The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the cornerstone of many renewable energy storage and conversion technologies such as metal-air batteries, fuel cells, and water electrolysis. [1][2][3] Both reactions, however, need highly active catalysts to achieve high efficiency since the oxygen electrode is a strongly irreversible system associated with high activation overpotential and sluggish kinetics. Noble metals (e.g., Pt) and their oxides (e.g., RuO 2 , IrO 2 ) have been found to be the most active catalysts for electrocatalytic reduction and evolution of molecular oxygen. However, their large-scale application is greatly prohibited by high cost, supply scarcity, and inferior durability. [4,5] On the other hand, as the universal choice of ORR catalyst, the OER activity of Pt is limited by the in situ formation of insulating platinum oxides in the process. IrO 2 and RuO 2 are unstable at high potentials due to the in situ transformation to higher-valent oxides, in spite of the highest activity towards OER. [6] To fulfill the demands in practical use, the development of lowcost yet durable bifunctional electrocatalysts with high activity toward both ORR and OER process is highly desired to reduce the cost and complexity of the renewable energy storage and conversion systems.Recent studies highlighted that transitional metal-N-doped carbon (NC) nanohybrids (MNC, MFe, Co, Ni, etc.) hold promise as substitutes of noble metal electrocatalysts in both acidic and alkaline medium. [7][8][9] In such catalysts, the presence of transitional metals helps to greatly improve the crystallinity and electrical conductivity of carbon matrix by catalytic graphitization upon preparation at high temperature, which in turn function to protect the metals from corrosion and aggregation during the electrochemical reactions. [10,11] More importantly, the interaction and synergy of metal species, the doped N species, and carbon lattice create sufficient localized reactive sites by modifying the charge distribution on carbon surface via the promoted electron transfer effect, which changes the local work function for O 2 adsorption and consequently facilitate the ORR or OER. [12,13] Very recently, the synergistic effect of metal@C nanoparticles and neighboring metal-N x coordination sites has been demonstrated to promote the O 2 adsorption The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are cornerstone reactions for many renewable energy technologies. Developing cheap yet durable substitutes of precious-metal catalysts, especially the bifunctional electrocatalysts with high activity for both ORR and OER reactions and their streamlined coupling process, are highly desirable to reduce the processing cost and complexity of renewable energy systems. Here, a facile strategy is reported for synthesizing double-shelled hybrid nanocages with outer shells of Co-N-doped graphitic carbon (Co-NGC) and inner shells of N-doped microporous carbon (NC) by templating against core-shell metal-orga...

Optical phase change materials (O-PCMs), a unique group of materials featuring exceptional optical property contrast upon a solid-state phase transition, have found widespread adoption in photonic applications such as switches, routers and reconfigurable meta-optics. Current O-PCMs, such as Ge–Sb–Te (GST), exhibit large contrast of both refractive index (Δn) and optical loss (Δk), simultaneously. The coupling of both optical properties fundamentally limits the performance of many applications. Here we introduce a new class of O-PCMs based on Ge–Sb–Se–Te (GSST) which breaks this traditional coupling. The optimized alloy, Ge2Sb2Se4Te1, combines broadband transparency (1–18.5 μm), large optical contrast (Δn = 2.0), and significantly improved glass forming ability, enabling an entirely new range of infrared and thermal photonic devices. We further demonstrate nonvolatile integrated optical switches with record low loss and large contrast ratio and an electrically-addressed spatial light modulator pixel, thereby validating its promise as a material for scalable nonvolatile photonics.

No abstract

Rechargeable aqueous Zn/MnO2 batteries are very attractive large‐scale energy storage technologies, but still suffer from limited cycle life and low capacity. Here the novel adoption of a near‐neutral acetate‐based electrolyte (pH ≈ 6) is presented to promote the two‐electron Mn4+/Mn2+ redox reaction and simultaneously enable a stable Zn anode. The acetate anion triggers a highly reversible MnO2/Mn2+ reaction, which ensures high capacity and avoids the issue of structural collapse of MnO2. Meanwhile, the anode‐friendly electrolyte enables a dendrite‐free Zn anode with outstanding stability and high plating/stripping Coulombic efficiency (99.8%). Hence, a high capacity of 556 mA h g−1, a lifetime of 4000 cycles without decay, and excellent rate capability up to 70 mA cm−2 are demonstated in this new near‐neutral aqueous Zn/MnO2 battery by simply manipulating the salt anion in the electrolyte. The acetate anion not only modifies the surface properties of MnO2 cathode but also creates a highly compatible environment for the Zn anode. This work provides a new opportunity for developing high‐performance Zn/MnO2 and other aqueous batteries based on the salt anion chemistry.

Precisely regulating the electronic structures of metal active species is highly desirable for electrocatalysis. However, carbon with inert surface provide weak metal–support interaction, which is insufficient to modulate the electronic structures of metal nanoparticles. Herein, we propose a new method to control the electrocatalytic behavior of supported metal nanoparticles by dispersing single metal atoms on an O‐doped graphene. Ideal atomic metal species are firstly computationally screened. We then verify this concept by deposition of Ru nanoparticles onto an O‐doped graphene decorated with single metal atoms (e.g., Fe, Co, and Ni) for hydrogen evolution reaction (HER). Consistent with theoretical predictions, such hybrid catalysts show outstanding HER performance, much superior to other reported electrocatalysts such as the state‐of‐the‐art Pt/C. This work offers a new strategy for modulating the activity and stability of metal nanoparticles for electrocatalysis processes.

Efficient generation of H2 via water-splitting is an underpinning technology for realizing the hydrogen economy. However, the sluggish anodic oxygen evolution reaction (OER) requires large energy input. Low-cost, transition metals...

The edge sites of MoS are catalytically active for the hydrogen evolution reaction (HER), and growing monolayer structures that are edge-rich is desirable. Here, we show the production of large-area highly branched MoS dendrites on amorphous SiO/Si substrates using an atmospheric pressure chemical vapor deposition and explore their use in electrocatalysis. By tailoring the substrate construction, the monolayer MoS evolves from triangular to dendritic morphology because of the change of growth conditions. The rough edges endow dendritic MoS with a fractal dimension down to 1.54. The highly crystalline basal plane and the edge of the dendrites are visualized at atomic resolution using an annular dark field scanning transmission electron microscope. The monolayer dendrites exhibit strong photoluminescence, which is indicative of the direct band gap emission, which is preserved after being transferred. Post-transfer sulfur annealing restores the structural defects and decreases the n-type doping in MoS monolayers. The annealed MoS dendrites show good and highly durable HER performance on the glassy carbon with a large exchange current density of 32 μA cm, demonstrating its viability as an efficient HER catalyst.

Room-temperature sodium–sulfur (RT-Na/S) batteries hold great promise for sustainable and cost-effective applications. Nevertheless, it remains a great challenge to achieve high capacity and cycling stability due to the low activity of sulfur and the sluggish conversion kinetics between polysulfide intermediates and sodium sulfide. Herein, an electrocatalyzing S cathode is fabricated, which consists of porous core–shell structure and multisulfiphilic sites. The flexible carbon structure effectively buffers volume changes during cycling and provides enclosed spaces to store S8 with exceptional conductivity. Significantly, the multisulfiphilic sites (ZnS and CoS2) enhance catalysis toward multistep S conversion, which effectively suppresses long-chain polysulfides dissolution and improves the kinetics of short-chain polysulfides. Thus, the obtained S cathodes achieve an enhanced cycling performance (570 mAh g–1 at 0.2 A g–1 over 1000 cycles), decent rate capability (250 mAh g–1 at 1.0 A g–1 over 2000 cycles), and high energy density of 384 Wh kg–1 toward practical applications.