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Electrocatalytic technology is essential to develop environmentally friendly energy technologies and to reduce dependence on non‐renewable resources. The construction of highly efficient, inexpensive, and robust electrocatalysts is the primary prerequisite to the large‐scale application of electrochemical devices. In recent years, selenium‐based catalysts (SBCs) have been extensively investigated and emerged as a promising candidate for electrocatalysis given their potential to reduce or replace the dosage of noble metals and their ability to catalyze a range of critical electrochemical processes. This Review minutely analyses the recent research advances in SBCs, highlighting the significant role of Se in enhancing the catalytic performance. First, it starts from the concepts related to SBCs, followed by the classification of SBCs as well as the strategies to regulate the activity of SBCs are elaborated. Then, the techniques for characterizing SBCs are systematically summed up, mainly focusing on morphological and structural characterization methods. Next, the applications of SBCs in various energy‐conversion reactions (e.g., hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, nitrogen reduction reaction, CO2 reduction reaction) are discussed, aiming at elucidating the association between their structure–activity correlations. Finally, the challenges related to SBCs and their future development trends are presented. [ABSTRACT FROM AUTHOR]

Fe–N–C materials are prospective candidates to displace platinum‐group‐based oxygen reduction reaction (ORR) catalysts, but their application is still impeded by the conundrums of unsatisfactory activity and stability. Herein, a feasible strategy of ligand engineering of the metal‐organic framework is proposed to steer the local electronic configuration of Fe–N–C‐based coupling catalysts by incorporating engineered sulfur functionalities. The obtained catalysts with rich Fe‐N4 sites and FeS nanoparticles are embedded on N/S‐doped carbon (denoted as FeS/FeNSC). In this unique structure, the engineered FeS nanoparticles and oxidized sulfur synergistically induce electron redistribution and modulate electronic configuration of Fe‐N4 sites, contributing to substantially accelerated kinetics and improved activity. Consequently, the optimized FeS/FeNSC catalyst displays outstanding ORR performance with a half‐wave potential of 0.91 V, better four electron pathway selectivity, lower H2O2 yield, and superior long‐term stability. As a proof‐of‐concept, zinc‐air batteries based on FeS/FeNSC deliver high capacity of 807.54 mA h g−1, a remarkable peak power density of 256.06 mW cm−2, and outstanding cycling stability over 600 h at 20 mA cm−2. This study delivers an efficacious approach to manipulate the electronic configuration of Fe–N–C catalysts toward elevated catalytic activity and stability for various energy conversion/storage devices. [ABSTRACT FROM AUTHOR]

2D transition metal carbides/nitrides (MXenes) have excellent physical–chemical properties, which makes them promising for electrochemical energy storage devices. However, because of their inherent self‐stacking and narrow interlayer spacing, it is rarely used in multivalent ion energy storage systems. In this study, fatty diamines and aromatic diamines with different molecular sizes are inserted between MXene interlayers as pillars through a one‐step amination process to inhibit the self‐stacking and obtain different expanded interlayer spacings with improved antioxidant stability. X‐ray diffraction results show that interlayer spacing of MXene increases from 1.23 to 1.40 nm. The p‐phenylenediamine‐intercalated MXene (PDA‐MXene) exhibits better matching interlayer spacing (1.38 nm) and pore structure for improved electrolyte‐accessible surface area, enhanced charge‐transport properties, and promoted Zn2+ ions storage. Therefore, zinc‐ion hybrid supercapacitor (ZHSC) using PDA‐MXene as cathode exhibits higher specific capacitance (124.4 F g−1 at 0.2 A g−1) in 2 m ZnSO4 electrolyte together with outstanding cycling stability (85% capacity retention after 10 000 cycles at 1 A g−1). This study provides a route for precise control of MXene interlayer spacing by small organic molecules, which can be used to observe efficient charge storage in MXene‐based electrochemical energy storage devices by optimizing interlayer spacing. [ABSTRACT FROM AUTHOR]

Fe3O4 nanoparticle-encapsulating N-doped porous carbon was synthesized. Owing to the large specific surface area, hierarchical porous structure, and sufficient number of active sites from the graphitic carbon wrapped Fe3O4 NPs as well as the joint effect with Fe–Nx moieties, the as-prepared 2D-Fe3O4@FeNC-700 electrocatalyst exhibits exceptional performance in Zn–air batteries. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical porous carbon (HPC) with a high specific surface area is a promising material for supercapacitors, owing to its effective ion diffusion paths and low transport resistance. Herein, a nitrogen‐doped hierarchical porous carbon (NHPC) material was successfully synthesized from a gelatin and graphene oxide composite through a combined solvation volatilization/nano‐CaCO3 template/KOH activation method. The obtained NHPC exhibits a large surface area (SBET=1091 m2 g−1) as well as a combination of electrical double layer capacitance and pseudocapacitance behavior. Benefiting from the advanced synergistic effect of the nitrogen‐doped property and the hierarchically porous structure, NHPC shows a specific capacitance of 234 F g−1 at 0.5 A g−1 in a three‐electrode system. Moreover, a supercapacitor based on NHPC exhibits an excellent cycle life (retaining>98 % after 5000 cycles) and a high energy density up to 9.43 Wh kg−1. [ABSTRACT FROM AUTHOR]

Recently, Pt‐free and highly efficient, nanostructured M–N–C catalysts employing earth‐abundant metals (M = Fe, Co, Ni, Mn, Cu, etc.) have been recognized as a very promising alternative to noble metal (in particular platinum)‐ based oxygen reduction reaction materials. Structural engineering of the M–N–C catalysts is expected to further boost their catalytic performance, and thus, intense efforts are currently ongoing. Herein, a report is prepared on X‐ray absorption fine structure (EXAFS) studies of different carbon‐based catalyst materials. EXAFS with its intrinsic sensitivity toward the local atomic arrangement around the X‐ray absorbing element allows to characterize isolated, active single‐atom transition metal centers and their atomic environments. In the case of Co and Fe, the analysis suggests in particular asymmetric, penta‐coordinated Co‐N5 and dual‐coordinated Fe–N–P sites. In both cases, a symmetric environment of the metals with only four nitrogen atoms appears to be unfavorable for the catalytic activity. In addition, for Fe–N4 centers embedded in a graphene host matrix, the EXAFS analysis allows to precisely determine the atomic arrangement around the iron atom, and thereby the geometry of the catalytic site. A discussion will be done on how EXAFS investigations can support the further development of single‐atom catalysts. [ABSTRACT FROM AUTHOR]

Microenvironmental modifications on metal sites are crucial to tune oxygen reduction catalytic behavior and decrypt intrinsic mechanism, whereas the stochastic properties of traditional pyrolyzed single-atom catalysts induce vague recognition on structure-reactivity relations. Herein, we report a theoretical descriptor relying on binding energies of oxygen adsorbates and directly associating the derived Sabatier volcano plot with calculated overpotential to forecast catalytic efficiency of cobalt porphyrin. This Sabatier volcano plot instructs that electron-withdrawing substituents mitigate the over-strong *OH intermediate adsorption by virtue of the decreased proportion of electrons in bonding orbital. To experimentally validate this speculation, we implement a secondary sphere microenvironment customization strategy on cobalt porphyrin-based polymer nanocomposite analogs. Systematic X-ray spectroscopic and in situ electrochemical characterizations capture the pronounced accessible active site density and the fast interfacial/outward charge migration kinetics contributions for the optimal carboxyl group-substituted catalyst. This work offers ample strategies for designing single-atom catalysts with well-managed microenvironment under the guidance of Sabatier volcano map., (© 2024. The Author(s).)

Iron phthalocyanine-based polymers (PFePc) are attractive noble-metal-free candidates for catalyzing oxygen reduction reaction (ORR). However, the low site-exposure degree and poor electrical conductivity of bulk PFePc restricted their practical applications. Herein, laminar PFePc nanosheets covalently and longitudinally linked to graphene (3D-G-PFePc) was prepared. Such structural engineering qualifies 3D-G-PFePc with high site utilization and rapid mass transfer. Thence, 3D-G-PFePc demonstrates efficient ORR performance with a high specific activity of 69.31 μA cm -2 , a high mass activity of 81.88 A g -1 , and a high turnover frequency of 0.93 e s -1  site -1 at 0.90 V vs. reversible hydrogen electrode in O 2 -saturated 0.1 M KOH, outperforming the lamellar PFePc wrapped graphene counterpart. Systematic electrochemical analyses integrating variable-frequency square wave voltammetry and in situ scanning electrochemical microscopy further underline the rapid kinetics of 3D-G-PFePc towards ORR., (© 2023 Wiley-VCH GmbH.)

The development of rechargeable metal-air batteries and water electrolyzers are highly constrained by electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). However, the construction of efficient trifunctional electrocatalysts for ORR/OER/HER are highly desirable yet challenging. Herein, hollow carbon nanotubes integrated single cobalt atoms with Co 9 S 8 nanoparticles (CoSA + Co 9 S 8 /HCNT) are fabricated by a straightforward in situ self-sacrificing strategy. The structure of the CoSA + Co 9 S 8 /HCNT are verified by X-ray absorption spectroscopy and aberration-corrected scanning transmission electron microscopy. Theoretical calculations and experimental results embrace the synergistic effects between Co 9 S 8 nanoparticles and single cobalt atoms through optimizing the electronic configuration of the CoN 4 active sites to lower the reaction barrier and facilitating the ORR, OER, and HER simultaneously. Consequently, rechargeable liquid and all-solid-state flexible Zn-air batteries based on CoSA + Co 9 S 8 /HCNT exhibit remarkable stability and excellent power density of 177.33 and 51.85 mW cm -2 , respectively, better than Pt/C + RuO 2 counterparts. Moreover, the as-fabricated Zn-air batteries can drive an overall water splitting device assembled with CoSA + Co 9 S 8 /HCNT and achieve a current density of 10 mA cm -2 at a low voltage of 1.59 V, also superior to Pt/C + RuO 2 . Therefore, this work presents a promising approach to an efficient trifunctional electrocatalyst toward practical applications., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Fe 3 O 4 nanoparticle-encapsulating N-doped porous carbon was synthesized. Owing to the large specific surface area, hierarchical porous structure, and sufficient number of active sites from the graphitic carbon wrapped Fe 3 O 4 NPs as well as the joint effect with Fe-N x moieties, the as-prepared 2D-Fe 3 O 4 @FeNC-700 electrocatalyst exhibits exceptional performance in Zn-air batteries.