Reconstruction induced by external environment (such as applied voltage bias and test electrolytes) changes catalyst component and catalytic behaviors. Investigations of complete reconstruction in energy conversion recently receive intensive attention, which promote the targeted design of top‐performance materials with maximum component utilization and good stability. However, the advantages of complete reconstruction, its design strategies, and extensive applications have not achieved the profound understandings and summaries it deserves. Here, this review systematically summarizes several important advances in complete reconstruction for the first time, which includes 1) fundamental understandings of complete reconstruction, the characteristics and advantages of completely reconstructed catalysts, and their design principles, 2) types of reconstruction‐involved precatalysts for oxygen evolution reaction catalysis in wide pH solution, and origins of limited reconstruction degree as well as design strategies/principles toward complete reconstruction, 3) complete reconstruction for novel material synthesis and other electrocatalysis fields, and 4) advanced in situ/operando or multiangle/level characterization techniques to capture the dynamic reconstruction processes and real catalytic contributors. Finally, the existing major challenges and unexplored/unsolved issues on studying the reconstruction chemistry are summarized, and an outlook for the further development of complete reconstruction is briefly proposed. This review will arouse the attention on complete reconstruction materials and their applications in diverse fields.

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.

Carbon dot is a type of carbon material with an ultrasmall size of less than 10 nm for all three dimensions, which has attracted more and more attention due to its useful merits. Unfortunately, the complicated synthesis method and low yield largely limit its wide large-scale application. Herein, an inexpensive and high-efficiency aldol condensation method under ambient temperature and pressure was proposed for the large-scale synthesis of CDs, which can obtain products with 1.083 kg in 2 h and realize the functionalization of carbon dots doped with nitrogen (NCDs) and sulfur/nitrogen doubly (NSCDs), and then the mechanism and structure of CDs formation were explained. Moreover, utilizing the feature of controllable assembly of carbon dots, and combined with theoretical calculations, we have designed functionalized 1D carbon fibers (CF) to construct high-performance potassium storage anode materials through the assembly of carbon dots induced by a Zn compound. Benefitting from the microstructure and surface functional groups derived from CDs, the N-doped CF (NCF700) exhibits superior electrochemical energy storage performance for potassium ion batteries (PIBs). This study provides a low-cost and high-yield method to produce CDs and promotes the practical application of CDs in electrochemical energy storage.

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.

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