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Samaria-doped ceria (SDC) overlayers were deposited on Ag cathodes by sputtering. The SDC sputtering time was varied to investigate the properties of the Ag–SDC overlayer cathode-coated fuel cells depending on the thickness of the SDC overlayers. Among the fabricated fuel cells, Ag with a 10-nm-thick SDC overlayer (Ag-SDC10) cathode-coated fuel cell exhibited the highest peak power density of 6.587 mW/cm2 at 450 °C, showing higher performance than a pristine Pt-coated fuel cell. Moreover, electrochemical impedance spectroscopy revealed that the Ag-SDC10 cathode-coated fuel cell significantly mitigated polarization loss originating from enhanced oxygen reduction reaction kinetics compared to the pristine Ag-coated fuel cell. [ABSTRACT FROM AUTHOR]

[Display omitted] Lowering the operating temperatures of solid-oxide fuel cells (SOFCs) is critical, although achieving success in this endeavor has proven challenging. Herein, Bi 0.15 Sr 0.85 Co 0.8 Fe 0.2 O 3−δ (BiSCF) is systematically evaluated as a carbon dioxide (CO 2)-tolerant and highly active cathode for SOFCs. BiSCF, which features Bi3+ with an ionic radius similar to Ba2+, exhibits activity (e.g., 0.062 Ω cm2 at 700 °C) comparable to that of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ and PrBaCo 2 O 5+δ , while demonstrating a considerable advantage over Bi-doped cathodes. Moreover, BiSCF exhibits long-term stability over a period of 500 h, and an anode-supported cell with BiSCF achieves a power density of 912 mW cm−2 at 650 °C. The CO 2 -poisoned BiSCF exhibits quick reversibility or slight activation after returning to normal conditions. The exceptional CO 2 tolerance of BiSCF can be attributed to its reduced basicity and high electronegativity, which effectively restrict surface Sr diffusion and hinder subsequent carbonate formation. These findings highlight the substantial potential of BiSCF for SOFCs operating below 700 °C. [ABSTRACT FROM AUTHOR]

Studying the ORR activity of platinum-based electrocatalysts is an urgent task in the development of materials for proton-exchange membrane fuel cells. The catalytic ink composition and the formation technique of a thin layer at the RDE play a significant role in studying ORR activity. The use of a polymer ionomer in the catalytic ink provides viscosity as well as proton conductivity. Nafion is widely used as an ionomer for research both at the RDE and in the MEA. The search for ionomers is a priority task in the development of the MEA components to replace Nafion. The study also considers the possibility of using the LF4-SK polymer as an alternative ionomer. The comparative results on the composition and techniques of applying the catalytic layer using LF4-SK and Nafion ionomers are presented, and the influence of the catalytic ink composition on the electrochemical characteristics of commercial platinum–carbon catalysts and a highly efficient platinum catalyst based on an N-doped carbon support is assessed. [ABSTRACT FROM AUTHOR]

[Display omitted] • We synthesized Au@PtNiAu concave octahedral core-shell nanocatalysts (Au@PtNiAu-COCS). • The mass activity of this catalyst is 11.22 times in ORR and 4.56 times in MOR than commercial Pt/C. • It exhibits a superior power density under fuel cell operation and better performance. • Its half-wave potential displacement after 30 k cycles is only 12 mV. • It retained the 78.8% of MA after 30 k cycles in ORR and lower CO oxidation overpotential in MOR. Despite the remarkable research efforts, the lack of ideal activity and state-of-the-art electrocatalysts remains a substantial challenge for the global application of fuel cell technology. Herein, is reported the synthesis of Au@PtNiAu concave octahedral core-shell nanocatalysts (Au@PtNiAu-COCS) via solvothermal synthesis modification and optimization approach. The special structure generating a large number of step atoms, enhancing the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activity and stability. The superior ORR mass activity of the Au@PtNiAu-COCS is 11.22 times than the exhibited of Pt/C initially by Pt loading, and 5.11 times by Pt + Au loading. After 30 k cycles the mass activity remains 78.8% (8.83 times the initial Pt/C activity) and the half-wave potential only shifts 12 mV. Au@PtNiAu-COCS has superior half-cell activity and gives ideal membrane electrode assemblies. Furthermore, for MOR the Au@PtNiAu-COCS show enhanced anti-toxic (tolerant) ability in CO. This work provides a new strategy to develop core-shell structure nanomaterials for electrocatalysis. [ABSTRACT FROM AUTHOR]

Polyazomethine (PAM) prepared from the polycondensation between p-phenylene diamine (PDA) and p-terephthalaldehyde (PTAl) via Schiff reaction can physically crosslink (complex) with Co ions. Co-complexed PAM (Co-PAM) in the form of gel is calcined to become a Co, N-co-doped carbonaceous matrix (Co-N-C), acting as cathode catalyst of an anion exchange membrane fuel cell (AEMFC). The obtained Co-N-C catalyst demonstrates a single-atom structure with active Co centers seen under the high-resolution transmission electron microscopy (HRTEM). The Co-N-C catalysts are also characterized by XRD, SEM, TEM, XPS, BET, and Raman spectroscopy. The Co-N-C catalysts demonstrate oxygen reduction reaction (ORR) activity in the KOH(aq) by expressing an onset potential of 1.19–1.37 V vs. RHE, a half wave potential of 0.70–0.92 V, a Tafel slope of 61–89 mV/dec., and number of exchange electrons of 2.48–3.79. Significant ORR peaks appear in the current–voltage (CV) polarization curves for the Co-N-C catalysts that experience two-stage calcination higher than 900 °C, followed by double acid leaching (CoNC-1000A-900A). The reduction current of CoNC-1000A-900A is comparable to that of commercial Pt-implanted carbon (Pt/C), and the max power density of the single cell using CoNC-1000A-900A as cathode catalyst reaches 275 mW cm−2. [ABSTRACT FROM AUTHOR]

Layered perovskite (La1−xSrx)2CoO4±δ (x = 0.3, 0.4, 0.5) oxides were prepared using sol–gel route and evaluated as the cathode materials for intermediate-temperature solid-oxide fuel cells. (La1−xSrx)2CoO4±δ has a tetragonal structure with space group of I4/mmm in all cases of x levels. The average thermal expansion coefficient of (La1−xSrx)2CoO4±δ is relatively low and slightly increases with x, which can be ascribed to the sway of Sr doping on the spin-state transition of Co ions. X-ray photoelectron spectroscopy and thermogravimetric analysis show that Co ions exist in mixed oxidation states, but the lattice oxygen content considerably varies with x. Regarding transport property, (La1−xSrx)2CoO4±δ behaves like a semiconductor in the temperature range of 200–800 °C, and the electrical conductivity significantly increases with x. As one of the most important results, electrochemical performance of (La1−xSrx)2CoO4±δ cathode is affected by x in a complex manner, and x = 0.4 cathode, i.e., La1.2Sr0.8CoO4±δ, has the most favored area-specific resistance of 0.062 Ω cm2 and the highest power density of 630 mW cm−2 in an electrolyte-supported single cell at 800 °C, showing a rapid kinetics toward oxygen reduction reaction. This study demonstrates that the structural, transport, thermal, and electrochemical properties of (La1−xSrx)2CoO4±δ cathodes significantly depend on the La/Sr ratio at the A-site of lattice. Rietveld refinement profile and temperature-dependent electrochemical performance for La1.2Sr0.8CoO4±δ cathode material [ABSTRACT FROM AUTHOR]

A cathode catalyst possessing increased activity for oxygen reduction reaction (ORR) with superior durability is greatly required for polymer electrolyte membrane fuel cells (PEMFCs). Although Platinum (Pt) alloys have been widely studied for ORR, their real time application in fuel cells still remains a challenging task. Chemically ordered Pt alloys have attracted widespread attention due to the unique electronic and geometric factors that boost their electrocatalytic activity. Therefore, it is highly urgent to fabricate such ordered alloys as efficient cathode catalysts in fuel cells. Herein we report for the first time, a one-step solid-state method for the preparation of Pt 3−x Co 0.5+y Ni 0.5+y /C (x = 0, 1, 2; y = 0, 0.5, 1) nanoparticles on carbon support. Different compositions of this catalyst were studied and Pt 2 Co 1 Ni 1 /C was found to be the optimal, best performing catalyst both under half-cell and full-cell conditions. Interestingly, the mass activity of Pt 2 Co 1 Ni 1 /C was found to be seven times higher than that of commercial Pt/C in an acidic medium, achieving the Department of Energy (DOE) target for 2025. Moreover, a retention in mass activity after 50k cycles confirmed the superiority of this catalyst in effectively catalysing ORR reactions under an acidic medium. Importantly, the peak power density achieved by Pt 2 Co 1 Ni 1 /C under actual PEMFC operating conditions outperforms the commercially used Pt/C. Thus, this work provides a new approach for the simple and scalable synthesis of optimal cathode catalysts for fuel cells, opening up new dimensions in the field of energy research. • One-step solid-state method for the preparation of Pt 3−x Co 0.5+y Ni 0.5+y /C (x = 0, 1, 2; y = 0, 0.5, 1) nanoparticles. • I m of Pt 2 Co 1 Ni 1 /C found to be seven times higher than that of commercial Pt/C in an acidic medium. • Retention in mass activity after 50k cycles. • The peak power density of Pt 2 Co 1 Ni 1 /C under PEMFC conditions outperforms Pt/C. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) flower-like Bi 2 SiO 5 nanomaterials (FLB) and 3D flower-like Bi 2 SiO 5 @nitrogen doped graphene nanomaterials (FLBNG) have been originally synthesized. Notably, as-synthesized FLB and FLBNG nanomaterials have not yet been discussed in previous reports. The FLBNG nanomaterials have been for the first time studied as the cathodic catalysts for Fuel cell. Research results have shown that the FLBNG-2 possesses perfectly 3D flower-like Bi 2 SiO 5 with numerous uniformly coiled nanowires and exhibits good methanol immunity, high activity and high durability during oxygen reduction reaction (ORR) process under acidic and basic electrolytes. The value of onset potential (E 0) for FLBNG-2 in alkaline electrolyte can reach to 1.091 V, Tafel slope of FLBNG-2 is 45.637 mV dec−1 and its limiting current density (J L) is 6.49 mA cm−2. Similarly, These ORR performances in acidic electrolyte are also better than those of 20 wt% commercial Pt/C and most of the associated reports. Thus, the FLBNG-2 could be a potential ORR catalyst, applied in the cathode of fuel cells to enhance the kinetic rate, decrease costs and enhance durability. And this synthesis method may be provide a good design to synthesize other 3D flower-like nanomaterials with desirable properties. [ABSTRACT FROM AUTHOR]

Abstract High-efficiency cathode catalysts are essential for microbial fuel cell development since they are one of the key components in chemical energy conversion in organic compounds into electricity. Here, novel Fe Mn bimetallic nanocatalysts are designed and hydrothermally synthesized for microbial fuel cells. Fe:Mn (atom%) = 1:4, 1:2, 1:1, and α-MnO 2 are applied in air-cathodes with Pt/C and activated carbon catalysts as benchmarks, and Fe Mn catalysts can enhance the performance. When Fe:Mn = 1:2, the FeMn 2 achieves a maximum power density of 1940 ± 31 mW m−2 in microbial fuel cells and a current density of 19.4 A m−2 at −0.056 V in abiotic electrochemical tests, 24% and 37% higher than Pt/C respectively. Material characteristics are systematically analyzed since they are directly related to the catalytic performance. The high catalytic activity of FeMn 2 proves to result from a combination of the weak Mn O bonds, large quantity of defects, large specific surface area and high Mn(III):Mn(IV) ratio, according to the proposed possible mechanisms of Fe Mn catalysts to enhance the output. This work not only puts forwards an easy-to-accomplish method to design and prepare bimetallic nanocatalysts, but also provides a potential alternative to Pt/C in microbial fuel cells for sustainable energy generation. Graphical abstract Image 1 Highlights • Fe Mn nanocatalysts were designed and prepared for MFC via hydrothermal method. • FeMn 2 air-cathode exhibited the highest MFC maximum power density of 1940 mW m−2. • The synergism of Fe3+ and α-MnO 2 lattice has been demonstrated. • The best performance of FeMn 2 was illustrated by proposed catalytic mechanisms. • The FeMn 2 outperformed commercial Pt/C and could be a potential alternative. [ABSTRACT FROM AUTHOR]

A carbon supported Pt catalyst with tetradecyltrimethylammonium bromide (TTAB) adsorbed to the nanoparticle surface was operated and tested as a cathode in a polymer electrolyte membrane fuel cell. The fuel cell with the TTAB@Pt/C catalyst showed a higher current relative to the amount of Pt used than the fuel cell with a commercial Pt/C catalyst. Besides, CO stripping evidenced that for the TTAB@Pt/C electrode large parts of the Pt surface were covered by TTAB. Hence, the fuel cell with the TTAB@Pt/C cathode showed a larger current related to the electrochemical active surface area as compared to the fuel cell with the commercial Pt/C cathode. This improvement in the ORR kinetics was further investigated by X-ray photoelectron and in-situ X-ray absorption spectroscopy, and was found to have been caused by two effects: (1) the presence of a metal-ligand charge transfer in the TTAB@Pt/C electrode and (2) the prevention of oxygen containing adsorbates which were being formed in large amounts on the Pt/C electrode. Furthermore, the latter effect also explains the higher stability observed for the TTAB@Pt/C compared to the Pt/C electrode. [ABSTRACT FROM AUTHOR]

AEMFC is becoming a prominent technology in portable energy sources. In an attempt to make it economical, non-platinum catalysts are necessary to recruit in the application. Numerous researches are accomplished on the development of platinum-free catalysts. This review summarizes the advancements in the synthesis of catalysts consisting of different components and structures. Rotating ring-disk electrode (RRDE) and fuel cell tests are commonly employed to evaluate the activity for oxygen reduction reaction (ORR) and performances of the catalysts. Here, along with the synthesis and characterization data, this information is assembled and analyzed correlating different factors. To the best of our knowledge, 13 among 203 catalysts have overcome the peak power density (PPD) threshold of 1000 mW.cm-2, which belong to the four categories i.e. Metal-Nitrogen-Carbon (M-N-C), Bimetals-Nitrogen-Carbon (MM-N-C), Transition metal oxides (TMO), and non-metallic catalysts (NMC). The improvement in catalyst's porosity, surface area, conjugation of active sites, and thereby the synthesis procedures have a great effect on the ORR activity and fuel cell performance. In addition to catalyst properties, there are several other significant factors involved such as water management, properties of anion-exchange membrane (AEM) and anion-exchange ionomer (AEI), optimized operating conditions, etc. The previously low-performing catalysts with high ORR activity cannot be ignored from the top-tier catalysts, since enormous improvements are accomplished in membrane conductivity and water management recently. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the performance and durability of platinum-iron-copper with an L10 ordered face-centered tetragonal structure (fct-PtFeCu) as cathode catalysts of membrane-electrode assemblies (MEAs) in polymer electrolyte fuel cells. The exchange current density per unit active surface area of Pt in fct-PtFeCu/C, measured in the MEA, was sufficiently higher than that of commercial Pt/C. The durability of the MEAs was evaluated by three accelerated degradation tests: (1) a load cycle durability test, which mainly accelerates the degradation of catalysts; (2) an open-circuit voltage (OCV) hold test, which mainly degrades membranes; and (3) a hybrid of the load cycle test and OCV hold test. Despite the possible negative effects of dissolved transition metals on the durability of MEAs, fct-PtFeCu/C showed higher durability than commercial Pt/C and at least comparable durability with in-house Pt/C in the OCV hold test, and showed high durability in the hybrid test up to 200 h. These results suggest that the presence of Fe and Cu did not negatively affect the durability of the MEA with fct-PtFeCu/C, and rather the other factor, carbon support, affected more in retaining the durability.Graphical Abstract: [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is a multi-step catalytic process occurring at the cathode in fuel cells. As an alternative to a conventional Platinum catalyst, PtSn-based alloy catalyst experimentally presents an enhanced ORR activity compared with pure Pt catalysts. However, how the ORR reaction proceeds on PtSn is not yet well understood. On this context, a systematic study of O 2 reduction on the (1 1 1) facets of Pt 3 Sn based on periodic density functional theory (DFT) calculation is presented. With the charge transfer from Sn to Pt, d -band center shifts away from the Fermi level, the electronic structure thoroughly differs from that of pure Pt thus producing ligand (electronic) effect. The ORR intermediates (H, O, OH, O 2 , OOH, H 2 O 2 , and H 2 O) species preferred site, adsorption configuration, binding energies, active barriers, rate constants, equilibrium constant are studied. Additionally, the corresponding transition states in seven elementary reactions are confirmed using the climbing image nudged elastic band (CI-NEB) method, and the thermodynamic and dynamic property in each reaction step are evaluated. Herein, the DFT results imply that on both the Pt 3 Sn(1 1 1) and Pt(1 1 1) surfaces, the ORR share the same mechanism following OOH ad dissociation pathway (O 2ad  → OOH ad  → O ad  → OH ad  → H 2 O ad ). The rate-determining step of the ORR on the (1 1 1) surfaces is found to be the O ad hydrogenation reaction which requires activation barrier of 0.66 eV on the Pt 3 Sn(1 1 1) surface and 0.77 eV on the pure Pt(1 1 1) surface, indicating the introduction of Sn significantly decreases the activation energy barrier. As the same temperature, the reaction rate of ORR on the Pt 3 Sn(1 1 1) surface is faster than that on the pure Pt(1 1 1) surface. Our thermodynamic and kinetic results verify the important role of tin in improving the catalytic activity of ORR. [ABSTRACT FROM AUTHOR]

A cathode of zinc-air fuel cells (ZAFCs) comprises a catalyst layer and a diffusion layer. We propose a new type of cathode, which overcomes the disadvantages of a double-layer cathode used in ZAFCs. To improve the performance of the single-layer cathode, dispersing the particles and reducing their size in the cathode mixture were conducted. The single-layer cathode had the same hydrophobicity as with the diffusion layer of the double-layer cathode and showed better electrochemical properties than the catalyst layer of the double-layer cathode. The single-layer cathode had a dense microstructure and a flat surface. The electrochemical performance and mechanical strength of the single-layer cathode were superior to those of a double-layer cathode. We showed single-layer cathode cell had better electrochemical performance than the double-layer cathode cell through a newly designed flexible-tubular-type ZAFC. [ABSTRACT FROM AUTHOR]

Due to the high cost of Pt catalyst, reducing the amount of Pt in electrodes is one of the primary issues in polymer electrolyte membrane fuel cells. In this study, the hybrid cathode catalyst using the electrochemically active carbon composite catalyst and Pt catalyst is developed in order to reduce the amount of Pt and increase the overall catalytic performance. The carbon composite catalyst (CCC) is synthesized by pyrolysis of Fe-Co chelate compound followed by acid leaching. The current density of Pt/CCC is 1.5–6-fold higher than that of Pt/CB when employing ultra-low Pt loading (0.04 mg Pt cm −2 ). It is found that the Pt/CCC with the ultra-low Pt loading at tuned operating conditions exhibits a higher fuel cell performance than the Pt/CB and commercial Pt/C with four times higher Pt loading (0.16 mg Pt cm −2 ). The extensive activity of Pt/CCC is ascribed to the synergistic effect through (1) the combined activity of catalytic sites present in the CCC support and Pt, (2) the well-distributed nanoparticles and (3) the increased metallic Pt 0 concentration which indicated that the pyridinic-N played a role of oxide-cleanser. [ABSTRACT FROM AUTHOR]

Direct methanol fuel cells (DMFCs) are promising electrochemical systems capable of producing electricity from the electrochemical oxidation of methanol and the reduction of oxygen. In this work, the effectiveness of the addition of sulfuric acid as a supporting electrolyte for methanol fuel composition was assessed. The results showed that the peak of power curve in DMFCs with Pt/C cathode electrocatalysts increased progressively from 70 mW cm−2 (0 mM of H 2 SO 4) to 115 mW cm−2 with a concentration of 100 mM of H 2 SO 4. These results underlined the positive effect of the addition of a supporting electrolyte in the methanol aqueous solution on the electrochemical output that was enhanced. Platinum group metal-free (PGM-free) electrocatalysts based on Fe-N x -C type were also tested being insensitive to methanol crossover and oxidation at the cathode. DMFC with Fe–N–C cathode catalysts result in a performance of 21.5 mW cm−2. In these operating conditions, the addition of supporting electrolyte does not seem to bring excessive advantage. Short stability tests are presented and an overall assessment of the resistances within the system is also discussed. • Addition of H 2 SO 4 in methanol feed boosts DMFC power density using Pt/C catalyst. • Power density is not dependent on H 2 SO 4 concentration using PGM-free catalyst for ORR. • Addition of H 2 SO 4 does not affect short-term cell performance. • Catalysts morphology and composition are not affected by H 2 SO 4 presence. [ABSTRACT FROM AUTHOR]

This study was conducted to develop new fabrication techniques and achieve improved performance of the cathode in liquid fuel cells. An integrated electrode with a sandwich-structured MnCo 2 O 4 /NC/MnO 2 catalyst was prepared by in-situ growth on nickel foam. The resulting integrated electrode was tested as the cathode of the alkaline direct methanol fuel cell (DMFC) and direct borohydride fuel cell (DBFC). The data indicated peak power density of 12.22 mW cm−2 for DMFC, and 33.65 mW cm−2 for DBFC. The in-situ growth of the MnCo 2 O 4 /NC/MnO 2 catalyst layer, without an organic binder, indicated a superior catalytic activity to that of MnCo 2 O 4 and MnCo 2 O 4 /NC. Moreover, stability test conducted at a constant-current discharge of 10 mA cm−2 for the integrated cathode-based DBFC revealed excellent stability for about 350 h. Compared to that of traditional cathode prepared by doctor-blade method, traditional cathode showed a significantly diminished discharge voltage. Thus, the highly dispersed nanocatalysts and the macroporous nickel foam accelerated the intrinsic catalytic activity and mass transfer in the cathode. This work provides a new strategy for the preparation and structure optimization of fuel cell electrodes. [Display omitted] • An integrated cathode with sandwich-structured MnCo 2 O 4 /NC/MnO 2 catalyst was prepared. • The sandwich-structured catalyst was prepared by in-situ growth on nickel foam (NF). • The integrated cathode was tested in alkaline DMFC and DBFC. • The cell stability was enhanced for the dispersed nanocatalysts and macroporous NF. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells (SOFCs) have attracted attention as clean and efficient energy conversion devices with low emissions. However, several degradation mechanisms limit the electrochemical performance of current SOFCs, with cathode degradation due to Cr-poisoning from metal interconnects particularly problematic. The acidity/basicity of binary additives has been found to be a sensitive descriptor of the oxygen exchange kinetics, indicating that acidic Cr-species/basic Ca-species can be expected to deactivate/activate the cathode surface, respectively. Inspired by recent advances, the feasibility of relative acidity as a tool for reviving degraded SOFCs is demonstrated by neutralizing Cr-poisoned SOFCs by subsequent serial infiltration of Ca-species. A model mixed ionic and electronic conducting oxide, Pr 0.1 Ce 0.9 O 2-δ (PCO), is selected as the cathode material. Area-specific resistances (ASR) of symmetric cells obtained by electrochemical impedance spectroscopy show that Cr-infiltration results in a seven-fold increase in ASR, while subsequent infiltration of Ca-species leads to complete recovery. Performance degradation and recovery are attributed to depressed/enhanced redox properties at the PCO surface, as supported by XPS analysis. Experiments using anode-supported fuel cells show a reduction in peak power density by 26% upon Cr-infiltration, reversed following Ca-infiltration, after which no degradation is observed during subsequent operation for 100 h. • Relative surface acidity can be used to recover degraded SOFC performance. • Acidic Cr-additives lead to severe degradation in cell power output by over 26%. • Serial infiltration of basic Ca-additives fully recovers Cr-degraded performance. • Change in local surface chemistry is correlated to change in performance. • Recovered SOFC power output shows no noticeable degradation for 100 h. [ABSTRACT FROM AUTHOR]

As a kind of nitrogen-containing material, polyamide acid (PAA) was doped by Fe using ferric trichloride (FeCl 3 ), thus obtaining a carbon material (Fe-PAA) containing iron and nitrogen. The preparation efficiency of this material as electrocatalyst was improved and the cost was reduced. In this study, Fe-PAA was used as cathode electrocatalyst in microbial fuel cells (MFCs), and the effect of holding time (HT) on the oxygen reduction was investigated. The oxygen reduction reaction (ORR) electron transfer number of the Fe-PAA was about 3.55 when the HT was 90 min. This result demonstrates that Fe-PAA could be a promising highly efficient and low-cost cathode catalyst which could be further applied in MFC expansion. [ABSTRACT FROM AUTHOR]

A new platinum group metal (PGM)-free proton exchange membrane fuel cell (PEMFC) cathode catalyst materials, synthesized using the VariPore™ method by Pajarito Powder, LLC, are characterized for their structure and activity. The physico-chemical analysis of the iron-nitrogen-carbon (Fe-N-C) electrocatalysts show mesoporous carbon material effectively doped with iron and nitrogen. The materials have an average pore size of 7–8 nm and high specific surface area. The Fe-N-C catalysts exhibit good oxygen reduction reaction (ORR) activity in 0.5 M H 2 SO 4 electrolyte with high half-wave potential and sustainable electrochemical stability over 10,000 repeated potential cycles with insignificant losses in their activities. As cathode catalysts in a PEMFC, the Fe-N-C materials deliver remarkably good fuel cell performance at low overpotential approaching that of the commercial Pt catalyst. The high ORR electrocatalytic activity of these Fe-N-C catalysts is credited to the synergy between nitrogen-moieties, specifically pyrrolic-N, pyridinic-N, and graphitic-N, and iron in addition to the high mesoporosity that facilitate an effective reaction path in boosting the electrocatalytic activity and stability. [Display omitted] • State-of-the-art commercial PGM-free catalysts for ORR were characterized and evaluated. • Was shown that active centres are atomically dispersed. • Performance of electrocatalysts was evaluated in industrially manufactured MEA form-factor. • The fuel cell performance is close to the state-of-the-art R&D PGM-free catalysts. [ABSTRACT FROM AUTHOR]

A planar iron-polyphthalocyanine (PPcFe) oxygen reduction reaction (ORR) catalyst for magnesium air fuel cells (MAFC) is prepared by dispersing PPcFe on carbon black (C) and heating under argon. Thermogravimetric analysis shows PPcFe is stable below 600 °C. The X-ray diffraction and X-ray photoelectron spectroscopy results show the active site of PPcFe/C is the FeN4 in the phthalocyanine ring. The rotating disk electrode measurements in 0.5 M L−1 H2SO4 solution show the initial potential for ORR is 0.82 V vs. RHE at 20 °C and that it mainly occurs via a four-electron process. Almost no performance degradation is observed over continuous cyclic voltammetry at 10,000 cycles, linear sweep voltammetry at 200 cycles, and 60 h of the chronoamperometry test. The infrared spectrum of PPcFe, after all the durability tests, shows no changes from the initial characteristics. The polarization curves of the air electrodes with PPcFe/C, iron-phthalocyanine/C and Pt/C catalysts exhibit excellent polarization performances. The discharge performance of a MAFC single cell with PPcFe/C cathode catalyst shows an open circuit potential of 1.74 V, with a peak power density of 50.5 mW cm−2 at 20 °C. The cell voltage decreases less than 0.01 V during continuing discharge @ 20 mA cm−2 for more than 11 h. [ABSTRACT FROM AUTHOR]

Abstract: A perovskite-type oxide LaNi0.8Co0.2O3 is prepared as a direct borohydride fuel cell (DBFC) cathode catalyst. Its electrochemical properties are studied by cyclic voltammetry. The results demonstrate that LaNi0.8Co0.2O3 exhibits excellent electrochemical activity with respect to the oxygen reduction reaction (ORR) and good tolerance of BH4 − ions. Maximum power densities of 114.5mWcm−2 at 30°C and 151.3mWcm−2 at 62°C are obtained, and good stability (300-h stable performance at 20mAcm−2) is also exhibited, which shows that such perovskite-type oxides as LaNi0.8Co0.2O3 can be excellent catalysts for DBFCs. [Copyright &y& Elsevier]

Abstract: Fuel cells, especially low temperature fuel cells are clean energy devices that are expected to help address the energy and environmental problems that have become prevalent in our society. Platinum-based electrocatalysts are usually used as the electrocatalysts for both the anode (hydrogen oxidation) and cathode (oxygen reduction) reactions. The high cost and limited resources of this precious metal hinder the commercialization of fuel cells. Recent efforts have focused on the discovery of palladium-based electrocatalysts with little or no platinum for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). This paper overviews the recent progress of electrocatalysis of palladium-based materials including both extended surfaces and nanostructured ones for HOR and ORR. The properties of CO and methanol tolerances of palladium-based electrocatalysts are also summarized. [Copyright &y& Elsevier]

Abstract: The development of new cost-effective cathode catalysts with high methanol tolerance and at a high catalyst loading is highly desirable for the direct methanol fuel cell. The Pd3Pt1 bimetallic alloy nanoparticles highly loaded on different carbon supports, including Vulcan XC-72R carbon, single and multi-walled carbon nanotubes (SWCNTs/MWCNTs) and ordered mesoporous carbon (OMC), have been prepared by a modified polyol reduction route. The activities of the catalysts for the oxygen reduction reaction (ORR) have been studied based on the rotating disk and ring-disk electrode (RDE/RRDE) techniques in pure and methanol-containing electrolytes. X-ray diffraction indicates that all the Pd3Pt1/C nanoparticles evidence a single-phase fcc disordered structure. The mean particle size of Pd3Pt1 alloy nanoparticles on different supports is ca. 4–5nm even at a metal loading of 50wt%. Among various carbons supported catalysts, the highest ORR activity, found on the OMC-supported Pd3Pt1 catalyst, even surpasses that on the commercial Pt/C catalyst. Kinetic analysis reveals that the ORR on the Pd3Pt1/OMC catalyst predominantly undergoes a four-electron process, leading to water formation. Furthermore, the Pd3Pt1/OMC catalyst exhibited a higher methanol tolerance during the ORR than the commercial Pt/C catalyst; ensuring a higher ORR performance while diminishing Pt utilization. [Copyright &y& Elsevier]

Abstract: This paper reviews the compositions, design and methods of fabrication of air cathodes for alkali zinc–air fuel cells (ZAFCs), one of the few successfully commercialized fuel cells. The more promising compositions for air cathodes are based on individual oxides, or mixtures of such, with a spinel, perovskite, or pyrochlore structure: MnO2, Ag, Co3O4, La2O3, LaNiO3, NiCo2O4, LaMnO3, LaNiO3, etc. These compositions provide the optimal balance of ORR activity and chemical stability in an alkali electrolyte. The sol–gel and reverse micelle methods supply the most uniform distribution of the catalyst on carbon and the highest catalyst BET surface area. It is shown that the design of the air cathode, including types of carbon black, binding agents, current collectors, Teflon membranes, thermal treatment of the GDL, and catalyst layers, has a strong effect on performance. [Copyright &y& Elsevier]

Abstract: The performance of the positive electrode composed of a mixture of nickel hydroxide (Ni(OH)2) and a small amount of manganese dioxide (MnO2) was investigated for the positive electrode of Fuel Cell/Battery (FCB) system. It was found that the positive electrode can function not only as an active material of secondary batteries when it is charged but also as a catalyst of fuel cells when oxygen is supplied, which was confirmed by the following characterization: electrochemical characterization was performed with cyclic voltammetry (CV) and galvanostatic discharge curve in oxygen and oxygen-free atmosphere. CV of Ni(OH)2/MnO2 positive electrode exhibited the redox reaction of Ni(OH)2 as well as oxygen reduction reaction. It was observed that the discharge curves of positive electrode had two working potentials in half cell test when the electrode was charged and oxygen was supplied: one from the reactions of nickel oxyhydroxide (NiOOH); the other from the fuel cell reactions of manganese dioxide (MnO2). It was also observed that the discharge curves had two working voltages in full cell test when the cell was fully charged and oxygen was supplied: one at 1.2V from the battery reactions of NiOOH; the other at 0.8V from the fuel cell reactions of MnO2. In particular, the discharge capacity of overcharged cell was improved approximately 2 times compared with a battery of the same electrode quantity due to the additional function of this system as a fuel cell by using oxygen generated by water electrolysis. XRD analysis showed that there was no crystal structure change before and after (over)charge–discharge cycles. In summary, these experimental results showed that the novel bi-functional FCB system could provide an improved overall energy density per weight compared with conventional secondary batteries. [Copyright &y& Elsevier]

[Display omitted] • BCFZY and Ni doped BCFZY cathodes are synthetized. • Ni doped BCFZY improves the oxygen ion and proton conductivity of the cathode. • BCFZYN has a good thermal stability and a reduced thermal expansion coefficient. • Ni doping enhances the ORR activity in both O-SOFCs and PCFCs. • BCFZYN exhibits a prominent stability in both symmetrical cell and single cell test. To develop a cathode with excellent oxygen reduction reaction (ORR) activity and durability at intermediate-to-low temperatures is significant to boost the advancement of solid oxide fuel cells (SOFCs), a fascinating energy conversion technology with low emissions and high efficiency. Perovskite oxides have been extensively developed as cathodes, and doping is an important strategy to alter the lattice diffusion and surface exchange properties of perovskites, to tailor catalytic performances for various redox reactions, including ORR for SOFCs. The reported BaCo 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3-δ (BCFZY) is a promising cathode for SOFCs. Herein, to further improve the performance of BCFZY at reduced temperatures, we systematically investigate the partial doping of B-sites with different metal elements, including Mn, Ni, Cu and Zn at a fixed content of 5%. Among them, it is found that Ba(Co 0.4 Fe 0.4 Zr 0.1 Y 0.1) 0.95 Ni 0.05 O 3-δ (BCFZYN) exhibits the lowest polarization impedance in both oxygen ion and proton conducting fuel cells. Based on conductivity relaxation experiments and oxygen and hydrogen permeation tests, it is found that nickel doping improves oxygen mobility, surface exchange kinetics, and bulk oxygen ion and proton conductivity. Thereby, a high ORR activity on oxygen ion and proton conducting electrolytes is achieved, reaching 0.038 and 0.607 Ω cm2 at 550 °C, respectively. The cells with the BCFZYN electrode show outstanding operational stability (200 h of operation in a symmetrical cell and 1000 h of operation in a single cell). This suggests that the BCFZYN is a promising cathode of next-generation SOFCs. [ABSTRACT FROM AUTHOR]

Abstract: The efficiency of fuel cells suffers from the high activation polarisation at the cathode, where the oxygen reduction reaction takes place. In order to improve the performance, air electrodes composed of carbon nanotubes (CNTs) and the perovskite La0.6Sr0.4CoO3 are produced by two different methods and investigated. In the first method CNTs are directly grown on the perovskite and in the second method CNTs and perovskite are combined by ultrasonic mixing. Their catalytic activity towards oxygen reduction in alkaline solution is evaluated by polarisation curves and electrochemical impedance spectroscopy. Best performance shows the electrode composed of 25wt% CNTs, 55wt% La0.6Sr0.4CoO3 and 20wt% PTFE as binder, produced by ultrasonic mixing. The Nyquist plot of this electrode displays two potential-dependent semi-circles, accounting for processes on the catalyst surface and for processes depending on the morphology of the electrode. [Copyright &y& Elsevier]

Alkaline fuel cells (AFC) are an interesting alternative to polymer electrolyte fuel cells (PEFC). In AFC no expensive platinum metal is necessary; silver can be used for the oxygen reduction reaction (ORR) (cathode catalyst). For technical use of AFC the long term behavior of AFC components is important, especially that of the electrodes. The investigated cathodes for AFC consist of a mixture of silver catalyst and polytetrafluorethylene (PTFE) as organic binder rolled onto a metal web. The electrodes were electrochemically investigated through measuring V–i curves and electrochemical impedance spectroscopy (EIS). The electrochemical characterization and the long term tests were performed in half-cells at 70 °C using pure oxygen (1 bar) under galvanostatic conditions. The cathodes were electrochemically investigated in half-cells using reference electrodes (Hg/HgO) by periodically recording V–i curve and electrochemical impedance spectroscopy. In addition, the cathodes were physically characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). [Copyright &y& Elsevier]

Direct urea fuel cells (DUFCs) have recently drawn increased attention as sustainable power generation devices because of their considerable advantages. Nonetheless, the kinetics of the oxidation-reduction reaction, particularly the electrochemical oxidation and oxygen reduction reaction (ORR), in direct urea fuel cells are slow and hence considered to be inefficient. To overcome these disadvantages in DUFCs, Pd nanoparticles loaded onto Co3O4 supported by multi-walled carbon nanotubes (Pd/Co3O4@MWCNT) were employed as a promising cathode catalyst for enhancing the electrocatalytic activity and oxygen reduction reaction at the cathode in DUFCs. Co3O4@MWCNT and Pd/Co3O4@MWCNT were synthesized via a facile two-step hydrothermal process. A Pd/MWCNT catalyst was also prepared and evaluated to study the effect of Co3O4 on the performance of the Pd/Co3O4@MWCNT catalyst. A current density of 13.963 mA cm−2 and a maximum power density of 2.792 mW cm−2 at 20 °C were obtained. Pd/Co3O4@MWCNT is a prospectively effective cathode catalyst for DUFCs. The dilution of Pd with non-precious metal oxides in adequate amounts is economically conducive to highly practical catalysts with promising electrocatalytic activity in fuel cell applications. [ABSTRACT FROM AUTHOR]

The construction of optimized biological fuel cells requires a cathode which combines the longevity of a microbial catalyst with the current density of an enzymatic catalyst. Laccase-secreting fungi were grown directly on the cathode of a biological fuel cell to facilitate the exchange of inactive enzymes with active enzymes, with the goal of extending the lifetime of laccase cathodes. Directly incorporating the laccase-producing fungus at the cathode extends the operational lifetime of laccase cathodes while eliminating the need for frequent replenishment of the electrolyte. The hybrid microbial–enzymatic cathode addresses the issue of enzyme inactivation by using the natural ability of fungi to exchange inactive laccases at the cathode with active laccases. Finally, enzyme adsorption was increased through the use of a functionally graded coating containing an optimized ratio of titanium dioxide nanoparticles and single-walled carbon nanotubes. The hybrid microbial–enzymatic fuel cell combines the higher current density of enzymatic fuel cells with the longevity of microbial fuel cells, and demonstrates the feasibility of a self-regenerating fuel cell in which inactive laccases are continuously exchanged with active laccases. [ABSTRACT FROM AUTHOR]

This study reports on protonic ceramic fuel cells (PCFCs) that exhibit enhanced performance after the addition of palladium (Pd) interlayers at the cathode–electrode interface. The Pd interlayer is deposited by sputtering on the BaZr 0.2 Ce 0.6 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) electrolyte surface, followed by the inkjet printing of PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (PBSCF) and sintering. The proposed method successfully has produced a Pd layer that was well integrated between the BZCYYb and PBSCF layers, with no undesired reactions or phase formation. The Pd layer is diffused along the inner surface of the porous PBSCF cathode with the desired gradient composition. In our experiment, the fuel cell power is enhanced by up to 60% compared to the untreated PCFCs. In the former, the peak power density of the optimal cell is 420 mW cm−2, while that of the untreated sample is 260 mW cm−2 at 500 °C. The long-term stability of the Pd interlayer is confirmed during cell operation. The impedance analysis has revealed that the presence of the Pd significantly enhances the current collection and reduces the polarization impedance at the cathode–electrolyte interface, especially at low temperatures. These results indicate that the proposed method is promising for the fabrication of high-performance and robust PCFCs. • Palladium-rich layer is inserted between electrolyte and cathode of PCFC using DC sputter. • Co-sintering of palladium and cathode formed gradient palladium-rich layer. • Palladium-rich layer enhanced the reaction at the cathode of PCFC. • Fuel cell performance is highly affected by the amount of palladium. [ABSTRACT FROM AUTHOR]

Nd 0.9 Ln 0.1 BaCo 2 O 6- δ (NLnBCO, Ln = La, Sm, Gd) materials are synthesized by EDTA-citrate method. The effects of rare earth element doping on crystal structure, thermal expansion behavior, electrical conductivity and electrochemical properties are investigated. Nd 0.9 Ln 0.1 BaCo 2 O 6- δ crystallizes in tetragonal symmetry with the space group P4/mmm. It is found that both the unit cell volume and the average valence of cobalt in NLnBCO increase, whereas the oxygen vacancy content (δ value) decreases with the gradual enlargement of the radius of the doped rare earth elements. XPS and O 2 -TPD results prove that the surface oxygen adsorption ability of NLnBCO improves gradually with the steady increase of Co4+ concentration in the material. The electrochemical impedance spectroscopy measurement results indicate that among the doped materials, Nd 0.9 La 0.1 BaCo 2 O 6- δ exhibits the lowest polarization resistance of 0.083 Ω cm2 at 700 °C in air. The anode-supported fuel cell constructed with this cathode shows a power output of 1.045 W cm−2 at 700 °C, and stable current density of 1.7 A cm−2 has been obtained with the load of 0.6 V for prolonged 100 h consecutive measurement. The rate limiting step of the oxygen reduction reaction (ORR) is the charge transfer process on Nd 0.9 La 0.1 BaCo 2 O 6- δ cathode. Our studies prove that doping La3+ with larger radius than Nd3+ is an effective way to promote the ORR reaction on NdBaCo 2 O 6- δ cathode. • The effects of rare earth element doping on the electrochemical properties of Nd 0.9 Ln 0.1 BaCo 2 O 6- δ are investigated. • La3+ doping improves the surface oxygen adsorption ability of Nd 0.9 Lan 0.1 BaCo 2 O 6- δ. • The anode-supported fuel cell constructed with Nd 0.9 Lan 0.1 BaCo 2 O 6- δ cathode shows a power output of 1.045 W cm−2 at 700 °C. [ABSTRACT FROM AUTHOR]

Designing affordable high efficient oxygen reaction (ORR/OER) electrocatalyst is a major task for promoting sustainable energy conversion batteries (such as Zn-air batteries and fuel cells). Herein, a bifunctional oxygen reaction electrocatalyst with excellent activity and stability constructed using the peasecod-like N-doped carbon nanotubes (N/CNT) in situ confinement encapsulate bimetallic FeCu alloy (FeCu–N/C). The bimetallic FeCu alloy embedded into N/CNT that inhibits serious polymerization of copper, increases Fe/Cu–N bimetallic active sites, improves conductivity, reduces the energy barrier of oxygen reaction and speeds up reaction kinetics, thus obtaining efficient ORR/OER performance. The optimal FeCu–N/C electrocatalyst reveal more positive half-wave potential for ORR, smaller overpotential for OER and lower ORR/OER potential gap than those of commercial grade Pt/C, IrO 2 and many reported catalysts. Moreover, the zinc-air batteries constructed using FeCu–N/C as the air electrode indicate the high power density and excellent stability. The alkaline anion exchange membrane fuel cells assembled with FeCu–N/C as cathode also exhibit enhanced power density compared to single metal-based catalysts (Fe–N/C and Cu–N/C). This work demonstrates potential use of FeCu–N/C for energy conversion and storage applications, provides a new sight for the reasonable design of bifunctional oxygen reaction electrocatalysts. Image 1 • A bifunctional oxygen reaction catalyst constructed using FeCu alloy encapsulated in peasecod-like N-rich carbon nanotubes. • The FeCu alloy increases Fe/Cu-N bimetallic active sites, conductivity and electrocatalytic oxygen reaction activity. • The FeCu 0.3 -N/C exhibited the low ORR/OER potential gap (△ E) of 0.777 V and extraordinary stability. • The FeCu 0.3 -N/C reveals superb cathode catalytic activity in zinc-air batteries and anion exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is a key process for the operation of fuel cells. To accelerate the sluggish kinetics of ORR, a wide range of catalysts have been proposed and tested. In this work, a nano-dispersed copper-impregnated platinum catalyst prepared by electrodeposition of platinum on a poly[Cu(Salen)] template followed by polymer destruction is described. In addition to the high activity of the thus prepared catalyst in the oxygen reduction reaction surpassing that of both polycrystalline platinum catalyst and the commercial carbon-platinum catalyst ("E-TEK"), it showed remarkable tolerance to the presence of methanol in solution. [ABSTRACT FROM AUTHOR]

Development of non-noble metal cathode catalysts was a continuous hotspots of fuel cell research. In this work, the CoO nanorods/C with different mass content of CoO were prepared by hydrothermal method and were investigated as cathode catalysts in direct borohydride fuel cell. The CoO nanorods exhibited an average length about 1–2 μm and an average diameter about 15 nm. The 10 wt% CoO nanorods/C achieved the best oxygen reduction reaction (ORR) activity compared to the 5 wt% CoO nanorods/C and 20 wt% CoO nanorods/C. The onset reduction reaction potential of the 10 wt% CoO nanorods/C catalyst toward ORR was 0.821 V (vs. reversible hydrogen electrode), and the number of electron transfer was about 4.01. The ORR on the catalyst was mainly based on an appropriate four-electron reaction pathway. The half-wave potential difference of the 10 wt% CoO nanorods/C after 5000 cycles was 26 mV, suggesting a good catalytic stability. The DBFC using the cathode catalyst achieved a maximum power density of 410 mW cm−2 at 60 °C. The experimental results confirmed that the CoO nanorods/C had excellent catalytic performance in DBFCs. Image 1 • CoO nanorods/C was prepared by hydrothermal method. • An appropriate 4e reaction was realized on CoO nanorods/C towards ORR. • CoO nanorods/C had much better stability than Pt/C towards ORR in alkaline solution. • DBFC using CoO nanorods/C cathode achieved a maximum power density of 410 mW cm−2. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is still the most research-intensive aspect of a fuel cell. The sluggish kinetics of the electrocatalysts toward the ORR requires large amounts of platinum to be used as cathode material, which calls for alternatives to replace or minimize the amount of the noble metals used. This study describes the synthesis and complete characterization of a copper metallopolymer (Cu MP) based on a conducting polymer (CP) and single-site catalytic centers for the electrocatalytic ORR. The copper (II) catalyst, embedded in a redox-active and conducting polymeric environment, was pursued as a potential candidate to replace noble metals in fuel cell applications. Performance studies at a rotating disk electrode (RDE) showed that the metallopolymer exhibited a direct four-electron reduction at potentials between −150 and −350 mV vs. the reversible hydrogen electrode (RHE) and high kinetic current densities of over 22.62 mA/cm2. The kinetic current densities obtained at the Cu MP electrode outperformed most of the reported state-of-the art electrocatalysts toward the ORR. Further analysis of the Cu/CP hybrid revealed the copper being largely reduced to the oxidation state +I. [ABSTRACT FROM AUTHOR]