Direct carbon solid oxide fuel cells (DC-SOFCs) offer the potential for clean and efficient conversion of chemical energy in carbon fuels into electricity. However, the reverse Boudouard gasification of carbon requires a high operating temperature (>= 800 degrees C), which hinders the development of DC-SOFCs. We present a completely sealed DC-SOFC with in situ steam-carbon gasification. The cells have a symmetrical cell structure (Ag-Ce0.8Gd0.2O1.9/La0.9Sr0.1Ga0.8Mg0.2O3-delta/Ag-Ce0.8Gd0.2O1.9) and are loaded with K-loaded activated carbon fuel. Ca(OH)(2) and Li4SiO4 are loaded into the anode chamber as the steam feedstock and CO2 sorbent, respectively. Completely sealed DC-SOFCs with Ca(OH)(2)-C of 0 %, 5 %, 10 %, 15 %, and 20 % have been tested at 700 degrees C. Compared with a cell with a conventional structure and a completely sealed cell without Ca(OH)(2) loading, the electrochemical performances of all the completely sealed cells with Ca(OH)(2) loading are significantly enhanced. The cell with Ca (OH)(2) to C of 15 % obtained the highest maximum power density of 75 mW cm(-2), which is approximately two-fold that of the conventional DC-SOFC. The mechanism for improving the performance of the cell is the introduction of steam. This study offers a new method to develop high-performance DC-SOFCs and reduce their operating temperatures.

It is highly challenging to activate the basal plane and minimize the pi-pi stacking of MoS2 sheets, thus enhancing its catalytic performance. Here, we display an approach for making well-dispersed MoS2. By using the N-doped multi-walled carbon nanotubes (NMWCNTs) as an isolation unit, the aggregation of MoS2 sheets was effectively reduced, favoring the dispersion of Pt nanoparticles (noted as Pt/NMWCNTs-isolated-MoS2). Excellent bifunctional catalytic performance for methanol oxidation and oxygen reduction reaction (MOR/ORR) were demonstrated by the produced Pt/NMWCNTs-isolated-MoS2. In comparison to Pt nanoparticles supported on MoS2 (Pt/MoS2), the MOR activity (2314.14 mA mg(pt)(-1)) and stability (317.69 mA mg(pt)(-1) after 2 h of operation) on Pt/NMWCNTs-isolatedMoS(2) were 24 and 232 times higher, respectively. As for ORR, Pt/NMWCNTs-isolated-MoS2 holds large half-wave potential (0.88 V) and high stability (92.71 % after 22 h of operation). This work presents a tactic for activating the basal planes and reducing the pi-pi stacking of 2D materials to satisfy their applications in electrocatalysis. In addition, the proposed sheet-isolation method can be used for fabricating other 2D materials to promote the dispersion of nanoparticles, which assist its application in other fields of energy as well as the environment.

Tailoring the electronic structure of Pt-based catalysts can effectively facilitate their methanol oxidation reaction (MOR). Despite a great deal of effort, the fabrication of Pt-based catalysts with both tunable electronic structure and well-dispersion is still challenging. Herein, the PtNi alloy nanoparticles supported on poly (3, 4-ethylenedioxythiophene) modified multi-walled carbon nanotubes (PtNi/PEDOT-MWCNTs) was prepared for MOR. Transmission electron microscopy reveals the successful synthesis of PtNi nanoparticles (3.5 nm) by the reduction of H2. The X-ray photoelectron spectroscopy confirmed the strong electronic interaction between Ni and Pt, and the electronic environment of Pt atoms can be tailored by alloying different atomic content of Ni. Thus, the obtained PtNi/PEDOT-MWCNTs was suitable to design an effective electro-catalyst. As revealed through the electrochemical measurements, the fabricated PtNi/PEDOT-MWCNTs catalyst displayed higher peak current density, better stability, and excellent CO-tolerance than those of Pt nanoparticles dispersed on PEDOTMWCNTs, MWCNTs, and commercial carbon black. The surface/interface engineering tactic highlights the tailoring of the electronic structure of Pt-based catalysts, which can be applied in various fields, including methanol fuel cells and other catalytic reactions.

The application of Pt alloy catalysts for oxygen reduction reactions (ORRs) in proton-exchange membrane fuel cells is severely impeded by base metal leaching, since the produced metal ions can resu...

Efficacious regulation of the geometric and electronic structures of carbon nanomaterials via the introduction of defects and their synergy is essential to achieving good electrochemical performance. However, the guidelines for designing hybrid materials with advantageous structures and the fundamental understanding of their electrocatalytic mechanisms remain unclear. Herein, superfine Pt and PtCu nanoparticles supported by novel S,N-co-doped multi-walled CNT (MWCNTs) were prepared through the innovative pyrolysis of a poly(3,4-ethylenedioxythiophene)/polyaniline copolymer as a source of S and N. The uniform wrapping of the copolymer around the MWCNTs provides a high density of evenly distributed defects on the surface after the pyrolysis treatment, facilitating the uniform distribution of ultrafine Pt and PtCu nanoparticles. Remarkably, the Pt1Cu2/SN-MWCNTs show an obviously larger electroactive surface area and higher mass activity, stability, and CO poisoning resistance in methanol oxidation compared to Pt/SN-MWCNTs, Pt/S-MWCNTs, Pt/N-MWCNTs, and commercial Pt/C. Density functional theory studies confirm that the co-doping of S and N considerably deforms the CNTs and polarizes the adjacent C atoms. Consequently, both the adsorption of Pt1Cu2 onto the SN-MWCNTs and the subsequent adsorption of methanol are enhanced; in addition, the catalytic activity of Pt1Cu2/SN-MWCNTs for methanol oxidation is thermodynamically and kinetically more favorable than that of its CNT and N-CNT counterparts. This work provides a novel method to fabricate high-performance fuel cell electrocatalysts with highly dispersed and stable Pt-based nanoparticles on a carbon substrate.

Direct methanol fuel cell (DMFC) with near-zero pollution emission, large energy density, and low operating temperature provides a beneficial and sustainable way for alleviating fossil energy crisis and ecological pollution issues. In this work, a systematic protocol was explored for the design of novel electrocatalyst based on PEDOT-PSS coated amino-functionalized SiO2 microspheres (SiO2-NH2@PEDOT-PSS) support, and then Pt nanoparticles (NPs) were uniformly anchored for the anodic process of DMFCs. Characterization techniques, e.g. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that the dispersity and homogeneity of Pt NPs on the surface of SiO2-NH2@PEDOT-PSS were markedly improved due to PEDOT-PSS modification, and the distribution of Pt NPs was in a smaller mean-size similar to 2.8 nm. Subsequently, X-ray photoelectron spectroscopy (XPS) study exposed fast electron shift phenomenon from SiO2-NH2@PEDOT-PSS support to Pt NPs in the catalyst. The various electrochemical tests such as cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) revealed that the prepared Pt/SiO2-NH2@PEDOT-PSS catalyst presented higher electrocatalytic efficacy, excellent durability with improved CO-tolerance towards methanol oxidation reaction rather than commercial Pt/C catalyst. These distinctive physical and chemical features of designed catalyst raise the spirit to design an efficient electrocatalyst based on Pt/SiO2-NH2@PEDOT-PSS in DMFC applications. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Carbon atomic layers with encapsulated transition metal nanoparticles exhibit high catalytic activity for the oxygen reduction reaction (ORR), and good tolerance for poisoning species and acid leaching. However, the active sites and catalytic mechanism are not yet clear, mainly due to the highly heterogeneous structure of encapsulated types of catalysts. In this study, we developed a new model catalyst to mimic encapsulated types of catalysts by covering the well-defined active sites of iron phthalocyanine (FePc) with a monolayer of graphene. It was found that the FePc can activate the surface carbon layer to catalyze the ORR. Unlike exposed FePc on graphene, the embedded catalyst is insensitive to poisoning by SCN- ions. The designed model catalyst demonstrates that molecular type active sites, as well as metal nanoparticles, can form encapsulated catalysts for ORR. The simple and well-defined structure of this model catalyst is helpful for investigating the active sites and the catalytic mechanism at the atomic scale.

Improving the slow kinetics of hydrogen evolution/oxidation reaction(HER/HOR) on Pt in the alkaline electrolyte is key to the development of water splitting and hydroxide exchange membrane fuel cells, which feature a potential cost advantage over their acid-operating counterparts. However, it is still unconfirmed whether adsorbed surface hydroxyl species (OHad) plays a significant role in determining HER/HOR activity. Moreover, the active sites should be different in the alkaline due to the sluggish reaction rate. In the present work, electrochemical tests have shown that for modified bulk Pt surface and Pt3Ni nanoalloy, HER rate is co-determined by the oxophilic effect and electronic effect, while the rate of HOR is associated with the electronic effect. Density functional theory (DFT) calculations reveal the fundamentally different HER and HOR mechanism of Pt-based nanoparticles, and the surface charge may account for such difference. Finally, the adsorption and oxidation of carbon monoxide (CO) as a novel descriptor are provided to predicate the activity of HER and HOR.

As a cost-effective element, Mg has been applied as doped inactive atom to improve the electrochemical performance of sodium-ion cathode materials. Herein, we report Mg-substituted Na0.67Mn0.65Ni0.2Co0.15-xMgxO2 composites as high-performance cathode for sodium-ion batteries and investigate the underlying working mechanism using in situ investigation techniques to monitor the operando changes of electrodes. In situ X-ray diffraction investigation demonstrates P2-type structure is well preserved even charged to 4.3 V and the changes of lattice parameters and unit cell volume of Na0.67Mn0.65Ni0.2Mg0.15O2 are alleviated via Mg replacement. As a result, the capacity retention increases from 62% in Na0.67Mn0.65Ni0.2Co0.15O2 to 94% in Na0.67Mn0.65Ni0.2Mg0.15O2. Meanwhile, less CO2 evolution was detected in the coin cell with Na0.67Mn0.65Ni0.2Mg0.15O2 electrode than in that with Na0.67Mn0.65Ni0.2Co0.15O2 electrode in online differential electrochemical mass spectrometry test, suggesting a depressed side reaction between electrode and electrolyte after Mg completely replacing Co. In situ electrochemical impedance spectroscopy investigation further proves Mg is beneficial for the interfacial conductivity enhancement compared to Co, which provides evidence for enhanced high rate capabilities. These comprehensive results provide new viewpoints to explain the improved cycling and rate capabilities from the aspects of crystal structure evolution, coin cell gas evolution and electrolyte/electrode interface conductivity during charge/discharge process.

Transition-metal and nitrogen co-doped carbon materials (M/N/C) have received increasing attention as electrocatalysts for the oxygen reduction reaction (ORR). M/N/C catalysts usually exhibit distinct ORR catalytic activity between acidic and alkaline media. The origin of such pH-dependent activity is so far unclear. Herein, we investigate the dependence of ORR activity of FePc/C catalysts on the pyrolysis temperature (300-1000 degrees C) in both acidic and alkaline media to speculate the difference between active sites in the different media. The highest ORR activity is achieved at 800 degrees C and 500 degrees C in acidic and alkaline media, respectively. In particular, at 600-800 degrees C, the ORR activity increases greatly with increasing pyrolysis temperature in acidic medium, whereas it decreases in alkaline medium, indicating different active sites present in the two media. Thermal decomposition analysis of FePc suggests that highly active sites in acidic medium are formed through the decomposition of FePc or Fe-N-4 structures at 600-800 degrees C after releasing phthalonitrile (C6H5-C2N2), whereas intact FePc or Fe-N-4 incorporated in the carbon matrix are the main active sites in alkaline medium. XPS measurements show that there is a good relationship between the ORR activity and metal N in alkaline medium. This study is of significance to the development of highly active non-precious metal catalysts.

Reasonable design and synthesis of Fe/N/C-based catalysts is one of the most promising way for developing precious metal-free oxygen reduction reaction (ORR) catalysts in acidic mediums. Herein, we developed a highly active metal-organic framework-derived S-doped Fe/N/C catalyst [S-Fe/Z8/2-aminothiazole (2-AT)] prepared by thermal treatment. The S-Fe/Z8/2-AT catalyst with uniform S-doping possesses a three-dimensional macro-meso-micro hierarchically porous structure. Moreover, the chemical composition and structural features have been well-optimized and characterized for such S-Fe/Z8/2-AT catalysts; and their formation mechanism was also revealed. Significantly, applying the optimal S-Fe/Z8/2-AT catalysts into electrocatalytic test exhibits remarkable ORR catalytic activity with a half-wave potential of 0.82 V (vs reversible hydrogen electrode) and a mass activity of 18.3 A g-1 at 0.8 V in 0.1 M H2SO4 solution; the polymer electrolyte membrane fuel cell test also confirmed their excellent catalytic activity, which gives a maximal power density as high as 800 mW cm-2 at 1 bar. A series of designed experiments disclosed that the favorable structural merits and desirable chemical compositions of S-Fe/Z8/2-AT catalysts are critical factors for efficient electrocatalytic performance. The work provides a new approach to open an avenue for accurately controlling the composition and structure of Fe/N/C catalysts with highly activity for ORR.

Sulfur-doped multi-walled carbon nanotubes (S-MWCNTs) derived from PEDOT-functionalized MWCNTs can significantly improve the dispersion of supported Pt nanoparticles and enhance their electrocatalytic performance for the MOR.

A novel electrocatalyst of PdPtNi ternary alloy nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) for formic acid oxidation (FAO) reaction is synthesized by a simple hydrogen co-reduction process. The as-synthesized catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). It is found that highly dispersed PdPtNi alloy nanoparticles of ca. 2.56 nm are homogeneously deposited on the MWCNT surface, and the alloying with Pt and Ni alters the electronic structure of Pd atoms with the downshift of Pd d-band center. Studies of cyclic voltammetry and chronoamperometry indicate that the electrocatalytic activity and durability of the PdPtNi/MWCNT for FAO are significantly enhanced as compared with the PdPt/MWCNT and commercial Pd/C catalysts. This study implies that the prepared PdPtNi/MWCNT composite is a promising anode electrocatalyst of direct formic acid fuel cells. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

A novel strategy in DESs for the fabrication of MWCNTs-supported PdSn alloy nanostructures is reported. The prepared PdSn/MWCNT shows remarkably improved electrocatalytic performance towards formic acid oxidation reaction.

Herein, we report a novel electrocatalyst consisting of Pt nanoparticles supported on a polyindole (PIn)-functionalized multi-walled carbon nanotube (MWCNT) composite (Pt/PIn-MWCNT) for use in the methanol oxidation reaction (MOR). The PIn-MWCNT support is synthesized via in situ chemical polymerization of indole on the MWCNT surface. The transmission electron microscopy (TEM) images indicated that the Pt nanoparticles were approximately 3.0 nm in size and were uniformly deposited on the surface of PIn-MWCNTs with no aggregation into larger clusters. X-ray photoelectron spectroscopy (XPS) measurements confirm the strong electron interaction between the Pt nanoparticles and the PIn-MWCNT support as well as the formation of the Pt-N bond. The electrochemical tests demonstrate that the Pt/PIn-MWCNT composite exhibits much higher electrocatalytic activity, durability and CO tolerance than the Pt/MWCNT and commercial Pt/C catalysts toward MOR. The results indicate that the as-prepared Pt/PIn-MWCNTs are promising for use as an anode electrocatalyst in direct methanol fuel cells (DMFCs). (C) 2015 Elsevier B.V. All rights reserved.

A novel nanostructured catalyst of platinum nanoparticles supported on 5,10,15,20-tetrakis(1-methyl-4-pyridinio) porphyrin tetra(p-toluenesulfonate) (TMPyP) functionalized graphene (TMPyP-graphene) is synthesized by the hydrothermal polyol process. The as-synthesized nanocomposites are characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis absorption spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests. It has been found that Pt nanoparticles of ca. 3.4 nm are uniformly dispersed on the surface of TMPyP-graphene, and hold a high electrochemical active surface area (ECSA) of 126.2 m(2) g(-1). The results demonstrate that the Pt/TMPyP-graphene catalyst exhibits a much higher electrocatalytic activity and stability than the Pt/graphene and commercial Pt/C catalysts for methanol oxidation, which is of significant importance in improving the efficiency of Pt-based electrocatalysts for DMFCs applications.

The hydrothermal synthesis of a novel Pd electrocatalyst using copper phthalocyanine-3,4′,4″,4′″-tetrasulfonic acid tetrasodium salt (TSCuPc) functionalized multi-walled carbon nanotubes (MWCNTs) composite as catalyst support for Pd nanoparticles is reported. The prepared nanocomposites were characterized by UV–vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests. It is found that Pd nanoparticles are uniformly deposited on the surface of TSCuPc-MWCNTs, and their dispersion and electrochemical active surface area (ECSA) are significantly improved. Studies of cyclic voltammetry and chronoamperometry demonstrate that the Pd/TSCuPc-MWCNTs exhibits much higher electrocatalytic activity and stability than the Pd/AO-MWCNTs catalyst for formic acid oxidation. This study implies that the as-prepared Pd/TSCuPc-MWCNTs will be a promising candidate as an anode electrocatalyst in direct formic acid fuel cell (DFAFC).

A novel electrocatalyst using nickel (II) phthalocyanine-tetrasulfonic acid tetrasodium salt (TSNiPc) functionalized graphene (TSNiPc-graphene) composite as catalyst support for Pt nanoparticles is reported. The surface morphology, composition and structure of the prepared nanocomposites as well as their electrocatalytic properties toward methanol oxidation are characterized by UV-vis absorption spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical tests. Pt nanoparticles are found uniformly dispersed on the surface of TSNiPc-graphene composite, with the small particle size of about 3.1 nm. Studies of cyclic voltammetry and chronoamperometry demonstrate that the Pt/TSNiPc-graphene exhibits much higher electrocatalytic activity and stability than the Pt/graphene catalyst for methanol oxidation. (C) 2013 Elsevier Ltd. All rights reserved.

We herein report a facile and effective ultrasonication method to non-covalently functionalize graphene with copper phthalocyanine-3,4′,4″,4‴-tetrasulfonic acid tetrasodium salt (TSCuPc) as a promising catalyst support for Pt nanoparticles. With the assistance of TSCuPc, Pt nanoparticles are homogeneously deposited on the surface of graphene, and their dispersivity and electrochemical active surface area (ECSA) are obviously enhanced. Studies of cyclic voltammetry and chronoamperometry demonstrate that the as-prepared Pt/TSCuPc–graphene catalyst exhibits much higher electrocatalytic activity and stability than the Pt/graphene and commercial Pt/C catalysts for methanol oxidation. It is concluded that the strategy of TSCuPc-functionalized graphene with Pt catalysts will be potential in design and synthesis of the highly efficient electrocatalysts for DMFCs applications.

We herein report a novel Pt-based electrocatalyst for direct methanol fuel cells (DMFCs) using multi-walled carbon nanotubes (MWCNTs) supported manganese oxide and poly(3,4-ethylenedioxythiophene) (PEDOT) nanocomposite (MnOx–PEDOT–MWCNTs) as catalyst support for Pt nanoparticles. The prepared nanocomposites are characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests. The results demonstrate that Pt nanoparticles are uniformly deposited on the surface of MnOx–PEDOT–MWCNTs, and their dispersion and electrochemical active surface area (ECSA) are obviously improved. The methanol electrooxidation activity and stability of the Pt/MnOx–PEDOT–MWCNTs are significantly enhanced as compared with the Pt/PEDOT–MWCNTs and Pt/MWCNTs catalysts. This study implies that the as-prepared Pt/MnOx–PEDOT–MWCNTs will be a promising candidate as an anode electrocatalyst in DMFCs.