Electrochemical Oxygen Reduction Research Articles

N-Doped porous carbons obtained from chitosan and spent coffee as electrocatalysts with tuneable oxygen reduction reaction selectivity for H2O2 generation.

Nitrogen-containing porous carbons prepared by the pyrolysis of adequate biopolymer-based precursors have shown potential in several electrochemical energy-related applications. However, it is still of crucial interest to find the optimal precursors and process conditions which would allow the preparation of carbons with adequate porous structure as well as suitable nitrogen content and distribution of functional groups. In the present work we suggested a straightforward approach to prepare N-doped porous carbons by direct pyrolysis under nitrogen of chitosan : coffee blends of different compositions and using KOH for simultaneous surface activation. The synthetized carbon materials were tested for the electrochemical oxygen reduction to hydrogen peroxide (H2O2). A higher fraction of chitosan in the precursor led to a decrease in meso- and nano-porosity of the formed porous carbons, while their activity towards H2O2 generation increased. The nitrogen species derived from chitosan seem to play a very important role. Out of the synthesized catalysts the one with the largest content of pyridinic nitrogen sites exhibited the highest faradaic efficiency. The faradaic efficiencies and current densities of the synthesized materials were comparable with the ones of other commercially available carbons obtained from less renewable precursors.

Synthesis and electrochemical oxygen reduction reaction activities of palladium-based intermetallic nano-electrocatalysts

Changing the atomic structure of a material to alter its characteristics is a key and powerful technique in materials research. Electrocatalytic applications are a growing field for structurally long range ordered materials. Similar electrocatalysts with a disordered structure, however, are unable to perform as well as those with an ordered structure because of the specific functionalities that may be achieved by the ordered structure. There has been a lot of interest in using highly active and stable ordered intermetallics as electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs). Electrocatalysts based on palladium have lately emerged as one of the most promising classes for the oxygen reduction reaction (ORR) in alkaline media because of their superior ORR activity and durability at lower prices than platinum. As electrocatalysts for fuel cells, palladium-based intermetallic nano-electrocatalysts (Pd-INECs) have gained a lot of interest in recent years. Pd-INECs have exceptional catalytic activity and great stability due to their well-defined composition and predictable control over structural, geometric, and electronic effects. In this short article, we will briefly go through the current state of knowledge on Pd-INECs for cathodic ORR in fuel cells. The first step is a brief review of the synthetic ways in which Pd-INECs with a predetermined stoichiometry and a well-defined atomic structure will be discussed. We also emphasized the use of Pd-INECs in electrochemical ORR operations as a second part of the review. Methods are comprehensively reviewed for enhancing the electrocatalytic activity of Pd-INECs. Finally, suggestions for future research directions and current difficulties are made.

Defect-stabilized and oxygen-coordinated iron single-atom sites facilitate hydrogen peroxide electrosynthesis.

The selective two-electron electrochemical oxygen reduction reaction (ORR) for hydrogen peroxide (H2O2) production is a promising and green alternative method to the current energy-intensive anthraquinone process used in industry. In this study, we develop a single-atom catalyst (CNT-D-O-Fe) by anchoring defect-stabilized and oxygen-coordinated iron atomic sites (Fe-O4) onto porous carbon nanotubes using a local etching strategy. Compared to O-doped CNTs with vacancy defects (CNT-D-O) and oxygen-coordinated Fe single-atom site modifying CNTs without a porous structure (CNT-O-Fe), CNT-D-O-Fe exhibits the highest H2O2 selectivity of 94.4% with a kinetic current density of 13.4 mA cm-2. Fe-O4 single-atom sites in the catalyst probably contribute to the intrinsic reactivity for the two-electron transfer process while vacancy defects greatly enhance the electrocatalytic stability. Theoretical calculations further support that the coordinated environment and defective moiety in CNT-D-O-Fe could efficiently optimize the adsorption strength of the *OOH intermediate over the Fe single atomic active sites. This contribution sheds light on the potential of defect-stabilized and oxygen-coordinated single-atom metal sites as a promising avenue for the rational design of highly efficient and selective catalysts towards various electrocatalytic reactions.

Metal-Free Triazine-Based Porous Organic Polymer-Derived N-Doped Porous Carbons as Effective Electrocatalysts for Oxygen Reduction Reaction

In recent years, porous heteroatom-doped carbon materials have been very promising for energy conversion. A newly designed porous organic polymer (POPQ) has been synthesized using two organic monomers, i.e., 2,6-diaminoanthraquinone and cyanuric chloride, under reflux conditions for 72 h in an inert atmosphere. The triazine-containing porous organic polymers undergo pyrolysis, which produces two nitrogen-doped porous carbon materials, N/POPQ600 and N/POPQ800, at 600 and 800 °C temperatures, respectively. Since the resultant N-doped porous materials have a higher surface area than the parent porous organic polymer and the materials have a synergistic effect due to the enriched nitrogen content throughout the matrix, the metal-free N/POPQ600 and N/POPQ800 materials exhibit good electrocatalytic activity toward oxygen reduction reaction (ORR). Among these, the N/POPQ800 material shows excellent ORR activity with a nearly four-electron oxygen reduction pathway where the half-wave potential is estimated to be 0.728 V vs reversible hydrogen electrode (RHE), comparable with the commercially available Pt/C catalyst. Most interestingly, the N/POPQ800 catalyst displays outstanding long-lasting stability. It shows a better methanol tolerance capability than Pt/C, which can be attributed to the high specific surface area and N-doped well-defined crystalline porous structure. Also, the homogeneously distributed active sites throughout the carbon framework are the most precious for the electrochemical oxygen reduction reaction.

Superoxide intermediate in the oxygen reduction on a zinc hydroxide model corrosion product.

The inhibition of the electrochemical oxygen reduction reaction (ORR) by zinc corrosion products plays an important role in the corrosion protection of galvanized steel. Hence, the electrocatalytic mechanism of the ORR on electrodeposited zinc hydroxide-based model corrosion products was investigated by in situ and operando attenuated total reflection infrared (ATR-IR) spectroscopy, supplemented by density functional theory (DFT) calculations. Model corrosion products containing flake-like crystalline Zn5(NO3)2(OH)8 were cathodically electrodeposited on germanium(100) electrodes from a zinc nitrate precursor electrolyte. Substantial amounts of the films are non-crystalline, and their surfaces predominantly consist of zinc oxide and hydroxide species, as evidenced by x-ray photoelectron spectroscopy. ATR-IR spectra show a peak at 1180 cm-1 during cathodic currents in O2-saturated NaClO4 solution. This peak is assigned to a surface-bound superoxide, the only ORR intermediate detected. Absorbance from the intermediate increases with increasing cathodic current, indicating an increase in surface concentration of superoxide intermediates at larger ORR current densities. The zinc hydroxide ages in the experiments, most likely by a transformation into zinc oxide, consistent with the observed decrease in absorbance over time of the OH bending mode of zinc hydroxide at 1380 cm-1. This aging is a time-dependent chemical process, implying that pure chemical aging is important in actual corrosion products as well. DFT calculations of adsorbed superoxide yield a Zn-O bond length similar to the bond length in Zn-O, thus enhancing superoxide interaction with undercoordinated tetrahedral Zn2+ sites on the surface. Thus, such active sites catalyze the first reduction step in the ORR.

Recycling of value-added products from spent lithium-ion batteries for oxygen reduction and methanol oxidation reactions

Environmentally friendly technology for recycling spent lithium-ion battery (LIB) electrodes was developed to explore the efficiency of regenerated electrocatalysts for electrochemical oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). First, LixCoO2 electrodes from spent LIBs were subjected to a lixiviation process using tartaric acid as the lixiviant and H2O2 as an oxidizing agent; then, graphite was converted into graphene oxide (GO), which was combined with lixiviant to regenerate different ratios of cobalt oxide-supported reduced graphene oxide (Co3O4/rGO). The regenerated composite material displayed good ORR activity with an onset potential of 0.936 V vs. RHE. The catalytic activity of Co3O4/rGO towards MOR was also investigated, exhibiting a mass activity of 49.3 A g−1. These findings demonstrate that end-of-life LIBs may be utilized as high-performance electrocatalysts in energy conversion devices which realize resource conservation in addition to minimizing associated environmental issues.

Hollow polyhedral Fe-N-C nanostructures derived from ZIF-8 highlighting markable morphology effect on electrochemical oxygen reduction and carbon dioxide reduction

Iron and nitrogen co-doped carbon materials (Fe-N-C) have been identified as one promising class of electrocatalysts toward both electrochemical oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR), which are profoundly influenced by both intrinsic and extrinsic factors. Herein a well-defined hollow polyhedral Fe-N-C nanostructure (FeNC-H) is obtained by pyrolyzing ZIF-8 precursor involving FeCl3 absorption and KOH treatment. In comparison, direct pyrolysis of FeCl3-absorbed ZIF-8 only leads to densely fused carbon particles (FeNC-R). Albeit similar pore characteristics between FeNC-H and FeNC-R, FeNC-H exhibits superior ORR and CO2RR performance to FeNC-R due to its markable hollow morphology effect. In O2-saturated 0.1 M KOH solution, FeNC-H delivers an onset potential of 0.966 V (vs. RHE) and a half-wave potential of 0.865 V (vs. RHE), surpassing the benchmark Pt/C. Meanwhile, FeNC-H achieves 91.8 % FE of CO at − 0.5 V (vs. RHE) in CO2-saturated 0.5 M KHCO3 solution. It is found that the unique hollow morphology endows FeNC-H with high surface area, large pore volume and fast mass transfer kinetics, thus boosting both ORR and CO2RR.

Efficient and durable electrochemical oxygen reduction to H2O2 in acidic media assisted through catalyst layer design

Electrochemical synthesis of hydrogen peroxide (H2O2) through 2-electron oxygen reduction reaction (ORR) is a sustainable alternative to the industrialized anthraquinone oxidation process. Gas-diffusion electrode (GDE) is employed to overcome the mass transport limitation of O2 to deliver high current density. However, long-term stability in practical electrolyzer with GDE is still challenging due to electrode flooding. Here, we propose a double catalyst layer (CL) strategy with gradient Nafion distribution to balance the mass transport of O2 and H+ and improve the flood-proof ability. Our design achieved H2O2 production rate up to 2.16 mmol h−1 cm−2 with a selectivity of about 90% and enabled 48 h stable electrolysis at 100 mA cm−2. Compared to the state-of-the-art H2O2 electrosynthesis system in acidic media, the full-cell voltage improved significantly to 2.3 V at 100 mA cm−2, indicating its potential for practical production and utilization.

Fabrication of platinum-cobalt nanowires by centrifugal electrospinning as oxygen reduction catalyst for PEMFC

Investigation for novel catalytic materials is quite important for the development of fuel cell as well as hydrogen economy. In this study, platinum-cobalt (PtCo) bimetallic nanowires are prepared successfully by the centrifugal electrospinning technique and their potential as electrocatalyst is evaluated for proton exchange membrane fuel cell (PEMFC). The influences of operation conditions on nanowire morphology are studied, which include the rotation rate of spinneret, applied electric field, and nanowire composition. The electrochemical performance of the prepared nanowires is studied by performing the tests of cyclic voltammetry (CV) and linear sweep voltammetry (LSV) to characterize the electrochemical active surface area (ECSA) and oxygen reduction reaction (ORR) activity. The accelerated degradation tests (ADT) are also conducted to examine the durability of the nanowires. The membrane electrode assembly (MEA) using PtCo nanowires as cathode electrocatalyst is also made and its performance is compared with conventional MEA using Pt/C catalyst. It is found that under the situation of 1600 rpm of rotation rate, 12 cm of collection distance, and 13 kV of applied voltage, PtCo nanowires can be obtained with excellent morphology and the minimum mean diameter is 76 nm for the case of atomic ratio Pt:Co = 4:1. The corresponding ECSA is 41.2 m2g−1 and the LSV and ADT results show the resultant PtCo nanowires exhibit better ORR activity and durability than Pt/C catalyst.

Following Paths of Maximum Catalytic Activity in the Composition Space of High‐Entropy Alloys

AbstractThe search for better and cheaper electrocatalysts is vital in the global transition to renewable energy resources. High‐entropy alloys (HEAs) provide a near‐infinite number of different alloys with approximately continuous properties such as catalytic activity. In this work, the catalytic activity for the electrochemical oxygen reduction reaction as a function of molar composition of Ag‐Ir‐Pd‐Pt‐Ru HEA is treated as a landscape wherein it is shown that the maxima are connected through ridges. By following the ridges, it is possible to navigate between the maxima using a modified nudged elastic band (NEB) model integrated in a machine learning NEB algorithm. These results provide a new understanding of the composition space being similar to an evolutionary landscape. This provides a possible new search and design strategy for new catalysts in which the composition of known catalysts can be optimized by following ridges rather than exploring the whole alloy composition space.

Regulating the FeN4 Moiety by Constructing Fe-Mo Dual-Metal Atom Sites for Efficient Electrochemical Oxygen Reduction.

An Fe-N-C catalyst with an FeN4 active moiety has gained ever-increasing attention for the oxygen reduction reaction (ORR); however, the catalytic performance is sluggish in acidic solutions and the regulation is still a challenge. Herein, Fe-Mo dual-metal sites were constructed to tune the ORR activity of a mononuclear Fe site embedded in porous nitrogen-doped carbon. The cracking of O-O bonds is much more facile on the Fe-Mo atomic pair site due to the preferred bridge-cis adsorption model of oxygen molecules. The downshift of the Fe d band center when an Mo atom is introduced to the FeNx configuration optimizes the absorption-desorption behavior of ORR intermediates in the FeMoN6 active moiety, thus boosting the catalytic performance. The construction of dual-metal atom sites to regulate the catalytically active moiety paves the way for boosting the electrocatalytic performance of other similar non-precious-metal catalysts.

New Folding 2D-Layered Nitro-Oxygenated Carbon Containing Ultra High-Loading Copper Single Atoms.

The discoveries of 2D nanomaterials have made huge impacts on the scientific community. Their unique properties unlock new technologies and bring significant advances to diverse applications. Herein, an unprecedented 2D-stacked material consisting of copper (Cu) on nitro-oxygenated carbon is disclosed. Unlike any known 2D stacked structures that are usually constructed by stacking of separate 2D layers, this material forms a continuously folded 2D-stacked structure. Interestingly, advanced characterizations indicate that Cu atoms inside the structure are in an atomically-dispersed form with extraordinarily high Cu loading up to 15.9±1.2wt.%, which is among the highest reported metal loading for single-atom catalysts on 2D supports. Facile exfoliation results in thin 2D nanosheets that maximize the exposure of the unique active sites (two neighboring Cu single atoms), leading to impressive catalytic performance, as demonstrated in the electrochemical oxygen reduction reaction.

In-situ efficient electrosynthesis of H2O2–NaClO based on the media pH and catalyst mutual selection mechanism

Electrochemical two-electron oxygen reduction (2e− ORR) as a promising H2O2 synthesis strategy has been extensively explored, while the study on the relation between active sites at the catalyst surface and pH of applied medium is still scarce. Here in, the as-prepared catalysts by anodizing graphite felt in different media exhibit excellent H2O2 production activity in acidic (151.73 mg L−1 h −1 cm−2), neutral (53.72 mg L−1 h −1 cm−2) and alkaline (188.85 mg L−1 h −1 cm−2) media, which is superior to the current advanced felt-supported carbon-based catalysts. According to characterizations, a mutual selection mechanism between the catalysts and media pH is proposed, in which it is the catalysts’ specific functional groups and structures matching with the pH-dependent electron transfer mechanism leading to the efficient H2O2 production. When anolyte simulates the seawater environment in H-type cell, the simultaneous production of NaClO and H2O2 and degradation of rhodamine B are realized, and H2O2 accumulative concentration in solution reaches a breakthrough of 6.58 g L−1. In general, this work provides new insights into the relation between the pH-dependent surface properties of catalysts and 2e− ORR reaction mechanism. In-situ H2O2–NaClO synthesis is also a promising route for chemicals synthesis and pollutant degradation.

Thienothiophene and Triphenylbenzene Based Electroactive Conjugated Porous Polymer for Oxygen Reduction Reaction (ORR)

Catalysts based on metal-free conjugated porous polymers (CPPs) are still rare for electrochemical oxygen reduction reactions (ORR). In this study, a conjugated porous polymer, TT-TPB, based on thieno[3,2-b]thiophene (TT) and triphenylbenzene (TPB), was synthesized applying palladium(0) catalyzed Suzuki coupling reaction and its ORR activity was investigated in alkaline condition. It demonstrated comparable electrocatalytic performance of ≈0.89–0.9 V Eonset vs RHE with the commercially available Pt/C. Density-functional theory (DFT) calculations revealed that TT-TPB featured efficient electrocatalytic active sites derived from volumetric, areal, and O2 adsorbing calculations, which were in line with the experimental results. Moreover, semiconducting and surface properties of TT-TPB were investigated in detail using electrochemical and spectrophotometric techniques. This work shows the potential application of thienothiophene-based metal-free CPP in the electrochemical conversion process.

Regulating the scaling relationship for high catalytic kinetics and selectivity of the oxygen reduction reaction

The electrochemical oxygen reduction reaction (ORR) is at the heart of modern sustainable energy technologies. However, the linear scaling relationship of this multistep reaction now becomes the bottleneck for accelerating kinetics. Herein, we propose a strategy of using intermetallic-distance-regulated atomic-scale bimetal assembly (ABA) that can catalyse direct O‒O radical breakage without the formation of redundant *OOH intermediates, which could regulate the inherent linear scaling relationship and cause the ORR on ABA to follow a fast-kinetic dual-sites mechanism. Using in situ synchrotron spectroscopy, we directly observe that a self-adjustable N-bridged Pt = N2 = Fe assembly promotes the generation of a key intermediate state (Pt‒O‒O‒Fe) during the ORR process, resulting in high reaction kinetics and selectivity. The well-designed Pt = N2 = Fe ABA catalyst achieves a nearly two orders of magnitude enhanced kinetic current density at the half-wave potential of 0.95 V relative to commercial Pt/C and an almost 99% efficiency of 4-electron pathway selectivity, making it one of the potential ORR catalysts for application to the energy device of zinc‒air cells. This study provides a helpful design principle for developing and optimizing other efficient ORR electrocatalysts.

Synchronized integration of iron/cobalt dual-metal in nitrogen-doped carbon hollow spheres for enriched supercapacitive and oxygen reduction reaction performances

The development of nonprecious metals in conjunction with heteroatoms doped carbon material as an effective electrocatalyst is critical for enhanced energy storage and conversion (ESC) properties. Nonprecious metals co-doping in a nitrogen-doped carbon matrix are considered potential candidates for this purpose, but their stability and activity remain insufficient to meet the demands of practical applications. In this work, the iron‑cobalt particles integrated nitrogen-doped carbon hollow spheres (FeCoNCHSs) as an efficient electrocatalyst for electrochemical supercapacitors and oxygen reduction reaction (ORR) towards alkaline fuel cells are reported. FeCoNCHSs were prepared by Fe+3/Co+2-mediated in-situ polymerization of dopamine on modified polystyrene and later pyrolysis under N2 atmosphere at 700 °C for 3 h. The as-synthesized materials were characterized and analyzed by various electrochemical and electroanalytical techniques. Importantly, the FeCoNCHSs show remarkable supercapacitive properties with the maximum capacitance value of 287.3 F g−1 at a scan rate of 2 m Vs−1. Moreover, the FeCoNCHSs exhibited an inspiring positive half-wave potential of ~0.83 V during ORR. Density functional theory (DFT) calculations further explain that the N-coordinated metal (Fe/Co) species are the main active sites to effectively improve the charge transfer and electrochemical activities. The efficient response of the electrode material can be attributed to their meso−/macroporous intact hollow spherical morphology, large porous surface area, and high N(pyridinic/pyrrolic/graphitic)-contents. Significantly, the synergistic effects of N-doping along with N-coordinated dual-metal (Fe/Co) species are also responsible for the superior supercapacitive and ORR performances.

Tin Nanoclusters Confined in Nitrogenated Carbon for the Oxygen Reduction Reaction.

The oxygen reduction reaction is essential for fuel cells and metal-air batteries in renewable energy technologies. Developing platinum-group-metal (PGM)-free catalysts with comparable catalytic performance is highly desired for cost efficiency. Here, we report a tin (Sn) nanocluster confined catalyst for the electrochemical oxygen reduction. The catalyst was fabricated by confining 1-1.5 nm sized Sn nanoclusters in situ in microporous nitrogen-doped carbon polyhedra (SnxNC) with an average pore size of 0.7 nm. SnxNC exhibited high catalytic performance in acidic media, including positive onset and half-wave potentials, comparable to those of the state-of-the-art Pt/C and far exceeding those of the Sn single-atom catalyst. Combined structural and theoretical analyses reveal that the confined Sn nanoclusters, which have favorable oxygen adsorption behaviors, are responsible for the high catalytic performance, but not Sn single atoms.

Thermally-Activated Cobalt Hexacyanocobaltate Dispersed on Reduced-Graphene-Oxide As Electrocatalyst Towards Oxygen Reduction in an Alkaline Medium

In the recent research years is observed huge interest in design of new functional nanomaterials for developing new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The research has been focused on developing carbon nanostructures materials with the different transition metals (e.g. Co, Ni, Ag, Au, Cu, Mn) analogue of polynuclear Prussian Blue for fuel cell applications. The development of electrocatalytic material prepared by heat-treating a composite of a Prussian Blue analogue - cobalt hexacyanocobaltate immobilized on a reduced graphene oxide. The pyrolysis process, forms a new type of catalyst with efficient active cobalt centers (Co-N-C and Co-C-N) of electrochemical oxygen reduction reaction in alkaline media. Physicochemical properties of this catalytic material containing cobalt in differing oxidation states were elucidated using microscopic, spectroscopic methods and various electrochemical diagnostic techniques. Experimental results showed that the cobalt analogue of Prussian Blue displayed comparable electrocatalytic activity (e.g., a half-wave potential and overpotential) towards oxygen reduction reaction in alkaline media to Vulcan-supported platinum nanoparticles. Furthermore, the presence of cyanide-bridged cobalt ionic sites tended to decrease formation of undesirable peroxide intermediate species, as demonstrated by monitoring ring currents during RRDE measurements. Furthermore, the proposed electrocatalytic material exhibits great stability and tolerance to alcohols (e.g. methanol). Acknowledgement The study was supported by the National Science Center (NCN), Poland, Project Number 2015/19/B/ST4/03758

Synthesis of Single-Atom and Dual-Atom Catalyst Using N-Defective C3N4

Single-atom catalysts, which have been studied tremendously in the past decade, are emerging as a new class of heterogeneous catalysts. It is now generally known that defect sites play an important role in forming single-atomic structures. In the case of SACs, defective sites provide not only space for fixation of metal precursor, but also electrons for stabilizing positive metal ions. Graphitic carbon nitride (g-C3N4) is one of the ideal 2D materials for the synthesis of SACs. C3N4 has enough anchoring sites which originate from the ordered structure of tri-s-triazines connected together. Furthermore, abundant nitrogen atoms in C3N4 can provide electrons to single metal atoms. however, C3N4 is unsuitable as support for electrochemical catalysts due to its low electrical conductivity. Therefore, we made a C3N4 shell on the outer surface of carbon black (Ketjen Black EC-600JD) to obtain conductive support (C@C3N4).[1] Pt was supported on C@C3N4 at 1, 2, 4, and 8 wt% by wetness impregnation method. Through XRD, HAADF-STEM, and XAFS analysis, it was confirmed that a single-atomic structure was formed only when the Pt content was 1 or 2 wt%. In addition, I confirmed that the H2O2 selectivity (%) in the electrochemical oxygen reduction reaction was different according to the Pt content of the catalysts.In terms of controlling reaction sites at the atomic level, the challenge above creating single-atomic structures is creating structures in which two or three atoms are formed as dimer or trimer. Unlike single-atom catalysts, in a dimer or trimer structure, two or more atoms are adjacent to each other, so they can exhibit completely different catalytic properties. Finely controlling the defect site of the support can be a good strategy. Therefore, I adopted the strategy of making a defect in C3N4 to synthesize a dimer structure. It has been reported that N-vacancy can be selectively formed on C3N4 by additional heat treatment with NaBH4.[2, 3] In addition, DFT calculation results have been reported that Pd-Cu dimer structure can be stably formed on nitrogen-defective C3N4.[4]In this work, I create N-vacancy on a Pt1/C@C3N4 by additional heat treatment with NaBH4, and Co atoms were deposited as a secondary transition metal. The research strategy was to anchor the Co atom to the N-vacancy formed around the Pt single-atom, resulting in the formation of a dimer structure. First of all, the formation of N-vacancy on C@C3N4 support was clearly confirmed by FT-IR and XPS analysis. To confirm the dimer structure of Pt and Co, XAFS analysis was conducted. As a result, although not all Pt and Co atoms formed a dimer structure due to the limitation of the synthesis method, the intended structure of Co atom connected to a Pt atom was confirmed. In the Pt L3 edge EXAFS, a peak arising from Pt-Co scattering was observed at 2.4 Å. Furthermore, to confirm that PtCo alloy particles were not formed, high-result HAADF-STEM images were taken. All metal atoms were atomically dispersed, and nanoparticles were not found. This research demonstrated that defect engineering on support material can successfully modify active site on the atomic scale.

Solid Oxide Fuel Cells with 3D Inkjet Printing Modified LSM-YSZ Interface

Solid oxide fuel cells (SOFCs) have drawn attention as an alternative power generation technology due to demonstrated high efficiency and low emissions. The lanthanum strontium manganite (LSM)-yttria-stabilized zirconia (YSZ) cathode is utilized widely for SOFCs due to its high performance and stability. The electrochemical oxygen reduction reaction that occurs in the cathode can be enhanced by the porous LSM-YSZ cathode with good electronic and ionic conductivity. With sufficient electrochemically active reaction sites, the oxygen ion transfer processes in the mixed ionic conductor (YSZ) and at the interface of cathode and electrolyte (LSM-YSZ) become critical for the activity of the cathode. Thus, the pillar shape YSZ microstructure with ~ 150 μm×150 μm×10 μm (L×W×H) size can be fabricated by 3D inkjet printing on the interface of electrolyte and cathode to increase the TPB area and enhance the connection between the dense YSZ electrolyte and mixed YSZ ionic conductor. Scanning Electron Microscopy (SEM) is utilized to assess the morphology and microstructure of the YSZ interface. To investigate the influence of the modified interface on the performance of the SOFC, electrochemical performance testing and characterization are conducted for the SOFCs with/without the modified YSZ layer. The microstructures with different pillar central spacing are also fabricated by 3D inkjet printer to optimize the geometry of the LSM-YSZ interface.