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Electrocatalysts play a pivotal role in advancing proton-exchange membrane fuel cell (PEMFC) for hydrogen energy applications. In this study, we investigate a novel PtCu/C N electrocatalyst synthesized via a gram-scale synthesis approach, which demonstrates remarkable activity and stability in the oxygen reduction reaction (ORR). The catalyst's effectiveness stems from its unique structure, combining bimetallic nanoparticles (NPs) and an N-doped carbon support. Employing identical location transmission electron microscopy (IL-TEM) imaging, we observe significant NP structure reorganization upon activation influenced by the upper limiting potential. Notably, the PtCu/C N catalyst activated to 1.0 V surpasses the United States Department of Energy (DOE) target for ORR activity by 3.3-fold. These findings underscore the potential of this catalyst in enhancing the performance of PEMFCs, marking a significant advancement in hydrogen energy technology. [Display omitted] • Catalyst's effectiveness attributed to unique structure of bimetallic NPs and N-doped support. • Vital reorganization of NPs occurs under the upper limiting potential of activation. • PtCu/C N catalyst activated to 1.0 V surpasses DOE target for ORR activity by 3.3-fold. • IL-TEM method comes to the rescue in assessing NPs' reorganization. • Findings highlight potential of bimetallic catalyst in enhancing PEMFC performance. [ABSTRACT FROM AUTHOR]

Efficient and stable electrocatalysts with low platinum content are crucial for the practical application of fuel cells. The development of Pt-based single atom catalysts (SACs) has emerged as a promising research direction. In this study, we design and prepare a SACs based on MoS 2 with Pt–S–Mo and Pd–S–Mo active sites (Pd, Pt–MoS 2) by successively occupying vacancies, while maintaining the individual characteristics of the active sites. The resulting Pd, Pt–MoS 2 catalyst exhibits excellent electrocatalytic activity for oxygen reduction reaction (ORR), long-term stability, and resistance to common poisons (SCN−, S2−, and methanol) under neutral conditions. Meanwhile, the microbial fuel cell (MFC) equipped with Pd, Pt–MoS 2 exhibits excellent performance in terms of actual electricity generation performance and sewage purification capacity with an ultrahigh power density, average chemical oxygen demand (COD) removal rate, and coulombic efficiency (CE) of 1398.6 ± 43.5 mW m−2, 96.2 ± 2.2 %, and 22.5 ± 0.5 %, respectively. This strategy will provide new insights into the development of advanced bimetallic as well as polymetallic doped vacancies of MoS 2 SACs. [Display omitted] • A feasible approach for the design of bimetallic single atom catalysts. • One SACs based on MoS 2 was prepared by successively occupying vacancies. • Pd, Pt–MoS 2 catalyst exhibits excellent electrocatalytic activity for ORR. • Optimized catalyst exhibits excellent capacity in electricity generation. [ABSTRACT FROM AUTHOR]

Designing an efficient and stable non-precious metal cathode catalyst is essential to reduce fuel cell cost and promote fuel cell commercialization. Herein, ZIF-67 and carbon powder are rapidly heated using a transient Joule heat device to pyrolyze ZIF-67 to form a CoO/N/C nanocatalysts. The prepared CoO/N/C-90 is comprised of 3–4 nm CoO nanoparticles loaded on a carbon substrate. In alkaline medium the Tafel slope of CoO/N/C-90 is 50 mV dec−1, and a half-wave potential (E 1/2) of 0.82 V towards oxygen reduction reaction (ORR). The E 1/2 only experiences a negative shift of 4 mV after 40,000 cyclic voltammetry (CV) cycles, demonstrating excellent catalytic reaction kinetics and durability. The CoO/N/C-90 is assembled into direct borohydride fuel cells (DBFC) as a cathode, achieving a maximum power density (P max) of 526 mW cm−2 at 60 °C. This work indicates that the CoO/N/C-90 is an efficient and stable non-precious metal catalyst for DBFCs. [Display omitted] • CoO/N/C nanoparticle with a size of 3–4 nm is prepared by CTS method. • CoO/N/C exhibits superior stability and highly electrochemically active area. • A DBFC with maximum power density of 526 mW cm−2 is achieved at 60 °C. [ABSTRACT FROM AUTHOR]

The development of the fuel cell catalysts with high durability and high activity for oxygen reaction reduction remains a great challenge. Various material designs such as alloys, core@shell structure and shape control provide the promising ways to improve the electrocatalytic performance. Herein, on the basis of both the alloy effect and the nanotube structure effect, we demonstrate a high-performance PtNi alloy catalyst with one-dimensional nanotube structure via a galvanic replacement reaction combined with Kirkendall effect. Meanwhile, the PtNi alloy phase and the tube structure are selectively controlled by tuning the PtNi atomic ratio and the wall thickness of the nanotube, respectively. Subsequently, the understanding of the composition effect and the shape effect on the activity and the durability is systematically investigated. The optimized PtNi nanotube catalyst shows significant improvements on the activity (6.2-fold increase in specific activity compared to the commercial Pt/C) and the durability (only 8.6% loss in mass activity after 10000 cycles), attributing to the alloy effect by introducing Ni to the Pt lattice, the Pt-rich surface and the shape effect of the unique one-dimensional hollow tube structure. Image 1 • PtNi alloy NTs are synthesized with tunable compositions and wall thicknesses. • Composition, size and nanotube effects on the performance are systematically studied. • PtNi-NTs show 1.1 times higher in MA and 6.2 times higher in SA at 0.9 V than Pt/C. • PtNi-NTs achieve an enhanced durability of 8.6% loss in MA after 10 k cycles. [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]

Abstract Novel cathode electrocatalysts based on Pd and cerium oxide nanorods (CeO 2-NR), supported on home-obtained graphene (G) and N-doped graphene (G D1, G D2), were synthesized. The electrocatalysts were identified as Pd CeO 2-NR /G, Pd CeO 2-NR /G D1 and Pd CeO 2-NR /G D2. In half cell measurements in 0.5 mol L−1 KOH, these electrocatalysts showed higher mass and specific activity for the Oxygen Reduction Reaction (ORR) than Vulcan-supported Pd/C and comparable to Pd CeO 2-NR /C. Tests in a dual-chamber Microbial Fuel Cell (MFC) were performed using pharmaceutical residual water (PRW) as anode substrate, while KOH (pH = 9.6) was the electrolyte in the cathode compartment. The bioanode was formed by commercial Pt/C electrocatalyst and Bacillus subtilis as the microorganism grown as a biofilm. Meanwhile, the gas diffusion electrode (GDE) cathode contained the above-mentioned Pd-based electrocatalysts. The MFC equipped with the Pd CeO 2-NR /G D1 electrocatalyst as cathode delivered an Open Circuit Voltage of 0.308 V and a maximum power density of 12.47 mW m−2. This performance was higher than those of the MFC with Pd/C (0.21 V and 4.50 mW m−2) and commercial Pt/C (0.21 V and 5.43 mW m−2) cathodes. Thus, Pd CeO 2-NR /G D1 is a promising cathode for MFCs. Moreover, B. subtilis demonstrated to be an active microorganism to generate electrical energy from PRW. Graphical abstract Image 1 Highlights • Application of cerium oxide nanorods (CeO 2-NR) as cathode co-catalyst. • CeO 2-NR and N-doped graphene enhance the performance of Pd for the ORR in KOH. • B. subtilis is an active microorganism to generate energy. • Pharmaceutical Residual Water is a suitable substrate for Microbial Fuel Cells. • Pd CeO 2-NR /G D1 cathode shows the higher performance in a Microbial Fuel Cell. [ABSTRACT FROM AUTHOR]

Abstract Nanostructuring of electrocatalysts is an important aspect of catalyst design as catalytic performance depends not only on the specific activity (reaction rate per surface area), but also on the dispersion of the catalyst. We present an industrially compatible, but effective preparation method for support-free nanostructured catalyst layers. Alternating sputtering was used to prepare heterogeneous Pt Cu templates ranging from 95 up to 99.5 at. % Cu. These templates were then electrochemically leached to form a nanostructured Pt Cu network and benchmarked with respect to the oxygen reduction reaction. It is shown that the templates with lower Cu:Pt ratios exhibit the highest initial specific activity but have a relatively low electrochemically active surface area. Subjecting the samples to extended accelerated stress tests, it is found that the support-free nanostructured Pt Cu networks are relatively resistant to high potential cycling, which can be explained by the lack of carbon corrosion. The loss in electrochemical surface area thereby depends on the initial Pt content. The specific oxygen reduction activity, however, approaches the value of bulk Pt. Although this decrease is not desirable, still an (specific) activity improvement of two to four times as compared carbon supported nanoparticles can be preserved. Graphical abstract Image 1 Highlights • Novel industrially scalable ORR electrode production method demonstrated. • Porous nanostructured material with a specific surface area up to 47 m2 g−1 Pt. • Specific activity at 0.9 V RHE up to 5.8 mA cm−2 Pt and mass activity up to 1.9 A mg−1 Pt. • Remaining Cu has positive effect on specific activity. • Electrochemical active surface area depends on as-deposited Cu content. [ABSTRACT FROM AUTHOR]

Abstract The exploration of cheap and stable electrocatalysts with high activity towards oxygen reduction reaction in the acidic and alkaline medium is a vital activity for large-scale applications of fuel cells. In recent years, one-dimensional nanofibrous electrode materials with high surface area and specific porosities have been drawing great attention in energy conversion devices such as fuel cells and metal-air batteries. Nanofibers with a one-dimensional nanostructure can be produced by electrospinning, which has been considered as a particularly low-cost and versatile method. In this review, we summarize the properties of electrospun nanofibers and the recent progress in designing of non-precious nanostructured electrocatalysts for oxygen reduction reaction in fuel cells. More importantly, we also highlight the interesting nanostructures, new synthetic approaches, and the electrocatalytic performance including active sites and stability of electrospun-based electrocatalysts. In addition, we describe the research challenges and future developmental perspectives of electrospun materials in energy technology. Highlights • Non-precious nanostructured electrocatalysts by electrospinning are summarized. • The active sites and reaction mechanism of the electrocatalysts are discussed. • Research challenges and future perspectives are described. [ABSTRACT FROM AUTHOR]

Abstract To improve the sluggish oxygen reduction reaction from the cathode of solid oxide fuel cells (SOFCs), a conformal layer of catalytic CoO x grains was deposited onto the internal surface of LSM/YSZ composite cathode of commercial cells, through atomic layer deposition (ALD). Upon the electrochemical operation, the ALD coated cell has dramatic reduction of the polarization resistance, and the power density exhibits continuous increase over the course of 172 h operation at 750 °C and reaches the cell performance enhancement by a factor of 1.6, in comparison with that from the baseline operated for 96 h. Such performance enhancement was attributed to the combination of the newly added triple phase boundaries for promoting the oxygen reduction reaction, as well as the accelerated oxygen transport on the cathode surface. The present work opens the further research direction for ALD coating of non-precious metal catalyst to boost the performance of as-fabricated SOFCs. Highlights • Conformal CoO x layer is deposited on LSM/YSZ backbone of SOFC cathode using ALD. • CoO x ALD layer continuously improves the oxygen reduction reaction upon operation. • CoO x ALD layer interacts with the backbone and formed catalytic Co 0.7 Mn 0.3 O x. • Co 0.7 Mn 0.3 O x exhibits Bi-model distribution on LSM and YSZ surfaces. [ABSTRACT FROM AUTHOR]

Abstract Presently, the practical application of Fe/N/C catalysts as replacements of Pt for oxygen reduction reaction is still limited by insufficient activity. Herein, we demonstrate a novel design for such catalyst. On one hand, the obtained Fe/N/C SiO 2 ZnCl 2 catalyst owns high densities of well-exposed active-sites derived from three-dimensional well-balanced macro-, meso-, and microporous structures constructed by adopting ZnCl 2 salt and SiO 2 microspheres as combined templates. On the other hand, simulation reveals that a high loading of catalyst in cathode catalyst layer would not benefit cell performance and fast oxygen reduction reaction process occurs only inside a limited thickness of catalyst layer. Particularly, the Fe/N/C SiO 2 ZnCl 2 shows a maximal output power density as high as 480 mW cm−2 at an ultra-low loading of 0.5 mg cm−2. This study firstly exhibits that development of catalysts with high-density active sites and construct of ultra-thin catalyst layer are of great significance for improving the performance of fuel cell. Highlights • Fe/N/C SiO 2 ZnCl 2 was synthesized using ZnCl 2 templating and silica templating. • Fe/N/C SiO 2 ZnCl 2 shows superior ORR activity in both alkaline and acidic medium. • The P max of Fe/N/C SiO 2 ZnCl 2 is as high as 480 mW cm−2 at a 0.5 mg cm−2 loading. [ABSTRACT FROM AUTHOR]

To improve the power generation of the microbial fuel cell, activated carbon is modified by the Co 3 O 4 /NiCo 2 O 4 double-shelled nanocage, which prepared via a metal-organic framework method. When tested as cathodic material, the mesoporous Co 3 O 4 /NiCo 2 O 4 double-shelled nanocage with a large surface (112.9 m 2  g −1 ) exhibits higher open circuit potential (0.252 V) and higher exchange current density (19.70 × 10 −4  A cm −2 ). Moreover, the maximum power density of the air-cathode microbial fuel cell equipped with the 5% as-prepared catalyst is 1810 mW m −2 , 104% higher than the control. The morphology and crystal structure of Co 3 O 4 /NiCo 2 O 4 are investigated by the Transmission electron microscope and X-ray diffraction. X-ray photoelectron spectroscopy analysis indicates that there exists Co 3+ /Co 2+ and Ni 3+ /Ni 2+ redox couples in the catalyst, and divalence - trivalence - divalence redox cycles contribute to the improved oxygen reduction reaction performance and enhanced power output. Owing to the structural merits and improved electrochemical activity, the synthesized Co 3 O 4 /NiCo 2 O 4 double-shelled nanocage would be considered as a replacement of the new material for Pt in microbial fuel cell. [ABSTRACT FROM AUTHOR]

Colloidal PtCu alloy nanoclusters (NCs) stabilized with acetate ions and ethylene glycol, with small particle size (∼2 nm) and tunable Pt/Cu ratio, are successfully synthesized by a modified alkaline-ethylene glycol method. As tractable building blocks, the prepared PtCu NCs are immobilized on a melem-modified carbon support (MMC) to assemble electrocatalysts (PtCu/MMC) for oxygen reduction reaction (ORR). The influence of Pt/Cu ratio in the alloy NCs of PtCu/MMC on the catalytic activity for ORR is investigated. Pt 75 Cu 25 /MMC exhibits the highest electrochemical mass activity (1.59 A mg −1 Pt ) and specific activity (3.98 mA cm −2 Pt ) at 0.9 V of supported NCs ever reported. After an aging test of 10,000 potential cycles, the loss of mass activity over Pt 75 Cu 25 /MMC is only 9%, which is the best durability compared to previously reported PtCu NCs catalysts measured at the similar conditions. Colloidal PtCu alloy NCs and the immobilization method reported in this work will find wide applications in the development of bimetallic catalysts. [ABSTRACT FROM AUTHOR]

This work reports the first account of perovskite oxide and carbon composite oxygen reduction reaction (ORR) catalysts integrated into anion exchange membrane fuel cells (AEMFCs). Perovskite oxides with a theoretical stoichiometry of Ca 0.9 La 0.1 Al 0.1 Mn 0.9 O 3-δ are synthesized by an aerogel method and calcined at various temperatures, resulting in a set of materials with varied surface chemistry and surface area. Material composition is evaluated by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The perovskite oxide calcined at 800 °C shows the importance of balance between surface area, purity of the perovskite phase, and surface composition, resulting in the highest ORR mass activity when evaluated in rotating disk electrodes. Integration of this catalyst into AEMFCs reveals that the best AEMFC performance is obtained when using composites with 30:70 perovskite oxide:carbon composition. Doubling the loading leads to an increase in the power density from 30 to 76 mW cm −2 . The AEMFC prepared with a composite based on perovskite oxide and N-carbon achieves a power density of 44 mW cm −2 , demonstrating an ∼50% increase when compared to the highest performing composite with undoped carbon at the same loading. [ABSTRACT FROM AUTHOR]

Network-like metallic alloys of solid nanoparticles have been frequently reported as promising electrocatalysts for fuel cells. The three-dimensional structure of such networks is rich in pores in the form of voids between nanoparticles, which collectively expose a large surface area for catalytic activity. Herein, we present a novel solution to this problem using a precursor comprising a flocculent core-shell PtNi@Ni to produce PtNi network catalysts with nanoparticle intraporosity after carefully controlled electrochemical dealloying. Physical characterization shows a hierarchical level of nanoporosity (intrapores within nanoparticles and pores between them) evolves during the controlled electrochemical dealloying, and that a Pt-rich surface also forms after 22 cycles of Ni leaching. In ORR cycling, the PtNi networks gain 4-fold activity in both j ECSA and j mass over a state of the art Pt/C electrocatalyst, and also significantly exceed previously reported PtNi networks. In ORR degradation tests, the PtNi networks also proved stable, dropping by 30.4% and 62.6% in j ECSA and j mass respectively. The enhanced performance of the catalyst is evident, and we also propose that the presented synthesis procedure can be generally applied to developing other metallic networks. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of oxygen is the heart of the next-generation energy technologies to fuel cells and metal-air batteries, of which the reference catalysts suffer from two critical bottlenecks lying in their insufficient electroactivities and unclear active site structures. Herein, we introduce the effectively hierarchically porous carbons (HPCs) as the active-sites enriched platform for oxygen electroreduction. Three quaternized copolymers (PUB, PAADDA and PICP) with different chemical structures are used to pursue Fe/N/S-tailored ORR electrocatalysts. The most efficient one prepared by PAADDA gives the onset potential of 0.94 V and a half-wave potential of 0.85 V in basic solution, as well as superb electroactivities of low H 2 O 2 % and high electron transfer number in both alkaline and acidic medium. Surprisingly, they all display high discharge power density as applied to Zn-air fuel cells, and the HPCs-PAADDA catalyst thrillingly reaches 516.3 mW cm −2 when catalyst loading is optimized to 5.0 mg cm −2 . The results elucidate that the polymer with long aliphatic chain is propitious to trap metals to create active sites and enwrap silica template to construct uniform pore structure. Only two kinds of nitrogen configuration (pyridinic-N and graphitic-N) are found with distinct structure in these HPCs, which happens to be active sites. [ABSTRACT FROM AUTHOR]

The catalytic activity and stability of electrocatalyst is critical for the commercialization of fuel cells, and recent reports reveal the great potential of the hollow structures with Pt skin coat for developing high-powered electrocatalysts due to their highly efficient utilization of the Pt atoms. Here, we provide a novel strategy to prepare the Pt skin coated hollow Ag-Pt structure (Ag-Pt@Pt) of ∼8 nm size at room temperature. As loaded on the graphene, the Ag-Pt@Pt exhibits a remarkable mass activity of 0.864 A/mg Pt (at 0.9 V, vs. reversible hydrogen electrode (RHE)) towards oxygen reduction reaction (ORR), which is 5.30 times of the commercial Pt/C catalyst, and the Ag-Pt@Pt also shows a better stability during the ORR catalytic process. The mechanism of this significant enhancement can be attributed to the higher Pt utilization and the unique Pt on Ag-Pt surface structure, which is confirmed by the density functional theory (DFT) calculations and other characterization methods. In conclusion, this original work offers a low-cost and environment-friendly method to prepare a high active electrocatalyst with cheaper price, and this work also discloses the correlation between surface structures and ORR catalytic activity for the hollow structures with Pt skin coat, which can be instructive for designing novel advanced electrocatalysts for fuel cells. [ABSTRACT FROM AUTHOR]

Adjusting catalyst/ionomer agglomerate is crucial to a high-performance catalyst layer (CL), particularly for non-precious metal catalysts. As a sacrificial component, the solvent plays a vital role during the CL formation process and resulting microstructure, determining the performance of the anion exchange membrane fuel cells (AEMFCs). Here, solvent mixtures of isopropanol (IPA) and tetrahydrofuran (THF) are studied for the controllable construction of the Co/Fe–N–C CL. The results indicate that the aggregate state of the ionomers and catalysts and the final CL microstructure strongly depend on the ratio of IPA and THF. The CL prepared with IPA: THF = 1:2 (v/v) shows a homogeneous distribution of Co/Fe–N–C catalysts, embedded in the ionomer matrix, due to the fast volatilization and low viscosity of the catalyst ink. The Co/Fe–N–C CL with high moisture adsorption behavior and retention ability results in a high performance AEMFC with peak power density of 545.3 mW cm−2 at 80 °C. The obtained results can guide the rational design of microstructure in non-precious metal CLs for high-performance AEMFCs. [Display omitted] • The influence of mixed solvents on the Co/Fe–N–C catalyst layer is investigated. • The ionomer is beneficial in inhibiting the Co/Fe–N–C aggregation in the inks. • Rapid evaporation results in the rational design of catalyst layer microstructure. • Adjusting the Co/Fe–N–C catalyst layer tunes water adsorption and retention ability. [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]

It is still a great challenge in preparing non-precious metal catalysts with high activity and long-term stability to substitute for precious metal catalysts for oxygen reduction reaction (ORR) in fuel cells. Herein, we report a novel and facile catalyst-N, S co-doped carbon spheres with highly dispersed CoO (CoO@NS-CSs), where biomass glucose spheres act as carbon precursor and H 2 S, NH 3 derived from the decomposition of thiourea not only provide N, S sources but also can etch carbon spheres to produce nanoporous structure. CoO@NS-CSs catalyst exhibits excellent ORR activity with a high onset potential of 0.946 V vs. RHE (reversible hydrogen electrode) and a half-wave potential of 0.821 V vs. RHE through a four-electron pathway in alkaline solution, which is comparable to commercial Pt/C catalyst (onset potential: 0.926 V vs. RHE, half-wave potential: 0.827 V vs. RHE). Furthermore, both the long-term stability and methanol-tolerance of CoO@NS-CSs catalyst are superior to those of commercial Pt/C catalyst. The excellent ORR performance of CoO@NS-CSs catalyst can be attributed to its micro-mesopore structure, high specific surface area (667 m 2 g −1 ), and highly dispersed CoO. This work manifests that the obtained CoO@NS-CSs catalyst is promising to be applied to fuel cells. [ABSTRACT FROM AUTHOR]

Nanostructured transition metal chalcogenides (TMCs) have significant interest towards electrochemical devices such as fuel cells, metal-ion batteries, due to their unique physical and electrochemical properties. Herein, we report a facile hydrothermal synthesis of flower-like nanostructured molybdenum sulphide and its incorporation on to graphene as a potential oxygen reduction reaction catalyst in alkaline medium. The phase purity and morphological evolution of MoS 2 is systematically studied through X-ray diffraction and scanning electron microscopic techniques. The electronic states of metal and non-metallic species are deeply studied by X-ray photoelectron spectroscopy. The effect of annealing temperatures and TMC concentrations are also investigated by electrochemical techniques such as cyclic and linear sweep voltammograms. The optimised electrocatalyst (MoS 2 /G-500) delivers significant ORR activity with onset and half-wave potentials of 0.91 and 0.80 V (vs. RHE), respectively. Superior durability compared to state-of-art Pt/C catalyst is ascertained by repeating potential cycles for about 5000 times and also by chronoamperometric technique. Finally, the hybrid catalyst is evaluated in AEMFC as cathode catalyst which delivers peak power density of about 29 mW cm −2 under ambient temperature and pressure. The present findings emphasis that MoS 2 /G catalyst is promising as cost-effective and alternative to noble metal-based catalysts for fuel cell applications. [ABSTRACT FROM AUTHOR]

Uniform cobalt and nitrogen co-doped carbon nanospheres (CoN–CNS) with high specific surface area (865 m 2 g −1 ) have been prepared by a simple but efficient method. The prepared CoN–CNS catalyst exhibits outstanding catalytic performance for the oxygen reduction reaction (ORR) in both alkaline and acidic electrolytes. In alkaline electrolyte, the prepared CoN–CNS has more positive half-wave potential and larger kinetic current density than commercial Pt/C. In acidic electrolyte, CoN–CNS also shows good ORR activity with high electron transfer number, its onset and half-wave potentials are all close to those of commercial carbon supported platinum catalyst (Pt/C). CoN–CNS catalyst shows more superior stability and higher methanol-tolerance than commercial Pt/C both in alkaline and in acidic electrolytes. The potassium thiocyanate-poisoning test further confirms that the cobalt-nitrogen active sites exist in CoN–CNS, which are dominating to endow high ORR catalytic activity in acidic electrolyte. This study develops a new method to prepare non-precious metal catalyst with excellent ORR performances for direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

Polypyrrole modified carbon supported CoOOH electrocatalyst (CoOOH-PPy-C) is prepared by impregnation-chemical method, and the catalytic properties for the oxygen reduction reaction (ORR) in alkaline media are investigated. The X-ray diffraction and transmission electron microscopy results confirm the presence of the expected CoOOH. The electrochemical tests show that the CoOOH-PPy-C catalyst exhibits good electrocatalytic activity towards ORR. The direct borohydride fuel cell using CoOOH-PPy-C as the cathode catalyst demonstrates a good stability performance. There is only 4% decrease of the cell voltage after 80-h operation. The ORR occurs an average 4-electron transfer pathway on the CoOOH-PPy-C catalyst. The good catalytic activity towards ORR benefits from the Co N bond, which is identified by X-ray photoelectron spectroscopy test. X-ray absorption fine structure experiments further show that two nearest O atoms are substituted by two N atoms bonding to Co ion at a distance of 1.64 Å. The CoOOH-PPy-C exhibits better electrochemical properties than the Co(OH) 2 counterpart even though the valence state of Co ion is +3 in CoOOH-PPy-C. Those results indicate that the bonding of Co ion with N atoms should be a key issue regardless the valence of Co ion. [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]

Metal-nitrogen-carbons (M-N-Cs) as a reliable substitution for platinum-group-metals (PGMs) for oxygen reduction reaction (ORR) are emerging candidates to rationalize the technology of fuel cells. The development of M-N-Cs can further be economized by consuming waste biomass as an inexpensive carbon source for the electrocatalyst support. Herein, we report the simple fabrication and in-depth characterization of electrocatalysts using lignin-derived activated char. The activated char (LAC) was functionalized with metal phthalocyanine (FePc and MnPc) via atmosphere-controlled pyrolysis to produce monometallic M-N-Cs (L_Mn and L_Fe) and bimetallic M1-M2-N-Cs (L_FeMn) electrocatalysts. Raman spectroscopy and transmission electron microscopy (TEM) revealed a defect-rich architecture. XPS confirmed the coexistence of various nitrogen-containing active moieties. L_Fe and L_FeMn demonstrated appreciable ORR in both acidic and alkaline conditions whereas L_FeMn helped in restricting the peroxide yield, particularly in alkaline media. L_Fe and L_FeMn demonstrated remarkable onset potential (E onset) of ∼0.942 V (vs RHE) with an E 1/2 of 0.874 V (vs RHE) in 0.1 M KOH. In acid, L_FeMn had an E onset of 0.817 V (vs RHE) and an E 1/2 of ∼0.76 V (vs RHE). Finally, the L_FeMn as a cathode electrocatalyst was integrated and tested in PEMFC and AEMFC. AEMFC demonstrated optimistic performance with a peak power density of 261 mW cm−2 at the current density of ∼577 mA cm−2. • Waste lignin was valorized through pyrolysis and high surface area char was synthesized. • The biochar was functionalized by Fe-, Mn- and Fe–Mn phthalocyanine. • Fe- and FeMn- catalysts showed superior ORR compared to Mn-catalyst. • Integration of PGM-free FeMn-catalyst in PEMFC reached a P max of ∼72 mW cm−2. • Integration of PGM-free FeMn-catalyst in AEMFC reached a P max of ∼261 mW cm−2. [ABSTRACT FROM AUTHOR]

A promising strategy for achieving enhanced catalytic activity involves the use of nanoscale electrocatalysts; however, their low stability remains a major challenge. Among the various performance-degradation mechanisms, atomic dissolution is known to cause severe nanoparticle deactivation. To date, the factors influencing these catalysts' durability are not understood. Herein, we assess the role of low-coordination surface sites, focusing on the atomic dissolution of Pt nanoparticles. The density of low-coordination sites was finely controlled, and no significant size change occurred. Based on our findings, we suggest that the initial low-coordination sites trigger metal dissolution, which subsequently accelerates Pt dissolution. We believe that controlling the surface coordination number can open new routes for the design of highly durable nanoscale electrocatalysts. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks were used as metal-nitrogen-carbon templates to synthesize Co–N–C catalysts through a facile synthesis approach that combined a cobalt-based zeolitic imidazolate framework (ZIF) structure and conductive carbon support. The spectroscopic, structural, and thermogravimetric analysis confirmed the synthesis of the Co-based ZIF, used to prepare catalysts with different ZIF/carbon support ratios by pyrolysis under inert atmosphere. Electrochemical characterization at alkaline pH demonstrated high activity towards oxygen reduction reaction (ORR). In addition to ORR activity, the Co–N–C electrocatalysts showed high methanol tolerance in the preliminary tests in a half-cell configuration. When assembled at the cathode side of both a hydrogen-fed anion exchange membrane fuel cell and an alkaline direct methanol fuel cell (ADMFC), the Co–N–C electrocatalysts showed competitive performance with the state-of-the-art Pt/C and other platinum-group-metal-free materials, using a FUMASEP® FAA-3-50 membrane. Exceptionally high performance (higher than 45 mW cm−2) was achieved in ADMFC fed with high methanol concentration (up to 10 M), due to the high methanol tolerance of Co–N–C electrocatalysts. Normalizing the performance to Pt loading, a value of 31.0 mW mg Pt −1 was obtained, which is the highest power up to now recorded with this kind of membrane and one of the highest values in the literature for ADMFCs. [Display omitted] • Metal-organic-framework-derived Co–N–C electrocatalysts. • High catalytic activity towards oxygen reduction in an alkaline environment. • Remarkable methanol tolerance of Co–N–C electrocatalysts. • Application in H 2 -fed anion exchange membrane fuel cells cathodes. • Application in alkaline direct methanol fuel cells cathodes with high power output. [ABSTRACT FROM AUTHOR]

The distribution of platinum group metal (PGM) nanoparticle catalysts throughout the porous structure of the carbon support has been widely reported to have a significant impact on the performance of the catalyst. For catalysts having Pt primarily on the outer surface of the carbon, low mass activity but excellent performance at high current densities is often observed. Conversely, when Pt is deposited within the pores of the carbon, high mass activity but poor performance at high current density is observed. This relationship has been well studied, and the mechanism has been clearly elucidated. A key method in the literature to study Pt distribution has been the 'Pt accessibility' tests, which are based on monitoring roughness factor (cm2Pt/cm2 membrane electrode assembly (MEA)) vs. relative humidity (RH). While these tests have now been correlated with performance, most of the polarization testing during these studies is performed under one single RH condition. In this work, the relationship between Pt spatial distribution and RH tolerance is probed to gain further insight into how the materials-level properties of the catalyst impact MEA-level characteristics. This work provides an additional design tool that can be used by MEA designers when selecting catalysts for their specific application. [Display omitted] • Study of relative humidity tolerance as a function of Pt spatial distribution. • New mechanism proposed to explain the relative humidity/performance relationship. • Recommendations provided for the design and selection of Pt/C catalysts. [ABSTRACT FROM AUTHOR]

Durability of catalysts for oxygen reduction reaction (ORR) is the key factor for governing the performance of microbial fuel cells (MFCs). The cobalt (Co) chelated polyaniline (PANI) is used as the nitrogen and carbon sources to prepare the N-doped Co/Co 9 S 8 /partly-graphitized carbon (Co/Co 9 S 8 /NPGC) catalysts. Structure-activity correlations for Co/Co 9 S 8 /NPGC are explored by tuning the heating temperature (600–1000 °C) to investigate how the active components (Co/Co 9 S 8 ) and N-doped functionalities (N-species) influence the ORR activity. As temperature increases, the gradual crystallization of Co originating from the reduction of Co 9 S 8 is conducted to form the Co/Co 9 S 8 heterojunction. MFCs with Co/Co 9 S 8 /NPGC (800 °C) cathode obtain the highest power density (1156 mW m −2 ) and the lowest charge transfer resistance (11.1 Ω) after 75 d running, which are better than commercial Pt/C (10 wt.%). Although the sole Co 9 S 8 plays a limited role in ORR, the resulting Co/Co 9 S 8 is found to be indispensable to achieve high activity and durability in MFCs cathodes. The dominant ORR pathways of Co/Co 9 S 8 /NPGC (800 and 900 °C) are the four-electron O 2 reduction, which are attributed to the co-existence of pyridinic N, graphitic N and Co-N x species. These new N-doped metal sulfide/PGC composites show promise for applications in MFCs. [ABSTRACT FROM AUTHOR]

Carbon-supported transition metal/nitrogen (M–N/C) materials are considered as one of the most promising electrocatalysts for the oxygen reduction reaction (ORR) owing to their high ORR electrocatalytic activity, long-term stability, and excellent methanol tolerance. So far only a few examples of such catalysts are prepared from N-containing polymers. Herein, we report a novel Fe–N/C catalyst using a nitrogen-rich polymeric network and iron(II) acetate as the precursors. The porous polymeric network is fabricated by one-step Friedel–Crafts reaction of a low-cost cross-linker, formaldehyde dimethyl acetal, with 2,4,6-tripyrrol-1,3,5-triazine. Compared to commercial Pt/C catalyst, the as-prepared Fe–N/C electrocatalyst exhibits superior ORR activity in alkaline electrolyte, and comparable ORR activity in acidic medium. The results obtained are significant for the development of new Fe–N/C electrocatalysts for fuel cells. [ABSTRACT FROM AUTHOR]

Cost-effective catalysts are of key importance to the successful deployment of microbial fuel cells (MFCs) for electricity generation from organic wastes. Herein, a novel catalyst prepared by one-step synthesis strategy is reported. The catalyst features N-doped bamboo-like carbon nanotube (BCNT) in which CoNi-alloy is encapsulated at the end and/or the middle section of the tube with many graphene layers inside inner cavities of BCNT (N-G@CoNi/BCNT). The prepared N-G@CoNi/BCNT exhibits a high oxygen reduction reaction (ORR) activity with an early onset potential of 0.06 V vs. Ag/AgCl and a comparable exchange current density to that of commercial Pt/C. The excellent catalytic activity is further evidenced by a high electron transfer number of 3.63. When being applied in MFCs, the N-G@CoNi/BCNT yields an average current density of 6.7 A m −2 , slightly lower than that of Pt/C but with a less mass transfer potential loss. The cost of the N-G@CoNi/BCNT for constructing a 1-m 2 cathode electrode is 200 times lower than that of Pt/C. With such a competitive price and excellent electrocatalytic-activity resulting from its unique morphology, CoNi-alloy/nitrogen dopants, considerable specific surface area, and carbon-coated alloy/graphene hybridization, the present catalyst is a promising candidate for ORR catalysts in MFCs for energy recovery from wastes. [ABSTRACT FROM AUTHOR]

To develop more efficient metal-free cathode electrocatalysts for fuel cells, novel arsenic (As)-doped, As and N-codoped carbon nanotubes are synthesized by chemical vapor deposition in this work. The as-prepared As-containing carbon nanotubes exhibit significantly enhanced activity and long-term durability for the oxygen reduction reaction (ORR) in alkaline medium, indicating that the doping of As or codoping As with other heteroatoms into carbon matrix could improve the ORR activity of carbon materials due to the changes in electronic and physical properties of carbon nanotubes evidenced by density functional theory calculations. Moreover, As-containing carbon nanotubes also display much better methanol tolerance, showing a good potential application for future fuel cells. [ABSTRACT FROM AUTHOR]

To maintain local pH levels near the electrode during electrochemical reactions, the use of buffer solutions is effective. Nevertheless, the critical effects of the buffer concentration on electrocatalytic performances have not been discussed in detail. In this study, two fundamental electrochemical reactions, oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR), on a platinum rotating disk electrode are chosen as model gas-related aqueous electrochemical reactions at various phosphate concentrations. Our detailed investigations revealed that the kinetic and limiting diffusion current densities for both the ORR and HOR logarithmically decrease with increasing solute concentration ( log | j O R R | = − 0.39 c + 0.92 , log | j H O R | = − 0.35 c + 0.73 ) . To clarify the physical aspects of this phenomenon, the electrolyte characteristics are addressed: with increasing phosphate concentration, the gas solubility decrease, the kinematic viscosity of the solution increase and the diffusion coefficient of the dissolved gases decrease. The simulated limiting diffusion currents using the aforementioned parameters match the measured ones very well ( log | j O R R | = − 0.43 c + 0.99 , log | j H O R | = − 0.40 c + 0.54 ) , accurately describing the consequences of the electrolyte concentration. These alterations of the electrolyte properties associated with the solute concentration are universally applicable to other aqueous gas-related electrochemical reactions because the currents are purely determined by mass transfer of the dissolved gases. [ABSTRACT FROM AUTHOR]

Nitrogen doped carbon nanotubes (NCNTs) with encapsulated Fe 3 C nanoparticles (Fe 3 C@NCNTs) are synthesized by a simple direct pyrolysis of melamine and ferric chloride. The characterization results reveal that Fe 3 C is mainly encapsulated in the interior of NCNTs and N species is mainly distributed on the outside surface of NCNTs. Iron and iron carbide catalyze the growth of NCNTs and are wrapped by carbon to form Fe 3 C@NCNTs. The as-prepared Fe 3 C@NCNTs catalyst exhibits superior oxygen reduction reaction (ORR) activity, excellent methanol tolerance and long-term stability in both acid and alkaline media. It is proven that the doped N is the main active site for ORR and the inner Fe 3 C with outside carbon form the synergetic active site to enhance ORR activity. The ORR mechanism of direct four electron transfer pathway is proved in acid and alkaline media. [ABSTRACT FROM AUTHOR]

The focus in recent years is on developing high performance non-precious metal catalysts (NPMCs) to reduce the catalyst cost in fuel cells. However, little attention has been paid to improve the utilization of NPMCs. Thus, this study focuses on the optimization of electrode component, particularly the Nafion content. With the synthesized graphene based oxygen reduction reaction (ORR) catalyst, the catalyst inks were prepared at various Nafion contents with suitable amounts of catalysts sprayed on the gas diffusion media. Twenty different single cells were assembled and measured for polarization, resistance and electrochemical impedance. Electrodes of 66.7 and 50.0% Nafion contents showed the highest performance for hydrogen/oxygen and hydrogen/air operation, respectively. These results were explained using the electrochemical impedance spectra, where the highest performance electrode resulted with the lowest charge transfer resistance. Moreover, negligible change in performance was observed during the 80 h of stability test. The optimization compositions of NPMC-based MEAs were very different to Pt-based MEAs, indicating the importance of optimization studies for the practical use of NPMCs. [ABSTRACT FROM AUTHOR]

We describe a facile route to the development of novel robust non-carbon titanium cobalt nitride (Ti 0.9 Co 0.1 N) used as a support for Pt, and the catalyst exhibits high activity and stability for the oxygen reduction reaction (ORR). XRD and TEM results show that the synthesized Ti 0.9 Co 0.1 N is formed as a single-phase solid solution with high purity. The XPS measurements verified the strong metal/support interaction between Pt nanoparticles (NPs) and the Ti 0.9 Co 0.1 N support. Most importantly, Ti 0.9 Co 0.1 N supported Pt catalyst (Pt/Ti 0.9 Co 0.1 N) exhibits a much higher mass activity and durability than that of the commercial JM Pt/C electrocatalyst for ORR. The accelerated durability test (ADT) reveals that the novel Ti 0.9 Co 0.1 N support can dramatically enhance the durability of the catalyst and maintain the electrochemical surface area (ECSA) of Pt. Pt/Ti 0.9 Co 0.1 N shows great improvement in ECSA preservation, with only 35% of the initial ECSA drop even after 10 000 ADT cycles. The experimental data indicate that the electronic structure of Pt can be modified by Co doping, and there exists a strong interaction between Pt and the Ti 0.9 Co 0.1 N support, both of them are playing an important role in improving the activity and durability of the Pt/Ti 0.9 Co 0.1 N catalyst. [ABSTRACT FROM AUTHOR]

New catalysts of reduced graphene oxide (rGO) with poly aniline (PANI) and cobalt ferrite (CF) have been successfully prepared by simple chemical reduction method. Their electrocatalytic activity for oxygen reduction reaction (ORR) was evaluated. Semi-crystalline nature of CF was analyzed by X-ray diffraction (XRD) study. Surface morphology by HR-SEM showed features of CF particles and PANI film on graphene sheets. FT-IR studies revealed changes in C–N and C N stretching vibrations of PANI confirming bonding of PANI to graphene sheets. Raman spectrum showed presence of PANI on distorted graphene layers. TG/DTA revealed thermal stability and extent of loading of CF in composite. ORR performance was studied using catalyst modified rotating disc electrode (RDE). A maximum kinetic current density of −3.46 mA cm −2 at −0.2 V was obtained for CF/PANI/rGO. Tafel slope, onset and half wave potentials for the catalyst were obtained from ORR response. Durability studies showed that synthesized electrocatalyst has better stability and methanol tolerance than commercial Pt/C catalyst. To the best of our knowledge, this is the first study aiming enhancement of ORR activity using PANI and CoFe 2 O 4 on graphene support. A trace amount of Pt in the composite boosted the performance of single PEM fuel cell. [ABSTRACT FROM AUTHOR]

Biofilms from anode heterotrophic bacteria are inevitably formed over cathodic catalytic sites, limiting the performances of single-chamber microbial fuel cells (MFCs). Graphitic carbon (GC) – based nano silver/iron oxide (AgNPs/Fe 3 O 4 /GC) composites are prepared from waste pomelo skin and used as antibacterial oxygen reduction catalysts for MFCs. AgNPs and Fe 3 O 4 are introduced in situ into the composites by one-step carbothermal reduction, enhancing their conductivity and catalytic activity. To investigate the effects of Fe species on the antibacterial and catalytic properties, AgNPs/Fe 3 O 4 /GC is washed with sulfuric acid (1 mol L −1 ) for 0.5 h, 1 h, and 5 h and marked as AgNPs/Fe 3 O 4 /GC-x (x = 0.5 h, 1 h and 5 h, respectively). A maximum power density of 1712 ± 35 mW m −2 is obtained by AgNPs/Fe 3 O 4 /GC-1 h, which declines by 4.12% after 17 cycles. Under catalysis of all AgNP-containing catalysts, oxygen reduction reaction (ORR) proceeds via the 4e − pathway, and no toxic effects to anode microorganisms result from inhibiting the cathodic biofilm overgrowth. With the exception of AgNPs/Fe 3 O 4 /GC-5 h, the AgNPs-containing composites exhibit remarkable power output and coulombic efficiency through lowering proton transfer resistance and air-cathode biofouling. This study provides a perspective for the practical application of MFCs using these efficient antibacterial ORR catalysts. [ABSTRACT FROM AUTHOR]

In this work, a low-cost and nitrogen-containing carbon material with mesopores and high surface area is synthesized by carbonizing carp with SiO 2 nanoparticles as template. It is found that pyridinic-N dominates the N species on the surface of obtained carbon material, which can act as active sites for oxygen reduction reaction (ORR). The BET surface area of obtained carbon material is 401.7 m 2 g −1 and the pore size is ca. 11.1 nm. Due to its high pyridinic-N content and mesoporous architecture, the ORR activity of obtained carbon material in alkaline media is comparable to that of commercial Pt/C catalyst. In addition, it shows a higher methanol tolerance than Pt/C catalyst, making it a potential alternative to Pt-based catalysts. [ABSTRACT FROM AUTHOR]

Simulation of the cathode electrode of a Microfluidic Fuel Cell (hereafter MFC) is performed with focus on the electrochemical reaction. Oxygen transport phenomena are modeled from the microchannel inlet to the reaction sites surface (on the platinum particles) in the catalyst layer. The dissolved oxygen in sulfuric acid and the formic acid are considered as the oxidant and the fuel, respectively. The cathode catalyst layer is modeled using the agglomerate model versus the homogenous model which is incapable of predicting concentration loss at high current densities. The results are validated versus the experiments of Choban et al. published in 2004. A set of parametric study is performed to investigate the influence of operating and structural parameters on the cell performance; at the end, a sensitivity analysis is implemented to rank the studied parameters with rank 1 for the most influential parameters. The results indicate that oxygen concentration at the inlet of microchannel within the range 0.1 M–0.7 M is the most influential parameter, and the cell performance can enhance by 2.615 W m −2 at the studied range. The results could be used by the microfluidic fuel cell manufacturers to overcome the current drawbacks of the MFCs. [ABSTRACT FROM AUTHOR]

PtCu/CNT alloy electrocatalysts were prepared by microwave assisted polyol synthesis. The influence of preparation pH and the presence of polyvinylpyrrolidone (PVP) as stabilizer on catalysts nanostructure and activity towards electrocatalytic oxygen reduction was evaluated. The catalysts were alloyed at 400–600 °C for 6 h in reductive atmosphere, and characterized by TEM and XRD. The XRD patterns display a positive shift in 2 θ of the Pt 111 peak, which is a good evidence for Pt–Cu alloy formation. Alloy nanoparticles already form at temperatures as low as 400 °C. Highly agglomerated PtCu nanoparticles were obtained in the absence of PVP while PVP addition resulted in dispersed and uniform nanoparticles with a mean particle size of 3.7 nm. Such small particles are a result of the considerably low temperature used during the heat treatment/alloying step. However, while Pt is nearly completely deposited on the CNTs, only smaller fractions of Cu are found in the final catalyst. A high extent of agglomeration was also noticed when the pH during polyol synthesis was increased, which is attributed to Cu-hydroxides precipitation. Pt–Cu core shell catalysts were obtained after voltammetric dealloying. Catalyst prepared at higher pH in the presence of PVP display the highest electrocatalytic activity. [ABSTRACT FROM AUTHOR]

We report here on a novel and facile technique for the simultaneous synthesis of a highly active and stable gold (Au) nanoparticle/reduced graphene oxide (rGO) sheet nanocomposite as an efficient electrocatalyst to facilitate the oxygen reduction reaction (ORR). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy and electrochemical methods were employed to characterize the Au and rGO nanocomposites formed on the electrode surface. The major advantage of the simultaneous synthetic method is the integration of the superb properties of both Au nanoparticles and graphene in a single-step with a 100% usage of the precursors. The Au/rGO nanocomposites exhibited pronounced electrocatalytic performance towards ORR with approximately three times higher than that of Au nanoparticles. The nanocomposites show the ORR onset peak potentials at 0.12 and −0.03 V ( vs Ag/AgCl), with reduction peaks at −0.06 and −0.16 V ( vs Ag/AgCl) in 0.1 M H 2 SO 4 and KOH media, which is ∼120–190 mV more positive than that of Au nanoparticles and a commercial Pt/C catalyst. Moreover, the nanocomposites exhibit excellent methanol tolerance and high durability in comparison with the commercial Pt/C. The new method demonstrated in this study provides an efficient route for the generation of ultrafine and highly dense Au nanoparticles that are homogeneously dispersed on rGO sheets for ORR. [ABSTRACT FROM AUTHOR]

In this paper, we report a template-free method to fabricate hollow nitrogen-doped carbon (HNC) by pyrolysis of hollow polyaniline microspheres, which were synthesized by suspension polymerization method. The entire synthesis is simple, environmentally benign, and economic. The oxygen reduction reaction (ORR) activity of the as-prepared HNC catalyst is close to that of the commercial Pt/C catalyst in alkaline media with four electron pathway. Moreover, the HNC shows much better fuel crossover resistance and long-term durability than the commercial Pt/C in alkaline medium. All these features make HNC a potentially promising and suitable substitute for the expensive noble metal catalysts in the next generation alkaline fuel cells. [ABSTRACT FROM AUTHOR]

The porous NiO/NiCo 2 O 4 nanotubes are prepared via a coaxial electrospinning technique followed by an annealing treatment. The resultant NiO/NiCo 2 O 4 hybrid is developed as a highly efficient electrocatalyst, which exhibits significantly enhanced electrocatalytic activity, long-term operation stability, and tolerance to crossover effect compared to NiO nanofibers, NiCo 2 O 4 nanofibers and commercial Pt(20%)/C for oxygen reduction reactions (ORR) in alkaline environment. The excellent electrocatalytic performance may be attributed to the unique microstructures of the porous NiO/NiCo 2 O 4 nanotubes, such as heterogeneous hybrid structure, open porous tubular structure, and the well dispersity of the two components. Moreover, the promising and straightforward coaxial electrospinning proves itself to be an efficient pathway for the preparation of nanomaterials with tubular architectures and it can be used for large-scale production of catalysts in fuel cells. [ABSTRACT FROM AUTHOR]

The successful commercialization of fuel cells requires the efficient electrocatalyst to make the oxygen reduction reaction (ORR) fast because of the sluggish nature of ORR and the high cost of the platinum catalysts. In this work, we report the excellent performance of metal-free nitrogen-doped porous carbon nanosheets (NPCN) with hierarchical porous structure and a high surface area of 1436.02 m 2 g −1 for catalyzing ORR. The active NPCN is synthesized via facile high-temperature carbonization of natural ginkgo leaves followed by purification and ammonia post-treatment without using additional supporting templates and activation processes. In O 2 -saturated 0.1 M KOH solution, the resultant NPCN exhibits a high kinetic-limiting current density of 13.57 mA cm −2 at −0.25 V (vs. Ag/AgCl) approaching that of the commercial Pt/C catalyst (14 mA cm −2 ) and long-term electrochemical stability. Notably, the NPCN shows a slightly negative ORR half-wave potential in comparison with Pt/C (Δ E 1/2 = 19 mV). The excellent electrocatalytic properties of NPCN originate from the combined effect of optimal nitrogen doping, high surface area, and porous architecture, which induce the high-density distribution of highly active and stable catalytic sites. [ABSTRACT FROM AUTHOR]

To develop low-cost and efficient cathode electrocatalysts for fuel cells in acidic media, phosphorus-doped carbon nanotubes (P-CNTs) supported low Pt loading catalyst (0.85% Pt) is designed. The as-prepared Pt/P-CNTs exhibit significantly enhanced electrocatalytic oxygen reduction reaction (ORR) activity and long-term stability due to the stronger interaction between Pt and P-CNTs, which is proven by X-ray photoelectron spectroscopic analysis and density functional theory calculations. Moreover, the as-prepared Pt/P-CNTs also display much better tolerance to methanol crossover effects, showing a good potential application for future proton exchange membrane fuel cell devices. [ABSTRACT FROM AUTHOR]

The catalyst of PtCu bimetallic nanoparticles anchored on hierarchical porous N-doped carbon (PtCu/NHPC) is successfully fabricated through a simple pyrolysis synthesis. The high surface area (827 m2 g−1) of N-doped porous carbon (NHPC) can effectively favor the high distribution of PtCu particles on carbon. The high mesopore ratio of NHPC helps to reduce mass transfer resistance. Furthermore, homogeneously distributed nitrogen in carbon can not only uniformly disperse nanoparticles but also optimize catalyst oxygen affinity, significantly improving catalytic efficiency for oxygen reduction reaction. PtCu/NHPC shows excellent electrocatalytic activity with a high half-wave potential (0.915 V vs. RHE) compared with commercial Pt/C (0.864 V) in half-cell test. In the single-cell system, PtCu/NHPC also behaves good performance, and its initial current density is 595 mA cm−2 at 0.85 V. PtCu/NHPC shows better durability (only 6.6% mass activity loss) after 10,000 potential cycles compared to JM Pt/C catalyst (30%). The research provides a simple preparation strategy for improving the oxygen reduction reaction activity and stability of fuel cell platinum-based catalysts. • Hierarchical porous N-doped carbon was prepared through a simple method. • NHPC aids in exposing more active sites and dispersing metal nanoparticles. • The Cu, and N atoms synergistically tune electronic structure of Pt. • Nitrogen doping could enhance the interaction between Pt and NHPC. [ABSTRACT FROM AUTHOR]

Low-cost, high-performances and durable hydrogen fuel cells are crucial for the success of the hydrogen economy. While Fe–N–C structures containing Fe-N x active sites are amongst the most promising platinum (Pt)-group metal (PGM)-free catalysts for the oxygen reduction reaction, their highest performances-to-date are still inferior to commercial Pt in real proton exchange membrane fuel cells. Herein, we shed light on this performance gap by using the distribution of relaxation times to quantify the proton transport and oxygen reduction reaction kinetics of a high-performance Fe–N–C catalyst (1.08 W cm−2) and a commercial Pt catalyst (1.7 W cm−2) in hydrogen fuel cell. This study unveils that the Fe–N–C catalyst has slower proton transport and oxygen reduction reaction kinetics than Pt as the Fe–N–C nanoporous carbon matrix limits active site accessibility. Furthermore, while increasing the Fe–N–C catalytic mass loading (from 1 to 3 mg Fe-N-C cm−2) enhances the power density in hydrogen fuel cells, it also slows down proton transport and oxygen reduction reaction kinetics by lengthening the gas, electron, and proton pathways to the active sites. This finding will drive the development of PGM-free catalysts for hydrogen fuel cells and of single-atom catalysts for electrochemical applications. [Display omitted] • The distribution of relaxation times captures ORR kinetics of PGM-free catalysts. • PGM-free catalysts nanoporous structure reduces ORR and proton transport kinetics. • Using high loadings of PGM-free catalysts increases the pathway to active sites. [ABSTRACT FROM AUTHOR]

Abstract: The electrocatalytic performances of carbon nanotubes supported platinum (Pt/CNTs) with different Pt loadings for oxygen reduction reaction (ORR) and methanol oxidation (MOR) are studied contrastively. Pt/CNTs showed an opposite change rule along different Pt loadings for ORR and MOR, which is discussed based on the charge transportation and mass transfer. The results show that at low Pt loading, proton conduction is the key factor, which determines the MOR activity; at high Pt loading, mass transfer is crucial, which decides the ORR activity of Pt/CNT catalysts. The viewpoint proposed in this paper can guide the design and preparation of Pt based catalysts for the commercialization of direct methanol fuel cells. [Copyright &y& Elsevier]

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]