Cathodic Oxygen Reduction Reaction Research Articles

Pyrazine‐linked Iron‐coordinated Tetrapyrrole Conjugated Organic Polymer Catalyst with Spatially Proximate Donor‐Acceptor Pairs for Oxygen Reduction in Fuel Cells

AbstractNitrogen‐coordinated iron (Fe−N4) materials represent the most promising non‐noble electrocatalysts for the cathodic oxygen reduction reaction (ORR) of fuel cells. However, molecular‐level structure design of Fe−N4 electrocatalyst remains a great challenge. In this study, we develop a novel Fe−N4 conjugated organic polymer (COP) electrocatalyst, which allows for precise design of the Fe−N4 structure, leading to unprecedented ORR performance. At the molecular level, we have successfully organized spatially proximate iron‐pyrrole/pyrazine (FePr/Pz) pairs into fully conjugated polymer networks, which in turn endows FePr sites with firmly covalent‐bonded matrix, strong d‐π electron coupling and highly dense distribution. The resulting pyrazine‐linked iron‐coordinated tetrapyrrole (Pz−FeTPr) COP electrocatalyst exhibits superior performance compared to most ORR electrocatalysts, with a half‐wave potential of 0.933 V and negligible activity decay after 40,000 cycles. When used as the cathode electrocatalyst in a hydroxide exchange membrane fuel cell, the Pz−FeTPr COP achieves a peak power density of ≈210 mW cm−2. We anticipate the COP based Fe−N4 catalyst design could be an effective strategy to develop high‐performance catalyst for facilitating the progress of fuel cells.

Development of conducting Bi0.5Sr0.5FeO3–δ-Gd0.1Ce0.9O2–δ composite cathodes for IT-SOFCs

Decreasing the working temperature of solid oxide fuel cells (SOFCs) to 400 °C–600 °C is a primary concern for current fuel cell research. Unfortunately decrease in operating temperatures leads to increase in cathode polarization, which deteriorates electrochemical activity of the cathode for oxygen reduction reaction (ORR). Consequently, the search of new cathode materialsis one of the critical bottle-neck towards the development of intermediate-temperature SOFCs (IT-SOFCs). In this study, we have successfully synthesized Bi0.5Sr0.5FeO3-δ and Bi0.5Sr0.5FeO3-δ-Gd0.1Ce0.9O2-δ((1-x) BSFO-xGDC) composite cathodes with varying compositions (x = 50, 40, 30, and 20wt%). The crystal structure, microstructure, electrochemical properties and performance stability of these composite cathodes have been comprehensively evaluated using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Our results demonstrate that the introduction of Gd0.1Ce0.9O2-δ( GDC) has a significant impact on the electrochemical performance of the composite cathodes. Among the different compositions studied, the cathode with a composition of x = 70 wt% exhibits particularly promising electrochemical properties. The electrode resistance polarization of 70BiSFO-30GDC is 0.39 Ωcm2 and 0.8 Ωcm2 for symmetrical and half-cell at 600 °C. The preliminary results of this study reveal that the 70BiSFO-30GDC composite cathode demonstrates remarkable ORR activity. Further investigations and comprehensive analyses are warranted to validate and explore the full potential of the 70BiSFO-30GDC composite cathode in the context of SOFC applications.

Atomic-Level Regulation of Cu-Based Electrocatalyst for Enhancing Oxygen Reduction Reaction: From Single Atoms to Polymetallic Active Sites.

The slow kinetics of cathodic oxygen reduction reactions (ORR) in fuel cells and the high cost of commercial Pt-based catalysts limit their large-scale application. Cu-based single-atom catalysts (SACs) have received increasing attention as a promising ORR catalyst due to their high atom utilization, high thermodynamic activity, adjustable electronic structure, and low cost. Herein, the recent research progress of Cu-based catalysts is reviewed from single atom to polymetallic active sites for ORR. First, the design and synthesis method of Cu-based SACs are summarized. Then the atomic-level structure regulation strategy of Cu-based catalyst is proposed to improve the ORR performance. The different ORR catalytic mechanism based on the different Cu active sites is further revealed. Finally, the design principle of high-performance Cu-based SACs is proposed for ORR and the opportunities and challenges are further prospected.

Preparation of Pr, Co co-doped BaFeO3–δ-based nanofiber cathode materials by electrospinning

The solid oxide fuel cell (SOFC) is considered promising technology that directly converts the chemical energy stored in the fuel into electrical energy. However, the undesired oxygen reduction reaction (ORR) activity and stability of the cathode have hindered its commercialization. In this work, a series of Pr-doped PrxBa1-xFe0.8Co0.2O3-δ (x = 0∼0.3) nanofibers and powder cathode materials with excellent performance are synthesized by electrospinning and sol-gel methods, respectively. The influence of different Pr doping amounts on the nanofiber morphology, phase structure, thermal stability and electrochemical properties of BaFe0.8Co0.2O3-δ (BFCO) nanofibers cathode materials were investigated. Compared the microstructures and electrochemical performance of Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber and powders prepared by different methods. The partial substitution of Pr for Ba (doping of a few of Pr) can effectively eliminate the BFCO hexagonal phase and induce the transformation to the cubic phase. The content of oxygen vacancies was significantly increased as well as the cathode ORR activity was well enhanced. In addition, we demonstrated by DRT that oxygen adsorption is the rate-limiting step at the cathode. Among them, Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber has the best electrochemical performance and the highest oxygen surface exchange kinetics performance. The area-specific resistance (ASR) of Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber is 0.1416 Ω cm2 at 700 °C. When the peak power density (PPD) of the YSZ-NiO/YSZ/GDC/PBCF1–F single cell shows 0.787 W cm−2, an anode-supported fuel cell with Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber demonstrates excellent stability after 100 h of long-term stability test. Electrospinning technology is an effective method to prepare high-performance cathodes, and Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber cathodes are expected to be high-performance cathode materials for IT-SOFCs.

Hofmann-type MOFs derived intermetallic L10-PtFe/NC electrocatalysts for boosting oxygen reduction reaction

Intermetallic electrocatalysts have demonstrated significant potential in facilitating the cathodic oxygen reduction reaction (ORR) in fuel cells with enhanced activity and durability. However, it is still an enormous challenge to the facile synthesis of Pt-based intermetallic catalysts with uniform size and high ordering degree. Here, we innovatively fabricate the core-shell structured L10-PtFe intermetallics with Pt skins supported on N-doped porous carbon matrix through one-step pyrolysis of PtFe Hofmann-type metal-organic frameworks (denoted as L10-PtFe/NC). Under the constraints of the porous structure and cyano-ligand bonding, most Fe atoms are alloyed with Pt to form uniform-ordered PtFe intermetallics, while some Fe atoms are atomically dispersed in the carbon framework to form FeNx moieties. Notably, a series of intermetallic PtFe catalysts with different ordering degrees are successfully constructed by adjusting the pyrolysis temperature, which verified that the increase of ordering degree is beneficial to promote the electrocatalytic performance. In particular, the ordered L10-PtFe/NC-800 exhibits superb ORR activity with both mass and specific activities, which are 2.7-folds higher than those of commercial Pt/C. Moreover, after an accelerated durability test, L10-PtFe/NC-800 retains over 90 % mass activity. This work provides a promising approach for the development of efficient Pt-based intermetallic electrocatalysts for fuel cells.

Illuminating Oxygen Reduction Reaction Kinetics in High Temperature Polymer Electrolyte Membrane Fuel Cells Using EIS

High Temperature Polymer Electrolyte Membrane Fuel Cells (HTPEMFCs) commercialization, is impeded by the sluggish, power intensive and elusive cathodic Oxygen Reduction Reaction (ORR) kinetics. In this work we provide solid experimental evidence that the simple three elementary step Dissociative Adsorption (DA) pathway, with two intermediate species (Oad and OHad), can accurately describe the steady state (IV) and the Electrochemical Impedance Spectra (EIS) response of a HTPEMFC. Deconvoluted EIS outlined the important role of Intrinsic Kinetic Inertia, which dominated both EIS and polarization resistance. The Degree of Rate Control (DRC) analysis, identified the O2(g) dissociative adsorption as the rate limiting step. Finally, Transition State Theory (TST) allowed the extraction and analysis of ORR energetics, demonstrating that the high ORR overpotential losses originate from the combined strength of both kinetically and thermodynamically imposed barriers, due to the high bonding strength of Oad on Pt and the high activation energy of O2(g) adsorption.

Synergistic Effect of Aluminum Lactate and Sodium Molybdate on Freshwater Corrosion of Carbon Steel Under Irradiation

In this study, a corrosion inhibitor suitable for the corrosion inhibition of primary containment vessels at the Fukushima Daiichi Nuclear Power Station is investigated. Considering the internal environment of the primary containment vessels, the corrosion inhibitor should inhibit the freshwater corrosion of carbon steel under irradiation and should not come under effluent standards in Japan. Herein, a corrosion inhibitor was devised by combining Al lactate and Na molybdate that met the above conditions, and its corrosion mechanism was investigated. It was found that 0.75 mM Al lactate and 0.25 mM Na molybdate were the most inhibitive to the corrosion of carbon steel. As Al lactate has never been reported as a corrosion inhibitor for metallic materials, it could be developed as a novel corrosion inhibitor in this study. The corrosion inhibitor inhibited the freshwater corrosion of carbon steel even under gamma irradiation of 200 Gy/h. Al and molybdate ions in the solution formed a metal cation layer on carbon steel with few defects and without iron. This metal cation layer inhibited both the cathodic oxygen reduction reaction and the anodic iron dissolving reaction, thereby enhancing the corrosion protection of carbon steel in freshwater.

Density functional theory investigation of the role of Fe doped in boron carbide nanotube as an electro-catalyst for oxygen reduction reaction in fuel cells

A critical issue in enhancing the performance of polymer electrolyte membrane fuel cells (FCs) is the slow kinetics of the cathodic oxygen reduction reaction (ORR). The development of electrocatalysts with selectivity toward the four-electron (4e) pathway and high electrochemical activity to ORR reaction is important for fuel cell applications. Within the present study, it was found that boron carbide nanotube (BC3NT) is an encouraging ORR-EC based on density functional theory computations. In the pristine BC3NT, the neighboring B atoms with positive charges on the surface of the material surface were incapable of providing active sites for the dissociation of O. However, the ORR catalytic activity of BC3NT improved under the ligand effect due to the replacement of Fe atom, where there was a slight over-potential that was similar or lower than that of platinum (111), which demonstrated its superior ORR activity. The results suggest that BC-based materials are considered promising for ORR catalysis and for designing highly efficient ORR-ECs as alternatives to platinum-based catalysts.

Constructing Nitrogen-Doped Carbon Hierarchy Structure Derived from Metal-Organic Framework as High-Performance ORR Cathode Material for Zn-Air Battery.

The development of efficient and low-cost catalysts for cathodic oxygen reduction reaction (ORR) in Zn-air battery (ZAB) is a key factor in reducing costs and achieving industrialization. Here, a novel segregated CoNiPt alloy embedded in N-doped porous carbon with a nanoflowers (NFs)-like hierarchy structure is synthesized through pyrolyzing Hofmann-type metal-organic frameworks (MOFs). The unique hierarchical NFs structure exposes more active sites and facilitates the transportation of reaction intermediates, thus accelerating the reaction kinetics. Impressively, the resulting 15% CoNiPt@C NFs catalyst exhibits outstanding alkaline ORR activity with a half-wave potential of 0.93V, and its mass activity is 7.5 times higher than that of commercial Pt/C catalyst, surpassing state-of-the-art noble metal-based catalysts. Furthermore, the assembled CoNiPt@C+RuO2 ZAB demonstrates a maximum power density of 172mW cm-2 , which is superior to that of commercial Pt/C+RuO2 ZAB. Experimental results reveal that the intrinsic ORR mass activity is attributed to the synergistic interaction between oxygen defects and pyrrolic/graphitic N species, which optimizes the adsorption energy of the intermediate species in the ORR process and greatly enhances catalytic activity. This work provides a practical and feasible strategy for synthesizing cost-effective alkaline ORR catalysts by optimizing the electronic structure of MOF-derived catalysts.

Calcined cobalt-chelated, N-containing poly(methylenediphenyl urea) as an ORR cathode catalyst

A Co(II)-chelated poly(methylenediphenyl urea) (Co-PMDUr) is successfully prepared from the condensation reaction between 4,4′-methylene diphenyl diamine (MDA) and 4,4′-methylene diphenyl diisocyanate (MDI) in the presence of cobalt chloride (CoCl2). After polymerization, the Co(II) ions chelate to the polymer backbones by coordinating with the urea units' carbonyl or amine groups, confirmed by the FTIR spectra. The Co-PMDUr converts to Co, N-codoped carbon network (Co-N-Cs) via calcination in nitrogen and ammonia gases. X-ray diffraction and Raman spectra of Co-N-Cs reveal the formation of highly conjugated carbon structure, similar to that of carbon nanotube (CNT) or carbon nano-ring (CNR) seen in SEM and TEM micropictures. Except for cobalt nitride (CoN), other nitrogen-related groups like pyridinic, graphitic, and pyrrolic-Ns are present in the Co-N-Cs, and higher temperature calcination creates more pyridinic-Ns and Co-Ns. The BET analysis reveals high surface area and micro-pores for Co-N-Cs. The current-voltage curves of Co-N-Cs show a significant oxygen reduction reaction (ORR) at ca. 0.8 V and a higher limited reduction current density (LRCD) than commercial platinum carbon (Pt/C) catalyst in the O2-saturated KOH(aq). The average number of electrons (n) transferred during ORR is close to 4. The Tafel slope of the Co-N-C catalyst is similar to Pt/C. The max. Current density (Imax) and max. Power density (Pmax) of the single cell with Co-N-C cathodes is comparable to that of Pt/C with less decadency during long-term redox reaction testing.

Corrosion of Reinforced A630-420H Steel in Direct Contact with NaCl Solution.

The deterioration of reinforced concrete structures in marine environments presents multiple problems due to the premature degradation of reinforced steel. This work aimed to study the corrosion of reinforced A630-420H steel when exposed to a 0.5 M NaCl solution. Although this carbon steel is the most widely used material for reinforced concrete structures in Chile, there is limited research on its resistance to corrosion when in contact with saline solutions. The electrochemical reactions and their roles in the corrosion rate were studied using linear sweep voltammetry, weight loss, scanning electron microscopy, and X-ray diffraction techniques. This analysis is unique as it used the superposition model based on mixed potential theory to determine the electrochemical and corrosion parameters. The outcomes of this study show that A630-420H steel has a higher corrosion rate than those of the other commercial carbon steels studied. This fact can be attributed to the competition between the cathodic oxygen reduction reaction and hydrogen evolution reaction, which also depends on the environmental conditions, exposure time, stabilization of the corrosion products layer, and presence of chloride ions. Additionally, the results under mechanical stress conditions show a brittle fracture of the corrosion product oriented longitudinally in the direction of the bend section, where the presence of pores and cracks were also observed. The corrosion products after corrosion were mainly composed of magnetite and lepidocrocite oxide phases, which is in concordance with the electrochemical results.

Towards Improved Cold-Start Capability of PEFCs: Patterned Gas Diffusion Layers

Polymer electrolyte fuel cells (PEFCs) are electrochemical energy converters with high efficiency and zero pollutant emissions. The unassisted cold-start of PEFCs at -30 °C is one of the major challenges for automotive applications due to the freezing of supercooled water generated by the cathodic oxygen reduction reaction (ORR). Once triggered by the nucleus in cathode gas diffusion layers (GDLs), ice propagates through the active area, leading to oxidant gas blockage and cold-start failure1.The cold-start capability of PEFCs can be improved by preventing ice propagation, especially in GDLs. In our previous work2,3, after the GDLs were segmented by polytetrafluoroethylene (PTFE) into two regions, the PEFC kept operating for another 30 minutes after the first freezing event in one region. Nevertheless, the PTFE barrier limited the active area as well as the heat and electric conductivity of PEFCs. In contrast, patterned GDLs allow water cluster separation without the abovementioned limitations. The improvement of water management and cell performance under technical operating conditions was demonstrated4. Yet, the cold-start capability with patterned GDL needs to be further investigated.This work studies the effect of patterned GDLs on the water-ice phase transition and cold-start capability of PEFCs. First, non-isothermal differential scanning calorimetry (DSC) measurements were conducted to determine the onset freezing temperature distribution of supercooled water in patterned GDLs, taking into account various properties such as coating load and pattern size. It was observed that independent freezing events occurred in patterned GDLs in all cycles, as several freezing/exothermic peaks can be seen in Figure 1b. In contrast, ice propagated immediately in untreated GDL, as only one freezing peak was observed in all cycles (Figure 1d). By computing the integral of the heat flux curve, we obtained the corresponding cumulative icing ratio over 60 cycles, as presented in Figures 1a and 1c. The effective prevention of ice propagation is only observed in patterned GDLs. Second, to assess the cold-start capability, statistical isothermal cold-start measurements were conducted using a 4.4 cm2 differential cell, with the cell temperature held at -7.5 °C, -10 °C, -15 °C, and 20 °C. In summary, nonconcurrent freezing events in patterned GDLs indicate that the use of patterned GDLs significantly improved the cold-start capability of PEFCs under isothermal subfreezing conditions.The findings of this work enhance the understanding of the cold-start dependence on the GDL and contribute to the development of unassisted freeze-start technology for PEFCs and the expansion of PEFCs applications. Figure 1

Atomically Dispersed Pt and Fe Sites and Pt-Fe Nanoparticles for Durable Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) as a promising clean energy conversion technology have gained considerable attention. However, the high cost and low durability of Pt-based nanocatalysts for the cathodic oxygen reduction reaction (ORR) hinder the wide adoption of this technology.1 Despite great efforts on the development of advanced Pt-based catalysts to improve the Pt utilization and mass activity toward ORR, 2-3 their high activities/durability measured in liquid cells have rarely been realized in fuel cells. On the other hand, carbon-based Pt group metal (PGM)-free ORR electrocatalysts consisting of highly dispersed transition-metal single atoms in nitrogen-coordinated carbon surfaces (Me-N-C) are promising candidates to replace Pt.4 Unfortunately, the poor durability of Me-N-C has limited their practical applications.5 Some early studies6-7 shown that Me-N-C as a support for Pt-based electrocatalyst could improve the stability of the latter.Herein, we report a hybrid electrocatalyst (denoted as Pt-Fe-N-C) consisting of Pt-Fe alloy nanoparticles on highly dispersed Pt and Fe single atoms in a nitrogen-doped carbon support (Figure 1a). The multiple types of active sites result in not only a 3.7 times higher Pt mass activity, but also excellent durability. The performance loss is negligible even after 100,000 potential cycles (Figure 1b), and no current drop is observed at 0.6 V in a fuel cell test with an ultra-low Pt loading (0.015 mgPt cm−2) in the cathode. The morphology and structure of Pt-Fe-N-C catalyst after 100,000 cycles in a fuel cell were further analyzed. Abundant single atoms were still uniformly distributed on the carbon support. No noticeable aggregation of Pt-Fe nanoparticles was observed. Most of particle size was smaller than 4 nm, a solid PtFe@Pt core-shell structure was formed. Around 7% large size particles formed a percolated structure.This work highlights the importance of the synergistic effects among different active sites in hybrid electrocatalysts and provide an alternative way to design more active and durable low-PGM electrocatalysts for fuel cells and other electrochemical devices.This work was supported by the Research Grant Council (HKUST C6011-20G) and Shenzhen Science and Technology Innovation Committee (SGDX2019081623340748).Figure 1. (a) Scanning transmission electron microscope image (the spots in the blue and red dashed circles are ascribed to the Fe and Pt single atoms, respectively). (b) H2/O2 fuel cell polarization (solid symbols and left axis) and power density (hollow symbols and right axis) plots of the Pt-Fe-N-C cathode before cycling (blue) and after 100,000 potential cycles (red) between 0.6 and 0.95 V. Figure 1

Surface-structure tailoring of Dendritic PtCo nanowires for efficient oxygen reduction reaction

Platinum-based alloy nanowire catalysts demonstrates great promise as electrocatalysts to facilitate the cathodic oxygen reduction reaction (ORR) of proton exchange membrane fuel cells (PEMFCs). However, it is still challenge to further improve the Pt atom utilization of Pt based nanowires featuring inherent structural stability. Herein, a new structure of PtCo nanowire with nanodendrites was developed using CO-assistance solvent thermal method. The dendrite structure with an average length of about 7 nm are characterized by a Pt-rich surface and the high-index facets of {533}, {331} and {311}, and grows from the ultra-fine wire structure with an average diameter of about 3 nm. PtCo nanowires with nanodendrites developed in this work shows outstanding performance for ORR, in which its mass activity of 1.036 A/mgPt is 5.76 times, 1.74 times higher than that of commercial Pt/C (0.180 A/mgPt) and PtCo nanowires without nanodendrites (0.595 A/mgPt), and its mass activity loss is only 18% under the accelerated durability tests (ADTs) for 5k cycles. The significant improvement is attributed to high exposure of active sites induced by the dendrite structure with Pt-rich surface with the high-index facets and Pt-rich surface. This structure may provide a new idea for developing novel 1D Pt based electrocatalysts.

A new and robust MnCo1.9Sb0.1O4 spinel cathode for proton-conducting solid oxide fuel cells

As a cathode material for proton-conducting SOFCs (H–SOFCs), a novel MnCo1.9Sb0.1O4 (MCSO) spinel material was suggested. The MCSO material was effectively produced, and it demonstrated excellent phase stability at elevated temperatures and chemical stability against CO2 and H2O. Doping Sb into the MnCo2O4 (MCO) allowed for enhanced proton diffusion and surface exchange, as evidenced by electrical conductivity relaxation tests. In addition, an oxygen-vacancy-rich surface was developed for the MCSO material, resulting in the possibility of a high cathode oxygen reduction reaction activity. The MCSO material was examined in the H–SOFC application, and the fuel cell with an MCSO cathode attained a high power density of 1380 mW cm−2 at 700 °C. At 700 °C, the cell employing the Sb-free MCO cathode, which had a comparable cell microstructure to the MCSO cell, only obtained a peak power density of 836 mW cm−2. The higher cell performance resulted from the Sb-modified MCO cathode's increased catalytic activity. In addition, the MCSO cell displayed excellent operational stability under fuel cell operating conditions, indicating that MCSO is a novel and effective spinel cathode for H–SOFCs.

Effect of Zn doping on Sr3Fe2O7-δ Ruddlesden-Popper oxides as active and robust cathodes for protonic ceramic fuel cells

Perovskite oxides are promising electrodes for protonic ceramic fuel cells (PCFCs) due to their good electrochemical performance and stability. However, the lower operating temperature results in a large polarization resistance and sluggish oxygen reduction reaction (ORR) in cathodes. Herein, Ruddlesden-Popper (R–P) type perovskite Sr3Fe2-xZnxO7-δ (SFZx, x = 0, 0.1, 0.5) were successfully synthesized and the partial replacement of Fe by Zn in SFZx demonstrates a superior ORR activity. At 750 °C, the polarization resistance of SFZ05 is 0.072 Ω cm−2, which is 47% lower than that of the undoped Sr3Fe2O7-δ (SFO), and the peak power density of the single-cell with an SFZ05 cathode reaches 523.56 mW cm−2. The distribution of relaxation time (DRT) results manifest that the rate-limiting steps of ORR are charge transfer and ionic migration processes. Furthermore, SFZ05 also presented better CO2 tolerance. These results show that SFZ05 is a promising cathode candidate with high activity and stability for PCFCs.

Machine learning and Shapley Additive Explanation-based interpretable prediction of the electrocatalytic performance of N-doped carbon materials

Enhancing the kinetic rate of cathodic oxygen reduction reaction (ORR) by catalysts is the key to improve the performance of microbial fuel cells (MFCs). Metal-free ORR catalysts represented by nitrogen-doped carbon materials have been extensively investigated and have shown excellent catalytic effects for oxygen reduction reaction. However, it is difficult to clarify the coupling effect physicochemical properties of nitrogen-doped carbon materials on their catalytic effect (i.e. electricity production performance of MFCs) by traditional experimental methods. Therefore, in this study, six machine learning models were combined with SHAP to develop prediction models for the power density ratio of MFCs for reflecting the catalytic performance of nitrogen-doped carbon materials by using physicochemical properties, such as elemental composition, functional group structure, and pore structure, as input features. The gradient boosting regression (GBR) model was found to have the highest prediction accuracy on the test set, with R2 and RMSE of 0.86 and 0.09, respectively. The SHAP method was used to interpret the output of the GBR model and reveal the mechanism of interaction between different characteristic variables. It was found that pyridine nitrogen is the most important input characteristic of the nitrogen elements, as its corresponding SHAP value reaches above 0.1. Surprisingly, an increase in the content of oxygen significantly attenuates the extent to which changes in nitrogen content affect the system, although its effect on power density prediction is inconsiderable. In addition, the optimal range of important physicochemical properties of nitrogen-doped carbon materials was obtained by the SHAP method. The carbon materials have relatively high catalytic performance under the conditions of C(at%) between 85% and 90%, N(at%) > 2.5%, Pyridine-N(at%) > 30%, Vtotal between 0.3 and 0.6 cm3g−1, and SBET > 1000 m2g−1. This study can provide theoretical guidance for subsequent experimental design of carbon-based nitrogen-doped electrocatalysts.

High-entropy L12-Pt(FeCoNiCuZn)3 intermetallics for ultrastable oxygen reduction reaction

Enhancing the stability of Pt-based electrocatalysts for the sluggish cathodic oxygen reduction reaction (ORR) is critical for proton exchange membrane fuel cells (PEMFCs). Herein, high-entropy intermetallic (HEI) L12-Pt(FeCoNiCuZn)3 is designed for durable ORR catalysis. Benefiting from the unique HEI structure and the enhanced intermetallic phase stability, Pt(FeCoNiCuZn)3/C nanoparticles demonstrate significantly improved stability over Pt/C and PtCu3/C catalysts. The Pt(FeCoNiCuZn)3/C exhibits a negligible decay of the half-wave potential during 30,000 potential cycles from 0.6 to 1.0 V, whereas Pt/C and PtCu3/C are negatively shifted by 46 and 36 mV, respectively. Even after 10,000 cycles at potential up to 1.5 V, the mass activity of Pt(FeCoNiCuZn)3/C still shows ∼70% retention. As evidenced by the structural characterizations, the HEI structure of Pt(FeCoNiCuZn)3/C is well maintained, while PtCu3/C nanoparticles undergo severe Cu leaching and particle growth. In addition, when assembled Pt(FeCoNiCuZn)3/C as the cathode in high-temperature PEMFC of 160 °C, the H2-O2 fuel cell delivers almost no degradation even after operating for 150 h, demonstrating the potential for fuel cell applications. This work provides a facile design strategy for the development of high-performance ultrastable electrocatalysts.

Neodymium-Doped Zinc Oxide Nanoparticles Catalytic Cathode for Enhanced Efficiency of Microbial Desalination Cells

The Microbial Desalination Cell is a novel method for desalinating water that also generates energy via substrate oxidation. The MDC comprises three chambers: the anode chamber, the desalination chamber, and the cathode chamber. The fundamental problem with the technology is that it generates very little power during the oxygen reduction reaction (ORR). One solution to this issue is to use a highly active cathode catalyst, which effectively increases the ORR rate. Neodymium-doped ZnO nanoparticles were produced and employed as a cathode catalyst in the three-chambered MDC1 to improve performance. Zn1−xNdxO nanocrystalline samples containing x = 0.0, 0.03, 0.6, and 0.10 were synthesized efficiently through the cost-efficient sol-gel method. Transmission electron microscopy (TEM) and X-ray diffraction techniques revealed the nanocrystalline nature and the phase purity of the Zn1−xNdxO samples. The structural properties of ZnO nanostructured materials were elucidated by Rietveld refinement of the XRD patterns, which showed displacement of Zn and O ions and revealed changes in the electron density around the Zn-O bond with Nd substitution. The local features of light emission from Zn1−xNdxO samples have been studied with photoluminescence. The UV and green-yellow emissions originate from the exciton transition and the transition between the Nd3+ deep level, oxygen vacancy and interstitial oxygen. The results were compared to MDC-2, which did not have a catalyst on the cathode. Both MDCs were tested using a saline water solution containing 15 g/L of NaCl to measure their desalination performance. The better reduction kinetics was confirmed by cyclic voltammetry of the MDC-1 cathode. MDC-1 had a higher desalination efficiency (77.02% ± 2.0%) due to the presence of an Nd-doped ZnO catalyst than MDC-2 (59.3% ± 8.3%). MDC-1’s maximum power density of 3.65 W/m3 was 2.78 times greater than MDC-2’s (0.78 W/m3). Furthermore, the coulombic efficiency of MDC-1 was found to be (8.8 ± 0.3%), which was much higher than that of MDC-2 (4.56 ± 0.2%). As a result, the Nd-doped ZnO-based catalyst developed in this study can potentially improve ORR in MDC cathodes, enabling them to generate more power.

Electronic communication between transition metal nanoparticle and single atom: Endohedral metallofullerenes single-atom catalysts for oxygen reduction reaction catalysis

Civil-used proton exchange membrane fuel cell (PEMFC) may be the potential candidate for the construction of the global new energy system including the use of hydrogen energy. Nevertheless, the cathode oxygen reduction reaction (ORR) occurs sluggishly, reining the conversion efficiency of it, which hinders the further commercialization of PEMFC. Currently, the replacement of undesirable Pt catalysts by more stable and economical catalytic materials is the main topic in the field of ORR. Herein, ferromagnetic metal-based endohedral metallofullerenes (EMFs) electrocatalyst with single-atomic shell decoration (M4@MN4C60, M = Fe, Co, Ni) are theoretically constructed and evaluated by the density functional theory method. The encapsulation energy calculation reveals that the synthesis of all EMFs requires additional external energy supply, which can explain why few successfully experimental synesis of EMFs have been reported. Among all studied catalysts, the CoN4C60 stands out with the highest ORR performance comparable to Pt, and the Fe- and Ni- based EMFs shows considerable activity enhancement after the cluster encapsulation. The electronic structure calculation reveals that the encapsulated Fe4 cluster leads to an electron accumulation around the Fe atom in active center, thereby weakening the *OH binding and enhance the ORR performance.