Reduction Reaction Properties Research Articles

Pt-surface stabilization by high-entropy alloys for enhancing oxygen reduction reaction property: Single-crystal model catalyst study

In this work, we study the oxygen reduction reaction (ORR) properties of Pt-containing 3d transition-metal high-entropy alloy (Pt-HEA) surfaces, focusing on the constituent alloying elements. The surface Pt and underlying Cr-Mn-Co-Ni(111) (Pt/Cr-Mn-Co-Ni(111)) stacked lattice layers, which are synthesized through the vacuum deposition of the underlying alloy and surface Pt stacking layers on Pt(111) substrate, exhibit high pristine ORR activity and structural stability under potential-cycle loading, compared to Pt/Cr-Co-Ni, Pt/Mn-Co-Ni, and Pt/Co-Ni(111) surfaces. The outperformed ORR properties are attributed to the effective suppression of the surface segregation of Cr. This study demonstrates that not only the “high-entropy” effect induced by increasing the numbers of constituent elements but also the “chemical affinity” of Pt and the individual HEA constituent elements determine the ORR performances of Pt-HEA.

Experimental study platform for electrocatalysis of atomic-level controlled high-entropy alloy surfaces

High-entropy alloys (HEAs) have attracted considerable attention to improve performance of various electrocatalyst materials. A comprehensive understanding of the relationship between surface atomic-level structures and catalytic properties is essential to boost the development of novel catalysts. In this study, we propose an experimental study platform that enables the vacuum synthesis of atomic-level-controlled single-crystal high-entropy alloy surfaces and evaluates their catalytic properties. The platform provides essential information that is crucial for the microstructural fundamentals of electrocatalysis, i.e., the detailed relationship between multi-component alloy surface microstructures and their catalytic properties. Nanometre-thick epitaxially stacking layers of Pt and equi-atomic-ratio Cr-Mn-Fe-Co-Ni, the so-called Cantor alloy, were synthesised on low-index single-crystal Pt substrates (Pt/Cr-Mn-Fe-Co-Ni/Pt(hkl)) as a Pt-based single-crystal alloy surface model for oxygen reduction reaction (ORR) electrocatalysis. The usefulness of the platform was demonstrated by showing the outperforming oxygen reduction reaction properties of high-entropy alloy surfaces when compared to Pt-Co binary surfaces.

One−Step Synthesis of a Non−Precious−Metal Tris (Fe/N/F)−Doped Carbon Catalyst for Oxygen Reduction Reactions

Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (21P2-Fe1-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl3 as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst's oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials.

Unveiling the Underlying Mechanism of Transition Metal Atoms Anchored Square Tetracyanoquinodimethane Monolayers as Electrocatalysts for N2 Fixation

We for the first time systematically studied the structures and electrochemical nitrogen reduction reaction properties of two‐dimensional single transition‐metal anchored square tetracyanoquinodimethane monolayers (labeled as: TM‐sTCNQ, TM = 3d, 4d, 5d series transition metals) by employing density functional theory method. Through high‐throughput screenings and full reaction path researches, two promising electrochemical nitrogen reduction reaction catalysts Nb‐sTCNQ and Mo‐sTCNQ have been obtained. The nitrogen reduction reaction onset potential on Nb‐sTCNQ is as low as −0.48 V. Furthermore, the Nb‐sTCNQ catalyst can quickly desorb NH3 produced with a free energy of 0.65 eV, giving Nb‐sTCNQ excellent catalytic cycle performance. The high catalytic activity of the two materials might be attributed to the effective charge transfer between the active center and adsorbed N2, which enables the active center to adsorb and activate inert N2 molecules well, and the reduction processes require small energy input (i.e., the maximum free energy changes are small). This work provides insights for finding highly efficient, stable, and low‐cost nitrogen reduction reaction electrocatalysts. We hope our results can promote further experimental and theoretical research of this field.

Oxygen reduction reaction properties of vacuum-deposited Pt on thermally grown epitaxial graphene layers

We prepared platinum nanostructures on epitaxial graphene layers (EGLs) generated via the thermal annealing of SiC(0001) substrates [Pt/EGLs/SiC(0001)], and the oxygen reduction reaction (ORR) properties were investigated. 4H_ and 6H_SiC(0001) substrates were annealed at 1600 °C in a vacuum to generate EGLs through the sublimation of Si atoms from the Si-terminated SiC(0001) substrate surfaces. Subsequently, a 1.2 nm thick Pt layer was vacuum-deposited on the EGLs/SiC(0001) surfaces at 10−8 Pa to synthesize Pt/EGLs/SiC(0001) nanostructures. Furthermore, the Pt nanostructures were fabricated separately on a 500 eV hydrogen-ion-beam (H2+-beam) irradiated EGL/6H_SiC(0001) [Pt/H2+-EGLs/SiC(0001)]. The ORR properties of the three vacuum-synthesized Pt/EGLs/SiC(0001) samples were evaluated, and the Pt/H2+-EGLs/SiC(0001) surface revealed improved electrochemical structural stability, that is, enhanced ORR durability relative to the non-H2+-irradiated Pt/EGLs/SiC(0001) surfaces.

Interfacial Assembly of Compressible Carbon Aerogels Featuring Oxygen Reduction Reaction Property for Rechargeable and Flexible Zn-Air Batteries

Interfacial Assembly of Compressible Carbon Aerogels Featuring Oxygen Reduction Reaction Property for Rechargeable and Flexible Zn-Air Batteries

Cobalt on boron‐doped carbon nitride for a novel bifunctional electrocatalyst in zinc‐air batteries

AbstractCarbon‐based materials have been widely applied in electrochemical field because of good conductivity and low cost. However, the electrochemical performances have been hindered by few active sites in themselves, heteroatom doping is a general method to solve the problem. Herein, boron (B) is doped into the carbon nitride (CN) derived from glucose and melamine by a facile way, and cobalt (Co) is introduced in the B‐doped carbon nitride (BNC) to form Co@BNC nanocomposites. Among the different contents of Co in Co@BNC series, 12%Co@BNC shows the best oxygen reduction reaction properties with half‐wave potential of 0.78 V, good stability and methanol tolerance in alkaline solution. Besides, 12%Co@BNC also shows oxygen evolution reaction voltage of 1.67 V, and good bifunctional electrocatalysis behaviors with ∆E of 0.89 V. This bifunctional electrocatalyst can be applied in zinc‐air batteries for transportation field.

Investigation of the Effect of Hydrophilicity on Oxygen Reduction Reaction Property with Measurement of Water Vapor Specific Surface Area

Investigation of the Effect of Hydrophilicity on Oxygen Reduction Reaction Property with Measurement of Water Vapor Specific Surface Area

(PEFCE&E 21 Best Student Poster - First Place) Oxygen Reduction Reaction Properties and Microstructures of Pt/Nb:SnO2 Model Catalysts Fabricated on Pt Single Crystal Surfaces

Introduction Considering strong acidic and severe potential fluctuation environments for operating conditions of Polymer Electrolyte Fuel Cells (PEFC), electrochemical degradation of electrode materials, such as elution and/or oxidation, is crucial for development of high-performance electrode materials, e.g., Pt-based nanoparticles (NPs) and C-based supports. Recently, replacing the C-based supports with metal-oxides aimed for improving electrochemical stabilization has attracted much attention. Among the candidates of metal-oxides used as support materials, X (=Nb, Sb, Ta etc.) doped tin dioxide (X:SnO2) shows relatively high electrical conductivity. Actually, Kakinuma et al. [1,2] demonstrated that superior oxygen reduction reaction (ORR) activity and durability of the Pt NPs supported on Nb-doped SnO2 (Pt NPs/Nb:SnO2). The results clearly show that such the metal-oxide supports are one of the powerful candidates for the next-generation cathode materials. Also, it is considered possible to use Nb:SnO2 as a core material (Pt@Nb:SnO2) for highly durable Pt-shell / metal-oxide-core type catalyst, although influences of microstructures of the Pt-based materials and metal-oxide interface on the ORR properties remains unclear. Therefore, in this study, we prepared Pt NPs/Nb:SnO2 and Pt@Nb:SnO2 model catalysts with atomically-controlled Pt/SnO2 interface under ultra-high vacuum (UHV; ~10-8 Pa) and investigated relationship between the surface and interface microstructures of the model catalysts and their ORR properties. Experimental Nb-doped Sn layer with 5 nm thickness was deposited on the surface-cleaned Pt(111) substrate (Ar+-sputtering and annealing) by arc-plasma deposition (APD) of Sn-Nb alloy target (composition ratio 96:4 (at.%)) at the substrate temperature of 300 K. Subsequently, the prepared sample was transferred to a furnace and thermally-oxidized in dry air (Nb:SnO2 / Pt(111)). Then, the Nb:SnO2 / Pt(111) sample was re-introduced into the UHV-chamber, Pt was vacuum-deposited by the APD for Pt NPs / Nb:SnO2 / Pt(111) and by e-beam evaporation for Pt-shell on the Nb:SnO2/Pt(111) (Pt shell / Nb:SnO2 / Pt(111)) (Fig1-(a) and Fig1-(b), respectively). The microstructures of the catalyst model samples were analyzed by STM, cross sectional STEM-EDS, XPS etc. The ORR properties were evaluated by CV and LSV with the RDE method conducted in N2-purged and O2-saturated 0.1 M HClO4, respectively. The ORR activity was evaluated from j k values at 0.9 V vs. RHE by using Koutecky-Levich equation. The electrochemical stability was discussed by the ORR activity changes during applying the potential cycles (PCs) of 0.6-1.0 V vs. RHE (each 3 s) in O2 saturated 0.1 M HClO4 at room temperature. Results and Discussion The STM image (Fig. 2-(a)) of the Pt NPs / Nb:SnO2 / Pt(111) for the Pt/SnO2 model catalyst showed Pt NPs with an average size of 3.6 nm were distributed over the Nb:SnO2 substrate surface. The ORR activity and durability for the Pt NPs / Nb:SnO2 / Pt(111) clearly outperformed relative to the Pt NPs formed on a highly oriented pyrolytic graphite (HOPG)[3] formed under the same Pt deposition condition: increase in Pt particle sizes and size distribution of Pt NPs by the 10000 PCs loading was suppressed compared to that of the Pt NPs / HOPG.A cross-sectional HAADF-STEM image of the Pt-shell / Nb:SnO2 / Pt(111) model core-shell sample (Fig. 2-(b)) reveals that the surface Pt layers with (111) orientation (ca. 2.5 nm in thickness) and SnO2(101) lattice of ca. 4 nm-thick Nb:SnO2 layer are grown on the Pt(111) substrate surface. This is probably due to lattice matching between the Pt(111) (0.48 × 0.56 nm) and SnO2(101) (0.48 × 0.58 nm)(Fig. 2-(c)). Such the lattice matching might correlate with the forementioned suppression of nanoparticle migration [4] in the Pt NPs / Nb:SnO2 / Pt(111) model catalyst. Furthermore, as shown in Fig. 2-(d), the Pt shell / Nb:SnO2 / Pt(111) shows that the ORR activity enhancement factor is at most × 4.1 vs. clean Pt(111) at 500 PCs and × 3.2 even after 5000 PCs loading. The ORR activity enhancement might stem from so-called the ligand effect of Sn and/or Nb on the surface Pt(111) layer through thermal diffusion such the elements into the surface Pt(111) layer during the model catalyst UHV preparation. At the meeting, I will show ORR properties of the Pt / Nb:SnO2 / Pt(110) and discuss influences of the lattice orientations of the surface Pt and underlaid SnO2 layer. Acknowledgement This study was supported by new energy and industrial technology development organization (NEDO) of Japan.Reference[1] K. Kakinuma et al., Electrochim. Acta., 110, 316-324 (2013).[2] K. Kakinuma et al., J. Electrochem. Soc., 165, 15, J3083-J3089 (2018).[3] S. Takahashi et al., Phys. Chem. Chem. Phys., 17, 18638-18644 (2015).[4] M. Wakisaka, et al., Phys. Chem. Chem. Phys., 12, 4184-4190 (2010). Figure 1

Oxygen Groups Enhancing the Mechanism of Nitrogen Reduction Reaction Properties on Ru- or Fe-Supported Nb2C MXene

Oxygen Groups Enhancing the Mechanism of Nitrogen Reduction Reaction Properties on Ru- or Fe-Supported Nb₂C MXene

Characterization and functional application of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ cathode material for IT-SOFC

The physicochemical properties for layered perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) oxide are systematically investigated to gain insight into the correlation between structure, surface state and oxygen reduction reaction properties. The PBSCF sample possesses orthorhombic structure and keeps better structural stability under operating conditions. X-ray photoelectron spectra analysis indicates that the mixed oxidation state of (Co, Fe) and Pr promotes the oxygen reduction reaction kinetics by creating oxygen vacancies at the surface. Mössbauer Spectroscopy affirms that the proportion of Fe3+ and Fe4+ in iron species is 79.1 % and 20.9 %, respectively. The electrode polarization resistance is 0.067 Ω cm2 at 800 °C in air. The oxygen-ion bulk diffusion plays the rate-limiting step during the electrode process. The cell with PBSCF cathode delivers the power density of 590 mW cm−2 at 800 °C. These results show the PBSCF exhibits a promising application prospect in intermediate temperature solid oxide fuel cell.

A “two-pronged” strategy: Boosting electrocatalytic oxygen reduction reaction property based on the Ni–MnO synergistic effect and high conductivity of rod-like Ni–MnO/N–C composites prepared via simple solution-free route

To develop a low-cost and high-efficient electrocatalyst as a substitution of Pt/C for oxygen reduction reaction (ORR) is of great significance. We propose simple “two-pronged” strategy to boost synchronously the electrocatalytic activity and stability via the combination of the active MnO and metallic Ni with the conductive N-doped carbon (N–C) materials. The synergistic effect of active species between MnO and metallic Ni enables Ni–MnO/N–C composites to motivate-boost catalytic activity, the N–C greatly enhances the conductivity and endows Ni–MnO/N–C composites with large surface area for ORR. To our satisfaction, the Ni–MnO/N–C composites exhibits robust electrocatalytic ORR activity with the limiting current density (J) of 6.39 mA cm−2, the half-wave potential (E1/2) of 0.81 V vs. RHE and an ideal four-electron transfer pathway, competing to the commercial Pt/C. Furthermore, the Ni–MnO/N–C composites as a cathode in assembled Zn-air battery shows the power density of 179 mW cm−2, delivers the specific capacity of 702 mA h g−1 at a discharge current density of 10 mA cm−2 while utilizing 84% of the theoretical capacity (~835 mA h g−1). This work highlights a new feasible strategy to explore an efficient electrocatalyst via synchronously heightening the catalytic activity and conductivity.

Oxygen Evolution Reaction/Oygen Reduction Reaction Properties of Massively Synthesized a NiMoS with Solvothermal Method

The oxygen electrode is the most important component in lithium-air batteries for oxygen reduction and evolution reaction (OER/ORR) to get closer to the theoretical energy density of 11,238 Wh/kg, which is the best among the batteries ever developed. Many carbon materials have been researched as a candidate oxygen electrode for lithium-air batteries such as a carbon black, CNTs and graphene. Compared to the many research results, there are still many controversies on the optimum oxygen electrode for lithium-air batteries. Besides that, carbon and binder have been known to deteriorate OER/ORR properties for lithium-air batteries by generating Li2CO3 and other bi-product. Recently, HER and OER properties of heterogeneous MoS2/Ni3S2 have been reported for water splitting. The heterogeneous HER and OER performances of MoS2/Ni3S2 were better than the commercial HER and OER catalysts. Up till now, to my best knowledge, there's no report on ORR properties for homogeneous NiMoS. Therefore, to investigate the ORR properties of homogeneous NiMoS, the homogeneous NiMoS has been synthesized on Ni-foam as well as Ni-powder by various solvothermal methods such as applying to stir during solvothermal synthesis, increasing the pressure or applying the both. Finally, we successfully synthesized NiMoS massively with stirring at the pressure of 15 bar. Characterization for NiMOSs variously synthesized were conducted with SEM, TEM as well as OER/ORR properties using RRDE (Ring Rotating Disk Electrode).As a result, homogeneous NiMoSs massively synthesized with stirring as well as high pressure of over 15 bar shows a unique homogeneous structure with sub-micron size. However, NiMoS synthesized under 2~3bar pressure with no stirring shows the tens of micron size as well as heterogeneous structure. Intriguingly, OER/ORR properties of massively synthesized NiMoS shows much better OER/ORR properties compared to the solvothermal synthesized NiMoS with no-stirring and at the pressure of 2~3 bar. These results show a very optimistic result for non-precious electrode material for the next generation Li-air battery as well as the fuel cell field.

The Effect of Oxygen Partial Pressure and Composition on the Oxygen Reduction Reaction Properties of Ba0.5Sr0.5Fe1-XCuxO3-δ as a Cathode for Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) face hurdles in market acceptability due to their high operating temperatures, which typically ranges from 750 oC – 1000 oC. Thus, current research is moving towards lowering the operating temperature to an intermediate temperature range from 500 oC - 700 oC by developing intermediate temperature (IT)-SOFCs. However, during IT operation, conventional cathodes show sluggish oxygen reduction reaction (ORR) kinetics. Till now, perovskite-type oxides have been at the forefront because of their mixed ionic electronic conductive (MIEC) nature. Additionally, Co-based perovskites have shown high catalytic activity for ORR in IT-SOFC cathodes. However, Co-leads to additional cost, high thermal expansion coefficient and toxicity. In this study, ORR properties of the Co-free perovskite-type Ba0.5Sr0.5Fe1-x Cu x O3-δ (x = 0.05 and 0.2) (BSFCu) cathodes were investigated by utilizing electrochemical impedance spectroscopy (EIS). BSFCu powders were synthesized through the sol-gel method with a final sintering temperature of 1050 °C. Powder X-ray diffraction was used test chemical compatibility between BSFCu and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) powders up to 1100 °C in air. Symmetrical cells of the following configurations BSFCu-LSGM/LSGM/BSFCu-LSGM were prepared for electrochemical measurements using varying ratios of cathode to electrolyte. Using a well-controlled set up, the effect of pO2 on the area specific resistance (ASR) for ORR of symmetrical cells was studied. BSFCu0.05-LSGM/LSGM/BSFCu0.05-LSGM showed the lowest ASR of 0.03 Ω/cm2 under ambient air at 800 °C, when sintered at 1000 °C. These ASR values are competitive with typical values for Co-based cathodes as reported in the literature. Thermo-gravimetric analysis, under O2/Ar atmospheres showed reversible oxygen intake/release capability of BSFCu powders, making them potential candidates for applications in oxygen-storage technologies.

Perspective of perovskite-type oxides for proton conducting solid oxide fuel cells

Solid oxide fuel cell (SOFC) is one of the promising solid-state electrochemical device that converts chemical energy of varied fuels into electricity with high efficiency. However, its market acceptability is hindered due to its high operating temperature (800–1000 °C) that is dictated by the use of conventional oxide ion conducting yttria-stabilized zirconia electrolyte and sluggish oxygen reduction reaction properties of conventional Sr-doped LaMnO3 cathodes. Hence, major focus in the field of SOFCs has been directed towards reducing the operating temperature of current SOFCs to intermediate temperatures (500–700 °C), with the emphasis on material development for advanced electrolytes and cathodes. Due to the ease of doping on both A and B sites, structural stability, and ability to show both ionic (O2−, H+) and electronic conductivity, perovskite-type ABO3 (A = Sr, Ba; B = Ce, Zr) ceramics has been the focus of research towards development of proton conducting SOFCs (H-SOFCs). Despite significant developments, there is a general lack of understanding regarding future research directions in this field. In this review article, we first present an overview of crystal structure, dopant composition and its correlation with chemical stability and electrical conductivity followed by existing challenges associated with cathode development for H-SOFCs and achieving high fuel cell performance. We also outline the recent efforts directed towards reducing the H-SOFCs operating temperature.

Effective surface termination with Au on PtCo@Pt core-shell nanoparticle: Microstructural investigations and oxygen reduction reaction properties

We investigated the microstructures of Au-deposited PtCo@Pt core-shell nanoparticles (NPs) and discussed enhancement of the oxygen reduction reaction (ORR) properties by Au termination of low-coordination sites of the Pt-shell. The Au-deposited PtCo@Pt NPs showed an improved electrochemical structural stability, together with slight increment in increased initial, pristine area-specific activity relative to the non-Au-deposited PtCo@Pt NPs. Atomic-level microstructural characterization was performed by a back-side illumination fluorescence X-ray absorption fine structure (BI-FXAFS) method and scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS). The BI-FXAFS results indicated that compressive lattice strain in the Pt-shells of the PtCo@Pt NPs was almost unchanged by the subsequent Au deposition. Furthermore, STEM-EDS mapping of Pt, Co, and Au clearly showed that the deposited Au tended to localize at low-coordination sites of the Pt-shell surface, e.g., edges and corners. The atomic-level microstructural characterization conducted in this study demonstrated that effective Au surface terminations of the Pt-shell enhance the ORR durability of Pt-based core-shell type NP catalysts.

Oxygen vacancy enhancing mechanism of nitrogen reduction reaction property in Ru/TiO2

Abstract To search the new effective nitrogen reduction reaction (NRR) electrocatalyst is very important for the ammonia-based industry. Herein, we reported the design of a novel NRR electrocatalyst with Ru NPs loaded on oxygen-vacancy TiO2 (Ru/TiO2-Vo). Structural characterizations revealed that oxygen vacancy was loaded in the matrix of Ru/TiO2-Vo. Electrocatalytic results indicated that Ru/TiO2-Vo showed good NRR performance (2.11 µg h−1 cm−2). Contrast tests showed that NRR property of Ru/TiO2-Vo was much better than those of Ru/TiO2(B) (0.53 µg h−1 cm−2) and Ru/P25 (0.42 µg h−1 cm−2). Furthermore, density functional theory calculation results indicated catalytic mechanism of NRR and rate-determining step (*N2 + 1/2H2 → *N+*NH) was the potential-determining step with the overpotential requirement of 0.21 V. A combination of electronic structure analysis and catalytic measurement shed light on the synergistic effect of Ru and oxygen vacancy on the NRR performance.

A perovskite-type Nd0.75Sr0.25Co0.8Fe0.2O3-δ cathode for advanced solid oxide fuel cells.

Perovskite-type Nd0.75Sr0.25Co0.8Fe0.2O3-δ (NSCF) has shown excellent oxygen reduction reaction (ORR) properties (an area specific polarization resistance of 0.1 Ω cm2 at 700 °C) as a composite cathode (30 wt% La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM)) with remarkable chemical stability under CO2. The mechanism for the ORR was established employing pO2 and temperature dependent studies.

Oxygen reduction reaction properties of nitrogen-incorporated nanographenes synthesized using in-liquid plasma from mixture of ethanol and iron phthalocyanine

Nanographenes were synthesized using in-liquid plasma from a mixture of iron phthalocyanine and ethanol. In a previous study, micrometer-scale flakes with nitrogen incorporation were obtained. A nonprecious metal catalytic activity was observed with 3.13 electrons in an oxygen reduction reaction under an acidic solute condition. Large-surface-area, high-graphene-crystallinity, and iron-carbon-bonding sites were found owing to a high catalytic activity in Fe–N/nanographene.

The Improvement of SiO2 Nanoparticles on the Oxygen Reduction Reaction Property of Nitrogen-Doped Mesoporous Graphene Spheres Prepared by Spray Drying

The Improvement of SiO₂ Nanoparticles on the Oxygen Reduction Reaction Property of Nitrogen-Doped Mesoporous Graphene Spheres Prepared by Spray Drying