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Overall water splitting (OWS) to produce hydrogen has attracted large attention in recent years due to its ecological‐friendliness and sustainability. However, the efficiency of OWS has been forced by the sluggish kinetics of the four‐electron oxygen evolution reaction (OER). The replacement of OER by alternative electrooxidation of small molecules with more thermodynamically favorable potentials may fundamentally break the limitation and achieve hydrogen production with low energy consumption, which may also be accompanied by the production of more value‐added chemicals than oxygen or by electrochemical degradation of pollutants. This review critically assesses the latest discoveries in the coupled electrooxidation of various small molecules with OWS, including alcohols, aldehydes, amides, urea, hydrazine, etc. Emphasis is placed on the corresponding electrocatalyst design and related reaction mechanisms (e.g., dual hydrogenation and N–N bond breaking of hydrazine and C═N bond regulation in urea splitting to inhibit hazardous NCO− and NO− productions, etc.), along with emerging alternative electrooxidation reactions (electrooxidation of tetrazoles, furazans, iodide, quinolines, ascorbic acid, sterol, trimethylamine, etc.). Some new decoupled electrolysis and self‐powered systems are also discussed in detail. Finally, the potential challenges and prospects of coupled water electrolysis systems are highlighted to aid future research directions. Replacing oxygen evolution reaction (OER) with thermodynamically favorable small molecules oxidation reactions to construct coupled water electrolysis systems has been extensively investigated in the last decade. This review focuses on the fundamental principle and development of coupled system, the electrocatalysts design, and proposed mechanism for small molecules oxidation reactions. Perspectives and challenges are highlighted for future advancement in this field.

HighlightsN-doped graphene-coated structure and mesoporous nano-sheet can efficiently boost active sites and stability for hydrogen and oxygen evolution reaction.NiCo@C-NiCoMoO/NF exhibits low overpotentials for HER (266 mV) and OER (390 mV) at ± 1000 mA cm−2.For water electrolysis, it can hold at 1000 mA cm−2 for 43 h in 6.0 M KOH + 60 °C condition.Developing highly effective and stable non-noble metal-based bifunctional catalyst working at high current density is an urgent issue for water electrolysis (WE). Herein, we prepare the N-doped graphene-decorated NiCo alloy coupled with mesoporous NiCoMoO nano-sheet grown on 3D nickel foam (NiCo@C-NiCoMoO/NF) for water splitting. NiCo@C-NiCoMoO/NF exhibits outstanding activity with low overpotentials for hydrogen and oxygen evolution reaction (HER: 39/266 mV; OER: 260/390 mV) at ± 10 and ± 1000 mA cm−2. More importantly, in 6.0 M KOH solution at 60 °C for WE, it only requires 1.90 V to reach 1000 mA cm−2 and shows excellent stability for 43 h, exhibiting the potential for actual application. The good performance can be assigned to N-doped graphene-decorated NiCo alloy and mesoporous NiCoMoO nano-sheet, which not only increase the intrinsic activity and expose abundant catalytic activity sites, but also enhance its chemical and mechanical stability. This work thus could provide a promising material for industrial hydrogen production.

The magnetotail current sheet plays a crucial role in substorm dynamics, affecting the entire magnetosphere. Formation and reconnection of thin (ion‐gyroscale) current sheets initiate magnetospheric substorms. Theoretical models suggest that a transient, demagnetized ion population is key element of the thin current sheet configuration. At lunar distances, the magnetotail provides a unique opportunity for in situ investigation of this population due to the high fraction of hot demagnetized ions. Using observations of thin current sheets by the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun mission, we show that the relative drift between demagnetized hot ions and magnetized cold ions, likely driven by a strong polarization electric field, reduces the ion current density to nearly zero in the spacecraft rest frame. Hot ions exhibit a crescent‐like velocity distribution, contributing to ion agyrotropy. We discuss this population in the context of advanced thin current sheet models, including transient ions performing Speiser‐like motion. These observations provide valuable insights for numerical and theoretical studies. Plain Language Summary The night‐side Earth's magnetosphere, the magnetotail, is characterized by stretched magnetic field lines and strong electric currents forming a narrow plasma layer, the thin current sheet. The dynamic evolution of this current sheet determines the efficiency of charged particle acceleration before their transport into Earth's radiation belts and their precipitation into the atmosphere. Its properties are largely governed by the mechanism responsible for the current density generation. Modern theoretical models suggest that demagnetized ions, which violate the conservation of the magnetic moment, play a critical role in supplying the total current density. In this study, we present unambiguous observational confirmation of the existence of such a demagnetized ion population in quiet (stationary) current sheets. Using magnetotail observations at the lunar orbit, where conditions for revealing this ion population are most favorable, we demonstrate that the main aspects of the observed ions align well with the main predictions of theories of the thin current sheet formation. Key Points We investigate ion velocity distributions in thin current sheet in the magnetotail at lunar distances We observe hot (demagnetized, agyrotropic) and cold (beam‐like) ion populations drifting duskward and dawnward, respectively The dawnward drift of cold ions, likely due to E ×${\\times} $B‐drift, suppresses the ion current in the spacecraft rest frame

The chlorine evolution reaction (CER) is a crucial step in the production of chlorine gas and active chlorine by chlor-alkali electrolysis. Currently, the endeavor to fabricate electrodes capable of yielding high current density at minimal overpotential remains a central challenge in advancing the realm of chlorine evolution reactions. Here, we grow TiO 2 and RuO 2 on MXene@carbon cloth (CC) through the favorable affinity and induced deposition effect between the surface functional groups of MXene and the metal. A self-supported electrode (RuTiO 2 /MXene@CC) with strong binding at the electrocatalyst–support interface and weak adhesion at electrocatalyst–bubble interface is constructed. The RuTiO 2 /MXene@CC can reduce the electron density of RuO 2 by regulating the electron redistribution at the heterogeneous interface, thus enhancing the adsorption of Cl − . RuTiO 2 /MXene@CC could achieve a high current density of 1000 mA·cm − 2 at a small overpotential of 220 mV, superior to commercial dimensionally stable anodes (DSA). This study provides a new strategy for constructing efficient CER catalysts at high current density.

Phreatic events may represent precursors of magmatic eruptions or occur independently as single or multiple episodes at volcanoes with hydrothermal systems. We examine the Breccia De Fiore deposit from the prolonged phreatic activity during September–October 1873 at the La Fossa cone of Vulcano (Aeolian Islands, Italy). By integrating data from historical chronicles, stratigraphy, sedimentology, physical analyses, and 3D numerical simulations, we investigate eruption dynamics. The sedimentological characteristics of the deposits, asymmetrically dispersed along the north-western flank of the cone, are interpreted as the simultaneous emplacement of pyroclastic density currents and ballistic projectiles. Numerical simulations model the eruptive mixture as an Eulerian gas-particle fluid coupled with Lagrangian ballistic particles. Results suggest the deposit originated from multiple, shallow, low-magnitude explosions (< 5 × 10 4 m 3 cumulative volume). The deposit dispersal is well reproduced by simulating explosions from an inclined vent, driven by pressure build-up (up to 5 MPa) at shallow depths (< 150 m) within the hydrothermal system. This study helps constrain critical parameters of phreatic scenarios at La Fossa volcano, including erupted mass and specific energy, emphasising the hazards posed by such small events and the crucial need for improving hazard assessment, especially given the close presence of populated, touristic sites.

Alkaline hydrogen evolution reaction (HER) for scalable hydrogen production largely hinges on addressing the sluggish bubble‐involved kinetics on the traditional Ni‐based electrode, especially for ampere‐level current densities and beyond. Herein, 3D‐printed Ni‐based sulfide (3DPNS) electrodes with varying scaffolds are designed and fabricated. In situ observations at microscopic levels demonstrate that the bubble escape velocity increases with the number of hole sides (HS) in the scaffolds. Subsequently, we conduct multiphysics field simulations to illustrate that as the hole shapes transition from square, pentagon, and hexagon to circle, where a noticeable reduction in the bubble‐attached HS length and the pressure balance time around the bubbles results in a decrease in bubble size and an acceleration in the rate of bubble escape. Ultimately, the 3DPNS electrode with circular hole configurations exhibits the most favorable HER performance with an overpotential of 297 mV at the current density of up to 1000 mA cm−2 for 120 h. The present study highlights a scalable and effective electrode scaffold design that promotes low‐cost and low‐energy green hydrogen production through the ampere‐level alkaline HER. Three‐dimensional‐printed Ni‐based sulfide (3DPNS) electrodes with different scaffolds are designed and manufactured, aiming at elucidating the relationship between the number of hole sides (HS) within the electrode scaffold and bubble escape. Notably, the 3DPNS‐circle electrode, with the highest number of HS, demonstrates exceptional activity in the ampere‐level alkaline hydrogen evolution reaction (HER).

Employing the alkaline water electrolysis system to generate hydrogen holds great prospects but still poses significant challenges, particularly for the construction of hydrogen evolution reaction (HER) catalysts operating at ampere-level current density. Herein, the unique Ru and RuP 2 dual nano-islands are deliberately implanted on N-doped carbon substrate (denoted as Ru-RuP 2 /NC), in which a built-in electric field (BEF) is spontaneously generated between Ru-RuP 2 dual nano-islands driven by their work function difference. Experimental and theoretical results unveil that such constructed BEF could serve as the driving force for triggering fast hydrogen spillover process on bridged Ru-RuP 2 dual nano-islands, which could invalidate the inhibitory effect of high hydrogen coverage at ampere-level current density, and synchronously speed up the water dissociation on Ru nano-islands and hydrogen adsorption/desorption on RuP 2 nano-islands through hydrogen spillover process. As a result, the Ru-RuP 2 /NC affords an ultra-low overpotential of 218 mV to achieve 1.0 A·cm −2 along with the superior stability over 1000 h, holding the great promising prospect in practical applications at ampere-level current density. More importantly, this work is the first to advance the scientific understanding of the relationship between the constructed BEF and hydrogen spillover process, which could be enlightening for the rational design of the cost-effective alkaline HER catalysts at ampere-level current density.

HighlightsA novel cascade strategy is proposed to construct Pd-NiCo2O4 electrocatalyst.First time discovery that Ni incorporation together with Pd loading is able to balance the competitive adsorption of OH– and 5-hydroxymethylfurfural.Pd–NiCo2O4 promotes both the indirect and direct synergistic oxidation process.Pd–NiCo2O4 catalyst exhibits extraordinary current density and excellent Faradaic Efficiency at a low potential.Electrocatalytic 5-hydroxymethylfurfural oxidation reaction (HMFOR) provides a promising strategy to convert biomass derivative to high-value-added chemicals. Herein, a cascade strategy is proposed to construct Pd–NiCo2O4 electrocatalyst by Pd loading on Ni-doped Co3O4 and for highly active and stable synergistic HMF oxidation. An elevated current density of 800 mA cm–2 can be achieved at 1.5 V, and both Faradaic efficiency and yield of 2,5-furandicarboxylic acid remained close to 100% over 10 consecutive electrolysis. Experimental and theoretical results unveil that the introduction of Pd atoms can modulate the local electronic structure of Ni/Co, which not only balances the competitive adsorption of HMF and OH– species, but also promote the active Ni3+ species formation, inducing high indirect oxidation activity. We have also discovered that Ni incorporation facilitates the Co2+ pre-oxidation and electrophilic OH* generation to contribute direct oxidation process. This work provides a new approach to design advanced electrocatalyst for biomass upgrading.

Here we report a comprehensive numerical study for the operating behavior and physical mechanism of nitride micro-light-emitting-diode (micro-LED) at low current density. Analysis for the polarization effect shows that micro-LED suffers a severer quantum-confined Stark effect at low current density, which poses challenges for improving efficiency and realizing stable full-color emission. Carrier transport and matching are analyzed to determine the best operating conditions and optimize the structure design of micro-LED at low current density. It is shown that less quantum well number in the active region enhances carrier matching and radiative recombination rate, leading to higher quantum efficiency and output power. Effectiveness of the electron blocking layer (EBL) for micro-LED is discussed. By removing the EBL, the electron confinement and hole injection are found to be improved simultaneously, hence the emission of micro-LED is enhanced significantly at low current density. The recombination processes regarding Auger and Shockley–Read–Hall are investigated, and the sensitivity to defect is highlighted for micro-LED at low current density.Synopsis: The polarization-induced QCSE, the carrier transport and matching, and recombination processes of InGaN micro-LEDs operating at low current density are numerically investigated. Based on the understanding of these device behaviors and mechanisms, specifically designed epitaxial structures including two QWs, highly doped or without EBL and p-GaN with high hole concentration for the efficient micro-LED emissive display are proposed. The sensitivity to defect density is also highlighted for micro-LED.

Efficient, durable and economic electrocatalysts are crucial for commercializing water electrolysis technology. Herein, we report an advanced bifunctional electrocatalyst for alkaline water splitting by growing NiFe-layered double hydroxide (NiFe-LDH) nanosheet arrays on the conductive NiMo-based nanorods deposited on Ni foam to form a three-dimensional (3D) architecture, which exhibits exceptional performances for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In overall water splitting, only the low operation voltages of 1.45/1.61 V are required to reach the current density of 10/500 mA·cm −2 , and the continuous water splitting at an industrial-level current density of 500 mA·cm −2 shows a negligible degradation (1.8%) of the cell voltage over 1000 h. The outstanding performance is ascribed to the synergism of the HER-active NiMo-based nanorods and the OER-active NiFe-LDH nanosheet arrays of the hybridized 3D architecture. Specifically, the dense NiFe-LDH nanosheet arrays enhance the local pH on cathode by retarding OH − diffusion and enlarge the electrochemically active surface area on anode, while the conductive NiMo-based nanorods on Ni foam much decrease the charge-transfer resistances of both electrodes. This study provides an efficient strategy to explore advanced bifunctional electrocatalysts for overall water splitting by rationally hybridizing HER- and OER-active components.