Iron-nitrogen-carbon (Fe-N-C) is hitherto considered as one of the most satisfactory alternatives to platinum for the oxygen reduction reaction (ORR). Major efforts currently are devoted to the identification and maximization of carbon-enclosed FeN moieties, which act as catalytically active centers. However, fine-tuning of their intrinsic ORR activity remains a huge challenge. Herein, a twofold activity improvement of pristine Fe-N-C through introducing Ti C T MXene as a support is realized. A series of spectroscopy and magnetic measurements reveal that the marriage of FeN moiety and MXene can induce remarkable Fe 3d electron delocalization and spin-state transition of Fe(II) ions. The lower local electron density and higher spin state of the Fe(II) centers greatly favor the Fe electron transfer, and lead to an easier oxygen adsorption and reduction on active FeN sites, and thus an enhanced ORR activity. The optimized catalyst shows a two- and fivefold higher specific ORR activity than those of pristine catalyst and Pt/C, respectively, even exceeding most Fe-N-C catalysts ever reported. This work opens up a new pathway in the rational design of Fe-N-C catalysts, and reflects the critical influence of Fe 3d electron states in FeN moiety supported on MXene in ORR catalysis.

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.

Electrochemical conversion of carbon dioxide (CO 2 ) into high-value chemical products has become a dramatic research area because of the efficient exploitation of carbon resources and simultaneous reduction of atmospheric CO 2 concentration. Herein, we report the bismuth-based catalyst in the efficient electroconversion of CO 2 for the formation of formate with a maximum Faradaic efficiency of 91% and partial current density of ∼8 mA cm −2 at −0.9 V vs RHE. Experimental and theoretical results show that the bismuth−oxygen structure of bismuth oxides is beneficial for a higher adsorption of CO 2 and the ratedetermining route switching from the initial fast pre-equilibrium of electron transfer process to the subsequent hydrogenation step, accompanied by a lower free energy of intermediate. This work may offer valuable insights into crystal structure engineering to achieve efficient electrocatalysts for selective CO 2 reduction toward generation of valuable products.

Aqueous zinc-ion batteries have drawn increasing attention due to the intrinsic safety, costeffectiveness and high energy density. However, parasitic reactions and non-uniform dendrite growth on the Zn anode side impede their application. Herein, a multifunctional additive, ammonium dihydrogen phosphate (NHP), is introduced to regulate uniform zinc deposition and to suppress side reactions. The results show that the NH 4 + tends to be preferably absorbed on the Zn surface to form a "shielding effect" and blocks the direct contact of water with Zn. Moreover, NH 4 + and (H 2 PO 4 ) À jointly maintain pH values of the electrode-electrolyte interface. Consequently, the NHP additive enables highly reversible Zn plating/stripping behaviors in Zn//Zn and Zn//Cu cells. Furthermore, the electrochemical performances of Zn//MnO 2 full cells and Zn//active carbon (AC) capacitors are improved. This work provides an efficient and general strategy for modifying Zn plating/stripping behaviors and suppressing side reactions in mild aqueous electrolyte.

The high theoretical capacity and natural abundance of SiO 2 make it a promising high-capacity anode material for lithium-ion batteries. However, its widespread application is significantly hampered by the intrinsic poor electronic conductivity and drastic volume variation. Herein, a unique hollow structured Ni/SiO 2 nanocomposite constructed by ultrafine Ni nanoparticle (≈3 nm) functionalized SiO 2 nanosheets is designed. The Ni nanoparticles boost not only the electronic conductivity but also the electrochemical activity of SiO 2 effectively. Meanwhile, the hollow cavity provides sufficient free space to accommodate the volume change of SiO 2 during repeated lithiation/ delithiation; the nanosheet building blocks reduce the diffusion lengths of lithium ions. Due to the synergistic effect between Ni and SiO 2 , the Ni/SiO 2 composite delivers a high reversible capacity of 676 mA h g −1 at 0.1 A g −1 . At a high current density of 10 A g −1 , a capacity of 337 mA h g −1 can be retained after 1000 cycles.