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Chemical looping ammonia generation (CLAG), including the N-sorption/desorption steps of the N-carrier, is increasingly important due to the high demand for formation of carbon-free fuel. The N-sorption step, the synthesis of aluminum nitride (AlN) by the carbothermal reduction, has been widely studied for improving the purity and stability of aluminum nitride. However, there are few studies on how to enhance the porosity and thus N-desorption reactivity of AlN, one of the key issues for the CLAG. Therefore, in this paper, a supported Al-based nitrogen carrier (AlN/Al 2 O 3) with mesoporous structure, in which 5% of Y 2 O 3 was added as a catalyst, was developed with excess aluminum oxide (γ-Al 2 O 3) and the corresponding N-desorption of the generated N-carrier was studied with a stationary bed reactor, X-ray diffraction (XRD), Brunner-Emmet-Teller (BET) measurements, Raman spectra and scanning electron microscope (SEM). The results showed that using the excess aluminum oxide in N-sorption step significantly led to the significant improvement in N-carrier's porosity and thus N-desorption reactivity, which did not vary with change in carbon types. Also, the N-sorption performance of γ-Al 2 O 3 with carbon black was better than that with graphite due to their different carbon crystal structures. In addition, the effect of other parameters including the mole ratio of Al 2 O 3 :C, reaction temperature on the N-sorption performance of the N-carrier were studied. It was found that the specific surface area of the mesoporous structured Al-based AlN, synthesized with mole ratio of Al 2 O 3 : C being 3:3 at 1200 °C, reached to>70 m2/g, which was the best one for good NH 3 synthesis performance. • A porous Al-based N-carrier with good N-desorption performances was generated from N-sorption reaction. • The reactivity of the disordered carbon is better than that of the ordered carbon in the N-sorption reaction. • Pore structure and specific surface area of the generated N-carrier plays an important role in the N-desorption reaction. [ABSTRACT FROM AUTHOR]

As well known, ruthenium is electrochemically unstable in direct methanol fuel cell (DMFC) operation shortening lifetime and deteriorating performance of DMFC device. In this work, a facile methodology for improvement in stability of PtRu electrocatalyst is described, in which PtRu alloyed nanoparticles are decorated by nitrogen-doped carbon (N x C) originating from the carburization of in-situ polymerized polyaniline (PANI). Deceleration in Ru dissolution of N x C protected PtRu electrocatalyst comes from the ionized Ru atoms induced by the carburization of PANI transferring electrons from Ru to nitrogen atoms evidenced by XPS measurement, which results in higher CO tolerance during potential sweeping from 0.6 to 1.0 V versus RHE for N x C decorated PtRu electrocatalyst. Meanwhile, N x C protected PtRu electrocatalyst only losses 10% of active sites after stability estimation; in contrast, 50% of active sites are lost for bare PtRu electrocatalyst. Moreover, fuel cell test illustrates that N x C protected PtRu electrocatalyst shows comparable performance to bare PtRu electrocatalyst. [ABSTRACT FROM AUTHOR]

Enhancement in durability of electrocatalyst is still one of the most important issues in polymer electrolyte fuel cells (PEFCs). Here, we report a structurally coated electrocatalyst supported on carbon nanotubes (CNT), in which platinum (Pt) nanoparticles are coated by nitrogen doped carbon (NC) layers. CNT/NC/Pt/NC shows comparable electrochemical surface area (ECSA) and oxygen reduction reaction (ORR) activity to the non-coated electrocatalyst (CNT/NC/Pt), indicating that NC layer on Pt nanoparticles almost negligibly affects the activities of electrocatalyst; while, CNT/NC/Pt/NC exhibits a higher Pt stability due to the unique structure, in which the Pt nanoparticles are stabilized by the NC layers and Pt aggregation is decelerated proved by TEM measurement. Maximum power density of CNT/NC/Pt/NC reached 604 mW cm −2 with Pt loading of 0.1 mg Pt cm −2 , which only decreases by 7% compared to CNT/NC/Pt (650 mW cm −2 ). The electrochemical analysis and fuel cell test illustrate that NC layer on Pt nanoparticles enhances the durability without serious deterioration of fuel cell performance. [ABSTRACT FROM AUTHOR]

The low durability and fuel cell performance of the platinum electrocatalyst block the widespread application of high-temperature polymer electrolyte fuel cells (HT-PEFCs). Here, we utilize a facile method to improve the durability as well as fuel cell performance of the platinum electrocatalyst supported on oxidized multi-walled carbon nanotubes ( ox -CNT/Pt), in which the electrocatalyst is coated by polybenzimidazole assisted by the COOH groups on the surface of ox -CNT. The coated and non-coated electrocatalysts remain 50% of the initial electrochemical surface areas (ECSAs) after 350,000 and 50,000 potential cycles from 1.0 to 1.5 V vs. RHE, respectively, indicating that polymer coating enhances the durability of the electrocatalyst. Meanwhile, power density of PBI-coated electrocatalyst measured under anhydrous condition is 1.6 times higher compared to that of non-coated electrocatalyst due to the PBI layer acted as proton conductor in the catalyst layer. This study offers useful knowledge for enhancement of durability and performance of Pt electrocatalyst used in HT-PEFCs. [ABSTRACT FROM AUTHOR]

The enhancements in fuel cell performance and durability are crucial for the commercialization of polymer electrolyte fuel cells (PEFCs). Here, we deposit platinum nanoparticles on nitrogen doped carbon nanotubes (N-CNT) and continuously coat the electrocatalyst with nitrogen doped carbon (NC) layer derived from the carbonization of poly(vinyl pyrrolidone) (PVP). The NC-coated electrocatalyst shows stable electrochemical surface area (ECSA) during the potential cycling from 0.6 V to 1.0 V vs . RHE; while, the commercial and non-coated electrocatalysts lose 50% and 33% of initial ECSAs, respectively. Moreover, the NC-coated electrocatalyst shows higher oxygen reaction reduction (ORR) activity compared to non-coated electrocatalyst due to the additional nitrogen atoms in the electrocatalyst. The maximum power density of the coated electrocatalyst reaches 676 mW cm −2 with Pt loading of 0.1 mg cm −2 , indicating that the mass power density of the electrocatalyst is one of the highest values in recently published literature. The NC layer is significantly important for simultaneous enhancements in durability and fuel cell performance. [ABSTRACT FROM AUTHOR]

Constructing high-performance catalyst for hydrogen evolution reaction (HER) is the effective way to eliminate energy crisis. Reasonable engineering of heterointerfaces can effectively create more active sites and promote electron transfer resulting in improvement in the catalytic activity. In this work, we synthesize the well-defined molybdenum carbides and tungsten carbides nano-heterostructure (Mo 2 C/W 2 C) by carbonization with CH 4 /H 2 at 800 °C showing excellent HER activity, fast kinetics and electrochemical stability in both alkaline and acidic electrolytes. Mo 2 C/W 2 C requires only 140 and 132 mV overpotentials to reach catalytic current density of 10 mA cm−2 in 0.5 M H 2 SO 4 and 1 M KOH electrolyte, respectively. Tafel slope is as low as 51 and 76 mV dec−1 in 0.5 M H 2 SO 4 and 1 M KOH comparable to the benchmarked Pt/C. Moreover, Mo 2 C/W 2 C exhibits a superior stability with slight deterioration in HER performance after 5000 potential cycles. This work elucidates that the rational construction of heterointerfaces is favorable for design of efficient non-noble metal electrocatalyst for HER catalysis. Image 1 • Mo 2 C/W 2 C heterogeneous electrocatalyst is successfully synthesized. • The overpotential is 140 mV for Mo 2 C/W 2 C to deliver 10 mA cm−2 in acidic medium. • Mo 2 C/W 2 C requires 132 mV overpotential to reach 10 mA cm−2 in alkaline medium. [ABSTRACT FROM AUTHOR]

CO tolerance and stability are of prominent importance for the anodic electrocatalyst utilized in direct methanol fuel cells (DMFCs). Due to the electrochemical instability of Ru atoms, the state-of-the-art DMFC anodic electrocatalyst (PtRu/C) is unable to survive for long time. Here, we report a newly designed Pt electrocatalyst with robust CO tolerance and stability after coating with poly(vinyl pyrrolidone) (PVP). Electrochemically active surface area (ESA) is negligibly affected by the PVP decoration; meanwhile, almost undetectable ESA loss is obtained for the PVP decorated Pt electrocatalyst. However, the ESA degradations for non-decorated and commercial CB/Pt electrocatalysts are found to be 30% and 40%, respectively. The improved stability is ascribed to the strong interaction between PVP and sulfonated carbon nanotubes. Also, the CO tolerance evaluated from the methanol oxidation reaction is ∼3 and 3.5 fold higher compared to non-decorated and commercial CB/Pt electrocatalysts, respectively, which is attributed to the hydrophilic PVP polymer accelerating the water absorption and formation of Pt(OH) ads species to re-activate nearby CO poisoned Pt nanoparticles. Thus, decoration with PVP polymer can simultaneously promote the stability and CO anti-poisoning of Pt electrocatalyst. Image 1 • Robust CO tolerance is achieved after coating Pt catalyst with hydrophilic polymer. • More Pt(OH) ads species is generated after coating with hydrophilic polymer. • Pt nanoparticles migration is decelerated by poly(vinyl pyrrolidone) layer. [ABSTRACT FROM AUTHOR]

Palladium (Pd) as an efficient anodic catalyst has been extensively investigated in direct formic acid fuel cells (DFAFCs); while, Pd catalyst is electrochemically unstable in acidic electrolyte resulting in low stability retarding the widespread application of DFAFCs. In this study, a new method is invented to prevent the Pd nanoparticles from rapid dissolution by carbon layer originated from the carbonization of glucose. Ascribing to the presence of carbon layer, Pd electrocatalyst demonstrates much higher stability in comparison with Pd electrocatalyst without carbon layer in the course of stability tests. Robust electrocatalytic activities toward formic acid and methanol/ethanol oxidation are observed for carbon-stabilized Pd electrocatalyst resulted from the higher content of metallic Pd atoms coming from the carbonization process, in which Pd (II) species are further reduced. Moreover, the fuel cell performance of carbon-stabilized Pd electrocatalyst reaches 90 mW cm Pd −2 measured with 1 M formic acid; while, power density of bare Pd electrocatalyst is only 74 mW cm Pd −2. This work highlights that carbon layer carbonized from glucose improves not only the stability of Pd electrocatalyst, but also the electrocatalytic activity. • Protective carbon layer is coated on Pd nanoparticles via carbonization of glucose. • High stability and catalytic activity are obtained after coating with carbon layer. • Carbon layer coated Pd catalyst exhibits a higher fuel cell output of 90 mW cm−2. [ABSTRACT FROM AUTHOR]

As a terrific hydrogen carrier, NH 3 can be wildly used as non-carbon gas fuel in energy area, because NH 3 can store a high density of H 2 and can be liquefied easily in ambient temperature and pressure. Chemical Looping Ammonia Generation (CLAG) is known to be a novel, efficient and environmentally friendly synthesis method for ammonia, in which the N-sorption/desorption of nitrogen carrier are included. The N-sorption step, which is known as the carbothermal reduction, is well studied while there are few reports on N-desorption step. Therefore, in this paper, stationary bed reactor and thermo-gravimetric analyzer (TGA) were used to study the N-desorption performance of the TiO 2 -loaded Al-based N-carrier and the corresponding NH 3 generation during the N-desorption reaction. The results showed that, TiO 2 performed a good catalytic effect on the N-desorption reaction, which is due to the good dissociative adsorption performance of H 2 O on TiO 2 surface, and the released hydroxyl (OH ) plays an important role in the N-desorption reaction. The conversion amount of aluminum nitride and the yield of NH 3 increased with the TiO 2 loading in the reactants, the reaction temperatures and the steam concentrations in the atmosphere, while the conversion efficiency of NH 3 , which is significantly affected by temperature, didn't affected by the TiO 2 loadings. [ABSTRACT FROM AUTHOR]

Porous materials such as 5A molecular sieve (5A) display huge thermal resistance due to high porosity and lots of voids between grains that is negative to hydrogen isotope separation engineering. Generally, introducing thermal conductive fillers contributes to reducing thermal resistance while results in decreasing volume ratio of porous materials and then certainly causes declined hydrogen adsorption capacity. Here, a liquid polydimethylsiloxane (PDMS) is pressed into the voids between 5A grains, which is further developed into a silicon, oxygen and carbon (SiOC) structure suffering from 350 °C sintering. 5A/SiOC composite at 10 wt% polydimethylsiloxane (5A/SiOC10) displays 0.74 W/mK of thermal conductivity, which is about 300% higher than that of neat 5A. More importantly, enhanced rather than reduced hydrogen adsorption capacities at a fixed volume of the composite are determined. 5A/SiOC10 shows adsorption capacities of H 2 (175.4 mL/cm3) and D 2 (188.4 mL/cm3) while neat 5A shows that of H 2 (171.6 mL/cm3) and D 2 (165.8 mmol/cm3) at 77 K with 1 bar. Besides, enhanced thermal conductivity of porous materials shortens the cycle time of hydrogen isotope separation that contributes to reducing energy consumption. This work proposes a novel strategy on void filling to tailor thermal resistance of porous materials, which open a window to improve hydrogen isotope separation with thermal management materials. [Display omitted] • Enhanced thermal conductivity without at the expense of hydrogen adsorption capacity of porous materials. • A close relationship between thermal conductivity and hydrogen adsorption of porous materials is constructed. • Thermal resistance of porous materials is effectively tailored with void filling. • Cycle time of hydrogen isotope separation process tends to be shortened for reducing energy consumption. [ABSTRACT FROM AUTHOR]

Improvements on durability and CO tolerance of the electrocatalyst are crucial for widespread commercialization of direct methanol fuel cells (DMFCs). In this work, we describe a new method to stabilize the PtRu electrocatalyst, in which the PtRu nanoparticles are coated by nitrogen doped carbon layer derived from the carbonization of poly(vinyl pyrrolidone). The coated electrocatalyst shows stable electrochemical surface area (ECSA) and methanol oxidation reaction (MOR) activity after 4200 potential cycles from 0.6 V to 1.0 V vs . RHE; while the non-coated and commercial electrocatalyst lose almost 50% of initial ECSA and MOR activity. Meanwhile, the coated electrocatalyst shows twice higher CO tolerance before and after durability test due to the deceleration of the Ru dissolution proved by the XPS measurement after durability test. The mechanism of the stabilization of Ru was the electron delocalization of Ru caused by the carbonization process of PVP, which changes the electronic structure of Ru and makes Ru difficult to be dissolved. The maximum power density of the coated electrocatalyst is 1.7 times higher than that of commercial CB/PtRu, suggesting the coated electrocatalyst is suitable for real DMFC application. The demonstrated method could be easily extended to obtain extraordinary durability of other electrocatalysts. [ABSTRACT FROM AUTHOR]

In this work, we focus on the durability, CO tolerance and sluggish methanol oxidation reaction (MOR) of PtRu electrocatalyst. Here, we fabricate a new PtRu electrocatalyst supported on carbon black (CB), in which the PtRu nanoparticles are structurally sandwiched by poly(vinyl pyrrolidone) (PVP) and poly(2,5-benzimidazole) (ABPBI). Due to the first coating (PVP) on CB, the micropores on CB are capped resulting in high Pt utilization efficiency (94%) and catalytic activity toward methanol oxidation. Meanwhile, the second coating (ABPBI) on PtRu nanoparticles fabricated via in-situ polymerization improves the PtRu stability and decelerates the Ru dissolution leading to stable electrochemical surface area (ECSA), MOR activity and CO tolerance during the durability test. Without ABPBI coating, ECSA and catalytic activity remain only 50% after potential cycling. Additionally, the fuel cell performance of double polymer coated electrocatalyst reaches 103 mW cm −2 , which is among the highest values reported in the recent literatures. [ABSTRACT FROM AUTHOR]

The high dimensional swelling has been considered as one of the most important issues for obstructing sulfonated poly (ether ether ketone) (SPEEK) membrane with high IEC value as an excellent performance proton exchange membrane (PEM) for direct methanol fuel cell (DMFC) application. Here, we present a facile way to overcome the issue via blending the fully aromatic polyamide ( fa -PA) into SPEEK membrane. The Influence of the fa -PA on the key properties of the fabricated fa -PA/SPEEK composite membranes ( fa -PASPs) was systematically investigated. As the promising dimensional stability of the fa -PA, the fa -PASPs display excellent dimensional stability both in water and methanol aqueous solution. In addition, the fa -PASPs exhibit uniform and smooth morphology due to the same fully aromatic polyamide backbones as SPEEK and strong hydrogen bonding interactions between fa -PA and SPEEK with significantly reduced methanol crossover. The remarkable cell performance at high methanol concentration up to neat methanol was significantly obtained, suggesting that the prepared fa -PASPs are suitable for using as PEMs in direct methanol fuel cells application. [ABSTRACT FROM AUTHOR]