressed structure distortion during the charge/discharge process. The ion migration mechanism and the possibility to serve as a universal host for other kinds of ions are further illuminated by density functional theory calculations. This work provides a new strategy for recycling wasted materials into high value-added materials for sustainable battery systems, and is adaptable in the nanomedicine, catalysis, sensors, and gas storage applications.

Both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are crucial to water splitting, but require alternative active sites. Now, a general π-electron-assisted strategy to anchor single-atom sites (M=Ir, Pt, Ru, Pd, Fe, Ni) on a heterogeneous support is reported. The M atoms can simultaneously anchor on two distinct domains of the hybrid support, four-fold N/C atoms (M@NC), and centers of Co octahedra (M@Co), which are expected to serve as bifunctional electrocatalysts towards the HER and the OER. The Ir catalyst exhibits the best water-splitting performance, showing a low applied potential of 1.603 V to achieve 10 mA cm in 1.0 m KOH solution with cycling over 5 h. DFT calculations indicate that the Ir@Co (Ir) sites can accelerate the OER, while the Ir@NC sites are responsible for the enhanced HER, clarifying the unprecedented performance of this bifunctional catalyst towards full water splitting.

Symmetric full-cells, which employ two identical electrodes as both the cathode and anode, attract great research attention, because it has high safety, facial fabrication and lower costs. Unfortunately, the practical utilization of full symmetric energy storage systems, especially the symmetric potassium ion batteries (KIBs), is hindered by the limited choice of the available electrode materials. In this work, a novel NASICON-type K 3 V 2 (PO 4 ) 3 is prepared and first employed for the symmetric KIBs. Through in-situ measurement, a highly lattice reversibility is found during the K + insertion/extraction process. KV 2 (PO 4 ) 3 and K 5 V 2 (PO 4 ) 3 was generated after the depotassiation and potassiation process at about 4.0 V and below 1.0 V, respectively. The reversible capacity of the full symmetric KIBs is about 90 mAh g −1 between 0.01 and 3.0 V at 25 mA g −1 , corresponding to an initial coulombic efficiency of 91.7% which is the highest one among all the previous reported symmetric energy storage systems (including the symmetric lithium/sodium ion batteries). 88.6% reversible capacity was maintained even after 500 cycling test. More importantly, a largest working potential at about 2.3 V was obtained in this work, benefiting the output energy of this symmetric energy storage system. The outstanding cycling stability, large working potential and the highest initial coulombic efficiency endow this work with promising advantages for the future development of the novel energy storage system.

Room-temperature sodium-sulfur (RT-Na/S) batteries hold significant promise for large-scale application because of low cost of both sodium and sulfur. However, the dissolution of polysulfides into the electrolyte limits practical application. Now, the design and testing of a new class of sulfur hosts as transition-metal (Fe, Cu, and Ni) nanoclusters (ca. 1.2 nm) wreathed on hollow carbon nanospheres (S@M-HC) for RT-Na/S batteries is reported. A chemical couple between the metal nanoclusters and sulfur is hypothesized to assist in immobilization of sulfur and to enhance conductivity and activity. S@Fe-HC exhibited an unprecedented reversible capacity of 394 mAh g-1 despite 1000 cycles at 100 mA g-1 , together with a rate capability of 220 mAh g-1 at a high current density of 5 A g-1 . DFT calculations underscore that these metal nanoclusters serve as electrocatalysts to rapidly reduce Na2 S4 into short-chain sulfides and thereby obviate the shuttle effect.

The low-cost room-temperature sodium-sulfur battery system is arousing extensive interest owing to its promise for large-scale applications. Although significant efforts have been made, resolving low sulfur reaction activity and severe polysulfide dissolution remains challenging. Here, a sulfur host comprised of atomic cobalt-decorated hollow carbon nanospheres is synthesized to enhance sulfur reactivity and to electrocatalytically reduce polysulfide into the final product, sodium sulfide. The constructed sulfur cathode delivers an initial reversible capacity of 1081 mA h g−1 with 64.7% sulfur utilization rate; significantly, the cell retained a high reversible capacity of 508 mA h g−1 at 100 mA g−1 after 600 cycles. An excellent rate capability is achieved with an average capacity of 220.3 mA h g−1 at the high current density of 5 A g−1. Moreover, the electrocatalytic effects of atomic cobalt are clearly evidenced by operando Raman spectroscopy, synchrotron X-ray diffraction, and density functional theory., Room-temperature sodium-sulfur batteries hold promise, but are hindered by low reversible capacity and fast capacity fade. Here the authors construct a multifunctional sulfur host comprised of cobalt-decorated carbon nanospheres that impart attractive performance as a cathode in a sodium sulfide battery.

“单原子层团簇”催化剂这一新概念, 不同于单原子催化剂和传统的纳米颗粒催化, 是由单原子建造新型的二维单原子层催化剂. 单原子层团簇催化剂的活性中心明确, 且原子间的相互作用会极大提高催化反应的选择性. 因此该催化剂材料不仅具有优异的催化性能, 还具有良好的选择性. 基于此, 作者同时分析和指出了未来的单原子层团簇催化剂的可能重点研究方向以及挑战.

Architectural control of porous solids, such as porous carbon cages, has received considerable attention for versatile applications because of their ability to interact with liquids and gases not only at the surface, but throughout the bulk. Herein we report a scalable, facile spray-pyrolysis route to synthesize holey carbon microcages with mosquito-net-like shells. Using the surfaces of water droplets as the growth templates, styrene-butadiene rubber macromolecules are controllably cross-linked, and size-controllable holes on the carbon shells are generated. The as-formed carbon microcages encapsulating Si nanoparticles exhibit enhanced lithium-storage performances for lithium-ion batteries. The scalable, inexpensive synthesis of porous carbon microcages with controlled porosity and the demonstration of outstanding electrochemical properties are expected to extend their uses in energy storage, molecular sieves, catalysis, adsorbents, water/air filters, and biomedical engineering.

Room-temperature sodium–sulfur batteries are competitive candidates for large-scale stationary energy storage because of their low price and high theoretical capacity. Herein, pure S nanosheet cathodes can be grown in situ on three-dimensional Cu foam substrate with the condensation between binary polymeric binders, serving as a model system to investigate the formation and electrochemical mechanism of unique S nanosheets on the Cu current collectors. On the basis of the confirmed conversion reactions to Na2S, The constructed cathode exhibits ultrahigh initial discharge/charge capacity of 3189/1403 mAh g–1. These results suggest that there is great potential to optimize S cathode by exploiting low-cost Cu substrates instead of conventional Al current collectors.

Improving the CO tolerance of Pt-based catalysts is very meaningful for the application in proton exchange membrane fuel cells and direct alcohol fuel cells. The behavior of Pt-based bimetallic catalysts is depended on their phase and surface composition. In this work, we tuned the surface composition of Pt3Co nanocatalysts by heat treatment under different atmosphere. The results of atomic-resolution HAADF-STEM, XRD, XPS and electrochemical characterization demonstrated that the surface composition of Pt3Co catalysts with Co-increased, Intermetallic and Pt-increased were obtained by metal segregation approach. Due to the differences in the surface atomic distribution and alloying extent, the nanocatalysts show different CO poisoning tolerance in the order of Co-increased>Intermetallic>Pt-increased. CO stripping voltammetry and in-situ Fourier transform infrared spectroscopy (FTIRS) were used together to investigate the origin of varied CO poisoning tolerance on three Pt3Co catalysts. The results illustrated that electronic effect plays a major role in weakening CO adsorption on Pt3Co nanocatalysts and thus promoting CO oxidation to form COOHad intermediate consistent with Langmuir-Hinselwood mechanism. Oxophilic effect promotes the oxidation of COOHad intermediate into the final products CO2/CO32-. This work provides a new insight into tuning phase and surface composition of catalysts thus enhancing CO tolerance of Pt-based bimetallic catalysts.

We report for the first time a facile preparation of double-shell pomegranate-like porous carbon microspheres (PCMs) by a modified templating technique. The microsized PCMs are encapsulated within integrated carbon coating layers and composed of interconnected nanosized hollow carbon spheres, giving rise to a special double-shell structure. Calcium carbonate (CaCO3) is employed as the primary sacrificial template and acetylene as the carbon precursor via chemical vapor deposition (CVD). The PCMs exhibit an initial coulombic efficiency of 91% and a reversible capacity of 650 mA h g−1 at a current density of 200 mA g−1 after 500 cycles. Moreover, PCMs show excellent rate capability with capacities of 580 and 520 mA h g−1 at current densities of 1000 and 2000 mA g−1, respectively. The outstanding electrochemical properties of PCMs are originated from their unique structure. The inner interconnected porous carbon framework encapsulated by a self-supporting outer carbon coating shell provides more lithium ion storage sites, high electronic conductivity and fast ion diffusion. Most importantly, different from the previous studies, the introduction of the carbon coating layers on the outer surface of the whole microsphere can effectively strengthen the mechanical properties and prevent the electrolyte ingress, limiting the formation of extra solid–electrolyte interface films.

In order to maximize the Pt utilization in catalysts and improve catalytic processes, we report a convenient strategy for preparation of Pt3Co with Pt-skin structured bimetallic nanocatalysts directly supported on porous graphitic carbon. Notably, the thickness of the Pt-skin is only 1–2 atomic layers, about 0.5 nm. Surprisingly, the bimetallic nanocatalysts composed of Pt3Co with Pt-skin are first used as ethanol electro-catalysts, with the mass activity of 0.79 mA μgPt–1, which is a 250% enhancement compared with commercial Pt/C (0.32 mA μgPt–1). On the basis of the results of electrochemical in situ Fourier transform infrared spectroscopy (FTIRS) and density functional theory (DFT), a new ethanol electro-oxidation enhancement mechanism is proposed in which Pt3Co with Pt-skin promotes partial oxidation of ethanol over C–C bond cleavage, thereby resulting in higher CH3COOH production than CO2 production.

A novel heterostructured Si@C@Ge anode is developed via a two-step sol–gel method. A facile and straightforward Ge decoration significantly boosts the Li-storage performance of core–shell Si@C nanoparticles on both mechanics and kinetics. The Si@C@Ge anode shows unprecedented electrochemical performance in terms of accessible capacity, cycling stability, and rate capability when compared to those of a core–shell Si@C anode. Based on the experimental results and analysis of the mechanism, it is evident that high-conductivity Ge nanograins on the surface facilitates the Li diffusivity and electron transport and guarantees high ion accessibility. Moreover, it is the Ge nanograins that serve as buffering cushion to tolerate the mechanic strain distribution on the electrode during lithiation/delithiation processes.

Confinement of polysulfides in sulfur cathodes is pivotal for eliminating the "shuttle effect" in metal-sulfur batteries, which represent promising solutions for large-scale and sustainable energy storage. However, mechanistic exploration and in-depth understanding for the confinement of polysulfides remain limited. Consequently, it is a critical challenge to achieve highly stable metal-sulfur batteries. Here, based on a 2D metal-organic framework (2D MOF), a new mechanism to realize effective confinement of polysulfides is proposed. A combination of in situ synchrotron X-ray diffraction, electrochemical measurements, and theoretical computations reveal that the dynamic electron states of the Ni centers in the 2D MOF enable the interaction between polysulfides and the MOF in the discharge/charge process to be tuned, resulting in both strong adsorption and fast conversion kinetics of polysulfides. The resultant room-temperature sodium-sulfur batteries are amongst the most stable reported so far, thus demonstrating that the new mechanism opens a promising avenue for the development of high-performance metal-sulfur batteries.

Bin-Wei Zhang, Yan Jiao, Dong-Liang Chao, Chao Ye, Yun-Xiao Wang, Kenneth Davey, Hua-Kun Liu, Shi-Xue Dou, and Shi-Zhang Qiao

Bimetallic PtPb nanodendrites with a single-crystalline structure were obtained by a facile one-pot strategy. The as-synthesized dendritic structure was well characterized and the growth mechanism was investigated. PtPb nanodendrites exhibited superior activity (5.1 times higher than commercial Pd black) and strong anti-poisoning ability for electrooxidation of formic acid.

Room temperature sodium-sulfur (RT-Na/S) batteries have recently regained a great deal of attention due to their high theoretical energy density and low cost, which make them promising candidates for application in large-scale energy storage, especially in stationary energy storage, such as with electrical grids. Research on this system is currently in its infancy, and it is encountering severe challenges in terms of low electroactivity, limited cycle life, and serious self-charging. Moreover, the reaction mechanism of S with Na ions varies with the electrolyte that is applied, and is very complicated and hard to detect due to the multi-step reactions and the formation of various polysulfides. Therefore, understanding the chemistry and optimizing the nanostructure of electrodes for RT-Na/S batteries are critical for their advancement and practical application in the future. In the present review, the electrochemical reactions between Na and S are reviewed, as well as recent progress on the crucial cathode materials. Furthermore, attention also is paid to electrolytes, separators, and cell configuration. Additionally, current challenges and future perspectives for the RT-Na/S batteries are discussed, and potential research directions toward improving RT-Na/S cells are proposed at the end.

Rechargeable sodium-ion batteries are proposed as the most appropriate alternative to lithium batteries due to the fast consumption of the limited lithium resources. Due to their improved safety, polyanion framework compounds have recently gained attention as potential candidates. With the earth-abundant element Fe being the redox center, the uniform carbon-coated Na3.32 Fe2.34 (P2 O7 )2 /C composite represents a promising alternative for sodium-ion batteries. The electrochemical results show that the as-prepared Na3.32 Fe2.34 (P2 O7 )2 /C composite can deliver capacity of ≈100 mA h g-1 at 0.1 C (1 C = 120 mA g-1 ), with capacity retention of 92.3% at 0.5 C after 300 cycles. After adding fluoroethylene carbonate additive to the electrolyte, 89.6% of the initial capacity is maintained, even after 1100 cycles at 5 C. The electrochemical mechanism is systematically investigated via both in situ synchrotron X-ray diffraction and density functional theory calculations. The results show that the sodiation and desodiation are single-phase-transition processes with two 1D sodium paths, which facilitates fast ionic diffusion. A small volume change, nearly 100% first-cycle Coulombic efficiency, and a pseudocapacitance contribution are also demonstrated. This research indicates that this new compound could be a potential competitor for other iron-based cathode electrodes for application in large-scale Na rechargeable batteries.

Controlling surface composition of bimetallic catalysts is of significance in energy conversion and storage. Here, we controlled thermal treatment to synthesize different surface composition of bimetallic catalysts with average diameter