Cation effects in electrocatalytic reduction reactions:Recent advances

Electrocatalytic reduction reactions,powered by clean energy sources such as solar energy and wind,offer a sustainable method for converting inexpensive feedstocks(e.g.,CO_(2),N_(2)/NO_(x),organics,and O_(2))into high-value-added chemicals or fuels.The design and modification of electrocatalysts have been widely implemented to improve their performance in these reactions.However,bottle-necks are encountered,making it challenging to further improve performance through catalyst development alone.Recently,cations in the electrolyte have emerged as critical factors for tuning both the activity and product selectivity of reduction reactions.This review summarizes recent advances in understanding the role of cation effects in electrocatalytic reduction reactions.First,we introduce the mechanisms underlying cation effects.We then provide a comprehensive overview of their application in electroreduction reactions.Characterization techniques and theoretical calcula-tion methods for studying cation effects are also discussed.Finally,we address remaining challeng-es and future perspectives in this field.We hope that this review offers fundamental insights and design guidance for utilizing cation effects,thereby advancing their development.

Nitrogen-doped ordered mesoporous carbon:Effect of carbon precursor on oxygen reduction reactions

Aniline,pyrrole and phenanthroline,which have different nitrogen compositions,are used as carbon precursors to synthesize nitrogen-doped ordered mesoporous carbons（NOMCs） by the nanocasting method.The effect of the precursor on the resultant NOMC is extensively investigated by nitrogen adsorption-desorption measurements,scanning electron microscopy,X-ray photoelectron spectroscopy（XPS）,cyclic voltammetry and rotating ring-disk electrode measurements.Salient findings are as follows.First,the precursor has a significant influence on the specific surface area and textural properties.The NOMC materials derived from pyrrole（C-PY-900：765 m^2/） and phenanthroline（C-Phen-900：746 m^2/） exhibit higher specific surface areas than the aniline analog（C-PA-900：569 m^2/）.Second,the XPS results indicate that the total nitrogen content（ca.3.1–3.3 at%） is similar for the three carbon sources,except for a slight difference in the nitrogen configuration.Furthermore,the content of the nitrogen-activated carbon atoms is found to closely depend on the precursor,which is the highest for the phenanthroline-derived carbon.Third,the electrochemical results reveal that the electrocatalytic activity follows in the order C-PA-900 C-PY-900 C-Phen-900,confirming that the nitrogen-activated carbon atoms are the active sites for the oxygen reduction reaction（ORR）.In summary,the precursor has considerable influence on the composition and textural properties of the NOMC materials,of which the ORR electrocatalytic activity can be enhanced through optimization of the NOMCs.

A Review of In‑Situ Techniques for Probing Active Sites and Mechanisms of Electrocatalytic Oxygen Reduction Reactions

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.

Bi-Atom Electrocatalyst for Electrochemical Nitrogen Reduction Reactions

The electrochemical nitrogen reduction reaction(NRR)to directly produce NH3 from N_(2) and H_(2)O under ambient conditions has attracted significant attention due to its ecofriendliness.Nevertheless,the electrochemical NRR presents several practical challenges,including sluggish reaction and low selectivity.Here,bi-atom catalysts have been proposed to achieve excellent activity and high selectivity toward the electrochemical NRR by Ma and his co-workers.It could accelerate the kinetics of N_(2)-to-NH_(3) electrochemical conversion and possess better electrochemical NRR selectivity.This work sheds light on the introduction of bi-atom catalysts to enhance the performance of the electrochemical NRR.

Co NP/NC hollow nanoparticles derived from yolk-shell structured ZIFs@polydopamine as bifunctional electrocatalysts for water oxidation and oxygen reduction reactions

The pyrolysis under inert atmosphere has been widely used for the synthesis of metal containing heteroatoms doped carbon materials, versatile catalysts for various reactions. However, it is difficult to prevent metal nanoparticles aggregation during pyrolysis process. Herein, we reported the efficient synthesis of nitrogen doped carbon hollow nanospheres with cobalt nanoparticles （Co NP, ca. 10nm in size） distributed uniformly in the shell via pyrolysis of yolk-shell structured Zn-Co-ZIFs@polydopamine （PDA）. PDA acted as both protection layer and carbon source, which successfully prevented the aggregation of cobalt nanoparticles during high-temperature pyrolysis process. The Co NP and N containing carbon （Co NP/NC） hollow nanospheres were active for both oxygen evolution reaction （OER） and oxygen reduction reaction （ORR）, affording overpotential of 430 mV at 10 mA/cm2 for OER in 1 M KOH and comparable half-wave potential to that of Pt/C （0.80V vs RHE） for ORR in 0.1 M KOH. The superior performance of carbon hollow nanospheres for both OER and ORR was mainly attributed to its small metal nanoparticles, N-doping and hollow nanostructure. The protection and confinement effect that originated from PDA coating strategy could be extended to the synthesis of other hollow structured carbon materials, especially the ones with small metal nanoparticles.

Meta-analysis of commercial Pt/C measurements for oxygen reduction reactions via data mining

The rotating disk electrode technique is commonly used for screening and characterizing the performance of electrocatalysts for the oxygen reduction reaction(ORR).However,a reliable performance comparison of different electrocatalysts from different labs remains a challenge because of the inconsistency in the measurement of commercial Pt/C.Commercial Pt/C has been adopted extensively as a reference for evaluating the ORR performance of a new electrocatalyst.However,the reported ORR performances of commercial Pt/C from different labs could be significantly different because of multiple factors.Herein,we conducted a meta‐analysis of the ORR performance of commercial Pt/C via data mining of the literature.This revealed the optimal testing conditions for the most repeatable ORR performance,with commercial Pt/C in both acid and alkaline electrolytes;the optimal Pt loading was 20μg/cm^(2) on a 4 mm glassy carbon working electrode.The value of 0.84±0.03 V was suggested as the“Golden reference”of the commercial Pt/C(with Pt 20 wt%)ORR half‐wave potential for the performance evaluation of other ORR catalysts in both acid and alkaline electrolytes.The conclusion obtained through the meta‐analysis was confirmed by experiments.This study provides general guidance for a reliable measurement of the ORR performance of commercial Pt/C as a reference.

Metal-organic framework-based materials as key components in electrocatalytic oxidation and reduction reactions

Studies have extensively addressed the development of electrocatalytic technologies for energy storage and conversion,fuel production,and environmental protection.Electrode processes such as different oxidation and reduction reactions play a vital and significant role in these technologies.In this regard,efficient,inexpensive,and stable electrocatalysts capable can significantly promote electrochemical reactions.Unique features of metal–organic frameworks(MOFs)such as their high porosity,tunable structure,size,and pore shape,high surface area,and redox properties have introduced them as an ideal electrocatalyst candidate.This review is thus aimed at elucidating the role of MOF-based materials(pristine,derivatives and composites)as efficient electrocatalysts in energy and sensing-related oxidation and reduction reactions such as oxygen reduction reaction(ORR),hydrogen oxidation reaction(HOR),carbon dioxide reduction reaction(CO_(2)RR),urea oxidation reaction(UOR),alcohol oxidation reaction(AOR),nitrogen reduction reaction(NRR),and glucose oxidation reaction(GOR)in advanced energy and sensing devices.Also,the structure–property relationship of the electrocatalyst was elaborated for each electrocatalytic reaction.Finally,perspectives on the potential research topics for practical use of MOF-based electrocatalysts are addressed.The present review can improve the interest in MOF-based electrocatalysts to study different oxidation and reduction reactions in energy and sensing systems.

Defect spinel oxides for electrocatalytic reduction reactions

Electrocatalytic reduction reactions play a crucial role in electrochemical energy conversion and storage technology,which are emerging technologies to ameliorate environmental problems.Spinel oxides are widely explored in electrocatalytic oxidation reactions but have a poor intrinsic ability to reduction reactions,making their electrocatalytic ability less effective.To improve this,defect engineering is a valuable method for regulating the electronic structure and coordination environment.Herein,this manuscript discusses the use of defect spinel oxides in electrocatalytic reduction reactions,including the different types of defects,construction methods,and characterization techniques.It also outlines the various applications of defect spinel oxides in different electrocatalytic reduction reactions.Finally,it goes over the challenges and future outlooks for defect spinels.This review aims to thoroughly explain how defect spinels work in electrocatalytic reduction reactions and serve as a helpful guide for creating effective electrocatalysts.

Coordination environments build up and tune a superior synergistic “genome” toward novel trifunctional (TM-N_(x)O_(4−x))@g- C_(16)N_(3)-H_(3): High-throughput inspection of ultra-high activity for water splitting and oxygen reduction reactions

Emerging as a prominent area of focus in energy conversion and storage technologies,the development of highly active metal-based single-atom catalysts(SACs)holds great significance in searching alternatives to replace precious metals toward the efficient,stable,and low-cost hydrogen evolution reaction(HER),as well as the oxygen evolution reaction(OER)and the oxygen reduction reaction(ORR).Combining the tremendous tunability of ligand and coordination environment with rich metal-based electrocatalysts can create breakthrough opportunities for achieving both high stability and activity.Herein,we propose a novel and stable holey graphene-like carbon nitride monolayer g-C_(16)N5(N_(4)@g-C_(16)N_(3))stoichiometries interestingly behaving as a natural substrate for constructing SACs((TM-N_(4))@g-C_(16)N_(3)),whose evenly distributed holes map rich and uniform nitrogen coordination positions with electron-rich lone pairs for anchoring transition metal(TM)atoms.Then,we employed density functional theory(DFT)calculations to systematically investigate the electrocatalytic activity of(TM-N_(4))@g-C_(16)N_(3) toward HER/OER/ORR,meanwhile considering the synergistic modulation of H-loading and O-coordination((TM-N_(x)O_(4-x))@g-C_(16)N_(3)^(-)H_(3),x=0–4).Together a“four-step procedure”screening mechanism with the first-principles high-throughput calculations,we find that(Rh-N_(4))and(Ir-N_(2)O_(2)-II)distributed on g-C_(16)N_(3)^(-)H_(3) can modulate the adsorption strength of the adsorbates,thus achieving the best HER/OER/ORR performance among 216 candidates,and the lowest overpotential of 0.098/0.3/0.46 V and 0.06/0.48/0.45 V,respectively.Additionally,the d-band center,crystal orbital Hamilton population(COHP),and molecular orbitals are used to reveal the OER/ORR activity source.Particularly,the Rh/Ir-d orbital is dramatically hybridized with the O-p orbital of the oxygenated adsorbates,so that the lone-electrons incipiently locate at the antibonding orbital pair up and populate the downward bonding orbital,allowing oxygenated intermediates to be adsorbed onto(TM-N_(x)O_(4-x))@g-C_(16)N_(3)^(-)H_(3) appropriately.

Combinations of electron and proton donors in transition-metal complex mediated nitrogen reduction reactions

Nitrogen fixation is a complex process involving the transfer of six electrons and protons.Diverging from the conventional Haber-Bosch process,which relies on hydrogen(H_(2))to provide both electrons and protons to reduce nitrogen(N_(2)),homogeneous transition metal complex-catalyzed N_(2)reduction reactions(NRR)employ an array of electron and proton donors or even electron donors combined with silanes.As the synthesis of diverse catalytic progress,the categories of donors have seen rapid expansion.However,existing literature only provides summaries regarding the metal,ligands,and mechanism.Despite the significance of electron and proton donor combinations in nitrogen reduction reactions,no literature has thoroughly reviewed this aspect.Therefore,we hereby compiled a comprehensive list of commonly used reagents in N_(2)reduction and classified them according to their specific donor combinations.This review presents clear and organized information about these combinations,along with a summary of their general performance trend in NRR with related catalysts.Finally,we conclude the discussion by highlighting key points for researchers to consider when selecting catalysts and donor combinations,with the ultimate goal of advancing the field of nitrogen fixation.

Synthesis techniques, mechanism, and prospects of high-loading single-atom catalysts for oxygen reduction reactions

The importance of the oxygen reduction reaction (ORR) in fuel cells and zinc-air batteries is self-evident, and effective catalysts could significantly improve the catalytic efficiency of ORR. Single-atom catalysts are gaining increasing interest due to their high atom efficiency and effective catalytic performance compared to other catalyst types. While the optimal loading of catalytic sites in single-atom catalysts significantly influences their catalytic efficiency. However, creating stable single-atom catalysts with high-loading remains a difficult task. Therefore, we showcase and describe the latest developments in techniques for producing single-atom catalysts with high-loadings. In addition, the performance of noble metal, non-precious metal, and diatomic catalysts in ORR processes is summarized. What’s more, the key difficulties and opportunities in the sector are demonstrated by examining the synthesis techniques and evaluating the performance and structure. This review will help researchers to advance the research process of high-loading single-atom catalysts and accelerate their practical application in the field of ORR research.

Periodic Defect Boundary-Mediated Activity of Electrocatalytic Oxygen Reduction Reactions of Fe-N-C Catalysts

The introduction of defects can adjust the activity of graphene-based single-atom catalysts for oxygen reduction reactions(ORR).Herein,we for the first time investigate the ORR catalytic activity of FeN_(4)sites embedded on graphene with four types of line-defective boundary via density functional theory calculations.Our results show that periodic line defects consisting of pentagon-pentagon-octagon(C_(585))or quad-octagon chains(C_(484))can significantly enhance ORR activity,owing to the optimized electronic structures of FeN_(4)sites.The spin magnetic moment and the valence state of the Fe atom are both well correlated with the ORR overpotential.Experimental investigations further corroborate that FeN_(4)with a high degree of defects exhibits better ORR activity and stability compared to FeN_(4)sites of pristine graphene and commercial Pt/C.This work unravels the influence of the periodic defect boundary on the ORR performance of Fe-N-C catalysts and paves the way towards the rational design of highly effective single-atom electrocatalysts.

Co_3O_4 supported on N,P-doped carbon as a bifunctional electrocatalyst for oxygen reduction and evolution reactions

Noble metals, such as platinum, ruthenium and iridium‐group metals, are often used as oxygen reduction or evolution reaction （ORR/OER） electrocatalysts. To reduce the cost and provide an application of bifunctional catalysis, in this work, cobalt oxide supported on nitrogen and phospho‐rus co‐doped carbon （Co3O4/NPC） was fabricated and examined as a bifunctional electrocatalyst for OER and ORR. To prepare Co3O4/NPC, NPC was pyrolyzed from melamine and phytic acid support‐ed on carbon, followed by the solvothermal synthesis of Co3O4 on NPC. Linear sweep voltammetry was used to evaluate the activity for OER and ORR. For OER, Co3O4/NPC showed an onset potential of 0.54 V （versus the saturated calomel electrode） and a current density of 21.95 mA/cm2 at 0.80 V, which was better than both Co3O4/C and NPC. The high activity of Co3O4/NPC was attributed to a synergistic effect of the N, P co‐dopants and Co3O4. For ORR, Co3O4/NPC exhibited an activity close to commercial Pt/C in terms of the diffusion limited current density （–4.49 vs–4.76 mA/cm2 at–0.80 V）, and Co3O4 played the key role for the catalysis. Chronoamperometry （current versus time） was used to evaluate the stability, which showed that Co3O4/NPC maintained 46%current after the chronoamperometry test for OER and 95% current for ORR. Overall, Co3O4/NPC exhibited high activity and improved stability for both OER and ORR.

Small-sized tungsten nitride anchoring into a 3D CNT- rGO framework as a superior bifunctional catalyst for the methanol oxidation and oxygen reduction reactions

The application of direct methanol fuel cells （DMFC） is hampered by high cost, low activity, and poor CO tolerance by the Pt catalyst. Herein, we designed a fancy 3D hybrid by anchoring tungsten nitride （WN） nanoparticles （NPs）, of about 3 nm in size, into a 3D carbon nanotube-reduced graphene oxide framework （CNT-rGO） using an assembly route. After depositing Pt, the contacted and strongly coupled Pt-WN NPs were formed, resulting in electron transfer from Pt to WN. The 3D Pt-WN/CNT-rGO hybrid can be used as a bifunctional electrocatalyst for both methanol oxidation reaction （MOR） and oxygen reduction reaction （ORR）. In MOR, the catalysts showed excellent CO tolerance and a high mass activity of 702.4 mA.mgpt-1, 2.44 and 3.81 times higher than those of Pt/CNT-rGO and Pt/C（JM） catalysts, respectively. The catalyst also exhibited a more positive onset potential （1.03 V）, higher mass activity （151.3 mA.mgpt-1）, and better cyclic stability and tolerance in MOR than ORR. The catalyst mainly exhibited a 4e-transfer mechanism with a low peroxide yield. The high activity was closely related to hybrid structure. That is, the 3D framework provided a favorable path for mass-transfer, the CNT-rGO support was favorable for charge transfer, and strongly coupled Pt-WN can enhance the catalytic activity and CO-tolerance of Pt. Pt-WN/CNT-rGO represents a new 3D catalytic platform that is promising as an electrocatalyst for DMFC because it can catalyze both ORR and MOR in an acidic medium with good stability and highly efficient Pt utilization.

Conversion of PtNi alloy from disordered to ordered for enhanced activity and durability in methanol-tolerant oxygen reduction reactions

The development of cost-effective oxygen reduction reaction （ORR） catalysts with a high methanol tolerance and enhanced durability is highly desirable for direct methanol fuel cells. This work focuses on the conversion of PtNi nanoparticles from a disordered solid solution to an ordered intermetallic compound. Here the effect of this conversion on ORR activity, durability, and methanol tolerance are characterized. X-ray diffraction and transmission electron microscopy results confirm the formation of ordered PtNi intermetallic nanoparticles with high dispersion and a mean particle size of about 7.6 nm. The PtNi intermetallic nanoparticles exhibited enhanced mass and specific activities toward the methanol-tolerant ORR in pure and methanol-containing electrolytes. The specific activity of the ORR at 0.85 V on the PtNi intermetallic nanoparticles is almost 6 times greater than on commercial Pt/C and 3 times greater than on disordered PtNi alloy. Durability tests indicated a minimal loss of ORR activity for PtNi intermetallic nanoparticles after 5,000 potential cycles, whereas the ORR activity decreased by 28% for disordered PtNi alloy. The enhanced methanoltolerant ORR activity and durability may be attributed to the structural and compositional stabilities of the ordered PtNi intermetallic nanoparticles compared relative to the stabilities of the disordered PtNi alloy, strongly suggesting that the PtNi intermetallic nanoparticles may serve as highly active and durable methanol-tolerant ORR electrocatalysts for practical applications.

Recent advances in spinel-type electrocatalysts for bifunctional oxygen reduction and oxygen evolution reactions

The demand for efficient and environmentally-benign electrocatalysts that help availably harness the renewable energy resources is growing rapidly. In recent years, increasing insights into the design of water electrolysers, fuel cells, and metal–air batteries emerge in response to the need for developing sustainable energy carriers, in which the oxygen evolution reaction and the oxygen reduction reaction play key roles. However, both reactions suffer from sluggish kinetics that restricts the reactivity. Therefore, it is vital to probe into the structure of the catalysts to exploit high-performance bifunctional oxygen electrocatalysts. Spinel-type catalysts are a class of materials with advantages of versatility, low toxicity, low expense, high abundance, flexible ion arrangement, and multivalence structure. In this review, we afford a basic overview of spinel-type materials and then introduce the relevant theoretical principles for electrocatalytic activity, following that we shed light on the structure–property relationship strategies for spinel-type catalysts including electronic structure, microstructure, phase and composition regulation,and coupling with electrically conductive supports. We elaborate the relationship between structure and property, in order to provide some insights into the design of spinel-type bifunctional oxygen electrocatalysts.

Hierarchically skeletal multi-layered Pt-Ni nanocrystals for highly efficient oxygen reduction and methanol oxidation reactions

Pt based materials are the most efficient electrocatalysts for the oxygen reduction reaction(ORR)and methanol oxidation reaction(MOR)in fuel cells.Maximizing the utilization of Pt based materials by modulating their morphologies to expose more active sites is a fundamental objective for the practical application of fuel cells.Herein,we report a new class of hierarchically skeletal Pt-Ni nanocrystals(HSNs)with a multi-layered structure,prepared by an inorganic acid-induced solvothermal method.The addition of H_(2)SO_(4)to the synthetic protocol provides a critical trigger for the successful growth of Pt-Ni nanocrystals with the desired structure.The Pt-Ni HSNs synthesized by this method exhibit enhanced mass activity of 1.25 A mgpt−1 at 0.9 V(versus the reversible hydrogen electrode)towards ORR in 0.1-M HClO_(4),which is superior to that of Pt-Ni multi-branched nanocrystals obtained by the same method in the absence of inorganic acid;it is additionally 8.9-fold higher than that of the commercial Pt/C catalyst.Meanwhile,it displays enhanced stability,with only 21.6%mass activity loss after 10,000 cycles(0.6–1.0 V)for ORR.Furthermore,the Pt-Ni HSNs show enhanced activity and anti-toxic ability in CO for MOR.The superb activity of the Pt-Ni HSNs for ORR and MOR is fully attributed to an extensively exposed electrochemical surface area and high intrinsic activity,induced by strain effects,provided by the unique hierarchically skeletal alloy structure.The novel open and hierarchical structure of Pt-Ni alloy provides a promising approach for significant improvements of the activity of Pt based alloy electrocatalysts.

Cobalt-based hydroxide nanoparticles @ N-doping carbonic frameworks core-shell structures as highly efficient bifunctional electrocatalysts for oxygen evolution and oxygen reduction reactions

The development of highly efficient and earth-abundant oxygen evolution/ reduction reaction （OER/ORR） catalysts is essential for rechargeable metal-air batteries. Herein, cobalt-based hydroxide nanoparticles @ N-doping carbonic framework （CoOHCat@NCF） core-shell structures have been designed as highly stable and efficient OER/ORR bifunctional catalysts. The obtained composite shows enhanced catalytic activities and excellent stability in alkaline media. In the OER, a high turnover frequency （2.03 s^-1 at an overpotential of 0.36 V）, low overpotential at high current density （100 mA.cm-2 requiring an overpotential of 0.38 V）, and excellent stability （100 mA·cm^-2 for one week with no activity loss） have been achieved. Furthermore, although cobalt species-based catalysts are known as good ORR catalysts, their hybridization with NCF obtained from metal organic frameworks successfully enhanced their ORR activities. The efficient activity of CoOHCat@NCF as a bifunctional oxygen electrocatalyst can be ascribed to the core-shell structures stabilizing the active catalytic sites and the porous shell structure favoring electrocatalysis-related mass transport.

Probing the active sites of site-specific nitrogen doping in metal-free graphdiyne for electrochemical oxygen reduction reactions

The development of highly active and low-cost catalysts for electrochemical reactions is one of the most attractive topics in the renewable energy technology.Herein,the site-specific nitrogen doping of graphdiyne(GDY)including grap-N,sp-N(Ⅰ)and sp-N(Ⅱ)GDY is systematically investigated as metal-free oxygen reduction electrocatalysts via density functional theory(DFT).Our results indicate that the doped nitrogen atom can significantly improve the oxygen(O2)adsorption activity of GDY through activating its neighboring carbon atoms.The free-energy landscape is employed to describe the electrochemical oxygen reduction reaction(ORR)in both O2 dissociation and association mechanisms.It is revealed that the association mechanism can provide higher ORR onset potential than dissociation mechanism on most of the substrates.Especially,sp-N(Ⅱ)GDY exhibits the highest ORR electrocatalytic activity through increasing the theoretical onset potential to 0.76 V.This work provides an atomic-level insight for the electrochemical ORR mechanism on metal-free N-doped GDY.

Rational confinement engineering of MOF-derived carbonbased electrocatalysts toward CO_(2)reduction and O_(2)reduction reactions

The goal of global carbon peak and neutrality gives an impetus to the utilization of clean energy(e.g.,fuel cell)and carbon dioxide(CO_(2))at a large scale,where the oxygen reduction reaction(ORR)and CO_(2)reduction reaction(CO_(2)RR)are the key reactions via the sustainable system,respectively.As a main precursor for fabricating affordable carbon-based electrocatalysts with uniformly dispersed active centers and tailorable performances for ORR and CO_(2)RR,metal organic frameworks(MOFs)have captured a surge of interest in recent years.Despite the facilitated development of MOF-derived carbon-based electrocatalysts by many investigations,it is still plagued by high overpotential and unsatisfied life span,which are greatly determined by the efficient and alterable confinement effect on synthesis and performance.In this review,firstly,the confined synthetic strategies(doping engineering,defect engineering,geometric engineering,etc.)of MOF-derived carbon-based electrocatalysts with multi-sized active centers(atom,atomic clusters and nanoparticles(NPs))are systematically summarized;secondly,the confinement effect on the interaction of ORR and CO_(2)RR intermediates,as well as the catalytic durability and activity,was discussed from chemical and physical aspects.In the end,the review discusses the remaining challenges and emerging research topics in the future,including support upgradation and catalyst innovation,high selectivity and effective confinement synthesis,in situ and operando characterization techniques,theoretical investigation,and artificial intelligence(AI)assistant.The new understanding and insights into these aspects will guide the rational confinement concept of MOF-derived carbon-based electrocatalysts for ORR and CO_(2)RR with optimized performances in terms of confinement engineering and are believed to be helpful for filling the existing gaps between scientific communities and practical use.