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Electrocatalysts play a pivotal role in reducing the reaction barriers for key reactions such as the oxygenreduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), which areessential for the development of environment-friendly energy conversion devices including metal air batteries(MABs), proton exchange mem...
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... efficient electron pathway for catalytic reactions [55,59] and can also be used directly as an active site [60]. These formed composites are known as heterostructures and can be created between carbon materials or metal-based composites [55,[61][62][63]. A comprehensive illustration plot summarizing these strategies mentioned above is provided in Fig. ...
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... that the coupling effect of metallic dopant with the metal atoms in the substrate can form unique partially occupied orbitals near the Fermi level, which can greatly affect the electron transfer ability and further enhance the adsorption ability during electrocatalytic reaction [112]. The illustration of the coupling effect is exhibited in Fig. 5h [21], when the atomic Pt atom is doped into the Fe 2 O 3 , both original fully occupied orbital in Fe 3+ and unoccupied orbital in Pt transfer into partially occupied orbitals, which is favorable for oxygen adsorption and dissociation. Moreover, the characteristic of atomic metallic dopant can benefit the semi-conductor type substrate by ...
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... reaction pathway which accelerates the electron transfer on this heterostructure through tuning the band gap, work function and constructing Mott-Schottky barrier. Second is the formed heterostructure itself can function as catalytic active sites with optimized binding energy of reaction intermediates, catalytic energy barrier and valence band. Fig. 10 presents these two strategies for benefiting the catalytic ...
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... electron transfer on it, providing enhanced charge transfer rate further benefits the catalytic reaction [142,143]. The electron redistribution can occur on the boundary of the heterostructure, contributing to the optimized electron transfer process on it. Hoa et al. implant Ru single atoms on the MoS 2 -Mo 2 C heterostructure, the DOS plots Fig. 11a and b show that the Ru-MoS 2 -Mo 2 C possess a higher electronic state around Fermi level [144], suggesting its better electron transfer ability. In transition metal-based catalyst, the electron coupling effect can occur at the boundary of the heterostructure [145], as shown in Fig. 11c, due to ...
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... atoms on the MoS 2 -Mo 2 C heterostructure, the DOS plots Fig. 11a and b show that the Ru-MoS 2 -Mo 2 C possess a higher electronic state around Fermi level [144], suggesting its better electron transfer ability. In transition metal-based catalyst, the electron coupling effect can occur at the boundary of the heterostructure [145], as shown in Fig. 11c, due to ...
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... 3 S 4 , facilitating the electron transfer process. Likewise, the heterostructure in carbon materials can also accelerate the electron transfer process during catalytic reactions. In Fig. 11d, two-dimensional covalent organic frameworks (COF) are decorated on the surface of one-dimensional carbon nanotubes (CNT) through van der Waals force [146], and operando FTIR measurement was conducted to confirm the S sites on the COF side of the COF/CNT van der Waals heterostructure serve as ORR and OER active sites (Fig. 11e and f). ...
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... reactions. In Fig. 11d, two-dimensional covalent organic frameworks (COF) are decorated on the surface of one-dimensional carbon nanotubes (CNT) through van der Waals force [146], and operando FTIR measurement was conducted to confirm the S sites on the COF side of the COF/CNT van der Waals heterostructure serve as ORR and OER active sites (Fig. 11e and f). The van der Waals heterostructure exhibits reduced energy band and work function compared with COF ( Fig. 11 g and h), which can function as an efficient pathway for electron transferring during ORR and OER, accelerating the progress of oxygen reduction on S active sites in COF. Moreover, a novel kind of Mott-Schottky heterostructure ...
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... carbon nanotubes (CNT) through van der Waals force [146], and operando FTIR measurement was conducted to confirm the S sites on the COF side of the COF/CNT van der Waals heterostructure serve as ORR and OER active sites (Fig. 11e and f). The van der Waals heterostructure exhibits reduced energy band and work function compared with COF ( Fig. 11 g and h), which can function as an efficient pathway for electron transferring during ORR and OER, accelerating the progress of oxygen reduction on S active sites in COF. Moreover, a novel kind of Mott-Schottky heterostructure has been proved to efficiently benefit the catalytic reaction through constructing electron transfer pathway. The ...
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... and semi-conductor can stimulate electron redistribution and provide an efficient pathway for electron transfer during catalytic reaction [151,152]. Yang et al. discovered that the Mott-Schottky heterojunction formed by Fe 3 C quantum dots and N-doped graphene carbon (NG) can effectively rearrange the charge of Fe 3 C and NG spontaneously (Fig. 11i) [6]. As a result, the boundary between Fe 3 C and NG can absorb more oxygen intermediates and ensure the rapid electron transfer during the ORR processes (Fig. 11j). Similarly, Sun et al. have also synthesized a novel kind of Fe/N-doped carbon (NG) heterostructure with Mott-Schottky effect [55]. The electron transfer mechanism of this ...
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... al. discovered that the Mott-Schottky heterojunction formed by Fe 3 C quantum dots and N-doped graphene carbon (NG) can effectively rearrange the charge of Fe 3 C and NG spontaneously (Fig. 11i) [6]. As a result, the boundary between Fe 3 C and NG can absorb more oxygen intermediates and ensure the rapid electron transfer during the ORR processes (Fig. 11j). Similarly, Sun et al. have also synthesized a novel kind of Fe/N-doped carbon (NG) heterostructure with Mott-Schottky effect [55]. The electron transfer mechanism of this Fe/NG Mott-Schottky heterostructure is shown in Fig. 11k, after the contact of Fe and NG, electrons flow from the Fe side to the NG side to maintain the balance of ...
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... Fe 3 C and NG can absorb more oxygen intermediates and ensure the rapid electron transfer during the ORR processes (Fig. 11j). Similarly, Sun et al. have also synthesized a novel kind of Fe/N-doped carbon (NG) heterostructure with Mott-Schottky effect [55]. The electron transfer mechanism of this Fe/NG Mott-Schottky heterostructure is shown in Fig. 11k, after the contact of Fe and NG, electrons flow from the Fe side to the NG side to maintain the balance of Fermi level. In this process, massive electrons transfer through this heterostructure and facilitating the ORR. The band modulation effect of Mott-Schottky heterostructure can be revealed by the DOSs plot (Fig. 11 l). The C 2p ...
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... heterostructure is shown in Fig. 11k, after the contact of Fe and NG, electrons flow from the Fe side to the NG side to maintain the balance of Fermi level. In this process, massive electrons transfer through this heterostructure and facilitating the ORR. The band modulation effect of Mott-Schottky heterostructure can be revealed by the DOSs plot (Fig. 11 l). The C 2p orbit of nitrogen doped graphene (NG) with a large band gap overlaps when connecting with Fe phase (Fig. 11 m), modulating the electronic structure of graphene and facilitating the electron transfer during electrocatalytic ...
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... the balance of Fermi level. In this process, massive electrons transfer through this heterostructure and facilitating the ORR. The band modulation effect of Mott-Schottky heterostructure can be revealed by the DOSs plot (Fig. 11 l). The C 2p orbit of nitrogen doped graphene (NG) with a large band gap overlaps when connecting with Fe phase (Fig. 11 m), modulating the electronic structure of graphene and facilitating the electron transfer during electrocatalytic ...
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... reactions [153,154]. DFT calculations are widely used to analyze the energy barrier of the four intermediate reactions of catalytic reactions determined by the absorbing energy of different intermediate products [155], offering a thorough insight that can potentially be utilized to design and develop electrocatalysts with high catalytic activity. Fig. 12a is the heterostructure of NiFe layered double hydroxide with NiTe (denoted as NiFe LDH/NiTe) with charge distribution and Fig. 12b is the optimized structure of O 2 * , OOH* , O* , OH* adsorbed on NiFe LDH/NiTe interface [156]. The absorbed energy of different intermediates further the Gibbs free energy for each intermediate reaction ...
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... reactions determined by the absorbing energy of different intermediate products [155], offering a thorough insight that can potentially be utilized to design and develop electrocatalysts with high catalytic activity. Fig. 12a is the heterostructure of NiFe layered double hydroxide with NiTe (denoted as NiFe LDH/NiTe) with charge distribution and Fig. 12b is the optimized structure of O 2 * , OOH* , O* , OH* adsorbed on NiFe LDH/NiTe interface [156]. The absorbed energy of different intermediates further the Gibbs free energy for each intermediate reaction can be calculated through these structures. Fig. 12c is the Gibbs free energy diagram for the four steps of OER, by creating ...
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... layered double hydroxide with NiTe (denoted as NiFe LDH/NiTe) with charge distribution and Fig. 12b is the optimized structure of O 2 * , OOH* , O* , OH* adsorbed on NiFe LDH/NiTe interface [156]. The absorbed energy of different intermediates further the Gibbs free energy for each intermediate reaction can be calculated through these structures. Fig. 12c is the Gibbs free energy diagram for the four steps of OER, by creating NiFeOOH/NiTe heterostructure interface, the adsorbed energy of intermediates on the active sites can be tuned. Compared to NiFeOOH and NiTe, NiFeOOH/NiTe has the lowest energy barrier, which indicates the highest catalytic activity of NiFe LDH/NiTe heterostructure. ...
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... NiFeOOH/NiTe heterostructure interface, the adsorbed energy of intermediates on the active sites can be tuned. Compared to NiFeOOH and NiTe, NiFeOOH/NiTe has the lowest energy barrier, which indicates the highest catalytic activity of NiFe LDH/NiTe heterostructure. Likewise, heterostructure constructing can also reduce the energy barrier of ORR. Fig. 12d is the Co 3 Fe 7 -Fe 3 C heterostructure with abundant interfaces deposited on the honeycomb-like N-doped carbon (denoted as Co 3 Fe 7 -Fe 3 C-HNC) [30]. Compared with its counterparts (HNC and Co 3 Fe 7 -HNC), Co 3 Fe 7 --Fe 3 C-HNC possesses higher limiting potential which enables all intermediates reactions to remain exothermic ...
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... ORR. Fig. 12d is the Co 3 Fe 7 -Fe 3 C heterostructure with abundant interfaces deposited on the honeycomb-like N-doped carbon (denoted as Co 3 Fe 7 -Fe 3 C-HNC) [30]. Compared with its counterparts (HNC and Co 3 Fe 7 -HNC), Co 3 Fe 7 --Fe 3 C-HNC possesses higher limiting potential which enables all intermediates reactions to remain exothermic (Fig. 12e). This indicates that Co 3 Fe 7 -Fe 3 C-HNC requires least external voltage to overcome the energy barrier and make all intermediates reactions carry out spontaneously. Moreover, a novel kind of heterostructural interface in Fe 3 C--TiN quantum dots on carbon nanotubes (CNT) is obtained through one-pot pyrolysis [157]. This ...
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... a novel kind of heterostructural interface in Fe 3 C--TiN quantum dots on carbon nanotubes (CNT) is obtained through one-pot pyrolysis [157]. This heterostructure can efficiently activate the O 2 molecule further promote the ORR. Optimized models indicate that ORR intermediates tend to absorb on the boundary of Fe 3 C-TiN heterostructure (Fig. 12f). The O-O bond in the oxygen reaction intermediates is extended on the boundary of Fe 3 C-TiN heterostructure, resulting in a lower reaction energy barrier. In addition, twin boundaries at both sides of heterostructures are also considered as high-energy active sites due to the existence of rich low-coordination atomic centers [158]. ...
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... for various electrolytic reactions [159]. The improved catalytic activity and reduced energy barrier of heterostructure can be ascribed to the interfacial synergy between different phases. Li et al. used a one-pot pyrolysis strategy to obtain a Co/MnO@N-doped carbon ORR catalyst with Co/MnO Mott-Schottky heterostructure [160]. In the Co 2p (Fig. 12g) and Mn 2p (Fig. 12h) XPS spectra, the Co δ+ peak shift toward high binding energy and Mn 2+ peaks shift toward low binding energy after forming Co/MnO hetero heterostructure, indicating the existence of electron flow from the Co side to the MnO side at the heterointerface. This electron flow can create a charge density increase area at ...
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... reactions [159]. The improved catalytic activity and reduced energy barrier of heterostructure can be ascribed to the interfacial synergy between different phases. Li et al. used a one-pot pyrolysis strategy to obtain a Co/MnO@N-doped carbon ORR catalyst with Co/MnO Mott-Schottky heterostructure [160]. In the Co 2p (Fig. 12g) and Mn 2p (Fig. 12h) XPS spectra, the Co δ+ peak shift toward high binding energy and Mn 2+ peaks shift toward low binding energy after forming Co/MnO hetero heterostructure, indicating the existence of electron flow from the Co side to the MnO side at the heterointerface. This electron flow can create a charge density increase area at the MnO side, which ...
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... forming Co/MnO hetero heterostructure, indicating the existence of electron flow from the Co side to the MnO side at the heterointerface. This electron flow can create a charge density increase area at the MnO side, which reduces the energy barrier for oxygen at the heterointerface to be reduced. This is proved by the energy band analysis in Fig. 12i. The valance band (E v ) positively shifts after the formation of the Co/MnO Mott-Schottky heterostructure (also more positive than the oxygen reduction potential E O2 , which is 0.401 V), indicating lower energy barrier required for electrons at the heterointerface to participate in ...
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... for designing low-cost effective electrocatalysts through modulating the electronic structure have been discussed and concluded. The ultimate goal is to apply these electrocatalysts to practical applications. The energy conversion and storage application of efficient low-cost electrocatalysts for oxygen and hydrogen electrocatalysis are extensive (Fig. 13). The applications of ORR include various kinds of fuel cells for energy storage such as metal-air battery (MAB), proton exchange membrane fuel cell (PEMFC), oxyhydrogen fuel cells (OFC), etc., and for OER and HER, the applications include water electrolyzers such as proton exchange membrane water electrolyzer (PEMWE) and anion exchange ...
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... strategy is by designing bind-free/integrated electrode structure, without binder and conductive enhancer, the charge transfer resistance on the electrode can be greatly reduced. Cheng et al. have designed a boron-nitrogen codoped graphene aerogel (B-N-G) towards ORR, which can serve as integrated air cathode in aluminum-air (Al-air) batteries (Fig. 14a) [64]. The maximum power density and discharge plateau of Al-air battery with free-standing air cathode is much higher than its counterparts with traditional slurry casted air cathode (Fig. 14b and c). Likewise, Sun et al. have used a one-step solvothermal synthesis to in-situ decorating NiFe-based metal organic framework (Mil-53(FeNi)) ...
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... have designed a boron-nitrogen codoped graphene aerogel (B-N-G) towards ORR, which can serve as integrated air cathode in aluminum-air (Al-air) batteries (Fig. 14a) [64]. The maximum power density and discharge plateau of Al-air battery with free-standing air cathode is much higher than its counterparts with traditional slurry casted air cathode (Fig. 14b and c). Likewise, Sun et al. have used a one-step solvothermal synthesis to in-situ decorating NiFe-based metal organic framework (Mil-53(FeNi)) on nickel foam (NF) to obtain a novel kind of binder-free electrode (Fig. 14d) [167], this kind of self-supported electrode with Mil-53(FeNi) exhibits ultra-low OER overpotential (233 mV at 10 mA cm ...
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... Al-air battery with free-standing air cathode is much higher than its counterparts with traditional slurry casted air cathode (Fig. 14b and c). Likewise, Sun et al. have used a one-step solvothermal synthesis to in-situ decorating NiFe-based metal organic framework (Mil-53(FeNi)) on nickel foam (NF) to obtain a novel kind of binder-free electrode (Fig. 14d) [167], this kind of self-supported electrode with Mil-53(FeNi) exhibits ultra-low OER overpotential (233 mV at 10 mA cm 2 ) and electronic resistance (less than 10 Ω) ( Fig. 14 e and ...
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... solvothermal synthesis to in-situ decorating NiFe-based metal organic framework (Mil-53(FeNi)) on nickel foam (NF) to obtain a novel kind of binder-free electrode (Fig. 14d) [167], this kind of self-supported electrode with Mil-53(FeNi) exhibits ultra-low OER overpotential (233 mV at 10 mA cm 2 ) and electronic resistance (less than 10 Ω) ( Fig. 14 e and ...
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... strategy is by constructing membrane electrode assembly (MEA) system to facilitate the charge transfer, which is widely used in fuel cells and water electrolyzers (Fig. 14g) [168]. For example, AEMWE with highly conductive gas diffusion layer (GDL) and MEA possesses extremely low charge transfer resistance during use at different temperatures to facilitate OER and HER processes on electrodes with commercial noble metal electrocatalysts (Fig. 14h) [169]. Therefore, it can withstand much larger current ...
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... transfer, which is widely used in fuel cells and water electrolyzers (Fig. 14g) [168]. For example, AEMWE with highly conductive gas diffusion layer (GDL) and MEA possesses extremely low charge transfer resistance during use at different temperatures to facilitate OER and HER processes on electrodes with commercial noble metal electrocatalysts (Fig. 14h) [169]. Therefore, it can withstand much larger current density during electrocatalytic overall water splitting compared with traditional laboratory two-electrode water splitting system under the same potential (Fig. 14i). The design of the optimized AEMWE structure successfully pushed forward the industrial electrolysis of water under ...
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... use at different temperatures to facilitate OER and HER processes on electrodes with commercial noble metal electrocatalysts (Fig. 14h) [169]. Therefore, it can withstand much larger current density during electrocatalytic overall water splitting compared with traditional laboratory two-electrode water splitting system under the same potential (Fig. 14i). The design of the optimized AEMWE structure successfully pushed forward the industrial electrolysis of water under large current. Similar strategies have also been used in PEMFCs (Fig. 14j) [170], the PEMFCs also comprise MEA and GDL, and due to the optimized structure, the reaction intermediate on the catalyst layer can rapidly ...
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... density during electrocatalytic overall water splitting compared with traditional laboratory two-electrode water splitting system under the same potential (Fig. 14i). The design of the optimized AEMWE structure successfully pushed forward the industrial electrolysis of water under large current. Similar strategies have also been used in PEMFCs (Fig. 14j) [170], the PEMFCs also comprise MEA and GDL, and due to the optimized structure, the reaction intermediate on the catalyst layer can rapidly accept elections, therefore enhancing the ORR kinetic for better discharging ...
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Comprehensive Summary
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