E fficient and cost-effective electrocatalysts play critical roles in energy conversion and storage [1][2][3] . Homogeneous and heterogeneous catalysts represent two parallel frontiers of electrocatalysts, each with their own merits and drawbacks 4,5 . Homogeneous catalysts are attractive for their highly uniform active sites, tunable coordination environment and maximized atom utilization efficiency, but are limited by their relatively poor stability and recyclability. Heterogeneous catalysts are appealing for their high durability, excellent recyclability, and easy immobilization and integration with electrodes, but usually have rather low atom utilization efficiency due to the limited surface sites accessible to reactants. To this end, considerable efforts have been devoted to developing nanoscale heterogeneous catalysts that can increase the exposed surface atoms 3 . However, the inhomogeneity in the distribution of particle sizes and facets poses a serious challenge for controlling active sites and fundamental mechanistic studies 6,7 . In contrast, homogeneous catalysts typically exhibit the well-defined atomic structure with tunable coordination environment that is essential for deciphering the catalytic reaction pathway and rational design of targeted catalysts with tailored catalytic properties 8 . Single-atom catalysts (SACs) with monodispersed single atoms supported on solid substrates are recently emerging as an exciting class of catalysts that combine the merits of both homogeneous and heterogeneous catalysts [9][10][11][12][13][14] . However, most SACs studied to date employ metal oxides (for example, TiO 2 , CeO 2 and FeO x ) as supporting substrates to prevent atom aggregation [15][16][17][18] , which cannot be readily applied in electrocatalytic applications due to their low electrical conductivity and/or poor stability in harsh liquid-phase electrolytes (for example, strong acid or base). Atomic transitionmetal-nitrogen moieties supported in carbon (M-N-Cs) represent a unique class of SACs with high electrical conductivity and superior (electro)chemical stability for electrocatalytic applications 19 . In particular, Fe-based M-N-Cs have been extensively studied as electrocatalysts towards the oxygen reduction reaction (ORR) with demonstrated activity and stability approaching those of commercial Pt/C catalysts 20,21 . In addition, as suggested by numerous theoretical studies, M-N-Cs are promising candidates for catalysing a wide range of electrochemical processes, such as hydrogen reduction/oxidation 22 , CO 2 /CO reduction 23 and N 2 reduction 24 . A significant advantage of SACs is that the well-defined single atomic site could allow precise understanding of the catalytic reaction pathway, and rational design of targeted catalysts with tailored activity (in a manner similar to homogeneous catalyst design). However, this perceived advantage has been investigated theoretically

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The basic units in our brain are neurons, and each neuron has more than 1,000 synapse connections. Synapse is the basic structure for information transfer in an ever-changing manner, and short-term plasticity allows synapses to perform critical computational functions in neural circuits. Therefore, the major challenge for the hardware implementation of neuromorphic computation is to develop artificial synapse network. Here in-plane lateral-coupled oxide-based artificial synapse network coupled by proton neurotransmitters are selfassembled on glass substrates at room-temperature. A strong lateral modulation is observed due to the proton-related electrical-double-layer effect. Short-term plasticity behaviours, including paired-pulse facilitation, dynamic filtering and spatiotemporally correlated signal processing are mimicked. Such laterally coupled oxide-based protonic/electronic hybrid artificial synapse network proposed here is interesting for building future neuromorphic systems.

The fundamental kinetics of the electrocatalytic sulfur reduction reaction (SRR), a complex 16-electron conversion process in lithium-sulfur batteries, is insufficiently explored to date. Herein, by directly profiling the activation energies in the multi-step SRR, we reveal that the initial reduction of sulfur to the soluble polysulfides is relatively easy with low activation energy, while the subsequent conversion of the polysulfides into the insoluble Li 2 S 2 /Li 2 S is more difficult with much higher activation energy, which contribute to the accumulation of polysulfides and exacerbate the polysulfide shuttling effect. We use heteroatom-doped graphene as a model system to explore electrocatalytic SRR. We show nitrogen and sulfur dual-doped graphene considerably reduces the activation energy to improve SRR kinetics. Density functional calculations confirm that the doping tunes the p-band center of the active carbons for an optimal adsorption strength of intermediates and electroactivity. This study establishes electrocatalysis as a promising pathway to high performance lithium-sulfur batteries. The sulfur reduction reaction (SRR) in lithium-sulfur (Li-S) chemistry undergoes a complex 16-electron conversion process, transforming S 8 ring molecules into a series of soluble lithium polysulfides (LiPSs) with variable chain lengths before fully converting them into 2 insoluble Li 2 S 2 /Li 2 S products. This 16-electron SRR process is of considerable interest for high-density energy storage with theoretical capacity of 1672 mAh g-1 , but the chemistry is plagued by sluggish sulfur reduction kinetics and polysulfide (PS) shuttling effect. In practical Li-S cells, these effects limit the rate capability and cycle life 1,2. These limitations are fundamentally associated with the slow and complex reduction reaction involving S 8 ring molecules. In general, the insulating nature of elemental sulfur and its reduced products, and the sluggish charge transfer kinetics lead to incomplete conversion of S 8 molecules to soluble LiPSs. These polysulfides may shuttle across the separator to react with and deposit on the lithium anode, resulting in rapid capacity fading 3. Considerable efforts have been devoted to combating the PS shuttling effect, typically by employing a passive strategy by using various sulfur host materials to physically or electrostatically trap the LiPSs in the cathode structure 4-13. These passive confinement/entrapping strategies have partly mitigated the PS shuttling

Ceramic aerogels are attractive for thermal insulation but plagued by poor mechanical stability and degradation under thermal shock. In this study, we designed and synthesized hyperbolic architectured ceramic aerogels with nanolayered double-pane walls with a negative Poisson’s ratio (−0.25) and a negative linear thermal expansion coefficient (−1.8 × 10−6 per °C). Our aerogels display robust mechanical and thermal stability and feature ultralow densities down to ~0.1 milligram per cubic centimeter, superelasticity up to 95%, and near-zero strength loss after sharp thermal shocks (275°C per second) or intense thermal stress at 1400°C, as well as ultralow thermal conductivity in vacuum [~2.4 milliwatts per meter-kelvin (mW/m·K)] and in air (~20 mW/m·K). This robust material system is ideal for thermal superinsulation under extreme conditions, such as those encountered by spacecraft.