Electrocatalytic oxygen reduction reaction (ORR) is one of the most important reactions in electrochemical energy technologies such as fuel cells and metal–O₂/air batteries, etc. However, the essential catalysts to overcome its slow reaction kinetic always undergo a complex dynamic evolution in the actual catalytic process, and the concomitant intermediates and catalytic products also occur continuous conversion and reconstruction. This makes them difficult to be accurately captured, making the identification of ORR active sites and the elucidation of ORR mechanisms difficult. Thus, it is necessary to use extensive in-situ characterization techniques to proceed the real-time monitoring of the catalyst structure and the evolution state of intermediates and products during ORR. This work reviews the major advances in the use of various in-situ techniques to characterize the catalytic processes of various catalysts. Specifically, the catalyst structure evolutions revealed directly by in-situ techniques are systematically summarized, such as phase, valence, electronic transfer, coordination, and spin states varies. In-situ revelation of intermediate adsorption/desorption behavior, and the real-time monitoring of the product nucleation, growth, and reconstruction evolution are equally emphasized in the discussion. Other interference factors, as well as in-situ signal assignment with the aid of theoretical calculations, are also covered. Finally, some major challenges and prospects of in-situ techniques for future catalysts research in the ORR process are proposed.

It has been a challenge to use transition metal oxides as anode materials in Li-ion batteries due to their low electronic conductivity, poor rate capability and large volume change during charge/discharge processes. Here, we present the first demonstration of a unique self-recovery of capacity in transition metal oxide anodes. This was achieved by reducing tungsten trioxide (WO₃) via the incorporation of urea, followed by annealing in a nitrogen environment. The reduced WO₃ successfully self-retained the Li-ion cell capacity after undergoing a sharp decrease upon cycling. Significantly, the reduced WO₃ also exhibited excellent rate capability. The reduced WO₃ exhibited an interesting cycling phenomenon where the capacity was significantly self-recovered after an initial sharp decrease. The quick self-recoveries of 193.21%, 179.19% and 166.38% for the reduced WO₃ were observed at the 15^th (521.59/457.41 mA h g⁻¹), 36^th (538.49/536.61 mA h g⁻¹) and 45^th (555.39/555.39 mA h g⁻¹) cycles respectively compared to their respective preceding discharge capacity. This unique self-recovery phenomenon can be attributed to the lithium plating and conversion reaction which might be due to the activation of oxygen vacancies that act as defects which make the WO₃ electrode more electrochemically reactive with cycling. The reduced WO₃ exhibited a superior electrochemical performance with 959.1/638.9 mA h g⁻¹ (1^st cycle) and 558.68/550.23 mA h g⁻¹ (100^th cycle) vs. pristine WO₃ with 670.16/403.79 mA h g⁻¹ (1^st cycle) and 236.53/234.39 mA h g⁻¹ (100^th cycle) at a current density of 100 mA g⁻¹.

Due to its characteristics of not being constrained by the lattice structure and cation size, electrochemical conversion reaction is becoming an increasingly prominent type of electrochemical reaction. Lithium‐ion batteries can achieve superior performance by utilizing conversion reactions, Moreover, Sodium‐ion batteries are expected to become alternatives to lithium‐ion because of the plentiful sodium resources. This review discusses the most current developments and unmet needs in anode materials based on conversion reactions of Lithium‐ion and sodium‐ion batteries, as well as various synthesis techniques, morphological characteristics, and electrochemical properties.

Electrocatalysts play critical roles in electrochemical energy storage and conversion technologies such as fuel cells, metal–air batteries, and H₂O/CO₂/N₂ electrolysis. Recently, metal–organic framework (MOF)-derived electrocatalysts have been extensively explored not only because of their superior electrocatalytic activities but also their well-defined active sites, particularly those of single-atom active sites, which have been recognized as role-model electrocatalysts for fundamental understanding of the catalytic mechanisms at both the molecular and electronic levels. In this paper, we have reviewed the recent progress in MOF-derived electrocatalysts with focus on the characterization of the catalytically active sites, their functional mechanisms and performance validation/optimization of the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂RR), and nitrogen reduction reaction (NRR). Regarding the synthesis of the electrocatalysts with active sites, the alloy and composite formation and the edge-defect/oxygen vacancy engineering are discussed. Regarding the characterization for fundamental understanding, some advanced in situ/ex situ characterization and theoretical calculations using first-principles Density Functional Theory (DFT) are summarized. Some technical challenges are analyzed and the corresponding further research directions for overcoming the challenges are also proposed for future research and development of practicable MOF-derived electrocatalysts.