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Single‐atom catalysts (SACs) have received significant interest for optimizing metal atom utilization and superior catalytic performance in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). In this study, we investigate a range of single‐transition metal (STM1 = Sc1, Ti1, V1, Cr1, Mn1, Fe1, Co1, Ni1, Cu1, Zr1, Nb1, Mo1, Ru1, Rh1, Pd1, Ag1, W1, Re1, Os1, Ir1, Pt1, and Au1) atoms supported on graphyne (GY) surface for HER/OER and ORR using first‐principle calculations. Ab initio molecular dynamics (AIMD) simulations and phonon dispersion spectra reveal the dynamic and thermal stabilities of the GY surface. The exceptional stability of all supported STM1 atoms within the H1 cavity of the GY surface exists in an isolated form, facilitating the uniform distribution and proper arrangement of single atoms on GY. In particular, Sc1, Co1, Fe1, and Au1/GY demonstrate promising catalytic efficiency in the HER due to idealistic ΔGH* values via the Volmer‐Heyrovsky pathway. Notably, Sc1 and Au1/GY exhibit superior HER catalytic activity compared to other studied catalysts. Co1/GY catalyst exhibits higher selectivity and activity for the OER, with an overpotential (0.46 V) comparable to MoC2, IrO2, and RuO2. Also, Rh1 and Co1/GY SACs exhibited promising electrocatalysts for the ORR, with an overpotential of 0.36 and 0.46 V, respectively. Therefore, Co1/GY is a versatile electrocatalyst for metal‐air batteries and water‐splitting. This study further incorporates computational analysis of the kinetic potential energy barriers of Co1 and Rh1 in the OER and ORR. A strong correlation is found between the estimated kinetic activation barriers for the thermodynamic outcomes and all proton‐coupled electron transfer steps. We establish a relation for the Gibbs free energy of intermediates to understand the mechanism of SACs supported on STM1/GY and introduce a key descriptor. This study highlights GY as a favorable single‐atom support for designing highly active and cost‐effective versatile electrocatalysts for practical applications. [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]

The advancement of economical and readily available electrocatalysts for the oxygen reduction reaction (ORR) holds paramount importance in the advancement of fuel cells and metal‐air batteries. Recently, 2D non‐metallic materials have obtained substantial attention as viable alternatives for ORR catalysts due to their manifold advantages, encompassing low cost, ample availability, substantial surface‐to‐volume ratio, high conductivity, exceptional durability, and competitive activity. The augmented ORR performances observed in metal‐free 2D materials typically arise from heteroatom doping, defects, or the formation of heterostructures. Here, the authors delve into the realm of electrocatalysts for the ORR, pivoting around metal‐free 2D materials. Initially, the merits of metal‐free 2D materials are explored and the reaction mechanism of the ORR is dissected. Subsequently, a comprehensive survey of diverse metal‐free 2D materials is presented, tracing their evolutionary journey from fundamental concepts to pragmatic applications in the context of ORR. Substantial importance is given on the exploration of various strategies for enhancing metal‐free 2D materials and assessing their impact on inherent material performance, including electronic properties. Finally, the challenges and future prospects that lie ahead for metal‐free 2D materials are underscored, as they aspire to serve as efficient ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

The unique properties of solid acid electrolytes, in particular CsH2PO4, are in many ways ideal for fuel cell operation. However, the technology is constrained by high cathode overpotentials. Here a simplified cathode geometry is employed to obtain the fundamental electrochemical parameters (exchange current density and charge transfer coefficient) describing the oxygen reduction reaction (ORR) at the CsH2PO4‐Pt‐gas interface. The parameters are incorporated into a 1D model of the voltage–current characteristics of realistic SAFC cathodes, which reproduced the measured polarization behavior of such cathodes without recourse to fitting adjustable parameters. Following this validation, the model is utilized to evaluate the impact of changes to cathode properties, microstructure, and operating conditions. Of these, the charge transfer coefficient, measured to have a value of ≈0.6 for ORR on Pt in the SAFC cathode environment, is found to have the greatest impact on power output. Nevertheless, even without material modifications, a combination of microstructural and operational modifications are identified with projected performance metrics meeting Department of Energy targets (0.8 V at 300 mA cm−2, and peak power density of 1 W cm−2), albeit at high Pt loadings. However, the analysis indicates that truly meaningful advances will likely necessitate the discovery of alternative ORR catalysts. [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]

The shortage and unevenness of fossil energy sources are affecting the development and progress of human civilization. The technology of efficiently converting material resources into energy for utilization and storage is attracting the attention of researchers. Environmentally friendly biomass materials are a treasure to drive the development of new‐generation energy sources. Electrochemical theory is used to efficiently convert the chemical energy of chemical substances into electrical energy. In recent years, significant progress has been made in the development of green and economical electrocatalysts for oxygen reduction reaction (ORR). Although many reviews have been reported around the application of biomass‐derived catalytically active carbon (CAC) catalysts in ORR, these reviews have only selected a single/partial topic (including synthesis and preparation of catalysts from different sources, structural optimization, or performance enhancement methods based on CAC catalysts, and application of biomass‐derived CACs) for discussion. There is no review that systematically addresses the latest progress in the synthesis, performance enhancement, and applications related to biomass‐derived CAC‐based oxygen reduction electrocatalysts synchronously. This review fills the gap by providing a timely and comprehensive review and summary from the following sections: the exposition of the basic catalytic principles of ORR, the summary of the chemical composition and structural properties of various types of biomass, the analysis of traditional and the latest popular biomass‐derived CAC synthesis methods and optimization strategies, and the summary of the practical applications of biomass‐derived CAC‐based oxidative reduction electrocatalysts. This review provides a comprehensive summary of the latest advances to provide research directions and design ideas for the development of catalyst synthesis/optimization and contributes to the industrialization of biomass‐derived CAC electrocatalysis and electric energy storage. [ABSTRACT FROM AUTHOR]

Trillion of cigarette butts are annually littered without being recycled. This work aims at valorizing the whole cigarette butts and their components (paper, filter and tobacco) into Fe‐Nx‐C electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The pristine wastes were pyrolyzed at 450 °C, activated with KOH at 700 °C, blended with iron phthalocyanine (FePc) precursor, and heat‐treated at 600 °C to produce a robust Fe‐Nx‐C material with ORR active units. The effect of the cigarette components on the final electrocatalytic activity was evaluated by thoroughly investigating the surface chemistry with XPS. The electrocatalysts displayed similar results among the different components in both media due to comparable surface chemistry, especially concerning the nitrogen functional groups. The highest performance was obtained in alkaline where the electrocatalysts from whole cigarettes and paper (CIGF_450 and CIGPF_450) showed an E1/2 of 0.89 V vs RHE, slightly larger than that of Pt/C with 40 wt % of Pt, which encouraged to replace Pt‐based electrocatalysts in alkaline fuel cells. [ABSTRACT FROM AUTHOR]

Understanding the electrode materials' surface is of fundamental importance for catalytic studies as most electrochemical reactions take place there. Although several operando techniques have been used to monitor the electrocatalytic process, real‐time imaging techniques for observing the surface change on electrode materials are still a challenge and limited to a few stable catalytic systems. Herein, the quasi‐in situ electrochemical transmission electron microscopy (TEM) was carried out to track the morphological and local structure evolution during the oxygen reduction reaction (ORR) on manganese dioxide (MnO2) for the first time. The α‐MnO2 nanorods exhibit comparable ORR electrocatalytic activity (half‐wave potential, E1/2: 0.83 vs. 0.85 V vs. RHE; diffusion‐limiting current density, Jd: −5.46 vs. −5.52 mA cm−2) and better methanol tolerance than Pt/C. An electrochemical TEM chip assembled with a three‐electrode system was used to perform the electrochemical experiments similar to typical testing procedures. The ex situ and quasi‐in situ TEM images consistently showed that MnO2 nanorods had undergone surface roughening, and lattice expansion with 0.97% and 1.97% in the a and c‐axis, respectively as ORR proceeded. The quasi‐in situ electrochemical TEM fills the gap between ex situ characterization and operando spectroscopies and deepens the mechanistic understanding of electrocatalytic processes. [ABSTRACT FROM AUTHOR]

In the past decade, remarkable progress has been made in advancing heterogeneous single‐atom catalysts (SACs), propelled by their extraordinary properties such as unique activities, high selectivity, and efficient metal utilization. In contrast to their nanoparticle counterparts, SACs showcase distinct advantages, yet they are not exempt from limitations. A primary constraint lies in their relatively low metal content and lack of ensemble sites, potentially impacting overall catalytic activity. Stability concerns also arise, as isolated metal atoms may be prone to aggregation, oxidation, and other structural changes. To surmount these challenges, there is a burgeoning exploration of synergies between SACs and other active species, such as single atoms, atomic clusters, or nanoparticles. This approach holds promise for augmenting the efficiency of complex catalytic reactions. However, a systematic examination of their integration and potential synergy has been notably absent. This review strives to fill that gap by comprehensively exploring key interactions, complementary effects, and bifunctional roles of single atoms, atomic clusters and nanoparticles when combined in different compositions and configurations, especially for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) applications. Additionally, the review sheds new light on the underlying catalytic mechanisms by offering insights through specific case studies. In particular, it emphasizes the dynamic nature of each active species and their interactions within these innovative catalytic entities, specifically in the context of heterogeneous electrocatalytic processes, backed by compelling in situ and operando evidence. Concluding the discussion, the review addresses the current challenges and provides a glimpse into the prospects of these integrated catalytic systems in the future. The contents can serve as a valuable guide for the design of advanced catalysts, promoting the deliberate combination and synergy of binary or multiple active species to further advance the field of catalysis with a clear roadmap and easy assessments. [ABSTRACT FROM AUTHOR]

The quest for alternatives to Pt as an oxygen reduction electrocatalyst, possessing high activity, stability, and abundant reserves, holds great significance for H2/O2 fuel cells. Recently, metal‐nitrogen‐carbon (M‐N‐C) electrocatalysts have garnered substantial attention as promising substitutes. These electrocatalysts not only exhibit well‐defined structures but also offer the flexibility to adjust the central metal atoms and coordination atoms. It is beneficial in elucidating the active sites during the catalytic process and in the design of highly active electrocatalysts. In this review, the real active site of M‐N‐C electrocatalyst‐driven ORR is investigated in depth by in situ characterization techniques such as X‐ray absorption spectroscopy, Raman spectroscopy, Fourier‐transform infrared spectroscopy. It′s worth noting that the catalytic activity of M‐N‐C electrocatalysts originates from the dynamic evolution of electrocatalyst structure. Subsequently, we review various synthetic strategies, including the wet chemistry method, spatial confinement, and template‐assisted method, aimed at the rational design of M‐N‐C electrocatalysts. Moreover, recent progresses of M‐N‐C electrocatalysts with varying configurations, encompassing single‐atom, and double‐atom electrocatalysts are discussed, Finally, summary and perspectives on the development of M‐N‐C are provided. [ABSTRACT FROM AUTHOR]

Iron‐nitrogen‐carbon (Fe‐N‐C) catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) have seriously been hindered by their poor ORR performance of Fe‐N‐C due to the low active site density (SD) and site utilization. Herein, we reported a melamine‐assisted vapor deposition approach to overcome these hindrances. The melamine not only compensates for the loss of nitrogen caused by high‐temperature pyrolysis but also effectively etches the carbon substrate, increasing the external surface area and mesoporous porosity of the carbon substrate. These can provide more useful area for subsequent vapor deposition on active sites. The prepared 0.20Mela‐FeNC catalyst shows a fourfold higher SD value and site utilization than the FeNC without the treatment of melamine. As a result, 0.20Mela‐FeNC catalyst exhibits a high ORR activity with a half‐wave potential (E1/2) of 0.861 V and 12‐fold higher ORR mass activity than the FeNC in acidic media. As the cathode in a H2‐O2 PEMFCs, 0.20Mela‐FeNC catalyst demonstrates a high peak power density of 1.30 W cm−2, outstripping most of the reported Fe‐N‐C catalysts. The developed melamine‐assisted vapor deposition approach for boosting the SD and utilization of Fe‐N‐C catalysts offers a new insight into high‐performance ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

The synthesis of efficient and stable Pt alloy catalysts is a major challenge for the commercialization of PEMFC. Herein, we report a PtCo/C(N) electrocatalyst prepared by Na2CO3‐assisted urea liquid‐phase deposition strategy as an efficient cathodic oxygen reduction reaction electrocatalyst, and test its activity and stability in a rotating disc electrode and a single‐cell. The membrane electrode prepared with PtCo/C(N)‐800 °C catalyst has an output voltage of 0.652 V at 2 A/cm2 and a maximum power density of 1.501 W/cm2, which are 36 mV and 81 W/cm2 higher than those of commercial Pt/C catalyst, respectively. In addition, the mass activity and half‐wave potential of PtCo/C(N)‐800 °C are 2.44 times and 50 mV higher than those of commercial Pt/C, respectively. After 5000 voltammetric cycles, its mass activity and half‐wave potential only lose 35 A/gPt and 9 mV, respectively. XPS results show that the binding energy of Pt 4f is positively shifted relative to Pt/C‐TKK, and the d‐band center of Pt decreases, leading to weak chemical interaction between the oxygen‐containing intermediate and the surface of the electrocatalyst, which is conducive to the improvement of the ORR activity and stability of the catalyst. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have been utilized as the ideal candidates to preciously construct electrocatalysts. However, the highly ordered degree of COFs renders the catalytic centers closely stacked, which limits the utilization efficiency of catalytic sites. Herein, we have first constructed dangling and staggered‐stacking aldehyde (–CHO) from [4 + 3] COFs as catalytic centers for 2e− oxygen reduction reaction (ORR). The new catalytic COFs have unreacted dangling ‐CHO out of the COFs' planes, which are more easily exposed in electrolytes than the sites in the frameworks. More importantly, these –CHO adopt staggered stacking models, and thus provide larger space for mass transport than those with eclipsed stacking models. In addition, by tuning the triratopic linkers in the COFs, the catalytic properties are well modulated. The optimized COF shows high selectivity and activity for 2e− ORR, with H2O2 selectivity of 91%, and mass activity of 12.2 A g−1, respectively. The theoretical calculation further reveals the higher activity for the pyridine‐contained B18C6‐PTTA‐COF due to the promoted binding ability of the intermediate OOH* at the carbon in dangling –CHO. This work provides us with a new insight into designing electrocatalysts based on COFs. [ABSTRACT FROM AUTHOR]

Developing efficient metal‐nitrogen‐carbon (M‐N‐C) single‐atom catalysts for oxygen reduction reaction (ORR) is significant for the widespread implementation of Zn‐air batteries, while the synergic design of the matrix microstructure and coordination environment of metal centers remains challenges. Herein, a novel salt effect‐induced strategy is proposed to engineer N and P coordinated atomically dispersed Fe atoms with extra‐axial Cl on interlinked porous carbon nanosheets, achieving a superior single‐atom Fe catalyst (denoted as Fe‐NP‐Cl‐C) for ORR and Zn‐air batteries. The hierarchical porous nanosheet architecture can provide rapid mass/electron transfer channels and facilitate the exposure of active sites. Experiments and density functional theory (DFT) calculations reveal the distinctive Fe‐N2P2‐Cl active sites afford significantly reduced energy barriers and promoted reaction kinetics for ORR. Consequently, the Fe‐NP‐Cl‐C catalyst exhibits distinguished ORR performance with a half‐wave potential (E1/2) of 0.92 V and excellent stability. Remarkably, the assembled Zn‐air battery based on Fe‐NP‐Cl‐C delivers an extremely high peak power density of 260 mW cm−2 and a large specific capacity of 812 mA h g−1, outperforming the commercial Pt/C and most reported congeneric catalysts. This study offers a new perspective on structural optimization and coordination engineering of single‐atom catalysts for efficient oxygen electrocatalysis and energy conversion devices. [ABSTRACT FROM AUTHOR]

Electrocatalysis enables the industrial transition to sustainable production of chemicals using abundant precursors and electricity from renewable sources. De‐centralized production of hydrogen peroxide (H2O2) from water and oxygen of air is highly desirable for daily life and industry. We report an effective electrochemical refinery (e‐refinery) for H2O2 by means of electrocatalysis‐controlled comproportionation reaction (2H2O+O2→2H2O2), feeding pure water and oxygen only. Mesoporous nickel (II) oxide (NiO) was used as electrocatalyst for oxygen evolution reaction (OER), producing oxygen at the anode. Conducting polymer poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) drove the oxygen reduction reaction (ORR), forming H2O2 on the cathode. The reactions were evaluated in both half‐cell and device configurations. The performance of the H2O2 e‐refinery, assembled on anion‐exchange solid electrolyte and fed with pure water, was limited by the unbalanced ionic transport. Optimization of the operation conditions allowed a conversion efficiency of 80%. [ABSTRACT FROM AUTHOR]

The Fe–N–C material represents an attractive oxygen reduction reaction electrocatalyst, and the FeN4 moiety has been identified as a very competitive catalytic active site. Fine tuning of the coordination structure of FeN4 has an essential impact on the catalytic performance. Herein, we construct a sulfur‐modified Fe–N–C catalyst with controllable local coordination environment, where the Fe is coordinated with four in‐plane N and an axial external S. The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN4 active site. The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons. With the above characteristics, the adsorption and desorption of the reactants at FeN4 active sites are optimized, thus promoting the oxygen reduction reaction activity. This work explores the key point in electronic configuration and coordination environment tuning of FeN4 through S doping and provides new insight into the construction of M–N–C‐based oxygen reduction reaction catalysts. [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]

Nowadays, the depletion of non‐renewable energy sources has become a prominent issue, and environmental concerns such as air pollution stemming from vehicle emissions have reached a critical stage. In this manuscript, we introduce a novel approach for the fabrication of Pt/C catalysts on a large scale, utilizing a simple, rapid, and continuous pipeline microwave synthesis method. Moreover, we incorporate a heating treatment process in an N2−H2 (5 % H2) environment to enhance the activity and durability of the catalyst. The synthesized Pt/C‐400 catalyst demonstrates an impressive electrochemical active surface area of 103.2 m2/gpt and a mass‐specific activity of 315 mA/mg at a half‐wave potential of 0.9 V. Following 30000 cycles of Pt attenuation testing and 30000 cycles of carrier attenuation testing, the Pt/C‐400 catalyst exhibits a remarkable retention rate of 75 %. Furthermore, based on single‐cell testing, the Pt/C‐400 catalyst achieves a voltage of 0.606 V at a current density of 2000 mA/cm2, surpassing the performance of other Pt/C catalysts discussed in this article. This study presents an efficient and practical method for large‐scale synthesis of high‐performance and durable catalysts. The findings hold significant implications for the commercialization of Proton Exchange Membrane Fuel Cells and contribute to addressing the pressing need for sustainable energy solutions. [ABSTRACT FROM AUTHOR]

The high overpotential of oxygen reduction reaction (ORR) prevents the wide commercialization of fuel cells and metal‐air batteries. To accelerate the reaction rate, porous electrocatalysts draw attention to obtain a higher specific surface area. However, the effect of micropores on ORR kinetics has not been understood because of the non‐uniform pore sizes, length, and tortuosity of practical electrocatalysts. In this study, we evaluate ORR activity in a micropore using platinum model electrodes with arrays of cylindrical pores with a uniform pore diameter of 1.8 nm. The model electrodes having pore lengths of 45, 100, and 380 nm are fabricated, and their ORR performances are examined by electrochemical measurements and numerical simulations in 0.1 mol dm−3 KOH aqueous solution. The intrinsic ORR activity of the micropore is successfully obtained with the electrode having a pore length of 45 nm, where oxygen transport resistance in the micropore has little effect on ORR. It is found that the intrinsic ORR activity of the micropore is higher than that of a planar Pt surface. X‐ray photoelectron spectroscopy and CO stripping voltammetry indicate a downshift of the d‐band center, which can be the origin of the high intrinsic ORR activity. [ABSTRACT FROM AUTHOR]

To reduce the costs of proton exchange membrane fuel cells, the amount of Pt necessary to drive efficient oxygen reduction reaction (ORR) should be minimized. Particle nanostructuring, (nano‐)alloying, and metal‐doping can yield higher activities per Pt mass through tailoring catalysts owning a high number of active sites and precise electronic properties. In this work, the atom‐precise [NBnMe3]2[Co8Pt4C2(CO)24] (Co8Pt4) cluster is encapsulated and activated in a zeolitic imidazolate framework (ZIF)‐8, which unlocks the access to defined, bare Pt−Co nanoclusters, Co8±xPt4±yNC@ZIF‐8, for the fabrication of highly active ORR catalysts. Upon controlled C‐interfacing and ZIF‐8‐digestion, Co‐doped Pt NPs (Pt27Co1) with a homogenous and narrow size distribution of (1.1±0.4) nm are produced on Vulcan® carbon. Restructuring of the Pt27Co1/C catalyst throughout the ORR measurement was monitored via high‐angle annular dark field‐scanning transmission electron microscopy and X‐ray photoelectron spectroscopy. The measured ORR mass activity of (0.42±0.07) A mgPt−1 and the specific activity of (0.67±0.06) mA cmECSA−2 compare favourably with the catalyst obtained by direct C‐interfacing the pristine Co8Pt4 cluster and with state‐of‐the‐art Pt/C reference catalysts. Our results demonstrate the potential of ZIF‐8‐mediated Pt−Co NP synthesis toward devising ORR catalysts with high Pt‐mass activity. [ABSTRACT FROM AUTHOR]

As the world faces an escalating energy crisis, the necessity of adopting alternative energy sources becomes increasingly evident. Despite challenges, the imperative to prioritise these eco‐friendly alternatives remains paramount in paving the way for a more sustainable and resilient future for our planet and its inhabitants. The pursuit of sustainable energy sources has brought the oxygen reduction reaction (ORR) into the spotlight as a crucial cathodic reaction in energy‐converting systems, notably fuel cells (FCs). These FCs hold tremendous promise in providing an eco‐friendly and efficient energy supply. However, the widespread implementation of FCs is hindered by their reliance on expensive and scarce noble metal catalysts, such as platinum (Pt), which pose economic and environmental challenges. Hence, this work reports the preparation, characterisation (FTIR, XPS, SEM and EDX) and application of four composites based on doped‐carbon materials (CM) and on the Wells‐Dawson POM salt K6⋅α‐[P2W12Mo6O62] ⋅ 19H2O (P2W12Mo6@MWCNT_N8, P2W12Mo6@MWCNT_N6, P2W12Mo6@MWCNT_S6, and P2W12Mo6@GF_S6) as ORR electrocatalysts in alkaline medium (pH=13). The successful doping of the carbon materials with nitrogen (N) and sulphur (S) and the incorporation of the polyoxometalate were verified through comprehensive structural characterisation. Overall, P2W12Mo6@MWCNT_N8 exhibited favourable onset potentials of 0.84 V vs. RHE, highlighting its high catalytic activity. Additionally, the catalyst showed excellent tolerance to methanol crossover, retaining 91 % of initial current, which is crucial for practical fuel cell applications. Furthermore, the P2W12Mo6@MWCNT_N8 catalyst showed commendable stability, retaining 81 % of its initial current after 36000 seconds at an operating potential of E=0.46 V vs. RHE. These encouraging results denote the significant potential of this electrocatalyst in advancing sustainable energy conversion technologies. [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]

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]

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]

Traditional synthesis methods of platinum‐rare earth metal (Pt‐RE) alloys usually involve harsh conditions and high energy consumption because of the low standard reduction potentials and high oxophilicity of RE metals. In this work, a one‐step strategy is developed by rapid Joule thermal‐shock (RJTS) to synthesize Pt‐RE alloys within tens of seconds. The method can not only realize the regulation of alloy size, but also a universal method for the preparation of a family of Pt‐RE alloys (RE = Ce, La, Gd, Sm, Tb, Y). In addition, the energy consumption of the Pt‐RE alloy preparation is only 0.052 kW h, which is 2–3 orders of magnitude lower than other reported methods. This method allows individual Pt‐RE alloy to be embedded in the carbon substrate, endowing the alloy catalyst excellent durability for oxygen reduction reaction (ORR). The performance of alloy catalyst shows negligible decay after 20k accelerated durability testing (ADT) cycles. This strategy offers a new route to synthesize noble/non‐noble metal alloys with diversified applications besides ORR. [ABSTRACT FROM AUTHOR]

High entropy oxides (HEOs) offer great potential as catalysts for oxygen electrocatalytic reactions in alkaline environments. Herein, a novel synthesis approach to prepare (FeCrCoMnZn)3O4‐δ high entropy spinel oxide in a vacuum atmosphere, with the primary objective of introducing oxygen vacancies into the crystal structure, is presented. As compared to the air‐synthesized counterpart, the (FeCrCoMnZn)3O4‐δ with abundant oxygen vacancies demonstrates a low (better) bifunctional (BI) index of 0.89 V in alkaline media, indicating enhanced electrocatalytic oxygen catalytic activity. Importantly, (FeCrCoMnZn)3O4‐δ demonstrates outstanding long‐term electrochemical and structural stability. When utilized as electrocatalysts in the air cathode of Zn‐air batteries, the vacuum atmosphere synthesized (FeCrCoMnZn)3O4‐δ catalysts outperform the samples treated in an air atmosphere, displaying superior peak power density, specific capacity, and cycling stability. These findings provide compelling evidence that manipulating the synthesis atmosphere of multi‐component oxides can serve as a novel approach to tailor their electrochemical performance. [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]

Electroreduction of oxygen driven by renewable electricity holds significant promise for the sustainable production of value‐added hydrogen peroxide (H2O2). While water is a desirable source of protons and electrons for this reaction, its low gas solubility often limits the transportation of gas molecules and consequently leads to large concentration overpotential, resulting in unsatisfactory energy efficiencies. Herein, a facile and effective strategy to promote the 2e− oxygen reduction reaction (ORR) through microenvironment modulation is presented. In this work, it is specifically aimed to facilitate oxygen transportation at the reaction interface, particularly at high rates. To achieve this, hydrophobic polytetrafluoroethylene (PTFE) particles are introduced into a catalyst layer containing amino‐group‐functionalized carbon nanotube (CNT‐NH2) as the ORR catalyst for H2O2 production. As a result, the PTFE‐modified CNT‐NH2‐based gas‐diffusion electrode (GDE) substantially improves ORR activity. At 100 mA cm−2, the PTFE‐modified CNT‐NH2 achieves a high cathodic energy efficiency of 92%, 1.5 times higher than the pristine CNT‐NH2‐based GDE (63%). Detailed kinetic analysis reveals that this enhanced ORR performance is indeed due to the enhanced oxygen transportation induced by the persistent hydrophobic microenvironment created by the PTFE‐modified catalyst layer, reducing the concentration overpotential during ORR. [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]

Single‐atomic transition metal–nitrogen–carbon (M–N–C) structures are promising alternatives toward noble‐metal‐based catalysts for oxygen reduction reaction (ORR) catalysis involved in sustainable energy devices. The symmetrical electronic density distribution of the M─N4 moieties, however, leads to unfavorable intermediate adsorption and sluggish kinetics. Herein, a Fe–N–C catalyst with electronic asymmetry induced by one nearest carbon vacancy adjacent to Fe─N4 is conceptually produced, which induces an optimized d‐band center, lowered free energy barrier, and thus superior ORR activity with a half‐wave potential (E1/2) of 0.934 V in a challenging acidic solution and 0.901 V in an alkaline solution. When assembled as the cathode of a Zinc–air battery (ZAB), a peak power density of 218 mW cm−2 and long‐term durability up to 200 h are recorded, 1.5 times higher than the noble metal‐based Pt/C+RuO2 catalyst. This work provides a new strategy on developing efficient M–N–C catalysts and offers an opportunity for the real‐world application of fuel cells and metal–air batteries. [ABSTRACT FROM AUTHOR]

Electrochemical oxygen reduction reaction (ORR) is an attractive and alternative route for the on‐site production of hydrogen peroxide (H2O2). The electrochemical synthesis of H2O2 in neutral electrolyte is in early studying stage and promising in ocean‐energy application. Herein, N‐doped carbon materials (N‐Cx) with different N types are prepared through the pyrolysis of zeolitic imidazolate frameworks. The N‐Cx catalysts, especially N‐C800, exhibit an attracting 2e− ORR catalytic activity, corresponding to a high H2O2 selectivity (≈95%) and preferable stability in 0.5 m NaCl solution. Additionally, the N‐C800 possesses an attractive H2O2 production amount up to 631.2 mmol g−1 h−1 and high Faraday efficiency (79.8%) in H‐type cell. The remarkable 2e− ORR electrocatalytic performance of N‐Cx catalysts is associated with the N species and N content in the materials. Density functional theory calculations suggest carbon atoms adjacent to graphitic N are the main catalytic sites and exhibit a smaller activation energy, which are more responsible than those in pyridinic N and pyrrolic N doped carbon materials. Furthermore, the N‐C800 catalyst demonstrates an effective antibacterial performance for marine bacteria in simulated seawater. This work provides a new insight for electro‐generation of H2O2 in neutral electrolyte and triggers a great promise in ocean‐energy application. [ABSTRACT FROM AUTHOR]

A novel recycling process of the conductive agent in spent lithium iron phosphate batteries is demonstrated. Wet chemistry is applied in recovering lithium and iron phosphate, and the filter residue is calcined with a small amount of recovered iron phosphate in N2 at 900 °C to form a FeNP‐codoped carbon catalyst, which exhibits a low half‐wave potential and excellent durability for oxygen reduction. When applied in a rechargeable Zn–air battery, the power density can reach 80 mW cm−2. [ABSTRACT FROM AUTHOR]

Due to their low cost, accessibility of resources, and improved stability and durability, carbon‐based nanomaterials have attracted significant attention as cathode materials for oxygen reduction reactions. These materials also exhibit intrinsic physical and electrochemical features. However, their potential for use in fuel cells is constrained by low ORR activity and slow kinetics. Carbon nanomaterials can be functionalized and doped with heteroatoms to change their morphologies and generate a large number of oxygen reduction active sites to lessen the problems. Doping the carbon lattice with heteroatoms like N, S, and P and functionalizing the carbon structure with −OCH3, −F, −COO−, −O− are two of these modifications that can change specific properties of the carbon nanomaterials like expanding interlayer distance, producing a large number of active sites, and enhancing oxygen reduction activity. When compared to pristine carbon‐based nanomaterials, these doped and functionalized carbon nanomaterials, including their composites, exhibit accelerated rate performance, outstanding stability, and higher methanol tolerance. This article summarizes the most recent developments in heteroatom‐doped and functionalized carbon‐based nanomaterials, covering different synthesis approaches, characterization methods, electrochemical performance, and oxygen reduction reaction mechanisms. As cathode materials for fuel cell technologies, the significance of heteroatom co‐doping and transition metal heteroatom co‐doping is also underlined. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cell technology is gaining significant attention as a promising alternative for decarbonizing automotive vehicles. At the heart of hydrogen fuel cell technology is the electrode, composed of catalysts, supports, binders, and pores, which facilitates the half‐cell reactions and often governs the efficiency of fuel cells. Over the last decade, scientists have made great strides in discovering catalyst, support, and binder materials featuring unique nanostructures and compositions that significantly enhance the efficiency of those devices. While innovations must continue, we must not overlook how these materials are put together to form an electrode and how it impacts the overall efficiency. This perspective article discusses the urgent need for developing alternative electrodes for designing next generation hydrogen fuel cells. [ABSTRACT FROM AUTHOR]

The correlation between lattice strain induced by metal dispersion into grain and the cathodic overpotential is studied for increasing oxygen‐dissociation activity and improving power density of solid oxide fuel cells (SOFC) at decreased temperature. Pt or Au dispersion in Pr1.90Ni0.71Cu0.21Ga0.05O4+d (PNCG) is prepared and the 3D tensile strain is successfully induced after sintering by a mismatch in thermal expansion coefficient. Due to higher hardness and melting temperature, Pt dispersion into bulk of PNCG introduces larger tensile strain than that by Au at the same amount. In particular, at 1 mol% Pt dispersion, large tensile strain of 0.67% is induced. Overpotential of 1 mol% Pt‐PNCG cathode is 8 times smaller (35 mV) than that of PNCG (270 mV) at 800 °C and 300 mA cm−2, and it is found that the cathodic overpotential of PNCG is decreased with tensile strain on both Pt and Au dispersion. This cathodic activity enhancement appears to be related with the increased diffusivity of oxide ion in PNCG. In this study, cathodic overpotential is more significantly influenced by the induced tensile strain comparing with the intrinsic catalytic activity of the dispersed metal. [ABSTRACT FROM AUTHOR]

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]

Rational design and construction of highly efficient nonprecious electrocatalysts for oxygen reduction and alcohols oxidation reactions (ORR, AOR) are extremely vital for the development of direct oxidation alkaline fuel cells, metal‐air batteries, and water electrolysis system involving hydrogen and value‐added organic products generation, but they remain a great challenge. Herein, a bifunctional electrocatalyst is prepared by anchoring CuS/NiS2 nanoparticles with abundant heterointerfaces and sulfur vacancies on graphene (Cu1Ni2‐S/G) for ORR and AOR. Benefiting from the synergistic effects between strong interfacial coupling and regulation of the sulfur vacancies, Cu1Ni2‐S/G achieves dramatically enhanced ORR activity with long term stability. Meanwhile, when ethanol is utilized as an oxidant for AOR, an ultralow potential (1.37 V) at a current density of 10 mA cm−2 is achieved, simultaneously delivering a high Faradaic efficiency of 96% for ethyl acetate production. Cu1Ni2‐S/G also exhibits catalytic activity for other alcohols electrooxidation process, indicating its multifunctionality. This work not only highlights a viable strategy for tailoring catalytic activity through the synergetic combination of interfacial and vacancies engineering, but also opens up new avenues for the construction of a self‐driven biomass electrocatalysis system for the generation of value‐added organic products and hydrogen under ambient conditions. [ABSTRACT FROM AUTHOR]

Much attention has been paid to the development of high‐performance electrocatalytic reactions by exploiting the plasmonic properties of noble metal nanoparticles. In this study, ultrathin Pt layers with different coverage ratios were prepared on plasmonic octahedral Au nanoparticles (NPs) by underpotential deposition (UPD) of Cu followed by redox replacement with Pt. The effect of the Cu UPD cycle on the deposited Cu and redox‐substituted Pt layers on octahedral Au NPs was investigated to evaluate the electrocatalytic activity of Pt‐decorated octahedral NPs for the oxygen reduction reaction (ORR). By varying the number of cycles of Cu UPD and Pt replacement, the coverage by the Pt layer on the Au NPs could be easily controlled. The resulting Pt‐coated octahedral Au NPs exhibited three times higher specific activity for ORR than commercial Pt/C nanocatalysts due to the deposited Pt layer reflecting the {111} plane of the core. The ORR activity of Pt‐coated octahedral Au NPs could be enhanced by photoexcitation with monochromatic LED irradiation, and the increase in enhancement factor was even greater when irradiated with a wavelength that could efficiently excite the localized surface plasmon resonance (LSPR) of the NPs. Analysis shows that this improvement is due to improved diffusion of oxygen to the electrode. [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]

Zn‐N‐C possesses the intrinsic inertia for Fenton‐like reaction and can retain robust durability in harsh circumstance, but it is often neglected in oxygen reduction reaction (ORR) because of its poor catalytic activity. Zn is of fully filled 3d104s2 configuration and is prone to evaporation, making it difficult to regulate the electronic and geometric structure of Zn center. Here, guided by theoretical calculations, five‐fold coordinated single‐atom Zn sites with four in‐plane N ligands is constructed and one axial O ligand (Zn‐N4‐O) by ionic liquid‐assisted molten salt template method. Additional axial O not only triggers a geometry transformation from the planar structure of Zn‐N4 to the non‐planar structure of Zn‐N4‐O, but also induces the electron transfer from Zn center to neighboring atoms and lower the d‐band center of Zn atom, which weakens the adsorption strength of *OH and decreases the energy barrier of rate determining step of ORR. Consequently, the Zn‐N4‐O sites exhibit improved ORR activity and excellent methanol tolerance with long‐term durability. The Zn‐air battery assembled by Zn‐N4‐O presents a maximum power density of 182 mW cm−2 and can operate continuously for over 160 h. This work provides new insights into the design of Zn‐based single atom catalysts through axial coordination engineering. [ABSTRACT FROM AUTHOR]

The design of highly efficient promoters for the oxygen reduction reaction (ORR) is an important challenge in the large‐scale distribution of proton exchange membrane (PEM) fuel cells. Hygroscopic cerium oxide (CeO2) is here proposed as co‐catalyst in combination with Pt. Physical chemical characterizations, by means of X‐ray diffraction, vibrational spectroscopy, morphological and thermal analyses, were carried out, demonstrating high water affinity of the synthesized CeO2 nanoparticles. Composite catalysts (i. e., Pt : CeO2 1 : 0.5 and 1 : 1 wt:wt), were studied by either rotating disk electrode (RDE) and fuel cell tests performed at 80 °C and 110 °C. Interestingly, the cell adopting the Pt : CeO2 1 : 0.5 catalyst enabled the achievement of high power densities reaching ∼80 and ∼35 mW cm−2 under low relative humidity and high temperatures. This result demonstrates that tuning material surface properties (e. g. oxygen vacancies) could significantly boost the electrochemical performance of cathodes as a combined result of optimized water retention and improved ORR kinetic. [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]

Highly efficient and low‐cost Pt‐Co/CAB bimetallic cathode electrocatalysts were synthesized for hydrogen‐based proton exchange membrane fuel cell (PEMFC) using three different types of solvent, namely, dimethyl sulphoxide (DMSO), dimethylformamide (DMF), and ethylene glycol (EG). The physical characterization of synthesized cathode electrocatalysts Pt‐Co/CAB‐DMSO, Pt‐Co/CAB‐DMF and Pt‐Co/CAB‐EG was performed by scanning electron microscope–energy‐dispersive X‐ray (SEM–EDX), X‐ray diffraction (XRD), and transmission electron microscopy (TEM) techniques, whereas the electrochemical investigation of all three Pt‐Co/CAB electrocatalysts was performed by CV and EIS studies. The synthesized Pt‐Co/C‐EG electrocatalyst produced the highest power density of 19.61 mW/cm2 at a room temperature of 33°C. The power density increased to 26.11 mW/cm2, that is, 133%, when the cell operating temperature was raised from 33 to 70°C. The excellent performance of the Pt‐Co/CAB‐EG cathode electrode proves that it can be recommended as a commercial electrocatalyst for PEMFC cathode. In addition, the EG/EG was identified as the best solvent for the synthesis of Pt‐Co/CAB cathode electrocatalysts. [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]

Platinum‐based ordered alloy catalysts possess higher intrinsic activity in oxygen reduction reactions (ORR). High‐temperature annealing during ordered alloy formation frequently results in larger nanoparticles, and the strategy for obtaining ordered alloys at 600 °C is still undefined. Herein, an ordered Fe‐doped PtCo catalyst (O‐PtCoFe/C) with a size of sub‐4 nm was prepared at 600 °C derived from PtFe@CoO. CoO can generate oxygen vacancies by H2 reduction, lowering the atomic migration barrier and serving as a protective layer to inhibit nanoparticle migration. Experimental analyses showed the formation of O‐PtCoFe/C and electron‐rich Pt atoms due to Pt, Co, and Fe, which was advantageous for ORR performance. The mass activity of the prepared catalyst for ORR was 382.8 mA mgPt−1, which is 5.4 times greater than Pt/C. After 10000 potential cycles, the half‐wave potential was only negatively shifted by 10 mV. In PEMFC (proton exchange membrane fuel cells) tests, the O‐PtCoFe/C showed only 3 % decay after 3000 cycles, whereas the Pt/C showed a significant loss (18.4 %). This work provides an effective method for preparing ordered PtCo alloys for fuel cell cathode catalysts at 600 °C. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cell (PEMFC) is one of the most promising energy conversion devices with high efficiency and zero emission. However, oxygen reduction reaction (ORR) at the cathode is still the dominant limiting factor for the practical development of PEMFC due to its sluggish kinetics and the vulnerability of ORR catalysts under harsh operating conditions. Thus, the development of high‐performance ORR catalysts is essential and requires a better understanding of the underlying ORR mechanism and the failure mechanisms of ORR catalysts with in situ characterization techniques. This review starts with the introduction of in situ techniques that have been used in the research of the ORR processes, including the principle of the techniques, the design of the in situ cells, and the application of the techniques. Then the in situ studies of the ORR mechanism as well as the failure mechanisms of ORR catalysts in terms of Pt nanoparticle degradation, Pt oxidation, and poisoning by air contaminants are elaborated. Furthermore, the development of high‐performance ORR catalysts with high activity, anti‐oxidation ability, and toxic‐resistance guided by the aforementioned mechanisms and other in situ studies are outlined. Finally, the prospects and challenges for in situ studies of ORR in the future are proposed. [ABSTRACT FROM AUTHOR]

Metal‐free carbon‐based catalysts have attracted significant attention owing to their unique electronic structure and excellent catalytic activity for the oxygen reduction reaction (ORR). Recently, several heteroatom‐doped carbon catalysts with ORR performances comparable with those of state‐of‐the‐art Pt‐based catalysts have been reported. However, the intrinsic influence of heteroatoms on the catalytic activity has not been thoroughly investigated to date. This paper reports porous carbons co‐doped with N and S, prepared using an ion‐exchange resin and tetramethylammonium cations, with an onset potential of 0.93 V versus reversible hydrogen electrode (RHE) and a half‐wave potential of 0.79 V versus RHE. First‐principles calculations reveal that the change in the atomic charge caused by the co‐doping of N and S is important for inducing a high ORR activity. This paper presents a rational synthetic strategy for metal‐free catalysts and provides fundamental insights into their electrocatalysis. [ABSTRACT FROM AUTHOR]

Developing efficient oxygen reduction reaction (ORR) catalyst is essential for the practical application of Zn‐air batteries (ZABs). In this contribution, we develop a novel zeolitic imidazolate framework (ZIF)‐mediated strategy to anchor Co species on N‐doped carbon nanorods for efficient ORR. Featuring ultrahigh N‐doping (10.29 at.%), monodisperse Co nanocrystal decoration, and well‐dispersed Co‐Nx functionalization, the obtained Co‐decorated N‐doped carbon nanorods (Co@NCNR) exhibit a decent ORR performance comparable to commercial Pt/C in alkaline media. Aqueous ZABs have been assembled using Co@NCNR as the cathode catalyst. The assembled ZABs manifest high initial open‐circuit voltage as well as high energy density. In addition, the Co@NCNR also demonstrates ideal ORR performance in quasi‐solid‐state ZABs. [ABSTRACT FROM AUTHOR]