Preparation and electroactivity of polymer-functionalized graphene oxide-supported platinum nanoparticles catalysts

Polymer-functionalized graphene oxide or pristine graphene oxide supported platinum nanoparticles (Pt NPs) was prepared to study the surface modification effects. The catalysts were characterized by transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction and thermogravimetric analysis. The electrochemical activities of Pt NPs were measured by cyclic voltammograms. The poly(diallyldimethylammonium chloride) (PDDA) was used as a modifier agent which formed a functionalized layer on graphene oxide (GO) sheets. As a result, the electrochemical active surface area (ESA) of PDDA functionalized GO supported Pt (Pt/PDDA–graphene) was shown to 66 m²/g that indicated higher hydrogen adsorption amount than 55 m²/g of the pristine Pt/graphene. In addition, an average particle size of Pt/PDDA–graphene NPs was measured to 1.8 nm slightly smaller than 2.0 nm of pristine Pt/graphene NPs.     

An effective electrocatalyst based on platinum nanoparticles supported with graphene nanoplatelets and carbon black hybrid for PEM fuel cells

A facile synthesis at room temperature and at solid-state directly on the support yielded small, homogeneous and well-dispersed Pt nanoparticles (NPs) on CB-carbon black, GNP-graphene nanoplatelets, and CB-GNP-50:50 hybrid support. Synthesized Pt/CB, Pt/GNP and Pt/CB:GNP NPs were used as electrocatalysts for polymer electrolyte membrane fuel cell (PEMFC) reactions. HRTEM results displayed very small, homogeneous and well-dispersed NPs with 1.7, 2.0 and 4.2 nm mean-diameters for the Pt/CB-GNP, Pt/GNP and Pt/CB electrocatalysts, respectively. Electrocatalysts were also characterized by RAMAN, XRD, BET and CV techniques. ECSA values indicated better activity for graphene-based supports with 19 m² g⁻¹_Pt for Pt/GNP and 55 m² g⁻¹_Pt for Pt/CB-GNP compared to 10 m² g⁻¹_Pt for Pt/CB. Oxygen reduction reaction (ORR) studies and fuel cell tests were in parallel with these results where highest maximum power density of 377 mW cm⁻² was achieved with Pt/CB-GNP hybrid electrocatalyst. Both fuel cell and ORR studies for Pt/CB-GNP indicated better dispersion of NPs on the support and efficient fuel cell performance that is believed to be due to the prevention of restacking of GNP by CB. To the best of our knowledge, Pt/GNP and Pt/CB-GNP electrocatalysts are the first in literature to be synthesized with the organometallic mild synthesis method using Pt(dba)₃ precursor for the PEMFC applications.     

Non-noble metal oxygen reduction electrocatalysts based on carbon nanotubes with controlled nitrogen contents

Nitrogen-doped carbon nanotubes (CN_x) were prepared via a floating catalyst chemical vapor deposition method using precursors consisting of ferrocene and melamine to control the nitrogen content. Structure, morphology and composition of all CN_x catalysts were characterized by SEM, TEM, and XPS. These results indicated that the surface nitrogen content (up to 7.7 at.%) increases with the increase of melamine used. Electrochemical methods were used to study the correlation between surface structure and the activity of oxygen reduction reaction (ORR) in acid and alkaline solutions. Electrochemical data indicated that the higher the nitrogen content is, the higher the oxygen reduction activity. Especially, the results from the rotating ring disk electrode technique demonstrated that CN_x (7.7%) has similar ORR activity and selectivity with commercial Pt/C in alkaline solution.     

Soybean milk derived carbon intercalated with reduced graphene oxide as high efficient electrocatalysts for oxygen reduction reaction

Exploring high-performance and low-cost metal-free oxygen reduction reaction (ORR) catalysts from biomass-derived materials is vital to the development of novel energy conversion devices such as fuel cells, etc. Herein, nitrogen-enriched soybean milk derived carbon (BDC/rGO-HT-NH₃) intercalated with reduced graphene oxide (rGO) electrocatalyst is prepared via one-pot hydrothermal synthesis method followed with nitridation by NH₃. The resultant catalyst with high surface area, good conductivity and high content of N (9.4 at.%) shows high electrocatalytic activity towards ORR in alkaline medium, which mainly happens through the direct 4-electron pathway. The onset potential of BDC/rGO-HT-NH₃ catalyzed ORR is 0.96 V vs RHE, which is only 0.11 V lower than that of the commercial Pt/C (20 wt%) catalyst. In addition, the BDC/rGO-HT-NH₃ catalyst shows superior long-term running durability. The desirable catalytic performances enable the facile synthesis approach of BDC/rGO-HT-NH₃ to be a promising methodology for transforming other biomass materials to N-enriched carbon based materials as low-cost and environmental friendly catalysts for ORR.     

Facile growth of N-doped CNTs on Vulcan carbon and the effects of iron content on electrochemical activity for oxygen reduction reaction

In order to develop cheap electrochemical oxygen reduction reaction (ORR) catalysts, N-doped CNTs grafted on Vulcan carbon were synthesized via pyrolysis of dicyandiamide on Fe₂O₃/C. Various contents of iron in Fe₂O₃/C (0, 20, 40 and 60 wt. %) were used as supports to investigate the effects and roles of iron content on ORR. It was shown that the iron acted as a promoter for doping nitrogen into carbon; as the iron content increased, the amount of nitrogen doping also increased. TEM and element analysis results indicated that iron induced growth of CNTs and facilitated N-doping in carbon. However, further increase in iron content higher than 20 wt. % showed negative effects on the ORR activity due to a decrease of the surface area of the prepared catalysts. Hence, the catalyst with the highest performance was observed when dicyandiamide was pyrolyzed with Fe₂O₃/C 20 wt. % (Fe-N-C-20) and the order of activity towards ORR was Fe-N-C-20 > Fe-N-C-40 > Fe-N-C-60 > Fe-N-C-0 > Vulcan XC-72R.     

Design of electrocatalysts with reduced Pt content supported on mesoporous NiWO4 and NiWO4-graphene nanoplatelets composite for oxygen reduction and hydrogen oxidation in acidic medium

Herein, a new direct synthesis route leading to a mesoporous NiWO₄ with crystalline framework and NiWO₄ - graphene nanoplatelets (GNP) composite is reported. Ni and W assembled into a mesoporous tungstate type of symmetry by co-precipitation synthesis route and its composite with GNP were used as supports for electrocatalysts, with reduced Pt content (8 wt.%), in oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) in acidic medium. A comprehensive assessment of the modifications related to the crystalline and porous structures, morphological aspects as well as the surface chemistry aiming to explain the electrochemical properties was performed. It was found that the presence of GNP during the synthesis process leads, mainly, to the enhanced growth of NiWO₄ nanocrystallites, as well as induces changes in the surface chemistry. The electrochemical results show that the introduction of GNPs into the NiWO₄ composite support leads to a significant improvement in the activity of the Pt electrocatalyst in ORR and HOR compared to both initial NiWO₄ and Pt/NiWO₄ samples, as well as mechanical mixtures of these catalysts with carbon. Mass activity for hydrogen oxidation, determined in a mixed kinetic-diffusion controlled region, obtained on the 8 wt.% Pt/NiWO₄-GNP catalyst was significantly higher compared to the commercial 20 wt.% Pt/C Quintech catalyst. Our comprehensive structural and surface chemistry assessments indicate this composite material as a viable electrocatalyst for PEMFCs using a broader type of fuels.     

In-situ synthesis of Fe,N, S co-doped graphene-like nanosheets around carbon nanoparticles with dual-nitrogen-source as efficient electrocatalyst for oxygen reduction reaction

Iron, nitrogen, sulfur co-doped Fe/N/C catalyst (poly-AT/Me–Fe/N/C) with the structure of graphene-like nanosheets around carbon nanoparticles were successfully synthesized for oxygen reduction reaction (ORR). 2-Aminothiazole and melamine were utilized as the dual-nitrogen-source. The results showed that 2-Aminothiazole, as the nitrogen and sulfur source, contributed to in-situ synthesizing graphene-like nanosheets around KJ-600 carbon nanoparticles with high specific surface area (1098 m²/g). Proper method to introduce melamine during the synthesis could increase the content of pyridinic-N and Fe-N_x moieties in the catalyst without changing the morphology. Due to the high surface area and high content of pyridinic-N and Fe-N_x moieties, the obtained poly-AT/Me–Fe/N/C catalyst exhibited high electrochemical activity and stability with the half-wave potential of 0.84 V (RHE) in 0.1 M NaOH solution, which is merely 17 mV lower than commercial Pt/C. The electron transfer number was 3.83, indicating a nearly 4e^? transfer for the ORR with low HO₂^? yield.     

Highly stable Ti–Co–Phen/C catalyst as the cathode for proton exchange membrane fuel cells

A Ti–Co–Phen/C catalyst was prepared for polymer electrolyte membrane fuel cells (PEMFCs) without precious metals using a modified polymer complex (PC) method with 1,10-phenanthroline (Phen) as the nitrogen precursor. The oxygen reduction reaction (ORR) activity of the Ti–Co–Phen/C catalyst was significantly higher than the ORR activity of the Ti–Co/C catalyst prepared with the PC method because the former had a larger N surface content due to its highly dispersed Co species. The catalyst also exhibited excellent chemical stability in acidic media due to the probable strong interactions between the highly dispersed Ti and Co species. A H₂/O₂ PEMFC using the Ti–Co–Phen/C catalyst as the cathode demonstrated excellent cell performance. A 0.68 W cm⁻² maximum power density was obtained. The cell performance stability did not drop perceptibly during its 550-h lifetime at 0.5 V and its 300-h lifetime at 0.7 V. The prepared Ti–Co–Phen/C catalyst exhibited both high ORR activity and excellent performance stability, making it a promising alternative for the cathode catalysts in PEMFCs.     

The influence of the structural properties of carbon on the oxygen reduction reaction of nitrogen modified carbon based catalysts

Nitrogen modified carbon based catalysts for the oxygen reduction reaction (ORR) were synthesized using three different types of carbon, carbon black (CB), carbon nanotube (CNT) and platelet carbon nanofiber (P-CNF) with nitrogen containing organic precursors. The relationship between the ORR activity and the carbon nanostructure was explored using various electrochemical and physical characterization methods. It was found that the ORR activity was affected by the type and content of the nitrogen functional group instead of the carbon surface area. The formation of nitrogen functional group, in turn, strongly depends on the carbon nanostructure. Unlike the basal plane, the edge plane exposure provides the appropriate geometry for the nitrogen incorporation into carbon structure, resulting in high nitrogen content and high pyridinic-N and graphitic-N content, providing an active site for ORR. Therefore, the P-CNF based catalyst with the highest edge plane exposure has the highest ORR activity despite having the smallest surface area.     

Preparation of electrochemically reduced graphene oxide-based silver-cobalt alloy nanocatalysts for efficient oxygen reduction reaction

The synthesis and performance of electrochemically reduced graphene oxide-based silver-cobalt (AgCo/ERGO) alloy electrocatalysts for the oxygen reduction reaction (ORR) are discussed in this study. The surface morphology, alloying nature, and chemical changes of the bimetallic precursors within the AgCo/ERGO catalyst has examined in detail. The presence of poly(ethylene glycol) (PEG) and a cobalt precursor during the electroreduction step is a necessary condition for synthesizing a highly active and stable alloy electrocatalyst for the ORR. Morphological analysis demonstrated that the AgCo nanoparticles (NPs) are homogeneously dispersed on the ERGO support with the assistance of PEG, thus resulting in higher electrochemical surface area and mass activity. X-ray analysis also confirmed the successful formation of the AgCo alloy NPs and the electrochemical reduction of graphene. The direct four-electron transfer pathway for ORR with minimal H₂O₂ yield has committed at the AgCo/ERGO catalyst over other catalysts. The as-prepared AgCo/ERGO catalyst has shown better electrocatalytic activity, stability, and tolerance to crossover effects compared to the state-of-the-art Pt/C catalyst for ORR.     

Two-step pyrolytic engineering to form porous nitrogen-rich carbons with a 3D network structure for Zn-air battery oxygen reduction electrocatalysis

It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl₂ activator and a FeCl₂ promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm^?2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices.     

A novel approach on ionic liquid-based poly(vinyl alcohol) proton conductive polymer electrolytes for fuel cell applications

The preparation of proton conducting-polymer electrolytes based on poly(vinyl alcohol) (PVA)/ammonium acetate (CH₃COONH₄)/1-butyl-3-methylimidazolium chloride (BmImCl) was done by solution casting technique. The ionic conductivity increased with ionic liquid mass loadings. The highest ionic conductivity of (5.74 ± 0.01) mS cm⁻¹ was achieved upon addition of 50 wt% of BmImCl. The thermal characteristic of proton conducting-polymer electrolytes is enhanced with doping of ionic liquid by showing higher initial decomposition temperature. The most conducting polymer electrolyte is stable up to 250 °C. Attenuated total reflectance-Fourier Transform Infrared (ATR-FTIR) confirmed the complexation between PVA, CH₃COONH₄ and BmImCl. Polymer electrolyte membrane fuel cell (PEMFC) was fabricated. This electrochemical cell achieved the maximum power density of 18 mW cm⁻² at room temperature.     

Enhancement of hydrogen storage capacity in polyaniline-vanadium pentoxide nanocomposites

The high-pressure H₂ sorption isotherms of polyaniline–vanadium pentoxide nanocomposites (PANI–VONC) have been performed at liquid nitrogen temperature. A large increment of hydrogen storage capacity occurs in PANI–VONC (∼1.8 wt%) in contrast to that in pristine vanadium pentoxide (∼0.2 wt%) and in non-treated polyaniline (∼0.2 wt%). It is considered that the reason for the enhancement of hydrogen storage in PANI–VONC is the intercalation of polyaniline (PANI) into the vanadium pentoxide layers. The intercalation of PANI decreases the interlayer distance from 1.1 nm between vanadium pentoxide layers to 0.72 nm between vanadium pentoxide layer and polyaniline layer.     

S,N co-doped graphene quantum dots decorated TiO2 and supported with carbon for oxygen reduction reaction catalysis

Sluggish kinetics and catalyst instability in oxygen reduction reaction are the central issues in fuel cell and metal-air battery technologies. For that, highly active, stable, and low-cost non-platinum based electrocatalysts for oxygen reduction reaction are an immediate requirement in fuel cell and metal-air battery technologies. A new composite (S,N-GQD/TiO₂/C-800) is synthesized, made of sulfur (S) and nitrogen (N) co-doped graphene quantum dot (GQD) with TiO₂. This composite is supported on carbon on heating at 800 °C under N₂ atmosphere and is explored for oxygen reduction reaction (ORR) catalyst. The synthesized composite S,N-GQD/TiO₂/C-800, shows outstanding catalytic activity with an onset potential of 0.91 V and a half-wave potential of 0.82 V vs. RHE, an alkaline medium. The Tafel slope of the catalyst is 61 mV dec^?1. The catalyst is an excellent methanol tolerant and shows good stability in an alkaline medium. The excellent ORR activity of S,N-GQD/TiO₂/C-800 is ascribed to well-built interactivity between the S,N-GQD/TiO₂, and the carbon support. The unique structure offers advantages, with outstanding electrical conductivity, high surface area, and excellent charge transfer kinetics between the doped GQD and TiO₂ interface and subsequently from the carbon surface to the S,N-GQD/TiO_2.     

High stability and activity of Pt electrocatalyst on atomic layer deposited metal oxide/nitrogen-doped graphene hybrid support

A novel nanostructured support of ZrO₂/nitrogen-doped graphene nanosheets (ZrO₂/NGNs) hybrid was synthesized successfully by atomic layer deposition (ALD) technology to significantly improve the activity and stability of Pt electrocatalyst. Electrochemical test shows that Pt–ZrO₂/NGNs catalyst has 2.1 times higher activity towards methanol oxidation reaction (MOR) than Pt/NGNs catalyst, due to the promotion by ZrO₂ to the MOR on Pt surface. Pt–ZrO₂/NGNs catalyst has higher electrochemical surface area (ECSA) and better oxygen reduction reaction (ORR) activity than Pt/NGNs catalyst. Pt–ZrO₂/NGNs catalyst has also demonstrated 2.2 times higher durability than that of Pt/NGNs. The enhanced activity and durability were attributed to the unique triple-interaction of ZrO₂–Pt–NGNs. These findings indicate that metal oxide-metal-support is a promising catalyst structure for low temperature fuel cells.     

Iron-based sulfur and nitrogen dual doped porous carbon as durable electrocatalysts for oxygen reduction reaction

The widespread use of fuel cell technology is hampered by the use of expensive and scarce platinum metal in electrodes which is required to facilitate the sluggish oxygen reduction reaction (ORR). In this work, a viable synthetic approach was developed to prepare iron-based sulfur and nitrogen dual doped porous carbon (Fe@SNDC) for use in ORR. Benzimidazole, a commercially available monomer, was used as a precursor for N doped carbon and calcined with potassium thiocyanate at different temperatures to tune the pore size, nitrogen content and different types of nitrogen functionality such as pyridinic, pyrrolic and graphitic. The Fe@SNDC–950 with high surface area, optimum N content of about 5 at% and high amount of pyridinic and graphitic N displayed an onset potential and half-wave potential of 0.98 and 0.83 V vs RHE, respectively, in 0.1 M KOH solution. The catalyst also exhibits similar oxygen reduction reaction performance compared to Pt/C (20 wt%) in acidic media. Furthermore, when compared to commercially available Pt/C (20 wt%), Fe@SNDC–950 showed enhanced durability over 6 h and poison tolerance in case of methanol crossover with the concentration up to 3.0 M in oxygen saturated alkaline electrolyte. Our study demonstrates that the presence of N and S along with Fe-N moieties synergistically served as ORR active sites while the high surface area with accessible pores allowed for efficient mass transfer and interaction of oxygen molecules to the active sites contributing to the ORR activity of the catalyst.     

Cattail leaf-derived nitrogen-doped carbons via hydrothermal ammonia treatment for electrocatalytic oxygen reduction in an alkaline electrolyte

Cattail leaf-derived nitrogen-doped carbons (CL-NCs) were prepared by hydrothermal treatment in ammonia solution and subsequent pyrolysis for application as catalysts for the oxygen reduction reaction (ORR). The ammonia concentration was varied at 1.0, 1.5, and 2.0 M to alter the nitrogen doping content. The characterization results revealed that CL-NCs exhibited an amorphous structure, while the density of structural defects increased as the ammonia concentration increased. The CL-NC prepared without hydrothermal ammonia treatment had a nonporous structure with a low specific surface area (5 m² g^?1). With hydrothermal ammonia treatment, CL-NCs exhibited a micro–mesoporous structure with a higher surface area (113–496 m² g^?1); however, the surface area was significantly diminished at higher ammonia concentrations due to the deterioration of the pore structure. The nitrogen-doping content in CL-NCs varied from 0.65 to 1.55 atom% with the predominant ratios of pyridinic-N and graphitic-N. For electrochemical evaluation in an alkaline electrolyte (0.1 M KOH), CL-NC prepared at an ammonia concentration of 1.0 M showed the highest ORR activity among all samples, as indicated by the most positive onset potential (?0.05 V vs. Ag/AgCl) and half-wave potential (?0.22 V vs. Ag/AgCl) as well as the highest diffusion-limiting current density with a more favorable reduction via a direct four-electron pathway (n = 3.23–3.52). The ORR activity of CL-NCs had a similar trend to their specific surface area rather than nitrogen doping content, indicating the important role of surface area and porosity in enhancing the ORR activity. Moreover, it possessed excellent stability under long-term operation and exposure to methanol. The results obtained in this work could be helpful information for the further development and utilization of biomass-derived NCs for ORR catalysts.     

Preparation of iron and nitrogen co-doped carbon material Fe/N-CCM-T for oxygen reduction reaction

In this paper, iron and nitrogen co-doped carbon material with nanotube structure (Fe/N-C_CM-T) was synthesized by pyrolyzing a mixture of Fe salt, chitosan and melamine and displayed high electrocatalytic performance for oxygen reduction reaction (ORR). The structure of the Fe/N-C_CM-T was characterized and their ORR performance in alkaline media was investigated by linear sweep voltammetry, cyclic voltammetry and chronoamperometry. Fe/N-C_CM-T displayed better ORR performance than other carbon materials like Fe/N-C_C-800. The Fe/N-C_CM-800 with a large surface area (302.5 m²/g) especially exhibited the best ORR electrocatalytic performance among the prepared carbon materials, which was also proved by its similar Tafel slope (76 mV decade^?1) to Pt/C catalyst (74 mV decade^?1). Fe/N-C_CM-800 showed similar ORR activity as commercial Pt/C catalyst, but superior tolerance to methanol and stability. Such high ORR performance of the Fe/N-C_CM-T can be attributed to its nanotube structure, high specific surface area (SSA), high graphitic-N and pyridinic-N contents.     

Mechanisms insight into oxygen reduction reaction on sulfur-doped Fe–N2 graphene electrocatalysts

The density functional theory (DFT) calculations were performed to investigate the stability of the S-doped Fe–N₂G electrocatalysts, as well as ORR mechanism and activity. The most stable configuration is the Fe–N₂S1G because of forming a strong bond structure of Fe–S. In addition, the structures of Fe–N₂S3G and Fe–N₂S4G also exhibit the higher stability compared to the undoped Fe–N₂G. According to the distinct charge difference on the surface, the O-contained intermediates would like to adsorb on the active sites of Fe–N₂ complex active sites. The binding strength of OH on these different catalysts follows the increasing order of Fe–N₂S4G < Fe–N₂S3G < FeN₂G < Fe–N₂S1G < Fe–N₂S5G < Fe–N₂S2G < Fe–N₂S6G < Fe–N₂S7G, implying the opposite order of the catalytic activity. The calculations of the free energy diagrams show that all elementary reaction steps on Fe–N₂S4G, Fe–N₂S3G, FeN₂G and Fe–N₂S1G are downhill. Besides, the rate determining step (RDS) for these catalysts (excluded Fe–N₂S4G) is the fourth reduction step (OH*+H⁺+e⁻→H₂O+*). The study of the reaction mechanisms predicted that the direct 4-electron reduction process is the favorable ORR pathway, and the alternative reaction pathways containing the formation of OH* + OH* co-adsorbate also process without the formation of H₂O₂ for these catalysts. Particularly, Fe–N₂S4G also exhibits the outstanding performance for H₂O₂ reduction. In general, since the higher stability and working potential for ORR, Fe–N₂S4G is predicted to be the prior candidate site for ORR among S-doped FeN₂G catalysts.     

Sm0.5Sr0.5Co0.4Ni0.6O3−δ–Sm0.2Ce0.8O1.9 as a potential cathode for intermediate-temperature solid oxide fuel cells

The mixed ionic and electronic conductors (MIECs) of Sm_0.5Sr_0.5Co_0.4Ni_0.6O_3−δ (SSCN)–Sm_0.2Ce_0.8O_1.9 (SDC) were investigated for potential application as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on an SDC electrolyte. Electrochemical impedance spectroscopy (EIS) technique was performed over the temperature range of 600–850 °C to determine the cathode polarization resistance which is represented by area specific resistance (ASR). To investigate the ORR mechanism, the impedance diagram for 70SSCN–30SDC was measured under applied cathodic voltage from E = 0.0 to E = −0.3 V. It indicated that the charge transfer dominated the rate-determining step at the temperature of 600 °C; whereas the diffusion or dissociative adsorption of oxygen dominated the rate-determining step at the temperature of 800 °C. In this study, the exchange current density (i₀) for oxygen reduction reaction (ORR) was determined from the EIS data. The i₀ value of 70SSCN–30SDC/SDC was 187.6 mA cm⁻² which is larger than the i₀ value of 160 mA cm⁻² for traditional cathode/electrolyte, i.e. LSM/YSZ at 800 °C, indicating that the 70SSCN–30SDC composite cathode with a high catalytically active surface area could provide the oxygen reduction reaction areas not only at the triple-phase boundaries but also in the whole composite cathode.