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With the incorporation of heteroatomic B into single-atom Fe catalyst (Fe SA -NC), a catalyst named Fe SA -BNC with a configuration of Fe-N 3 B 1 had been synthesized for the oxygen reduction reaction (ORR). The low electronegativity of B induced charge redistribution around the active center Fe, thereby modulating the ORR activity. The Fe SA -BNC catalyst demonstrated an outstanding ORR performance in alkaline conditions, with a half-wave potential of 0.87 V. [Display omitted] • Coordination of low electronegativity B with Fe atom. • Regulating the charge states of the active site Fe. • The decrease of the d -band center of Fe promoting the desorption of ORR intermediates and enhancing the ORR performance. Despite extensive research has been conducted on atomic dispersion catalysts for various reactions, altering the electronic structure of the central metal to enhance electrochemical reactivity remains a challenging task. Herein, the electrochemical reactivity was considerably enhanced by introducing heteroatomic B to adjust the d -band of single Fe center. In specific, the obtained Fe SA -BNC catalyst demonstrated an outstanding ORR performance (E 1/2 = 0.87 V) and exhibited greater long-term durability in alkaline media compared to Pt/C. The performance of Fe SA -BNC in Zn–air battery was also higher than that of Pt/C. According to theoretical calculations, a downward shift in the d -band center of Fe was induced by introducing B, thereby improving the desorption of intermediates and facilitating the oxygen reduction reaction (ORR). [ABSTRACT FROM AUTHOR]

Here, an approach to produce a hierarchical porous Fe‐N‐C@TABOH catalyst with densely accessible high intrinsic active FeNx sites is proposed. The method involves a single‐step pyrolysis of Zn/Fe‐zeolitic imidazolate framework (Zn/Fe‐ZIF‐H) with tetrabutylammonium hydroxide (TABOH) micelles, which is obtained by utilizing TABOH as a structural template and electronic mediator at room temperature for a brief duration of 16 min. Notably, the yield of Zn/Fe‐ZIF‐H is 3.5 times that of Zn/Fe‐ZIF‐N prepared by conventional method. Results indicate that in addition to expediting synthesis and increasing yield of the Zn/Fe‐ZIF‐H, the TABOH induces a hierarchical porous structure and fosters the formation of more and higher intrinsic active FeNx moieties in Fex‐N‐C@TABOH, showing that TABOH is a multifunctional template. Crucially, the increased mesoporosity/external surface area and optimized microenvironment of Fe‐N‐C@TABOH significantly enhance ORR activity by facilitating the formation of high intrinsic active FeNx sites, increasing accessible FeNx sites, and reducing mass transfer resistance. Through structure tailoring and microenvironment optimization, the resulting Fe‐N‐C@TABOH exhibits superior ORR performance. DFT calculation further validates that the synergistic effect of these two factors leads to low ORR barrier and optimized *OH adsorption energy. This study underscores the importance of structure and electronic engineering in the development of highly active ORR catalysts. [ABSTRACT FROM AUTHOR]

Direct Methanol fuel cells (DMFC) have been limited in their utilization due to their slow cathodic oxygen reduction reaction (ORR) kinetics and the expensive cost of commercial Pt/C catalysts. It is critical to design an oxygen reduction process with high-efficiency catalysts. An approach for modulating the ratio of cellulose, hemicellulose, and lignin in the wheat stalk (WS)/wheat stalk binder (WS binder) precursor materials is proposed in this work. WS binder from alkalization and hydrothermal treatment was added to the WS to change the structure and shape of WS-based carbon materials by varying the ratios, which increased the ORR catalytic activity. The half-wave potential (E 1/2) of the produced carbon material (15 wt% N/C (WS)) is 0.76 V, which was enhanced by 80 mV by adjusting the ratio of the WS/WS binder compared to 0 wt% N/C(WS). The E 1/2 of 15 wt% Fe–N/C (WS) (0.85 V) was greater than that of commercial Pt/C (0.84 V). Besides, its catalytic oxygen reduction process was close to the 4-electron transfer pathway and had good methanol tolerance. The power density obtained with a cathode catalyst of 15 wt% Fe–N/C (WS) for DMFC was 1.39 mW cm−2 at 30 °C and 3.33 mW cm−2 at 60 °C. At different temperatures, the power densities were 1.59 and 1.54 times greater than those of commercial Pt/C catalysts, respectively. [Display omitted] • Binders were added to wheat stalk carbon substrates to change their morphology and structure. • Introduction of Hemin-prepared iron single-atom catalysts with excellent ORR performance. • In DMFC, 15 wt% Fe–N/C(WS) demonstrated a good power density that was better than commercial Pt/C. [ABSTRACT FROM AUTHOR]

Single‐atom catalysts (SACs) are widely studied in various chemical transformations due to their high catalytic activity and atom utilization. However, modulating the catalytic performance of catalysts by adjusting the microenvironment remains a great challenge. In this paper, a novel master‐double guest vulcanization‐assisted strategy is reported for synthesizing Fe single‐atom catalysts on N,S codoped porous hollow leaf carbon (FeSA/N,S‐PHLC) with highly exposed FeN3SOH sites. Fe(mIm) (guest I) is loaded on the surface of ZIF‐L (host) and then trithiocyanuric acid (TCA, guest II) is bonded with Fe(mIm), and the resulting ZIF‐L@Fe(mIm)@TCA precursors can be converted to FeSA/N,S‐PHLC with controllable structures. In addition, XPS analysis yield an increase in pyridine N content in FeSA/N,S‐PHLC compared to FeSA/N‐PHLC. It can be demonstrated by theoretical calculations that the N,S‐coordinated axially hydroxy‐coordinated asymmetric Fe centers synergistically with the abundance of pyridinic nitrogen facilitate the adsorption and desorption of oxygen intermediates, and the 3d orbitals of the Fe active centers can be optimized. The prepared FeSA/N,S‐PHLC catalyst has a half‐wave potential (E1/2) of 0.91 V under alkaline conditions, and E1/2 = 0.75 V under acidic conditions. It shows excellent cycle stability (882 h) and power density (217 mW cm−2) in the assembly of zinc–air battery (ZABs) devices. [ABSTRACT FROM AUTHOR]

Atomically dispersed metal‐nitrogen‐carbon catalysts have been extensively explored for various sustainable energy‐related reactions. From a material perspective, these catalysts are likely to consist of a combination of single‐atom, dual‐atom and possibly even multi‐atom sites. However, pinpointing their true active sites has remained a challenging task. In this study, a model catalyst is introduced, Co/CoMn‐NC, featuring both Co single‐atom sites and CoMn dual‐atom sites on a nitrogen‐doped carbon substrate. By employing a combination of X‐ray adsorption spectroscopy and density functional theory calculations, the atomic configuration of Co/CoMn‐NC has been determined. Density functional theory calculations are also used to unequivocally identify Co‐atom within the CoMn dual‐atom motif as the predominate active site of the Co/CoMn‐NC model catalyst toward oxygen reduction reaction (ORR), which is further confirmed by in situ Raman spectroscopy. The cooperative interactions between Co single‐atom sites and CoMn dual‐atom sites can finely tune the d‐band center and ameliorate the adsorption and desorption behaviors of the intermediates, thereby facilitating ORR kinetic. Overall, the study introduces a systematic strategy to elucidate the structure and the superiority of the model system and provides new insights into atomically dispersed multi‐metal active sites, showcasing that enhanced catalytic performance extends beyond unified diatomic sites or monatomic sites. [ABSTRACT FROM AUTHOR]

Introducing the second metal is an effective strategy to ameliorate oxygen reduction reaction (ORR) performance of cobalt and nitrogen doped carbon materials (Co-NC). In this study, Sn modulated Co-NC catalysts with enriched active sites (CoSn-NC) were synthesized by using formamide as ligand. Co and Sn bimetals coexist on nitrogen-doped carbon carriers and coordinated with nitrogen to form M − N active centers. Compared with Co-NC, CoSn -NC exhibited outstanding catalytic activity in terms of early initial potential of 1.04 V and positive half-wave potential of 0.89 V. Electrochemical testing and XPS characterization proved that the addition of Sn enriched the active site of Co-NC. More importantly, the electronic structure of Co–N is adjusted to perfect adsorption energy of the intermediate. The study puts forward a new idea and direction for optimizing single metal Co-NC catalyst. Synopsis: This paper is committed to developing Cobalt-based bimetallic materials with enrich active sites to replace scarce Pt/C for ORR. [Display omitted] • Co and Sn bimetals coexist on nitrogen-doped carbon carriers. • Sn Modulated Co-NC catalysts with enriched active sites. • The M − N structure is the main catalytic site by SCN− toxicity experiments. • CoSn-NC shows enhanced ORR catalytic activity, stability and methanol resistance. [ABSTRACT FROM AUTHOR]

Search for a Platinum metal-free catalyst for Proton Exchange Membrane Fuel Cells (PEMFCs) is a concern to scientists as the Pt-catalyzed electrode comprises about 45% of the entire fuel cell stack cost. Due to layered structure, Two-dimensional (2D) MoS2 nanostructured materials have recently drawn attention as effective catalysts for oxygen reduction reaction (ORR). The 1T-phase of MoS2 (1T-MoS2) has higher electronic conductivity than the 2H-phase (2H-MoS2); high surface area 1T-MoS2 can have high electrocatalytic activity towards PEFFCs. Here, we report hydrothermally synthesized 2H-MoS2 and solvothermally synthesized mixed 1T/2H-MoS2 phases as a catalyst for ORR in PEM Fuel Cells. Owing to the high BET-specific surface area, hybrid 1T/2H-MoS2 showed better ORR activity than 2H-MoS2. The limiting current density of the 1T/2H-MoS2 hybrid structure is ‒7.1 mA cm−2 compared to Pt/C (‒8.2 mA cm−2) at 1600 rpm. The Tafel slope values of 2H-MoS2, 1T/2H-MoS2, and Pt/C are 92.7 mV dec−1, 57.5 mV dec−1, and 39.3 mV dec−1, respectively. The electron transferred during ORR are 3.8 and 1.8, respectively, for 1T/2H-MoS2 and 2H-MoS2 (in 0.1 M KOH) ; suggesting less formation of undesirable peroxide formation than 2H-MoS2. The 1T/2H-MoS2 displays better electrochemical durability compared to 2H-MoS2 (after 2000 CV cycles). [ABSTRACT FROM AUTHOR]

We introduce N-P pair into the carbon matrix to construct N,P-C electrocatalyst by a facile pyrolysis strategy. Benefiting from the moderate adsorption energy of *OH on the active sites (C adjacent to P atom in N-P), the achieved N,P-C-1000 displays outstanding alkaline ORR performance and high power density primary liquid and solid ZABs. [Display omitted] • N-P pair was introduced into the carbon matrix to construct N,P-C electrocatalyst by a facile pyrolysis strategy. • The catalyst exhibits superior ORR activity with a E 1/2 of 0.83 V, comparable to that of commercial 20 wt% Pt/C. • Its C-2p orbit has higher interaction strength with the intermediates, thus reducing the overall reaction energy barrier. • High power density primary liquid and solid ZABs are achieved using N,P-C-1000 as cathodic catalysts. Developing sustainable metal-free carbon-based electrocatalysts is essential for the deployment of metal-air batteries such as zinc-air batteries (ZABs), among which doping of heteroatoms has attracted tremendous interest over the past decade. However, the effect of the heteroatom covalent bonds in carbon matrix on catalysis was neglected in most studies. Here, an efficient metal-free oxygen reduction reaction (ORR) catalyst is demonstrated by the N-P bonds anchored carbon (termed N,P-C-1000). The N,P-C-1000 catalyst exhibits superior specific surface area of 1362 m2 g−1 and ORR activity with a half-wave potential of 0.83 V, close to that of 20 wt% Pt/C. Theoretical computations reveal that the p-band center for C-2p orbit in N,P-C-1000 has higher interaction strength with the intermediates, thus reducing the overall reaction energy barrier. The N,P-C-1000 assembled primary ZAB can attain a large peak power density of 121.9 mW cm−2 and a steady discharge platform of ∼1.20 V throughout 120 h. Besides, when served as the cathodic catalyst in a solid-state ZAB, the battery shows flexibility, conspicuous open circuit potential (1.423 V), and high peak power density (85.8 mW cm−2). Our findings offer a strategy to tune the intrinsic structure of carbon-based catalysts for improved electrocatalytic performance and shed light on future catalysts design for energy storage technologies beyond batteries. [ABSTRACT FROM AUTHOR]

During the past few years, single‐atom catalysts (SACs) have attracted considerable attention in electrolysis due to their outstanding catalytic performance and efficient atomic utilization. SACs exhibit a simple structure, high catalytic activity, consistent scaling relationships for single sites, and low metal content but their practical applications are still limited. Dual single‐atom catalysts (DACs), which feature excellent selectivity, high atomic utilization efficiency, and remarkable stability, are emerging as new frontiers in heterogeneous electrocatalysis. They increase catalytic activity by promoting synergistic effects between metal‐active sites. In this paper, we present a comprehensive overview of the latest developments in dual‐atom catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In addition, we explore the differences between homonuclear and heteronuclear configurations, the emergence of single/dual‐site metal catalysts, and the methods currently used for their synthesis. Lastly, this review discusses several perspectives for advancing the development of dual‐atom catalysts for OER and ORR electrocatalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] Lignin upgrading to various functional products is promising to realize high-value utilization of low-cost and renewable biomass waste, but is still in its infancy. Herein, using industry waste lignosulfonate as the biomass-based carbon source and urea as the dopant, we constructed a heteroatom-doped porous carbon nanosheet structure by a simple NaCl template-assisted pyrolytic strategy. Through the synergistic effect of the NaCl template and urea, the optimized lignin-derived porous carbon catalyst with high content of active nitrogen species and large specific surface area can be obtained. As a result, the fabricated catalysts exhibited excellent electrocatalytic oxygen reduction activity, as well as good methanol tolerance and stability, comparable to that of commercial Pt/C. Moreover, rechargeable Zn-air batteries assembled with this electrocatalyst have a peak power density of up to 150 mW cm-2 and prominent long-term cycling stability. This study offers an inexpensive and efficient way for the massive production of highly active metal-free catalysts from the plentiful, inexpensive and environmentally friendly lignin, offering a good direction for biomass waste recycling and utilization. [ABSTRACT FROM AUTHOR]

In this study, Co/Ni‐NC catalyst with hetero‐diatomic Co/Ni active sites dispersed on nitrogen‐doped carbon matrix is synthesized via the controlled pyrolysis of ZIF‐8 containing Co2+ and Ni2+ compounds. Experimental characterizations and theoretical calculations reveal that Co and Ni are atomically and uniformly dispersed in pairs of CoN4‐NiN4 with an intersite distance ≈0.41 nm, and there is long‐range d–d coupling between Co and Ni with more electron delocalization for higher bifunctional activity. Besides, the in situ grown carbon nanotubes at the edges of the catalyst particles allow high electronic conductivity for electrocatalysis process. Electrochemical evaluations demonstrate the superior ORR and OER bifunctionality of Co/Ni‐NC catalyst with a narrow potential gap of only 0.691 V and long‐term durability, significantly prevailing over the single‐atom Co‐NC and Ni‐NC catalysts and the benchmark Pt/C and RuO2 catalysts. Co/Ni‐NC catalyzed Zn–air batteries achieve a high specific capacity of 771 mAh g−1 and a long continuous operation period up to 340 h with a small voltage gap of ≈0.65 V, also much superior to Pt/C‐RuO2. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) and alkaline membrane fuel cells (AEMFCs) have received great attention as energy devices of the next generation. Accelerating oxygen reduction reaction (ORR) kinetics is the key to improve PEMFC and AEMFC performance. Platinum‐based catalysts are the most widely used catalysts for the ORR, but their high price and low abundance limit the commercialization of fuel cells. Non‐noble metal‐nitrogen‐carbon (M−N−C) is considered to be the most likely material class to replace Pt‐based catalysts, among which Fe−N−C and Co−N−C have been widely studied due to their excellent intrinsic ORR performance and have made great progress in the past decades. With the improvement of synthesis technology and a deeper understanding of the ORR mechanism, some reported Fe−N−C and Co−N−C catalysts have shown excellent ORR activity close to that of commercial Pt/C catalysts. Inspired by the progress, regulation strategies for Fe−N−C and Co−N−C catalysts are summarized in this Review from 5 perspectives: (1) coordinated atoms, (2) environmental heteroatoms and defects, (3) dual‐metal active sites, (4) metal‐based particle promoters, and (5) curved carbon layers. We also make suggestions on some challenges facing Fe−N−C and Co−N−C research. [ABSTRACT FROM AUTHOR]

Due to structural complexity and limited understanding, precise chemical modification in atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts requires theoretical calculations to optimize electronic, geometric, and catalytic performance and experimental implementation of learned lessons to improve their catalytic performance towards oxygen reduction reaction (ORR). Herein, we conducted a density functional theory (DFT) investigation to understand the effect of the replacement of O-atoms in Fe–O 4 –C by N-atoms in the first coordination shell of Fe-site (constructing five models: Fe–O 4 –C, Fe–O 3 N–C, Fe–N 2 O 2 –C, Fe–ON 3 –C and Fe–N 4 –C) towards ORR. The geometric and electronic calculations of these models suggested that replacing all the O-atoms with N-atoms around the Fe-site would make it more conducive to the adsorption of ORR intermediates. Moreover, the Gibbs free energy calculations demonstrated that the Fe-site becomes the active centre for 2e− ORR, leading to the dominant generation of H 2 O 2 when Fe is coordinated with four O-atoms (Fe–O 4 –C). Whereas in compounds like Fe–N 2 O 2 –C, Fe–O 3 N–C, and Fe–N 4 –C, where the Fe-site displays 4e− ORR, form water is a preferred product if the O-atoms are replaced by N-atoms, as in Fe–N 2 O 2 –C, Fe–O 3 N–C, and Fe–N 4 –C. This study would provide a fundamental understanding of how atomically dispersed M-N-C catalysts' electrocatalytic activity is affected by changes in the coordination environment of metal sites. [Display omitted] • A theoretical approach was used to construct the models of Fe-NxOy-C-based electrocatalysts. • The models Fe–O 4 –C, Fe–NO 3 –C, M–N 2 O 2 –C, M–N 3 O–C, and M-N4-C, were completely investigated via DFT approaches. • The O 2 adsorption at the Fe–N 4 –C catalyst was the determining step during the associative pathway. • The M-N 4 -C catalytic moel displayed 4e- ORR, while the M-O 4 -C catalyst showed 2e- ORR. [ABSTRACT FROM AUTHOR]

Facile synthesis of highly-dispersed Pt-based electrocatalysts on porous carbon supports with strong durability is extremely desirable for oxygen reduction reaction but remains challenging. The influence of pores in carbon supports on the stability and activity of catalysts is ambiguous and needs to be elucidated. Targeting this aim, herein, we prepared a series of carbon nanofibers with tunable pore diameter and specific surface area using the resorcinol-formaldehyde (RF) resins as a model system. Homogeneous composite precursors composed of RF resins and silica colloids were synthesized by the surfactant-assisted simultaneous polycondensation of RF resins and tetraethylorthosilicate (TEOS). The diameter of the pores induced by removal of silica could be controllable tailored through thermal treatment of the composite under various target temperatures. Pt 3 Co alloy nanoparticles loaded on the as-synthesized porous carbon nanofibers were prepared by an optimized wet-impregnation method. The experimental results indicated that the carbon nanofibers with pore size distribution focused on ∼1.27 nm and ∼2.34 nm provided the best stability without limiting current density decay, and negative shift of half-wave potential (E 1/2) and mass activity (MA) loss of Pt after 20000 potential cycles are relatively mild. Conversely, negative shift of 21 mV, 15 mV and 22 mV in E 1/2 and mass activity loss of 51.8%, 30.2% and 33.0% were observed for the Pt 3 Co nanoparticles supported on MC-60, MC-100 and MC-140 matrices which have pore size distribution focused on ∼2.73 nm, ∼2.73 nm as well as ∼4.66 nm, and ∼4.66 nm, respectively. This work demonstrates the importance of micropores and small mesopores for activity and long-term stability enhancement of carbon supported Pt-based electrocatalysts. Porous carbon nanofibers with tunable pore size distribution were synthesized by combining the surfactant-assisted simultaneous polycondensation of resorcinol-formaldehyde resins and TEOS with elaborate designed thermal treatment. Pt 3 Co nanoparticles loaded on the carbon with pore size distribution focuses on ∼1.27 nm and ∼2.34 nm provided the highest activity and best stability with no performance decay for ORR after 20000 potential cycles. [Display omitted] • Composite fibers of RF resins and Silica were synthesized by the developed surfactant-assisted polycondensation strategy. • Diameters of the mesopores in the synthesized carbon fibers could be controllable tuned. • Mesopores with diameter of ∼2.34 nm are efficient for boosting the stability of the carbon supported Pt 3 Co for the ORR. [ABSTRACT FROM AUTHOR]

The single‐atom Fe−N−C is a prominent material with exceptional reactivity in areas of sustainable energy and catalysis research. It is challenging to obtain the dense Fe‐N4 site without the Fe nanoparticles (NPs) sintering during the Fe−N−C synthesis via high‐temperature pyrolysis. Thus, a novel approach is devised for the Fe−N−C synthesis at low temperatures. Taking FeCl2 as Fe source, a hydrogen environment can facilitate oxygen removal and dichlorination processes in the synthesis, efficiently favouring Fe‐N4 site formation without Fe NPs clustering at as low as 360 °C. We shed light on the reaction mechanism about hydrogen promoting Fe‐N4 formation in the synthesis. By adjusting the temperature and duration, the Fe‐N4 structural evolution and site density can be precisely tuned to directly influence the catalytic behaviour of the Fe−N−C material. The FeNC‐H2‐360 catalyst demonstrates a remarkable Fe dispersion (8.3 wt %) and superior acid ORR activity with a half‐wave potential of 0.85 V and a peak power density of 1.21 W cm−2 in fuel cell. This method also generally facilitates the synthesis of various high‐performance M−N−C materials (M=Fe, Co, Mn, Ni, Zn, Ru) with elevated single‐atom loadings. [ABSTRACT FROM AUTHOR]

The single‐atom Fe−N−C is a prominent material with exceptional reactivity in areas of sustainable energy and catalysis research. It is challenging to obtain the dense Fe‐N4 site without the Fe nanoparticles (NPs) sintering during the Fe−N−C synthesis via high‐temperature pyrolysis. Thus, a novel approach is devised for the Fe−N−C synthesis at low temperatures. Taking FeCl2 as Fe source, a hydrogen environment can facilitate oxygen removal and dichlorination processes in the synthesis, efficiently favouring Fe‐N4 site formation without Fe NPs clustering at as low as 360 °C. We shed light on the reaction mechanism about hydrogen promoting Fe‐N4 formation in the synthesis. By adjusting the temperature and duration, the Fe‐N4 structural evolution and site density can be precisely tuned to directly influence the catalytic behaviour of the Fe−N−C material. The FeNC‐H2‐360 catalyst demonstrates a remarkable Fe dispersion (8.3 wt %) and superior acid ORR activity with a half‐wave potential of 0.85 V and a peak power density of 1.21 W cm−2 in fuel cell. This method also generally facilitates the synthesis of various high‐performance M−N−C materials (M=Fe, Co, Mn, Ni, Zn, Ru) with elevated single‐atom loadings. [ABSTRACT FROM AUTHOR]

Dual-atom site catalysts with the adjacent metal atomic sites can cooperatively catalyze oxygen reduction reaction (ORR), showing great potential in ORR field. Herein, the ORR activity and mechanism of a supported metal dual-atom site catalyst M2-DAC (M is 3d transition metal) is explored thoroughly by density functional theory methods. By calculating Ed of M2-DAC, all structures are thermodynamically stable and are used for subsequent studies. Considering the adsorption of O2, total 6 kinds of M2-DAC are identified as potential candidate materials for catalyzing ORR due to their moderate adsorption of O2. The binding energy of ORR species and the change of Gibbs free energy in each step of ORR are calculated, and Co2-DAC exhibits notable catalytic activity (ηORR = 0.39 V). Moreover, the charge analysis of Co2-DAC shows that the ORR activity of the catalyst mainly comes from the metal atom and the O atoms coordinated with the metal atoms. [ABSTRACT FROM AUTHOR]

[Display omitted] Fe N C single atom catalysts (SACs) have attracted great interest due to their highly active FeN 4 sites. However, the pyrolysis treatment often leads to inevitable metal migration and aggregation, which reduces the catalytic activity. Moreover, due to the Fenton reaction caused by Fe N C in alkaline and acidic solutions, the presence of Fe and peroxide in electrodes may generate free radicals, resulting in serious degradation of the organic ionomer and the membrane. Herein, we report an original strategy of introducing Co single atoms into Fe N C catalysts, forming atomically dispersed bimetallic active sites (Fe Co NC) and improving the activity and stability of the catalyst. Benefiting from this strategy, Fe Co NC catalyst exhibits excellent oxygen reduction reaction (ORR) activity in alkaline media (E 1/2 = 0.88 V) and in acidic media (E 1/2 = 0.77 V). As the cathode of Zn-air battery (ZAB), Fe Co NC shows an excellent peak power density of 142.8 mW cm−2 and a specific capacity of 806.6 mAh/g Zn. This work provides a novel avenue to optimize and enhance the ORR performance of atomic dispersed Fe N C catalysts. [ABSTRACT FROM AUTHOR]

Electrochemical oxygen reduction reaction (ORR) via the 2e− pathway in an acidic media shows great techno-economic potential for the production of hydrogen peroxide. Currently, carbon-based single-atom catalysts (C-SACs) have attracted extensive attention due to their tunable electronic structures, low cost, and sufficient stability in acidic media. This review summarizes recent advances in metal centers and their coordination environment in C-SACs for 2e−-ORR. Firstly, the reaction mechanism of 2e−-ORR on the active sites of C-SACs is systematically presented. Secondly, the structural regulation strategies for the active sites of 2e−-ORR are further summarized, including the metal active center, its species and configurations of nitrogen coordination or heteroatom coordination, and their near functional groups or substitute groups, which would provide available and proper ideas for developing superior acidic 2e−-ORR electrocatalysts of C-SACs. Finally, we propose the current challenges and future opportunities regarding the acidic 2e−-ORR pathway on C-SACs, which will eventually accelerate the development of the distributed H2O2 electrosynthesis process. [ABSTRACT FROM AUTHOR]

The main group metals are commonly perceived as catalytically inert in the context of oxygen reduction reactions (ORR) due to the delocalized valence orbitals. Regulating the local environment and structure of metal center coordinated by nitrogen ligands (M‐Nx) is a promising approach to accelerate catalytic dynamics. Herein, we, for the first time, report the atomically dispersed Al catalysts coordinated with N and C atoms for 4‐electron ORR. The axial coordinated pyrrolyl N group (No) is constructed in the Al‐N4‐No moiety to regulate the p‐band structure of Al center, effectively steering the local environment and structure of the square planar Al‐N4 sites, which typically exhibit too strong interaction with ORR intermediates. The dynamic covalency competition of axial Al‐No and Al‐O bonding could endow the Al center with moderate hybridization between Al 3p orbital and O 2p orbital, alleviating the binding energy of ORR intermediates. The as‐prepared Al‐N4‐No electrocatalyst exhibits excellent ORR activity, selectivity, and durability, along with the rapid kinetics as demonstrated by in situ Raman spectroscopy. This work offers a fundamental comprehension of the fine regulation on p‐band and guides the rational design of main‐group metal‐based single atom catalysts. [ABSTRACT FROM AUTHOR]

The main group metals are commonly perceived as catalytically inert in the context of oxygen reduction reactions (ORR) due to the delocalized valence orbitals. Regulating the local environment and structure of metal center coordinated by nitrogen ligands (M‐Nx) is a promising approach to accelerate catalytic dynamics. Herein, we, for the first time, report the atomically dispersed Al catalysts coordinated with N and C atoms for 4‐electron ORR. The axial coordinated pyrrolyl N group (No) is constructed in the Al‐N4‐No moiety to regulate the p‐band structure of Al center, effectively steering the local environment and structure of the square planar Al‐N4 sites, which typically exhibit too strong interaction with ORR intermediates. The dynamic covalency competition of axial Al‐No and Al‐O bonding could endow the Al center with moderate hybridization between Al 3p orbital and O 2p orbital, alleviating the binding energy of ORR intermediates. The as‐prepared Al‐N4‐No electrocatalyst exhibits excellent ORR activity, selectivity, and durability, along with the rapid kinetics as demonstrated by in situ Raman spectroscopy. This work offers a fundamental comprehension of the fine regulation on p‐band and guides the rational design of main‐group metal‐based single atom catalysts. [ABSTRACT FROM AUTHOR]

Platinum group catalysts are still the most effective catalysts for oxygen reduction reaction (ORR) of proton exchange membrane fuel cells. Thus, the high cost and susceptibility to deactivation during working process are becoming more and more prominent with the proceeding of the application. To meet the requirements of enhancing reaction kinetics and decreasing the cost of Pt-based catalysts, we design a N -doped hollow carbon nanorods (HCNR) supported platinum-nickel based catalyst for ORR. Compared with the benchmark commercial Pt/C catalyst, the HCNR supported PtNi catalysts (PtNi/HCNR) show excellent catalytic activity for ORR and long-time running durability. The onset potential (E 0) and half wave potential (E 1/2) of medium platinum content catalyst (PtNi/HCNR-2) catalyzed ORR are 1.02 V and 0.914 V, separately, which surpass than that of the 20 wt% Pt/C catalyst. Furthermore, PtNi/HCNR-2 catalyzed ORR has a lower Tafel slope (92.05 mV dec−1), faster electron transfer rate, lower H 2 O 2 yield rate and better stability. The synergistic effect between N -doped HCNR and PtNi alloy assures the high performance for ORR. HCNR improves the electrical conductivity, while the doped nitrogen provides "coordination nests" for PtNi catalyst, which provide more catalytic active sites for ORR. PtNi/HNCR-based catalysts have great potential to be low-cost, high performance catalysts for ORR. [Display omitted] • N -doped hollow carbon nanorods support for catalysts were synthesized. • HCNR supported PtNi catalysts show 20 mV higher onset potential for ORR than Pt/C. • Doping with nitrogen enhanced the affinity between HCNR and PtNi catalyst. • Hollow structure facilitates the transport of oxygen and electrons for ORR. [ABSTRACT FROM AUTHOR]

In this paper, we present a method to enhance the stability of Fe–N–C electrocatalysts, known for their significant oxygen reduction reaction (ORR) activity and positioned as promising alternatives to commercial noble metal-based catalysts. Despite the favorable ORR activity, Fe–N–C suffers from inadequate stability in acidic media, primarily attributed the loss of active FeN 4 sites resulted from Fe-demetalation. However, recent investigation reveals that pyridine N exhibits remarkable stability in retaining Fe atoms. To address this, we achieved a high proportion of pyridine N doping in carbon nanofibers through a process involving nano-SiO 2 shell coating and electrospinning. The nano-SiO 2 shell coating method demonstrates efficacy and versatility in transforming pyrrole-type FeN 4 into pyridine-type FeN 4 , irrespective of the origin material being trivalent or divalent Fe, whether organic or inorganic. [Display omitted] • Obtained a high pyridine proportion Fe–N–C electrocatalyst with long-term stability • Developed a method for the transformation from the pyrrole-type FeN 4 to pyridine-type FeN 4. • The method is applicable to both trivalent and bivalent iron, regardless of inorganic or organic. [ABSTRACT FROM AUTHOR]

Atomically dispersed nonprecious metal‐based catalysts have been considered as the most promising alternatives to Pt‐based catalysts since their excellent catalytic activities and almost 100 % atom utilization in oxygen reduction reaction. However, the agglomeration of metal atoms is unavoidable during pyrolysis process, thus leads to the decrease of electrocatalytic performance. Herein, hyperbranched phthalocyanine copper (HCuPc) wrapping nano‐silica is synthesized via in situ polymerization and served as precursor for preparing atomically dispersed Cu−N−C electrocatalysts. Owing to the confinement effect of chemical‐anchoring and spatial‐hindrance, the migration and agglomeration of Cu atoms are restricted in carbonization process. The aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray photoelectron spectroscopy (XPS) are performed to confirm the atomically dispersed of as‐synthesized catalyst, which is labelled as HCu−N−C/SiO2. In addition, the HCu−N−C/SiO2 possess superior ORR electrocatalytic activities with a half‐wave potential of 0.874 V vs RHE and a limiting current density of 5.7 mA cm−2. The zinc‐air batteries assembled with HCu−N−C/SiO2 catalyst exhibit a high specific capacity of 789 mAh g−1 as well as a maximum discharge power density of 176 mW cm−2. This work proves that hyperbranched phthalocyanine structure could be a useful confined framework to the fabrication of singles‐atom catalysts. [ABSTRACT FROM AUTHOR]

Li-O2 batteries are considered a highly promising energy storage solution. However, their practical implementation is hindered by the sluggish kinetics of the oxygen reduction (ORR) and oxygen evolution (OER) reactions at cathodes during discharging and charging, respectively. In this work, we investigated the catalytic performance of Wn+1Cn and Wn+1CnO2 MXenes (n = 1, 2, and 3) as cathodes for Li-O2 batteries using first principles calculations. Both Wn+1Cn and Wn+1CnO2 MXenes show high conductivity, and their conductivity is further enhanced with increasing atomic layers, as reflected by the elevated density of states at the Fermi level. The oxygen functionalization can change the electronic properties of WC MXenes from the electrophilic W surface of Wn+1Cn to the nucleophilic O surface of Wn+1CnO2, which is beneficial for the activation of the Li-O bond, and thus promotes the Li+ deintercalation during the charge–discharge process. On both Wn+1Cn and Wn+1CnO2, the rate-determining step (RDS) of ORR is the formation of the (Li2O)2* product, while the RDS of OER is the LiO2* decomposition. The overpotentials of ORR and OER are positively linearly correlated with the adsorption energy of the RDS LixO2* intermediates. By lowering the energy band center, the oxygen functionalization and increasing atomic layers can effectively reduce the adsorption strength of the LixO2* intermediates, thereby reducing the ORR and OER overpotentials. The W4C3O2 MXene shows immense potential as a cathode catalyst for Li-O2 batteries due to its outstanding conductivity and super-low ORR, OER, and total overpotentials (0.25, 0.38, and 0.63 V). [ABSTRACT FROM AUTHOR]

A vacancy-rich Co/MnO@NC was synthesized using hydrothermal and high-temperature pyrolysis strategies for oxygen reduction reaction (ORR). The abundant vacancies and synergistic coupling of metallic Co with MnO precisely tuned the electronic configuration, resulting in enhanced electron transport within Co/MnO@NC. Research indicates that the effective Co/MnO@NC ORR catalyst demonstrated elevated peak power densities, reaching 217.7 in liquid-state and 63.3 mW cm−2 in solid-state zinc-air batteries. [Display omitted] • Spherical Co/MnO@NC is synthesized by a hydrothermal-pyrolysis strategy. • The catalyst displays notable ORR activity (J L = 5.1 mAcm−2) comparable to Pt/C. • Aqueous/solid-state ZABs exhibit high power density (217.7/63.3 mW cm−2). • Vacancies, conductivity and hydrophilicity dominate the delightful performance. The pursuit of efficient and economically viable catalysts for liquid/solid-state zinc-air batteries (ZABs) is of paramount importance yet presents formidable challenge. Herein, we synthesized a vacancy-rich cobalt/manganese oxide catalyst (Co/MnO@NC) stabilized on a nitrogen-doped mesoporous carbon (NC) nanosphere matrix by leveraging hydrothermal and high-temperature pyrolysis strategy. The optimized Co/MnO@NC demonstrates fast reaction kinetics and large limiting current densities comparable to commercial Pt/C in alkaline electrolyte for oxygen reduction reaction (ORR). Moreover, the Co/MnO@NC serves as an incredible cathode material for both liquid and flexible solid-state ZABs, delivering impressive peak power densities of 217.7 and 63.3 mW cm−2 and robust long-term stability (459 h), outperforming the state-of-the-art Pt/C and majority of the currently reported catalysts. Research indicates that the superior performance of the Co/MnO@NC catalyst primarily stems from the synergy between the heightened electrical conductivity of metallic Co and the regulatory capacity of MnO on adsorbed oxygen intermediates. In addition, the abundance of vacancies regulates the electronic configuration, and superhydrophilicity facilitates efficient electrolyte diffusion, thereby effectively ensuring optimal contact between the active site and reactants. Besides, the coexisting NC layer avoids the shedding of active sites, resulting in high stability. This work provides a viable approach for designing and advancing high-performance liquid/solid-state ZABs, highlighting the great potential of energy storage technology. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploring highly active electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has become a growing interest in recent years. Herein, an efficient pathway for designing MXene-based ORR/OER catalysts is proposed. It involves introducing non-noble metals into Vo (vacancy site), H 1 and H 2 (the hollow sites on top of C and the metal atom, respectively) sites on M 2 CO 2 surfaces, named TM-V O /H 1 /H 2 -M 2 CO 2 (TM = Fe, Co, Ni, M = V, Nb, Ta). Among these recombination catalysts, Co-H 1 -V 2 CO 2 and Ni-H 1 -V 2 CO 2 exhibit the most promising ORR catalytic activities, with low overpotential values of 0.35 and 0.37 V, respectively. Similarly, Fe-H 1 -V 2 CO 2 , Co-V O -Nb 2 CO 2 , and Ni-H 2 -Nb 2 CO 2 possess low OER overpotential values of 0.29, 0.39, and 0.44 V, respectively, suggesting they have enormous potential as effective catalysts for OER. Notably, Co-H 2 -Ta 2 CO 2 possesses the lowest potential gap value of 0.53 V, demonstrating it has an extraordinary bifunctional catalytic activity. The excellent catalytic performance of these recombination catalysts can be elucidated through an electronic structure analysis, which primarily relies on the electron-donating capacity and synergistic effects between transition metals and sub-metals. These results provide theoretical guidance for designing new ORR and OER catalysts using 2D MXene materials. [ABSTRACT FROM AUTHOR]

The fine regulation of catalysts by the atomic-level removal of inactive atoms can promote the active site exposure for performance enhancement, whereas suffering from the difficulty in controllably removing atoms using current micro/nano-scale material fabrication technologies. Here, we developed a surface atom knockout method to promote the active site exposure in an alloy catalyst. Taking Cu3Pd alloy as an example, it refers to assemble a battery using Cu3Pd and Zn as cathode and anode, the charge process of which proceeds at about 1.1 V, equal to the theoretical potential difference between Cu2+/Cu and Zn2+/Zn, suggesting the electricity-driven dissolution of Cu atoms. The precise knockout of Cu atoms is confirmed by the linear relationship between the amount of the removed Cu atoms and the battery cumulative specific capacity, which is attributed to the inherent atom-electron-capacity correspondence. We observed the surface atom knockout process at different stages and studied the evolution of the chemical environment. The alloy catalyst achieves a higher current density for oxygen reduction reaction compared to the original alloy and Pt/C. This work provides an atomic fabrication method for material synthesis and regulation toward the wide applications in catalysis, energy, and others. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) play vital role in electrocatalysis due to large surface area and unique one-dimensional conductivity, reducing electron scattering. The abundance of the defect sites in CNTs, the catalytically active sites vary based on synthesis methodology. While chemical vapor deposition (CVD) technique has been widely studied, a detailed correlation of the synthetic parameters in the floating catalyst method, with activity is missing. Scalability is also crucial to study as in CVD technique carbon vapor is injected into the furnace but floating catalyst method relies on in-situ vapor generation from solid carbon precursors. We have mapped catalyst dosage and reaction atmosphere's impact on electrocatalytic efficiency for various CNTs produced under different conditions towards the oxygen reduction reaction (ORR) and rationalised the variation in activity by spectroscopic evidences. Optimized CNTs exhibit a high electrocatalytic ORR efficiency with prolonged durability, highlighting the role of the interaction between CNTs and encapsulated iron nanoparticles in response to reaction atmosphere. [Display omitted] • Comprehensive study on floating-catalyst technique to produce bamboo-like CNTs. • Rational portrayal of synthesis parameters affecting catalytic efficiency of CNTs. • Influence of catalyst dosage in determining the conductivity of CNTs. • Synthesis atmosphere dictates synergistic role of encapsulated iron in ORR activity. [ABSTRACT FROM AUTHOR]

More recently, sp3 defects have been reported to show great potential for enhancing the oxygen reduction reaction (ORR) activity of metal-free carbon catalysts. However, it is still a challenge to increase the sp3 defects for achieving superior ORR activity, especially using organics as precursors by ambient-pressure pyrolysis. Herein, sp3-hybridized C and N enriched melamine–formaldehyde resin microspheres were employed for pyrolysis to increase sp3 defects in derived carbons under activation of urea. Under the synergistic effects of intrinsic characteristics of MF microspheres and the activation of sacrificial urea, the derived carbon was endowed to abundant sp3 defects and N species couple with a hierarchical porous structure. Owing to these specific features, the derived metal-free carbon catalyst showed extremely superior ORR activity, zinc-air battery performance and durability. This study provides an insight into the inheritance of sp3 carbon from the precursor to the sp3 defects in final derived carbon catalysts. The sp3 defects were increased by pyrolysis sp3-hybridized C and N enriched melamine–formaldehyde microspheres under the activation of urea, by which a metal-free carbon catalyst with superior ORR activity was obtained. [ABSTRACT FROM AUTHOR]

Atomically dispersed transition metal–nitrogen–carbon (M–N–C) catalysts guide by the d‐band center theory have been extensively studied for oxygen reduction reaction (ORR) in various energy conversion and storage processes. However, asymmetric p‐block metal single‐atom catalysts (SACs) toward ORR have rarely been reported, and the origin of their catalytic activity is still unclear. Here, an asymmetric N, O coordinated Sn SAC is developed as an efficient ORR electrocatalyst. Remarkably, the optimized Sn SAC (e.g., Sn–N/O–C) exhibit outstanding ORR performance with a half‐wave potential of 0.910 V in alkaline media, outperforming most state‐of‐the‐art ORR catalysts. More importantly, the Sn–N/O–C possesses a long‐term durability in both alkaline and acidic electrolytes. Besides, Zn–air batteries based on the Sn–N/O–C cathode also show a higher energy density (254 mW cm‐2) than that of their reported M–N–C counterparts. Theoretical calculations suggest that the asymmetric N, O coordinated atomic Sn sites have a stronger binding interaction with O2 and better charge transfer ability compared with the symmetric SnN4 sites, thereby facilitating the ORR process. This work provides a nitrogen‐, oxygen‐coordinated engineering strategy for the rational design of highly active and durable carbon‐based catalysts with atomic p‐block metal sites for ORR and beyond. [ABSTRACT FROM AUTHOR]

Fe─N─C materials with Fe─N4 sites are considered as most promising non‐precious metal‐based electrocatalysts for low‐cost proton‐exchange‐membrane fuel cells (PEMFCs). Breaking the trade‐off between activity and stability has been a long‐standing challenge in the field of acidic oxygen reduction reaction (ORR). Herein, a "top‐down" thermally‐driven strategy is developed to achieve highly active pyrrolic N‐coordinated Fe sites in a high spin state with Fe atomic cluster (Fen@Fe─Npyrr─C) and discover that the neighboring Fen cluster can synergistically stabilize such vulnerable Fe─N4 sites by inhibiting their protonation. Consequently, the Fen@Fe─Npyrr─C catalysts exhibit much enhanced ORR activity and stability, endowing PEMFCs with a high power density of 804.6 mW cm−2 (testing conditions: 80 °C, 100% RH, 2.0 bar) and over 100 h durability (at 0.5 V). These findings open up opportunities for the exploration of durable Fe─N─C ORR electrocatalysts for non‐precious metal‐based PEMFCs and other applications. [ABSTRACT FROM AUTHOR]

Recently, theoretical calculations have played an irreplaceable role in the discovery of electrocatalysts as a relatively time‐efficient, cost‐effective, and predictable method. More importantly, theoretical calculations can help screen out the best active reaction sites and modulate them accordingly, which is beneficial for the development of efficient catalysts. In this concept, we focus on the important role of theoretical calculations in determining catalytic active sites and understanding reaction mechanisms, emphasizing its importance in assisting the design and synthesis of efficient oxygen reduction reaction catalysts. Finally, we provide an outlook on the challenges and future development trend in this field. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) occurred in acidic media, as the cathode reaction of proton exchange membrane fuel cells (PEMFCs) with great commercialization potential, has attracted much attention. However, the slow kinetics of ORR and the high cost of cathode catalysts (mainly platinum (Pt)-based materials in current) have become the main obstacle to the rapid development of PEMFCs. Therefore, the exploration of efficient and inexpensive non-precious metal-based ORR catalysts has emerged as an urgent issue. Non-noble transition metal-based materials have been widely investigated as ORR catalysts in acidic media. This review focused on the investigation of iron (Fe) based catalysts in acidic ORR processes. In this review, the ORR mechanism was first introduced. Subsequently, the fabrication method of Fe-based catalysts by co-pyrolysis of mixtures containing Fe, non-metal, and organic precursors was discussed. Finally, the recent advances of Fe-based materials (carbides, nitrides, oxides, phosphides, chalcogenides, hybrids, alloys and single atom catalysts) as acidic ORR catalysts were summarized, and mainly focused on catalytic performance, stability and catalytic mechanism studies with Density Functional Theory (DFT) calculation. Finally, the challenges and future perspectives of Fe-based catalysts were also proposed. [Display omitted] • The different fabrication methods of Fe-based catalysts are highlighted. • The recently acidic ORR property of various Fe-based catalysts has been explored. • Several challenges and outlooks of Fe-based catalysts are raised. [ABSTRACT FROM AUTHOR]

Challenges in rational designing dual‐atom catalysts (DACs) give a strong motivation to construct coordination‐activity correlations. Here, thorough coordination‐activity correlations of DACs based on how the changes in coordination shells (CSs) of dual‐atom Cu,Co centers influence their electrocatalytic activity in oxygen reduction reaction(ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is constructed. First, Cu,Co DACs with different CSs modifications are fabricated by using a controlled "precursors‐preselection" approach. Three DACs with unique coordination environments are characterized as secondary S atoms that directly bond to Cu,Co‐N6 in lower CSs, indirectly bond in neighboring CSs, and are doped in higher CSs, respectively. Then, experimentally and theoretically, a coordination correlation resembling a planet‐satellite system, where satellite coordinated atoms (heteroatom N, S) surround Cu‐Co dual‐atom entity in various orbitals CSs. By evaluating electrocatalytic activity indicators, differences are identified in electronic structure and electrocatalytic performance of Cu and Co centers in ORR, OER, and HER. Interestingly, initial CSs modifications for DACs may not always be advantageous for electrocatalysis. This work offers valuable insight for designing DACs for diverse applications. [ABSTRACT FROM AUTHOR]

Highlights: The advancement and current status of dual-atom catalysts are reported. The synergistic effects exhibited by recent dual-atom catalysts in mechanistic studies are classified and summarized. Challenges and prospects of dual-atom catalysts in synthesis, characterization, applications, and theory are discussed. The exploration of sustainable energy utilization requires the implementation of advanced electrochemical devices for efficient energy conversion and storage, which are enabled by the usage of cost-effective, high-performance electrocatalysts. Currently, heterogeneous atomically dispersed catalysts are considered as potential candidates for a wide range of applications. Compared to conventional catalysts, atomically dispersed metal atoms in carbon-based catalysts have more unsaturated coordination sites, quantum size effect, and strong metal–support interactions, resulting in exceptional catalytic activity. Of these, dual-atomic catalysts (DACs) have attracted extensive attention due to the additional synergistic effect between two adjacent metal atoms. DACs have the advantages of full active site exposure, high selectivity, theoretical 100% atom utilization, and the ability to break the scaling relationship of adsorption free energy on active sites. In this review, we summarize recent research advancement of DACs, which includes (1) the comprehensive understanding of the synergy between atomic pairs; (2) the synthesis of DACs; (3) characterization methods, especially aberration-corrected scanning transmission electron microscopy and synchrotron spectroscopy; and (4) electrochemical energy-related applications. The last part focuses on great potential for the electrochemical catalysis of energy-related small molecules, such as oxygen reduction reaction, CO2 reduction reaction, hydrogen evolution reaction, and N2 reduction reaction. The future research challenges and opportunities are also raised in prospective section. [ABSTRACT FROM AUTHOR]

Single-atom Fe–N–C catalysts have received ever-growing interest in proton exchange membrane fuel cells (PEMFCs) application for their utmost atomic utilization in oxygen reduction reaction (ORR). However, developing atomically dispersed Fe–N–C catalysts with both satisfactory activity and excellent stability presents great challenges. Herein, a template-activator combined strategy is developed to construct ORR catalysts with densely accessible single-atom Fe sites dispersed on hierarchically porous carbon networks. The optimized catalyst exhibits excellent oxygen reduction activity with a half-wave potential of 0.84 V and surprising stability with 93.6% retention of the initial current density after 24 hours of chronoamperometric test in acidic media. Notably, when assembled in a H 2 –O 2 fuel cell, it shows remarkable long-term durability with only 16% loss in current density during the first 10 hours. MgO template coupled with ZnCl 2 activation is an effective way to restrict the agglomeration of the iron atoms, reduces the N-evaporation from the precursor, modulate the porous structure, thus constructing densely exposed atomic dispersed Fe-Nx sites on a hierarchically porous carbon. The resultant Zn0.22-FeNC catalyst presents outstanding stability and satisfactory ORR activity in acidic environment and H 2 –O 2 fuel cell. [Display omitted] • A template-activator strategy to prepare atomically dispersed Fe on porous carbon is developed. • The hierarchical porous structure produces more accessible active sites and fast mass transfer. • The catalyst presents outstanding ORR stability and activity in acidic environment. • The catalyst shows only 16% loss in current density during the first 10 hours in fuel cell test. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are considered promising energy sources whereby chemical energy is converted into electricity via bioelectrochemical reactions utilizing microorganisms. Several factors affect MFC performance, including cathodic reduction of oxygen, electrode materials, cell internal and external resistances, and cell design. This work describes the effect of the catalyst coating in the air-cathode membrane electrode assembly (MEA) for a microbial fuel cell (MFC) prepared via electrodeposition of manganese oxide. The characterization of the synthesized air-cathode MFC, operating in a continuous mode, was made via electrochemical impedance spectroscopy (EIS) analyses for the determination of the intrinsic properties of the electrode that are crucial for scalability purposes. EIS analysis of the MFCs and of the MEA reveals that the anode and cathode contribute to polarization resistance by about 85% and 15%, respectively, confirming the high catalytic activity of the Mn-based air cathode. The maximum power density of the Mn-based cathode is about 20% higher than that recorded using a Pt/C electrode. [ABSTRACT FROM AUTHOR]

The efficiency and performance of proton exchange membrane fuel cells (PEMFCs) are primarily influenced by ORR electrocatalysts. In recent years, atomically dispersed metal–nitrogen–carbon (M-N-C) catalysts have gained significant attention due to their high active center density, high atomic utilization, and high activity. These catalysts are now considered the preferred alternative to traditional noble metal electrocatalysts. The unique properties of M-N-C catalysts are anticipated to enhance the energy conversion efficiency and lower the manufacturing cost of the entire system, thereby facilitating the commercialization and widespread application of fuel cell technology. This article initially delves into the origin of performance and degradation mechanisms of Fe-N-C catalysts from both experimental and theoretical perspectives. Building on this foundation, the focus shifts to strategies aimed at enhancing the activity and durability of atomically dispersed Fe-N-C catalysts. These strategies encompass the use of bimetallic atoms, atomic clusters, heteroatoms (B, S, and P), and morphology regulation to optimize catalytic active sites. This article concludes by detailing the current challenges and future prospects of atomically dispersed Fe-N-C catalysts. [ABSTRACT FROM AUTHOR]

Fe-based catalysts have a good prospect in oxygen reduction reaction (ORR) in fuel cells. However, the catalytic activity of Fe-based catalysts requires further improvement to satisfy the demand in industrial application and the working mechanism is still shrouded in ambiguity. Here, a ferromagnetic catalyst with nitrogen-doped carbon supported FeCoNi alloy was synthesized by impregnation-pyrolysis method. The micromorphology and structure of the catalyst was analyzed by XRD, SEM, TEM, XPS, BET and Raman spectroscopy. The trimetallic catalyst showed high ORR activity in 0.1 M KOH with a half-wave potential of 0.908 V and a limiting current density of 6.153 mA cm−2, which was superior to 20 % Pt/C. The synergistic effect of FeCoNi alloy regulated the spin polarization and the regulated spin state improved ORR performance by facilitating the adsorption of O 2 molecules and the conversion of the activated intermediates. [Display omitted] • FeCoNi@NC is derived from C 3 N 4 by impregnation-pyrolysis method. • FeCoNi@NC is highly active for oxygen reduction reaction. • The spin polarization is regulated by the synergistic effect of Fe, Co and Ni. [ABSTRACT FROM AUTHOR]

[Display omitted] Transition metal and nitrogen co-doped carbon electrocatalysts are promising candidates to replace the precious metal platinum (Pt) in oxygen reduction reactions (ORR). Unfortunately, the electrochemical performance of existing electrocatalysts is restricted due to limited accessibility of active sites. Inspired by jellyfish tentacles, we design an efficient ORR micro-reactor called Fe-N x /HC@NWs. It features abundant exposed Fe-N x active sites dispersed on nitrogen-doped cubic carbon cages, which have a hierarchically porous and hairy structure. The accessible, atomically dispersed Fe-N x sites and the elaborate substrate architecture synergize to provide the catalyst withremarkable ORR catalytic activity, extraordinary long-term stability, and favorable methanol tolerance in an alkaline electrolyte; overall, its performance is comparable to that of commercial carbon-supported Pt. Our synthesis is facile and controllable, paving a new avenue toward advanced non-precious metal-based electrocatalysts for energy storage and conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Catalysts have favorable ECSA, multiple active centers, and sufficient mass transport. • PtCo nanoparticles (about 2.5 nm) are uniformly distributed and firmly anchored in the matrix. • The synergistic effect of PtCo, Co 9 S 8 and Co-N strengthens the catalytic performance. • Strong chemical/electronic interactions enhance the anchoring of PtCo NPs on the carrier. • The catalysts exhibit more excellent ORR and HER performance than the Pt/C. The development of low-Pt bifunctional electrocatalysts with excellent performance for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is critical for the advancement of the hydrogen economy. Here, we have integrated low-loading Pt and Co metals into N, S doped porous carbon nanosheets to obtain composite catalysts encapsulating PtCo alloy nanoparticles (PtCo2@Co 9 S 8 / N -CNS and PtCo2@ N -CNS). The acquired PtCo nanoparticles, with dimensions of about 2.5 nm, are uniformly distributed and firmly anchored in N, S doped carbon nanosheets with large specific surface areas and rich pore structure, forming multiple active centers and effectively preventing the aggregation of metal nanoparticles. The PtCo2@Co 9 S 8 / N -CNS and PtCo2@ N -CNS display high ORR catalytic mass activity of 1.65 A mg Pt -1 and 1.01 A mg Pt -1 in 0.1 M HClO 4. The PtCo2@ N -CNS catalyst exhibits excellent HER performance in 0.5 M H 2 SO 4 , with a mass activity (at 50 mV) 4.3 times higher than that of Pt/C. The PtCo2@Co 9 S 8 / N -CNS and PtCo2@ N -CNS also exhibit stronger ORR and HER stability than Pt/C after accelerated durability tests. The superior catalytic activity performance of catalysts can be attributed to the synergistic effect of multiple active centers of PtCo, Co 9 S 8 and Co-N in the catalysts. The confinement of PtCo nanoparticles by Co metal and N, S doped porous nanosheets derived from graphitic carbon nitride (g-C 3 N 4) as the template, which can effectively prevent the corrosion and migration of the catalysts under acidic conditions, enhances the catalytic stability of the materials. This study provides a new perspective for the development of economical and efficient bifunctional low-Pt catalysts. [ABSTRACT FROM AUTHOR]

Platinum-group-metal free catalysts have been widely studied in the last decade as an alternative to Pt, employed in fuel cells. Several carbon precursors have been investigated as carbon matrix for iron-nitrogen-carbon (Fe–N–C) catalysts, characterized by a large amount of micropores, fundamental to create Fe-N x -C active sites. Nonetheless, it is also acknowledged that wider pores are needed to facilitate mass transfer of oxygen/water (reagent/product of fuel cells) towards/from the active sites. Organic xerogels are known as easily tunable materials, that allow doping with a variety of heteroatoms. The present manuscript presents an investigation on the use of organic xerogels combined with iron and nitrogen in a single-step to obtain Fe–N-CXG electro-catalysts for the oxygen reduction reaction (ORR) of proton exchange membrane fuel cells. Several features of both organic xerogels and catalysts on the ORR activity are assessed: the textural properties of the organic xerogel, the iron loading of the Fe–N–C catalysts and the effect of acid-leaching of the catalysts. The present study proves the feasibility of using organic xerogels as carbon precursor to obtain PGM-free catalysts in an easy manner and scalable single-step synthesis. Catalysts obtained from organic xerogels synthesized at mildly acid pHs (5.8 and 6), with a nominal iron loading of 2 wt%, and subjected to two sets of acid leaching/thermal treatments, present enhanced catalytic activity towards the ORR. • Organic carbon xerogels are investigated as carbon matrix for Fe–N–C catalysts. • One-step and template-free synthesis of Fe–N–C catalysts is proposed. • Balanced iron doping creates enough active sites without impacting porosity. • Acid/thermal treatments enhance catalysts improving chemical properties. • High mesopore volume organic xerogels (pH 5.8) yield highly active ORR catalysts. [ABSTRACT FROM AUTHOR]

The transition-metals carbon catalysts belong to intensively studied alternatives to the Pt-based catalysts promoting the oxygen reduction reaction (ORR) in electrochemical fuel cells (FCs). Commonly studied Fe,Co–N–C composites are usually obtained through pyrolysis and used as such or after a chemical post-treatment with an oxidizing agent. This treatment is applied to remove inactive metal species, thus, promoting the electrochemical activity. The impact of an oxidizing agent is poorly addressed in the literature, while its nature may negatively affect the catalyst's performance. Herein we report the first comparative study on the effect of post-treatment with the most common oxidizing agents such as HCl, HNO 3 , H 2 SO 4 and H 2 O 2 , on the structural and electrochemical properties of the Fe,Co–N–C catalyst. The catalyst is made by pyrolysis of the Co,Zn-ZIF metal-organic framework enriched with iron and nitrogen. Its structure was observed withstanding the action of mineral acids but suffers from hydrogen peroxide. The treatment with either nitric or chloric acid may improve the electrochemical performance up to 4%, while other agents decrease that by 6% and slow down the ORR rate. These findings are useful for the careful design of post-treatment procedures for carbon catalysts. • The Fe,Co–N–C carbon-based catalyst was obtained from Fe,Co-ZIF-8 MOF via pyrolysis at 700 °C in an inert atmosphere. • The Fe,Co–N–C catalyst was treated with four oxidizing agents - chloric, nitric and sulfuric acids, and hydrogen peroxide. • Structural and compositional changes were assessed with multi-technique characterization of the catalysts. • The catalysts treated with nitric and chloric acids demonstrated improved performance for ORR in an acidic medium. [ABSTRACT FROM AUTHOR]

The structural and electrochemical characteristics of Pt 3 Co alloy nanoparticles as novel magnetic catalysts are investigated experimentally to improve the performance of the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Pt 3 Co alloy nanoparticles are synthesized using a wet chemical reduction and seed-mediated method. The synthesized Pt 3 Co alloy nanoparticles are annealed at 400 °C (Pt 3 Co-400) and 700 °C (Pt 3 Co-700) to increase the remanent magnetizations. The synthesized Pt 3 Co alloy nanoparticles for magnetic catalysts are characterized using physicochemical and electrochemical methods. Physicochemical tests confirm that the Pt 3 Co alloy nanoparticles are properly synthesized with the desired atomic ratio for magnetization in the multidomain region. The remanent magnetizations of the Pt 3 Co alloy nanoparticles substantially increase after annealing at 400 °C. For the rotating ring-disk electrode tests, the electrocatalytic performance improvement of Pt 3 Co alloy nanoparticles by magnetization is very small under the liquid electrolyte condition. However, the performances of PEMFCs using Pt 3 Co-400 alloy nanoparticles are substantially improved after magnetization owing to the enhanced ORR activities and oxygen diffusivity. In addition, the optimal operating conditions for PEMFCs using Pt 3 Co-400 magnetic catalysts are determined to be a higher reactant flow rate and lower operating temperature with a Pt-to-Pt 3 Co-400 mass ratio of 8:2. • Pt 3 Co alloy nanoparticles are synthesized for magnetic catalysts. • The possibility of magnetization of synthesized Pt 3 Co is confirmed. • The effect of the magnetization of Pt 3 Co on oxygen reduction reaction is analyzed. • Magnetization of Pt 3 Co alloy nanoparticles improves PEMFC performance. • The optimized conditions for PEMFCs with magnetic catalysts are determined. [ABSTRACT FROM AUTHOR]

The supported nano-catalysts represented by platinum-carbon (Pt/C) are widely used with many advantages such as high surface area, high activity and cost-effective. Pt/C is one of the most important catalysts in modern industry and plays an indispensable role as the cathode for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) applications. However, due to the scarcity of noble metal, the large-scale preparation of novel Pt/C catalysts with higher catalytic activity has become a hot topic of research in both academia and industry. In this study, we develop an Fe3+ triggered micellization process to successfully obtain novel surface-engineered Pt/C catalyst with better oxygen reduction performance for fuel cell applications. This method has been scaled up and verified through pilot experiments, producing more than one kilogram of catalysts per batch with promising commercial values. This work will provide new ideas for the synthesis-route design and practical production of advanced nano-catalysts. [Display omitted] • An Fe3+ triggered micellization method is investigated to synthesize surface-engineered Pt/C catalyst. • The water-based synthesis method is facile to scale-up with a kilogram scale verification. • The simultaneous nitrogen doping during the synthesis process further promotes the oxygen reduction performance. • The surface-engineered Pt/C sample shows a superior performance than commercial Pt/C for oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Exploring the high activity of non-precious metal electrocatalysts for the oxygen reduction reaction (ORR) is necessary to reduce the cost of commercial application of fuel cells. In this work, MnO@Sm 2 O 2 CO 3 (MnO@SOC) nanosheets with abundant oxygen vacancies were synthesized by solvothermal method. The nanosheets showed the best ORR performance in 0.1 M KOH solution after annealing at 500 °C. In electron paramagnetic resonance (EPR) results reveal that annealing reduces the number of oxygen vacancies in the catalyst, increases the lattice oxygen, further enhances the ability of transition metals to combine with oxygen atoms during the reaction. Meanwhile, the support Sm 2 O 2 CO 3 is beneficial to accelerate the breaking of O–O bond, thus promoting the complete reduction of O 2 in the electrocatalytic reaction. This work enriches the family of lanthanide metal catalysts and provides a new strategy for the design and improvement of heterogeneous catalysts. • MnO x @SOC nanosheets were prepared by solvothermal method for the first time. • Annealing will affect oxygen vacancy and metal valence on catalyst surface. • The ratio of MnO/Mn 2 O 3 affected the catalytic performance of the catalyst. [ABSTRACT FROM AUTHOR]

Owing to the robust protection of carbon layers, Pt catalysts sheltered by carbon layers (Pt@C/C) show superior durability towards the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFs). Herein, we report a convenient method for synthesizing the Pt@C/C catalyst by the thermal treatment of carbon-supported Pt-pyrrole complexes which have a specific mole ratio of Pt and pyrrole of ∼2.2. The obtained Pt nanoparticles (∼3 nm) were well distributed and encapsulated by nitrogen-doped carbon layers. Notably, the pyrolyzing temperature has critical effects on the ORR activity of the Pt@C/C catalysts, with the Pt@C/C catalyst obtained at 700 °C (Pt@C/C700) exhibiting the best performance and far exceeding that of commercial Pt/C during potential cycling. TEM results show that the performance robustness of Pt@C/C700 is ascribed to the protection of ultra-thin carbon shells. In the cell test, the performance of the membrane-electrode-assembly with the Pt@C/C700 as the ORR catalyst was largely retained after the accelerated stress test, with a loss of only 12 mV at 0.8 A/cm2. The improved stability of Pt@C/C700 can result from the carbon shell's stabilizing effect which physically isolated the Pt nanoparticles from the harsh environment and prevented their degradation. This facile preparation method is promising for the mass production of Pt@C/C catalysts with enhanced durability for the ORR. • Carbon-shell-encapsulated Pt/C catalysts (Pt@C/C) are prepared by direct pyrolysis of Pt-pyrrole complexes. • The N-doped- carbon shell has little effect on oxygen transfer. • The Pt@C/C delivers great durability after cycling in MEA. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting by use of suitable electrocatalysts is an important process to establish water as sustainable energy material. Similarly, the Oxygen reduction reaction is an important step involved in fuel cells. Hence, suitable catalysts are required for low-cost and high-performance activity towards both processes. In this work, we synthesized Cobalt-free Lanthanum-based double Perovskites oxides La 0.5 Sr 0.5 Fe 0.8 Cu 0.2 O 3 and La 0.5 Sr 0.5 Fe 0.8 Zn 0.2 O 3 by sol-gel method followed by calcination at different temperatures (800 °C, 900 °C and 1000 °C). Prepared double Perovskite oxide materials exhibit bifunctional catalytic activity towards both oxygen evolution reaction and oxygen reduction reaction. Calcination temperatures and composition have a significant impact on catalytic performance because of morphological control along with tuning of surface composition. Powder X-ray diffraction study has been performed to characterize the materials and phases/composition of materials was further analyzed by Rietveld refinement. The morphology of the best catalyst was analyzed by SEM, EDS mapping and XPS analysis. The catalytic performances of the catalysts were examined using electrochemical methods such as linear sweep voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy in 0.1 M KOH solution. Preparation of noble-metal/cobalt-free catalysts is important finding towards establishing water as potential source for hydrogen production. • Cobalt-free catalyst of Lanthanum based double perovskites oxides were synthesized and characterized. • Characterization of prepared catalysts was done by SEM, PXRD and XPS analysis. • The atomic and electronic structures of these compounds can be controlled due to compositional differences, which results in high conductivity. • Prepared catalysts were used as bifunctional electrocatalysts in OER and ORR. • Prepared catalysts exhibit bifunctional catalytic activity towards both OER and ORR in an alkaline media. [ABSTRACT FROM AUTHOR]

Single atom catalysts had been widely used in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). However, the relationship between local coordination environment and catalytic activity were unclear. In this work, the effect of N‐defect and axial halogen atoms on electrocatalytic OER/ORR activity of FeN4 catalysts were investigated by density functional theory calculations (DFT). When the overpotential was the only criterion, FeN3Br was the optimal candidates for OER, followed by FeN3F, FeN4I, FeN4Cl and FeN4Br; FeN4I, FeN4Br and FeN4Cl were also the promising candidates for ORR. FeN4I, FeN4Br and FeN4Cl may be excellent ORR catalysts in an acidic media because of the low overpotential and reaction barrier of kinetics rate limiting step. In summary, N‐defect and axial halogen atoms can effectively balance kinetics, thermodynamics and catalytic activity. [ABSTRACT FROM AUTHOR]