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The design of diatomic catalysts with uniformly dispersed metal atoms is expected to improve catalytic performance, which is conducive to the intensive comprehending of the synergistic mechanism between dual-metal sites for the oxygen evolution reaction (OER) at the atomic level. Herein, we design a strategy to immobilize bimetallic Fe-Co atoms onto nitrogen-doped graphene to obtain a diatomic catalyst (DA-FC-NG) with FeN3-CoN3 configuration. The DA-FC-NG shows excellent OER activity with a low overpotential (η10 = 268 mV), which is superior to commercial iridium dioxide catalysts. Theoretical calculations uncover that the excellent activity of DA-FC-NG is due to the interaction between Fe and Co diatoms, which causes charge rearrangement and induces the adsorption of intermediates on the Fe–O–Co bridge structure, thus improving the catalytic OER performance. This work is of great significance for the design of highly active diatomic catalysts to replace noble metal catalysts for energy-related applications. [ABSTRACT FROM AUTHOR]

As a four-electron transfer reaction, oxygen evolution reaction (OER) is limited by large overpotential and slow kinetics. Here, we in-situ synthesized two-dimensional (2D) Ni-Fe metal-organic framework nanosheets on nickel foam (NixFe-TPA/NF, TPA = terephthalic acid) for oxygen evolution in alkaline and alkaline seawater electrolytes. In 1 M KOH, Ni3Fe-TPA/NF shows a low overpotential (η10) of 189 mV at 10 mA·cm−2 and an ultra-low overpotential of only 260 mV at 500 mA·cm−2. In alkaline seawater, Ni3Fe-TPA/NF still provides impressive OER performance, with an η10 of 265 mV. In-situ Raman characterization results show that the phase transition occurs during the OER, and Ni3FeOOH with more oxygen vacancies is in-situ formed, reducing the OER energy barrier. Density functional theory (DFT) reveals that the synergy between Ni and Fe reduces the energy barrier and accelerates the rate-determining step. In addition, the ultra-thin 2D sheet structure and the close combination of Ni3FeOOH and highly conductive NF support ensure the high catalytic OER activity. Therefore, the surface reconstruction and structural modification strategy can be used to design and prepare high-performance OER electrocatalysts for energy-related applications. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are crystalline organic porous polymers that can be precisely integrated by building blocks to achieve pre‐designed composition, components, and functions, making them a powerful platform for the development of molecular devices in the field of electrocatalysis. The precise control of channel/dopant positions and highly ordered network structures of COFs provide an ideal material system for the applications of advanced electrocatalysis. In this paper, the topological structure design and synthesis methods of COFs are reviewed in detail, and their design principles are deeply analyzed. In addition, the applications of COFs and their derivatives in the field of electrocatalysis are systematically summarized and the optimization strategies are proposed. Finally, the application prospects of COFs and their derivatives in electrocatalysis and the challenges that may be encountered in the future are prospected, providing helpful guidance for future research. [ABSTRACT FROM AUTHOR]

Dual-metal catalysts with synergistic effect exhibit enormous potential for sustainable electrocatalytic applications and mechanism research. Compared with mono-metal-site catalysts, dual-metal-site catalysts exhibit higher efficiency for the oxygen evolution reaction (OER) due to reduced energy barrier of the process involving proton-coupled multi-electron transfer. Herein, we construct dual-metal Fe-Co sites coordinated with nitrogen in graphene (FeCo-NG), which exhibits high OER performance with onset overpotential of only 126 mV and Tafel slope of 120 mV·dec−1, showing that the rate-determining step is controlled by the single-electron transfer step. Theoretical calculations reveal that the FeN4 site exhibits lower OER overpotential than the CoN4 site due to appropriate adsorption energy of OOH* on the former, while the O* adsorbed on the adjacent Co site could stabilize the OOH* on the FeN4 site through hydrogen bond interaction. [ABSTRACT FROM AUTHOR]

To solve the energy crisis and environmental pollution problems, the use of clean and renewable energy to replace fossil energy has become a top priority. The oxygen evolution reaction (OER) is the core of many renewable energy technologies. Developing low-cost and high-performance OER electrocatalysts is the key to implementing efficient energy conversion processes. Here, we synthesize ordered mesoporous iron–cobalt oxides using a hard template strategy. As a mesoporous oxide catalyst, meso-CoFe0.05Ox exhibits low OER overpotentials of 280 and 373 mV at current densities of 10 and 100 mA cm−2, respectively, and does not show deactivation for at least 18 hours at 100 mA cm−2. The introduction of iron can change the electronic structure of Co, and the orbital electrons are easily transferred from cobalt to iron. The enhanced OER performance can be attributed to concerted catalysis between the iron and cobalt sites that lowers the OER energy barrier, and the large specific surface area of the porous oxide providing efficient active sites for the reaction. [ABSTRACT FROM AUTHOR]

This review introduces how to optimize the structure of carbon-based diatomic catalysts to promote the electrocatalytic performances of HER, OER, ORR, CO 2 RR and NRR, including adjusting the electronic structure of bimetallic central atoms, regulating the local coordination environment of bimetallic central atoms and tuning the base environment of carbon-based materials. [Display omitted] • We summarize controllable synthesis methods for the fabrication of DACs. • The electronic structure of bimetallic central atoms can be adjusted. • The local coordination environment of bimetallic central atoms can be regulated. • The base environment of carbon-based materials can be tuned. • Several strategies for optimizing electrocatalytic performance are proposed. As an extension of single-atom catalysts (SACs), diatomic catalysts (DACs) perfectly inherit the advantages of SACs but break some theoretical limitations of SACs due to the interaction between dual-atom sites. However, there are still challenges for the electrocatalytic applications of carbon-based DACs, such as difficult in controllable synthesis and identification of bimetallic dimer, hard to adjust the coordination environments of bimetallic sites, poor structural stability, and unclear reaction mechanisms. Here, we summarize controllable synthesis methods for the fabrication of DACs and introduce the characterization techniques in comprehending the geometrical configuration of bimetallic dimer, local electronic structure, coordination environments, and insights into reaction mechanisms by combining in situ characterization and theoretical investigation. Moreover, several important electrocatalytic applications of DACs, including for the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, CO 2 reduction reaction, and nitrogen reduction reaction are reviewed. To precipitate the future development of high-performance carbon-based DACs, we put forward several strategies to adjust the electronic structure for optimizing the electrocatalytic performances, including adjusting the electronic structure of bimetallic central atoms, regulating the local coordination environment of bimetallic central atoms, and tuning the base environment. Finally, future research directions of developing advanced carbon-based DACs for electrocatalytic application are proposed. [ABSTRACT FROM AUTHOR]

2D MOFs and their derivatives are promising electrocatalysts due to their ultrathin nanosheets, large specific surface area and adjustable structure. This review summarizes the recent advances of 2D MOFs from their basics, synthesis, characterizations and simulations, as well as the potential applications in electrocatalytic OER, HER, ORR, CO 2 RR and NRR. Moreover, the development prospects and challenges of 2D MOFs and their derivatives are also put forward. [Display omitted] • The principles and methods in constructing 2D MOFs and their derivatives are provided. • The electrocatalytic applications of 2D MOFs and their derivatives are summarized. • Electrocatalytic activity and its relationship with structural modulation are discussed. • Current challenges are discussed and future trends are envisioned for electrocatalytic field. Metal organic frameworks (MOFs) are promising electrocatalysts due to their high porosity, large specific surface area and adjustable structure. Especially, two-dimensional (2D) MOFs with ultra-thin structure provide more active sites and shorter diffusion distance for heterogeneous catalytic reactions. However, the poor conductivity and poor stability of 2D MOFs impede their practical electrocatalytic applications greatly. Therefore, 2D MOF-derived transition metal carbides, sulfides, phosphides, oxides, and single-atom catalysts have been fabricated by carbonization, vulcanization, phosphorization or oxidation strategies, which improve the conductivity and stability significantly. Here, the synthesis strategies of 2D MOFs and their derivatives are summarized, and the factors affecting the geometries and electronic structures of active sites are commented in detail. The electrocatalytic applications of 2D MOFs and their derivatives in oxygen evolution reaction (OER), hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO 2 RR) and nitrogen reduction reaction (NRR) are reviewed. The effect of the geometric construction and electronic configuration of active sites (including metals, nonmetals, and defects) of 2D MOFs and their derivatives on the electrocatalytic performance is detailedly discussed by combining experimental achievements and theoretical analysis. Finally, the development prospects and challenges of 2D MOFs and their derivatives are proposed. [ABSTRACT FROM AUTHOR]

Searching for highly active and durable oxygen evolution reaction (OER) electrocatalysts is the key to break through the bottleneck of overall water splitting. Here, we prepare Ni x Fe-BDC (H 2 BDC = terephthalic acid) nanorods with different Ni/Fe ratios by a facile solvothermal method for the OER. The optimal Ni 3 Fe-BDC exhibits a low overpotential (η 10) of 265 mV and a Tafel slope of 90 mV·dec−1 in 1 M KOH. Moreover, it shows a low η 10 of 280 mV and excellent stability in the mixture of 1 M NaCl and 1 M KOH, which has strong corrosion resistance to Cl− anions. The role of Fe3+ not only increases the charge transfer rate of Ni 3 Fe-BDC, but also affects the specific surface area of the catalyst with high electrochemical activity. Kinetic studies show that both Fe and Ni sites act as active centers, which catalyze synergistically to reduce the reaction kinetic energy barrier. Characterization results of the used Ni 3 Fe-BDC reveal that the in situ formed rod-like Ni 3 FeOOH is the active site for the OER. Ni 3 Fe-BDC shows low η 10 of 265 mV and 280 mV for the OER in 1 M KOH and in 1 M NaCl + 1 M KOH, respectively. In situ transformation of nanorod-like Ni 3 Fe-BDC MOF to Ni 3 FeOOH can efficiently remain the advantages of MOF, e.g. porous structure, high specific surface area and uniformly dispersed metal sites. [Display omitted] • Ni 3 Fe-BDC shows low η 10 of 265 mV for the OER in 1 M KOH. • Ni 3 Fe-BDC shows η 10 of only 280 mV for the OER in 1 M NaCl +1 M KOH. • Ni 3 Fe-BDC exhibits a low OER energy barrier of 13.7 kJ/mol. • The in-situ formed rod-like Ni 3 FeOOH serves as efficient active site for the OER. [ABSTRACT FROM AUTHOR]