Water-electrolysis technology can realize zero CO 2 emission and acquire large-scale hydrogen with high purity (>99.9%), and thus potentially serves as a key component in future sustainable energy systems. [1,2] However, this technology accounts for only 4% of current hydrogen production, which is mainly attributed to its higher cost in comparison with other methods such as the conversion of natural fossil fuels. [3] For commercial water electrolysis systems, the existing key problems mainly focus on the use of efficient but exorbitant iridium, ruthenium or platinum catalysts, or economically practical nickel meshes and stainless steel with the unsatisfying activity. [4] Exploring highly active and costeffective catalysts with good durability is imperative but challenging. Though important breakthroughs have been made recently in investigating high-efficiency first-row transition metal catalysts for oxygen and hydrogen evolution reactions (OER and HER), [5-9] a certain gap still exists between the test condition (almost at room temperature, Table S1, Supporting Information) and the industrial one (at 50-80 °C). Therefore, it is essential to evaluate the catalytic performance and compatibility of catalysts under such harsh operating condition for further practical applications. Rational design of HER and OER catalysts which can be well operated at industrial temperatures is highly desirable for practical alkaline water electrolysis (AWE) application. Our reported MoO 2-Ni arrays exhibited a Pt-like HER activity at 25.0 °C, and the convenient synthesis route was beneficial to its mass production. [10] Such a catalyst serves as a potential candidate because its heterogeneous components may avoid agglomeration under high-temperature catalytic conditions. For anodic OER, some researchers recently evaluated the catalytic performance at 80 °C, such as NiFe-LDH [11] in alkali or CoFePbO x [12] in acid, however with only ≈20 h operation. Our recent works have focused on the reconstruction chemistry of catalysts, demonstrating that the deeply/completely reconstructed (denoted as DR/CR) catalysts are a potential choice. The reported DR-NiOOH was operated well with activity decay of 0.35 mV h −1 in 40 h tested at 52.8 °C. [13] In addition, the DR catalysts with abundant active species can realize high component utilization and thus high-mass-activity catalysis. Nevertheless, the lithiation Evaluating the alkaline water electrolysis (AWE) at 50-80 °C required in industry can veritably promote practical applications. Here, the thermally induced complete reconstruction (TICR) of molybdate oxygen evolution reaction (OER) pre-catalysts at 51.9 °C and its fundamental mechanism are uncovered. The dynamic reconstruction processes, the real active species, and stereoscopic structural characteristics are identified by in situ low-/ high-temperature Raman, ex situ microscopy, and electron tomography. The completely reconstructed (CR) catalyst (denoted as cat.-51.9) is interconnected by thermodynamically stable (oxy)hydroxide nanopartic...

Oxygen evolution reaction (OER)-induced reconstruction on precatalysts generally results in surface-reconstructed catalysts with less active species and thus low mass activity. Herein, the deeply reconstructed (DR) catalyst is proposed and derived from a sub-10 nm precatalyst to achieve high-mass-activity catalysis. As a proof-of-concept, the DR-NiOOH with a multilevel nanosheet structure interconnected by sub-5 nm nanoparticles was obtained via a lithiation-induced deep reconstruction strategy. The robust DR-NiOOH with abundant active species enables its significantly enhanced mass activity (170 mV decrease in OER overpotential to achieve 5 mA mg–1) and better durability (>10 days) than that of incompletely reconstructed Ni@NiOOH. Its strong corrosion resistance (30 wt % KOH, 72 h) and high thermal stability (52.8 °C, >40 h) were also confirmed. Theoretical analyses support that the unsaturated OH coverages on orthorhombic NiOOH endow its good OER-active property. This work highlights the merits of high-utilization DR catalysts toward potential catalytic applications under realistic conditions.

No abstract

Unique interfacial properties within heterostructures play vital roles in enhancing hydrogen evolution reaction (HER) electrocatalysis. On the basis of the MoO2-Ni heterostructure, we hereby propose an upraised atomic orbital promoted catalytic mechanism for accelerating the HER kinetics. A controllable gradient-pyrolysis approach is adopted on molybdates to integrate Ni with MoO2, possessing numerous phase-separation-induced intimate interfaces. In situ characterizations demonstrate the formation process of MoO2-Ni interfaces and excellent compositional stability under alkaline conditions. The optimized MoO2-Ni catalyst delivers remarkable Pt-like HER activity and good stability with 50 h operation in 1 M KOH. An enhancement of 3 orders of magnitude on the exchange current density is achieved for MoO2-Ni in comparison to the simplex MoO2. Further experimental and theoretical analyses verify the existence of a concentrated surface charge at MoO2-Ni interfaces. Meanwhile, with the incorporation of Ni into MoO2, the most active sites dramatically change from Mo to O atoms at MoO2-Ni interfaces. The Ni contact upraises the O 2p orbital in MoO2, thus strengthening the hydrogen adsorption for enhanced HER kinetics.

The calcium-ion battery is an emerging energy storage system that has attracted considerable attention recently. However, the absence of high-performance cathode materials is one of the main challenges for the development of calcium-ion batteries. Herein, a bilayered Mg0.25V2O5·H2O as a stable cathode for rechargeable calcium-ion batteries is identified. Remarkably, an unexpected stable structure of the material for Ca2+ storage is demonstrated. It is found that the interlayer spacing shows only a tiny variation of ∼0.09 Å during Ca2+ insertion/extraction, which results in its outstanding cycling stability (capacity retention of 86.9% after 500 cycles) for Ca2+ storage. On the basis of in situ/ex situ experimental characterizations and ab initio simulation, the origin of such superior structural stability is revealed. This ultrastable cathode together with the understanding lays a strong foundation for developing high-performance calcium-ion batteries.

No abstract

The calcium-ion-storage mechanism of VOPO4·2H2O is studied by in situ XRD and in situ Raman for the first time.

Amorphous carbon shows great potential as an anode material for high-performance potassium-ion batteries; however, its abundant defects or micropores generally capture K ions, thus resulting in high irreversible capacity with low initial Coulombic efficiency (ICE) and limited practical application. Herein, pore engineering via a facile self-etching strategy is applied to achieve mesoporous carbon (meso-C) nanowires with interconnected framework. Abundant and evenly distributed mesopores could provide short K+ pathways for its rapid diffusion. Compared to microporous carbon with highly disordered structure, the meso-C with Zn-catalyzed short-range ordered structure enables more K+ to reversibly intercalate into the graphitic layers. Consequently, the meso-C shows an increased capacity by ~ 100 mAh g−1 at 0.1 A g−1, and the capacity retention is 70.7% after 1000 cycles at 1 A g−1. Multiple in/ex situ characterizations reveal the reversible structural changes during the charging/discharging process. Particularly, benefiting from the mesoporous structure with reduced specific surface area by 31.5 times and less defects, the meso-C generates less irreversible capacity with high ICE up to 76.7%, one of the best reported values so far. This work provides a new perspective that mesopores engineering can effectively accelerate K+ diffusion and enhance K+ adsorption/intercalation storage.