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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]

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]

[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]

[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]

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]

Proton exchange membrane fuel cells (PEMFCs), which have the advantages of high-power density, zero emission, and low noise, are considered ideal electrochemical conversion systems for converting hydrogen (H2) and oxygen (O2)/air into electricity. However, the oxygen reduction reaction (ORR), which is accompanied by multiple electrons, results in voltage loss and low conversion efficiency of PEMFCs. Currently, PEMFCs mainly use highload precious platinum (Pt) to promote the ORR process; however, the high cost of Pt hinders the widespread commercialization of PEMFCs. Over the past few years, metal-nitrogen-carbon single-atom catalysts (M-N-C SACs) have attracted considerable attention and have been recognized as potential Pt-based catalysts owing to their outstanding ORR activity. This review briefly introduces the components of PEMFCs. Second, we discuss the catalytic mechanisms of the M-N-C SACs for the ORR. Third, the latest advances in noble, non-noble, and heteroatom-doped M-N-C SACs used as ORR and PEMFCs cathode catalysts are systematically reviewed. In summary, we have outlined the current challenges and proposed a future perspective of M-N-C SACs for PEMFCs cathodes. [ABSTRACT FROM AUTHOR]

The emerging of single‐atom catalysts (SACs) offers a great opportunity for the development of advanced energy storage and conversion devices due to their excellent activity and durability, but the actual mass production of high‐loading SACs is still challenging. Herein, a facile and green boron acid (H3BO3)‐assisted pyrolysis strategy is put forward to synthesize SACs by only using chitosan, cobalt salt and H3BO3 as precursor, and the effect of H3BO3 is deeply investigated. The results show that molten boron oxide derived from H3BO3 as ideal high‐temperature carbonization media and blocking media play important role in the synthesis process. As a result, the acquired Co/N/B tri‐doped porous carbon framework (Co–N–B–C) not only presents hierarchical porous structure, large specific surface area and abundant carbon edges but also possesses high‐loading single Co atom (4.2 wt.%), thus giving rise to outstanding oxygen catalytic performance. When employed as a catalyst for air cathode in Zn‐air batteries, the resultant Co–N–B–C catalyst shows remarkable power density and long‐term stability. Clearly, our work gains deep insight into the role of H3BO3 and provides a new avenue to synthesis of high‐performance SACs. [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]

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]

[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]

Metal‐Organic Frameworks (MOFs) hold great potential to be used as porous (photo)‐electrocatalytic platforms containing large concentration of immobilized molecular catalysts. Indeed, the use of MOFs in a photo‐electrochemical devices was recently demonstrated. However, so far there are no reports of MOFs used for photo‐electrochemical O2 reduction to H2O2. Herein, we utilize a Co‐porphyrin based MOF (Co‐MOF‐525), that produces H2O2 at high faradaic efficiency (95 %), both electrochemically and photo‐electrochemically. Electrochemical characterization show that the active catalytic site is a MOF‐tethered Co(I)‐porphyrin. Additionally, under light illumination, the MOF's intrinsic catalytic rate is significantly accelerated compared to dark electrolysis conditions. Thus, this work could open a path for future implementation of photoactive MOFs in solar fuel schemes. [ABSTRACT FROM AUTHOR]

The development of efficient and low-cost non-metallic catalysts is of great significance for the oxygen reduction reaction (ORR) in fuel cells. Heteroatom-doped carbon-based catalysts are one of the popular candidates, although their preparation method is still under exploration. In this work, single (CS)-, double (NCS)-, and triple (NBCS)-heteroatom-doped carbon-based catalysts were successfully prepared by a "cook-off" process. The morphology, elemental composition, and bonding structure of the catalysts were investigated by SEM, TEM, Raman spectra, BET, and XPS. ORR catalytic performance measurements suggested an activity trend of CS < NCS < NBCS, and NBCS demonstrated better methanol resistance and slightly higher stability than the commercial Pt/C catalyst, as evaluated with both rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) systems. The mechanism for the promoted performance was also proposed based on the conductivity of the catalysts. In this paper, the heteroatoms N, B, and S were co-doped into activated carbon using a simple, fast, and efficient preparation method with high electrical conductivity and also increased active sites, showing high electrocatalytic activity and good stability. This work provides a new approach to preparing highly active non-Pt catalysts for oxygen reduction reactions. [ABSTRACT FROM AUTHOR]

Plasma etching treatment is an effective strategy to improve the electrocatalytic activity, but the improvement mechanism is still unclear. In this work, a nitrogen‐doped carbon nanotube‐encased iron nanoparticles (Fe@NCNT) catalyst is synthesized as the model catalyst, followed by plasma etching treatment with different parameters. The electrocatalytic activity improvement mechanism of the plasma etching treatment is revealed by combining the physicochemical characterizations and electrochemical results. As a result, highly active metal–nitrogen species introduced by nitrogen plasma etching treatment are recognized as the main contribution to the improved electrocatalytic activity, and the defects induced by plasma etching treatment also contribute to the improvement of the electrocatalytic activity. In addition, the prepared catalyst also demonstrates superior ORR activity and stability than the commercial Pt/C catalyst. [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]

Fe−N−C catalysts are an interesting option for polymer electrolyte fuel cells due to their low cost and high activity towards the oxygen reduction reaction (ORR). Since Fe−N−C active sites are preferentially formed in the micropores of the carbon matrix, increasing the microporosity is highly appealing. In this work, carbon xerogels (CXG) were activated by physical and chemical methods to favor the formation of micropores, used as carbon matrices for Fe−N−C catalysts, and investigated for the ORR. The catalysts were characterized by solid‐state techniques to determine chemical composition and pore structure. Physical activation increased microporosity up to 2‐fold leading to catalysts with a larger density of active sites (more than twice iron and nitrogen uptake, pyridinic N and Nx−Fe). This entailed a higher ORR intrinsic activity determined in a 3‐electrode cell (80 mV better half‐wave potential). At the cathode of a fuel cell, the catalysts based on activated carbon materials showed 26 % lower power density ascribed to a more hydrophilic surface, causing a larger extent of flooding of the electrode that counterbalances the higher intrinsic activity. Interestingly, a more stable behavior was observed for the activated catalysts, with up to 2‐fold better relative power density retention after 20‐hour operation. [ABSTRACT FROM AUTHOR]

Atomically dispersed Fe-N-C catalysts for the oxygen reduction reaction (ORR) have been synthesized with a template-free method using carbon xerogels (CXG) as a porous matrix. The porosity of the CXGs is easily tunable through slight variations in the synthesis procedure. In this work, CXGs are prepared by formaldehyde and resorcinol polymerization, modifying the pH during the process. Materials with a broad range of porous structures are obtained: from non-porous to micro-/meso-/macroporous materials. The porous properties of CXG have a direct effect on Fe-N-CXG activity against ORR in an acidic medium (0.5 M H2SO4). Macropores and wide mesopores are vital to favor the mass transport of reagents to the active sites available in the micropores, while narrower mesopores can generate additional tortuosity. The role of microporosity is investigated by comparing two Fe-N-C catalysts using the same CXG as the matrix but following a different Fe and N doping procedure. In one case, the carbonization of CXG occurs rapidly and simultaneously with Fe and N doping, whereas in the other case it proceeds slowly, under controlled conditions and before the doping process, resulting in the formation of more micropores and active sites and achieving higher activity in a three-electrode cell and a better durability during fuel cell measurements. This work proves the feasibility of the template-free method using CXG as a carbon matrix for Fe-N-C catalysts, with the novelty of the controlled porous properties of the carbon material and its effect on the catalytic activity of the Fe-N-C catalyst. Moreover, the results obtained highlight the importance of the carbon matrix's porous structure in influencing the activity of Fe-N-C catalysts against ORR. [ABSTRACT FROM AUTHOR]

An oxygen reduction reaction (ORR) is the key half reaction of proton exchange membrane fuel cells (PEMFCs), and is highly dependent on Pt-based nanocrystals as core electrocatalysts. Despite the exceptional ORR activity from adjusting the electronic structures of surface or near-surface atoms, several serious issues, including the corrosion of carbon supports, the preferential leaching of active metal elements, the instability of surface low-coordinated atoms and the sintering/agglomeration of nanocrystals, still exist, challenging the ORR durability of developed Pt-based ORR catalysts. From the point of view of the catalyst structure design, in this review, we summarized the state-of-the-art structural regulation strategies for improving the ORR durability of Pt-based catalysts. The current limitation of Pt-based binary catalysts for ORR electrocatalysis is firstly discussed, and the detailed strategies are further classified into the optimization of supports, metal-doped alloys, core/shell structures, intermetallics and high-entropy alloys, etc. The structure–performance relationship is detailedly explained, especially emphasizing the elimination of the above restrictions. Finally, the existing challenges and future research direction are further presented, aiming at practicing the PEMFC devices of the ultradurable Pt-based catalysts. [ABSTRACT FROM AUTHOR]

The utilization of nanoscale catalysts represents a valuable and promising strategy for augmenting catalytic performance while mitigating the reliance on expensive noble metals. Nevertheless, a significant knowledge gap persists regarding the intricate interplay between catalyst size, physical properties, and catalytic behavior in the context of the oxygen reduction reaction. In this study, the synthesis of precisely controlled palladium catalysts is presented, spanning a wide range from individual atoms to metal clusters and nanoparticles, followed by a comprehensive evaluation of their performance in acidic conditions. The results show a significant increase in H2O2 selectivity of up to 96% with decreasing catalyst size and strategic approaches are identified to eliminate unselective sites, facilitating the attainment of active and selective catalysts. The enhanced selectivity of the catalysts highlights the potential of single atom catalytic sites and can be adapted to improve the performance of various catalytic processes. [ABSTRACT FROM AUTHOR]

Over the past decades, the design of active catalysts has been the subject of intense research efforts. However, there has been significantly less deliberate emphasis on rationally designing a catalyst system with a prolonged stability. A major obstacle comes from the ambiguity behind how catalyst degrades. Several degradation mechanisms are proposed in literature, but with a lack of systematic studies, the causal relations between degradation and those proposed mechanisms remain ambiguous. Here, a systematic study of a catalyst system comprising of small particles and single atoms of Pt sandwiched between graphene layers, GR/Pt/GR, is studied to unravel the degradation mechanism of the studied electrocatalyst for oxygen reduction reaction(ORR). Catalyst suffers from atomic dissolution under ORR harsh acidic and oxidizing operation voltages. Single atoms trapped in point defects within the top graphene layer on their way hopping through toward the surface of GR/Pt/GR architecture. Trapping mechanism renders individual Pt atoms as single atom catalyst sites catalyzing ORR for thousands of cycles before washed away in the electrolyte. The GR/Pt/GR catalysts also compare favorably to state‐of‐the‐art commercial Pt/C catalysts and demonstrates a rational design of a hybrid nanoarchitecture with a prolonged stability for thousands of operation cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1. A unique heterometallic bond Co-Fe3C pair sites supported on N -doped graphite catalyst of CNCo-Fe3C was synthesized. • 2. Electronic structure tunning and synergistic effect between Co and Fe3C pair sites improved the catalytical activities. • 3. The catalyst showed an excellent half-wave potential of 0.90 V for ORR. • 4. The catalyst exhibited high cycling stability exceeding 400 h and high peak power density in Zn-air batteries. Newly emerging metal-based pair sites catalysts show great potential because they can provide more metal active centers with synergistic effect for green catalysis, compared with single site catalysts. However, both the synthesis and catalytic mechanisms of the pair sites catalyst with new structural features need to be developed vigorously to promote the desired chemical reactions, especially carbon-based metal catalysts for green energy storage and conversion devices. Herein, we constructed highly active Co-Fe 3 C pair sites on N-doped graphite catalyst (CNCo-Fe 3 C) by a two-step strategy, which have electron interactions of heterometallic atoms and can play better synergistic effect. X-ray absorption spectra and density functional theory (DFT) calculation further identify the presence of heterometallic active sites in the pair sites catalyst, resulting in electron redistribution and positive d-band center due to the electron interactions. The more positive d-band center model predicts the optimization of the adsorption energy of oxygen-containing intermediates, and reduces the energy barrier of the determining step. This further results in superior oxygen reduction reaction (ORR) performance with a half-wave potential of 0.90 V versus reversible hydrogen electrode (vs.RHE) and superior long-term stability for about 20 h with only 2.3 % decrease at 0.75 V vs.RHE in 0.1 M KOH solution. Additionally, it also shows significant peak power density of 124 mW cm−2 and prominent cycling stability performance exceeding 400 h at 5 mA cm−2 in the Zn-air battery (ZAB) test, which is higher than that of Pt/C catalyst. This work provides a new idea for the regulation of intrinsic activity of non-noble metal ORR catalysts through the synergistic effect of the pair sites. [ABSTRACT FROM AUTHOR]

The pivotal role of oxygen electrocatalysis in the realm of energy conversion and storage is unmistakably significant. In an endeavor to diminish the reliance on precious metals, the development of innovative catalysts exhibiting exceptional bifunctional durability and heightened activity for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has garnered considerable scholarly interest. Employing a straightforward two-step methodology, we have successfully synthesized uniformly distributed MnCo2O4 and CoMn2O4 nanoparticles of diminutive size, meticulously anchored onto carbon nanotubes (CNTs). Owing to the synergistic covalent interplay between the spinel oxide nanoparticles and CNTs, these nanocomposites demonstrate ORR activity on par with, and notably superior OER activity compared to, commercially available Pt/C catalysts. The onset potential of MnCo2O4-CNTs stands at 1.03 V vs. RHE, maintaining 95.76% of its initial current density following a 10,000-s chronoamperometry test. Furthermore, MnCo2O4-CNTs outperform CoMn2O4-CNTs in OER catalysis. The outstanding performance of MnCo2O4-CNTs is attributed to the higher content of Co3+ ions, which are active for the oxygen electrocatalysis. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) plays a pivotal role in electrochemical energy conversion and chemical production. Two‐electron (2e−) charge transfer for oxygen reduction is considered a promising method for the on‐site production of hydrogen peroxide (H2O2), which requires electrocatalysts with high H2O2 selectivity and ORR activity. Noble metal alloys (e.g., Pt‐Hg and Pd‐Hg) have been prevalent materials of choice due to their desirable intrinsic activity, but their scarcity and high cost seriously hinder their widespread application in practice. Self‐doped heteroatomic carbon‐based electrocatalysts, derived from abundant and inexpensive biomass, have emerged as attractive candidates for on‐site H2O2 production. This review summarizes the fundamentals and recent advances in H2O2 production via 2e− ORR, including basic catalytic mechanisms, the influence of electrolyte pH and porous structure of catalysts, selectivity assessment methods, determination of the cumulative H2O2 concentration, development of biomass‐derived carbon‐based catalyst, and electrochemical device designs. Current challenges and proposed opportunities are also presented with an emphasis on large‐scale electrochemical H2O2 synthesis. [ABSTRACT FROM AUTHOR]

Due to their great efficiency, low cost and pollution, and flexible fuel choice, solid oxide fuel cells (SOFCs) have been applied to energy conversion filed. However, one challenge for developing SOFCs is sluggish oxygen reduction reaction (ORR) rate. Herein, a series of Ruddlesden-Popper-type Sr 2.7 Pr 0.3 Fe 2– x Cu x O 7– δ (SPFC x) oxides are successfully synthesized and thoroughly assessed as potential SOFCs cathodes. Among all compositions, Sr 2.7 Pr 0.3 Fe 1 · 9 Cu 0 · 1 O 7– δ (SPFC10) possesses the best electrocatalysis performance and improved oxygen reduction kinetics, with the lowest polarization resistance (R p , 0.13 Ω cm2) at 700 °C. Cu-doping will contribute to improving oxygen transport kinetics, increasing oxygen vacancy concentration, and O 2p band centers close to the Fermi level, hence, enhancing the electrocatalysis performance. At 700 °C, the maximum output of the single cell with SPFC10 cathode is 704 mW cm−2. These results highlight a highly active SPFC10 cathode with Ruddlesden-Popper structure for SOFCs. [ABSTRACT FROM AUTHOR]

Replacing expensive platinum oxygen reduction reaction (ORR) catalysts with atomically dispersed single-atom catalysts is an effective way to improve the energy conversion efficiency of fuel cells. Herein, a series of single-atom catalysts, TM-N2O2Cx (TM=Sc-Zn) with TM-N2O2 active units, were designed, and their catalytic performance for electrocatalytic O2 reduction was investigated based on density functional theory. The results show that TM-N2O2Cx exhibits excellent catalytic activity and stability in acidic media. The eight catalysts (TM=Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) are all 4e− reaction paths, among which Sc-N2O2Cx, Ti-N2O2Cx, and V-N2O2Cx follow dissociative mechanisms and the rest are consistent with associative mechanisms. In particular, Co-N2O2Cx and Ni-N2O2Cx enable a smooth reduction in O2 at small overpotentials (0.44 V and 0.49 V, respectively). Furthermore, a linear relationship between the adsorption free energies of the ORR oxygen-containing intermediates was evident, leading to the development of a volcano plot for the purpose of screening exceptional catalysts for ORR. This research will offer a novel strategy for the design and fabrication of exceptionally efficient non-precious metal catalysts on an atomic scale. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal-organic framework (MOF) materials are promising precursors to transition into metal-nitrogen-carbon (M-N-C) catalysts with high catalytic performance. Pyrolysis is one of the most common ways to convert MOFs into electrically conductive MOF-derived M-N-C catalysts. General interests in using MOFs as precursors derive from changing the MOFs' porous structure into the carbonaceous frame. However, this favorable structure is not always maintained, with the reason unidentified since pyrolysis is currently still more of an empirical process. Understanding the pyrolysis processes leading to the transformation of MOFs into M-N-C catalysts is essential to broaden the development of MOF-derived catalysts. We report here complete chemical and morphological evolution and transformation of two commercial MOFs with the same sodalite topology, the ZIF-8 and ZIF-67, via series of in situ and ex situ techniques. The results reveal that the structure of the ZIF-67 collapses after the pyrolysis due to the graphitization of the carbon. Graphitization is catalyzed by the metallic cobalt particles formed when the temperature rose above 460 °C. The ZIF-8 was found to be a promising precursor material since most of the metal evaporates at the early stages and does not aggregate to form metal particles. However, the insufficient metal-N active sites and intrinsic low electrocatalysis availability of Zn limit the performance of the final catalyst. To maintain the porous structure of MOFs it is important to control the metal species and prevent them from agglomeration. Direct utilization of high-concentration MOFs as pyrolysis precursors is not recommended without rational design to inhibit agglomeration and graphitization that are undesirable for catalyst activity. [ABSTRACT FROM AUTHOR]

Exploring non-precious metal-based catalysts for oxygen reduction reactions (ORR) as a substitute for precious metal catalysts has attracted great attention in recent times. In this paper, we report a general methodology for preparing nitrogen-doped reduced graphene oxide (N–rGO)-supported, FeCo alloy (FeCo@N–rGO)-based catalysts for ORR. The structure of the FeCo@N–rGO based catalysts is investigated using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and transition electron microscopy, etc. Results show that the FeCo alloy is supported by the rGO and carbon that derives from the organic ligand of Fe and Co ions. The eletrocatalytic performance is examined by cyclic voltammetry, linear scanning voltammetry, Tafel, electrochemical spectroscopy impedance, rotate disc electrode, and rotate ring disc electrode, etc. Results show that FeCo@N–rGO based catalysts exhibit an onset potential of 0.98 V (vs. RHE) and a half-wave potential of 0.93 V (vs. RHE). The excellent catalytic performance of FeCo@N–rGO is ascribed to its large surface area and the synergistic effect between FeCo alloy and N–rGO, which provides a large number of active sites and a sufficient surface area. [ABSTRACT FROM AUTHOR]

ABSTRACTThe increasing demand for universal metrics in material development, particularly in the context of material informatics (MI), emphasises the need for catalytic activity metrics in fuel-cell research, specifically for the oxygen reduction reaction (ORR). In this study, we comprehensively analyse 10 Pt/C catalysts using a constant-current density protocol and correlate the ORR activity with the constant kinetic current density, thereby demonstrating the effectiveness of this alternative metric. Our results reveal that the constant-current density protocol offers a reliable and consistent assessment of catalyst performance, providing a promising alternative to existing evaluation methods. By evaluating various protocols for extracting activity metrics from the datasets of fuel-cell catalysts, we establish an optimised protocol that accounts for experimental and analytical errors in obtaining universal activity metrics. Conventional methods relying on data obtained at a fixed potential are inadequate due to variable contributions of mass transport among the different materials. Instead, we propose a protocol using a constant kinetic current density obtained by the anodic scans of voltammetry (in the range of below 8 μA cm−2, normalized by absolute electrochemically active surface area, or 6 × 10−21 A per active site) to minimise influence of un-compensated resistance and non-ORR current, enabling robust analysis of catalyst activity trends. Depending on the purpose of the MI prediction, multiple metrics obtained at different conditions such as cathodic scans are preferable, and thus a range of metrics should be deposited in a database with their metadata. This unbiased comparison of catalysts emphasises the importance of revisiting assessment protocols. The resulting database of universal activity metrics is expected to be valuable for accelerating catalyst development through the application of materials informatics.

To date, precisely tailoring local active sites of well‐defined earth‐abundant metal‐free carbon‐based electrocatalysts for attractive electrocatalytic oxygen reduction reaction (ORR), remains challenging. Herein, the authors successfully introduce a strain effect on active C–C bonds adjacent to edged graphitic nitrogen (N), which raises appropriate spin‐polarization and charge density of carbon active sites and kinetically favor the facilitation of O2 adsorption and the activation of O‐containing intermediates. Thus, the constructed metal‐free carbon nanoribbons (CNRs‐C) with high‐curved edges exhibit outstanding ORR activity with half‐wave potentials of 0.78 and 0.9 V in 0.5 m H2SO4 and 0.1 m KOH, respectively, overwhelming the planar one (0.52 and 0.81 V) and the N‐doped carbon sheet (0.41 and 0.71 V). Especially in acidic media, the kinetic current density (Jk) is 18 times higher than that of the planar one and the N‐doped carbon sheet. Notably, these findings show the spin polarization of the asymmetric structure by introducing a strain effect on the C–C bonds for boosting ORR. [ABSTRACT FROM AUTHOR]

The search of active, stable and low costs catalysts for the oxygen reduction reaction (ORR) is crucial for the extensive use of fuel cells and metal–air batteries. The development of metal-free catalysts, instead of platinum-based materials, can dramatically reduce the cost and increase the efficiency of these devices. In this work, carbon nanohorns (CNHs) have been covalently functionalized with N-containing heterocycles by the Tour reaction protocol and tested as metal-free ORR catalysts. The insertion of N-functionalities favored the complete reduction of oxygen to hydroxyl ions, while their absence favored the production of hydrogen peroxide. With the aim of determining the N-species responsible for the ORR activity of CNHs, photoemission and electrochemical measurements were combined. Results suggest that protonated N is the main species involved in the ORR process, facilitating the adsorption of oxygen, with their consequent reduction to neutral hydrogenated N species. [ABSTRACT FROM AUTHOR]

N -doped porous carbon monatomic iron catalysts (Fe SA /NPCs) obtained by polydopamine modification strategy were used for high efficiency oxygen reduction reactions and zinc-air batteries. [Display omitted] • Nitrogen doped porous carbon materials (NPCs) were prepared based on ZIF-L. • Stable hollow leaf-like morphology was maintained by coating PDA and nitrogen content was adjusted. • Fe SA was easily anchored on NPCs with luxuriant anchoring sites. • Fe SA /NPCs shows excellent electrochemical performance in oxygen reduction and zinc air batteries. Metal-nitrogen-carbon (M N C) catalysts, especially Fe N C catalysts, are considered promising candidates to replace Pt-based catalysts, but Fe N C catalysts still present certain challenges in controlled-synthesis and energy device applications. In this paper, through the modification strategy of poly-dopamine (PDA) to maintain 2D leaf morphology to obtain more active sites and further adjust the N content, N -doped porous carbon monatomic iron catalyst (Fe SA /NPCs) with rich-nitrogen content was prepared. XPS analysis showed that compared with C-ZIF-Fe, the contents of graphite nitrogen and pyridine nitrogen increased in Fe SA /NPCs. The hollow structure with defects and Fe-N 4 configuration of Fe single atom show more active sites for the catalyst, and positively promote the diffusion of reactants, oxygen exchange and electron transport, thus changing the reaction kinetics and promoting the improvement of ORR activity. Fe SA /NPCs electrocatalyst exhibits good half-wave potential and onset potential at low loading (E 1/2 = 0.93 V, E onset = 1.0 V). In addition, the methanol tolerance, stability and Tafel slope are better than those of commercial Pt/C. Excitingly, the zinc-air cell with Fe SA /NPCs as cathode material achieves a power density of 223 mW cm−2 and exhibits a long-term stability higher than 200 h. This work shows that nitrogen-doped porous carbon materials as well as iron monoatoms play important roles in improving electrocatalytic performance. [ABSTRACT FROM AUTHOR]

A Pt‐free cathode catalyst is necessary for proton‐exchange membrane fuel cell (PEMFC) to enable the widespread use of these environmentally friendly energy conversion devices at affordable price. Herein, a pyrolyzed electrospun carbon nanofibre (CNF) catalyst is prepared embedded with cobalt(II) phthalocyanine and iron(II) phthalocyanine compounds to provide the transition metal N4‐macrocyclic complex‐derived sites (MNX) possessing better electrocatalytic oxygen reduction reaction (ORR) activity. The physical characterisation showed the nanofibrous structure of catalyst with rough surface texture and considerable amount of N, Fe, and Co. The D−MN4−CNF−IL−A catalyst prepared using ionic liquid as a porogen displayed the best electrocatalytic activity for O2 electroreduction proceeding via 4e− pathway in 0.5 M H2SO4 electrolyte solution with the ORR onset and half‐wave potential of 0.83 and 0.71 V vs reversible hydrogen electrode (RHE), respectively. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction （ORR） is an important cathode reaction for metal-air batteries and proton exchange membrane fuel cells （PEMFCs）. It is of great significance to study non-noble metal catalysts with high activity and stability. In this paper， MIL-101（- Al-Fe） with hierarchical porous structure is innovatively used as the metal precursor template， and Fe-N-C catalysts with rich mesoporous structure are successfully prepared. Electrochemical test results show that Fe-N-C-MIL-900 shows the best ORR activity with half-wave potential of 0. 905 V in 0. 1 mol/L KOH electrolyte. The ORR electron transfer number of Fe-N-C-MIL-900 catalyst is 3. 98， and the H2O2 yield is less than 3%， demonstrating an obvious 4-electron ORR pathway. This work provides a new way to prepare hierarchically porous Fe-N-C catalysts with high ORR activity. [ABSTRACT FROM AUTHOR]

As an eco-friendly oxidant and energy carrier, H2O2 is used in various fields. The industrial production of H2O2 mostly depends on the large-scale anthraquinone oxidation processes with high costs. Electrocatalytic production of H2O2 has attracted attention as a renewable and cost-effective approach to replace traditional ones. With the recent development of oxygen reduction reaction (ORR) catalysts, remarkable progress in electrocatalysts for electrocatalytic H2O2 production by 2e- ORR has been reported. This review summarizes a detailed overview of the recent progress in 2e- ORR for H2O2 production with the mechanism and various efficient catalysts. The catalysts were divided into three parts: noble metal-based catalyst, non-noble metal-based catalyst, and non-metalbased catalyst. The influences of the catalytic activity and selectivity were also discussed. Finally, this review explores the prospects of electrocatalytic 2e- ORR for H2O2 synthesis and potential research directions for electrocatalysts. It aims to offer guidance in designing efficient 2e- ORR electrocatalysts and inspire further innovation in electrocatalytic H2O2 synthesis. [ABSTRACT FROM AUTHOR]

The advancement of efficient and stable single-atom catalysts (SACs) has become a pivotal pursuit in the field of proton exchange membrane fuel cells (PEMFCs) and metal-air batteries (MABs), aiming to enhance the utilization of clean and sustainable energy sources. The development of such SACs has been greatly significant in facilitating the oxygen reduction reaction (ORR) process, thereby contributing to the progress of these energy conversion technologies. However, while transition metal-based SACs have been extensively studied, there has been comparatively less exploration of SACs based on p-block main-group metals. In this study, we conducted an investigation into the potential of p-block main-group Sn-based SACs as a cost-effective and efficient alternative to platinum-based catalysts for the ORR. Our approach involved employing density functional theory (DFT) calculations to systematically examine the catalyst properties of Sn-based N-doped graphene SACs, the ORR mechanism, and their electrocatalytic performance. Notably, we employed an H atom-decorated N-based graphene matrix as a support to anchor single Sn atoms, creating a contrast catalyst to elucidate the differences in activity and properties compared to pristine Sn-based N-doped graphene SACs. Through our theoretical analysis, we gained a comprehensive understanding of the active structure of Sn-based N-doped graphene electrocatalysts, which provided a rational explanation for the observed high four-electron reactivity in the ORR process. Additionally, we analyzed the relationship between the estimated overpotential and the electronic structure properties, revealing that the single Sn atom was in a +2 oxidation state based on electronic analysis. Overall, this work represented a significant step towards the development of efficient and cost-effective SACs for ORR which could alleviate environmental crises, advance clean and sustainable energy sources, and contribute to a more sustainable future. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction is crucial in the cathode of fuel cells and metal–air batteries. Consequently, designing robust and durable ORR catalysts is vital to developing metal–air batteries and fuel cells. Metal–organic frameworks feature an adjustable structure, a periodic porosity, and a large specific surface area, endowing their derivative materials with a unique structure. In this study, F and N co-doped on the carbon support surface (Co/FN-C) via the pyrolysis of ZIF-67 as a sacrificial template while using Co/FN-C as the non-noble metal catalysts. The Co/FN-C displays excellent long-term durability and electrochemical catalytic performance in acidic solutions. These performance improvements are achieved because the CQDs alleviate the structural collapse during the pyrolysis of ZIF-67, which increases the active sites in the Co nanoparticles. Moreover, F- and N-doping improves the catalytic activity of the carbon support by providing additional electrons and active sites. Furthermore, F anions are redox-stable ligands that exhibit long-term operational stability. Therefore, the well-dispersed Co NPs on the surface of the Co/FN-C are promising as the non-noble metal catalysts for ORR. [ABSTRACT FROM AUTHOR]

A Co‐based zeolitic imidazolate framework (ZIF‐67) derived catalyst with ultrafine CoPt nanoalloy particles is designed via a two‐step space confinement method, to achieve a robust oxygen reduction reaction (ORR) performance for proton exchange membrane fuel cell (PEMFC). The core–shell structure of ZIF‐67 (core) and SiO2 (shell) is carefully adjusted to inhibit the agglomeration of Co nanoparticles. In the subsequent adsorption−annealing process, the in situ formed graphene shell on the surface of Co nanoparticles further protects metal particles from coalescence, leading to the ultrafine CoPt nanoalloy (average diameter is 2.61 nm). Benefitting from the high utilization of Pt metal, the mass activity of CoPt nanoalloy catalyst reaches 681.8 mA mgPt−1 at 0.9 V versus RHE according to the rotating disk electrode test in 0.1 m HClO4 solution. The CoPt nanoalloy‐based PEMFC provides a high maximum power density of 2.22 W cm−2 (H2/O2) and 0.923 W cm−2 (H2/air). Simultaneously, it shows good stability in the long‐time dynamic test at low humidity, due to the robust CoPt@graphene core–shell nanostructure. This work provides a viable strategy for designing Pt‐based nanoalloy catalysts with ultrafine metal particles and high stability. [ABSTRACT FROM AUTHOR]

In this study, ex situ and operando X‐ray absorption spectroscopy (XAS) is employed to shed light on structure and degradation mechanism of Fe‐based catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Ex situ XAS on pristine Fe0.07Zr0.93O2‐δ/C catalyst confirms the incorporation of Fe3+ in the ZrO2 structure and clearly exclude any significant presence of Fe−N−C‐type structures. The edge shift in data on in‐house aged samples demonstrates a mixed oxidation state of Fe (Fe3+ and Fe2+), consistent with Fe demetalation from the ZrO2 structure. Furthermore, a more symmetric coordination in the pre‐edge shape points towards the formation of oxidic Fe clusters upon aging. Fe demetalation is inferred also from the edge shift to higher energy (presence of Fe3+) in operando XAS data at 0.3 V, due to Fe phases not electrically polarizable/reducible at the applied voltage. Electrochemical data exclude any correlation between extent of aging and type of test, also for a commercial Fe−N−C catalyst by Pajarito Powder. The observed faster aging for Fe0.07Zr0.93O2‐δ compared to Fe−N−C is attributed to an improved mass transport to/from active sites, manifest also in very similar initial current densities at 0.3 V, despite much higher catalyst activity for Fe−N−C. [ABSTRACT FROM AUTHOR]

As a key role in hindering the large-scale application of fuel cells, oxygen reduction reaction has always been a hot issue and nodus. Aiming to explore state-of-art electrocatalysts, this paper reviews the latest development of nonmetallic catalysts in oxygen reduction reactions, including single atoms doped with carbon materials such as N, B, P or S and multi-doped carbon materials. Afterward, the remaining challenges and research directions of carbon-based nonmetallic catalysts are prospected. [ABSTRACT FROM AUTHOR]

PtCuCo nanoframes with internal structural support exhibit superior activity and durability for both of ORR and MOR. [Display omitted] • PtCuCo nanoframes with internal structural support were prepared via a facile approach. • The inner-positioned structural support can boost the structural robustness. • PtCuCo nanoframes showed outstanding activity and durability in both ORR and MOR. Developing highly durable and active catalysts with the morphology of structurally robust nanoframes toward oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in acidic environment is crucial but still a great challenge to completely achieve in a single material. Herein, PtCuCo nanoframes (PtCuCo NFs) with internal support structures as enhanced bifunctional electrocatalysts were prepared by a facile one-pot approach. PtCuCo NFs exhibited remarkable activity and durability for ORR and MOR owing to the ternary compositions and the structure-fortifying frame structures. Impressively, the specific/mass activity of PtCuCo NFs were 12.8/7.5 times as large as that of commercial Pt/C for ORR in perchloric acid solution. For MOR in sulfuric acid solution, the mass/specific activity of PtCuCo NFs was 1.66 A mg Pt -1/4.24 mA cm−2, which was 5.4/9.4 times as large as that of Pt/C. This work may provide a promising nanoframe material to develop dual catalysts for fuel cells. [ABSTRACT FROM AUTHOR]

Structural instability under working conditions is critical issue that restricts applications of perovskite O 2 catalysts in the field of solid oxide fuel cells. Inspired by plant leaves, a biomimetic ceramic catalyst with PrBaCo 2 O 5+δ 'mesophyll' and Gd 0.1 Ce 0.9 O 1.95 'epidermis' and 'vein' was successfully engineered in this work. The 'epidermis' reduces the polarization resistance of O 2 reduction reaction on catalyst surface by ∼24%, and the 'vein' reduces resistance of O2− transport through cathode layer by ∼65%. Moreover, this biomimetic catalyst increases output power density of the cell by 79% and reverses rapid decay trend of the cell with a 23% increase in power density during first 20 h followed by stabilization at 0.91 W cm−2 (at 750 °C and 0.7 V). This discovery provides new avenue for the development of high-performance O 2 catalysts with practical applications and enriches the scientific understanding of catalysis. [Display omitted] • Inspired by leaves, a biomimetic ceramic catalyst is proposed for SOFCs. • The 'epidermis' with a thickness of ∼5 nm reduces the resistance for ORR by ∼24%. • The in-situ grown 'vein' reduces the resistance of O2− transport by ∼65%. • The biomimetic catalyst has excellent oxygen catalytic activity and durability. • The biomimetic catalyst offers a new strategy for oxygen catalyst development. [ABSTRACT FROM AUTHOR]

The development of highly active and low-cost catalysts for use in oxygen reduction reaction (ORR) is crucial to many advanced and eco-friendly energy techniques. N-doped carbons are promising ORR catalysts. However, their performance is still limited. In this work, a zinc-mediated template synthesis strategy for the development of a highly active ORR catalyst with hierarchical porous structures was presented. The optimal catalyst exhibited high ORR performance in a 0.1 M KOH solution, with a half-wave potential of 0.89 V vs. RHE. Additionally, the catalyst exhibited excellent methanol tolerance and stability. After a 20,000 s continuous operation, no obvious performance decay was observed. When used as the air–electrode catalyst in a zinc–air battery (ZAB), it delivered an outstanding discharging performance, with peak power density and specific capacity as high as 196.3 mW cm−2 and 811.5 mAh gZn−1, respectively. Its high performance and stability endow it with potential in practical and commercial applications as a highly active ORR catalyst. Additionally, it is believed that the presented strategy can be applied to the rational design and fabrication of highly active and stable ORR catalysts for use in eco-friendly and future-oriented energy techniques. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the durability of the commercial Pt/C catalysts with platinum loading of 20% and 40% using two different accelerated durability tests, i.e., using Ar or O2 when bubbling the electrolyte during testing. The structural analysis of the changes in the morphology of the catalysts was performed by XRD and TEM as well as the assessment of the degradation degree of the catalysts using the values of the specific surface area and ORR activity, both, before and after the stress testing. Regardless of the stress testing conditions, the JM20 material was established to degrade ESA and the catalytic activity to a greater extent than JM40, which may be due to the structural and morphological features of the catalysts and their evolution during the stress testing under various conditions. The JM20 material has been reported to exhibit a greater degree of degradation when bubbling the electrolyte with oxygen during the stress testing compared to argon, which may be explained by a different mechanism of degradation for the catalyst with the predominant oxidation of the carbon support, leading to a different nature of the distribution of the platinum nanoparticles over the surface of the carbon support, according to results that have estimated the number of nanoparticle intersections. [ABSTRACT FROM AUTHOR]