An environmentally friendly precursor, adenosine, has been used as a dual source of C and N to synthesize nitrogen-doped carbon catalyst with/without Fe. A hydrothermal carbonization method has been used and water is the carbonization media. The morphology of samples with/without Fe component has been compared by HRTEM, and the result shows that Fe can promote the graphitization of carbon. Further electro-chemical test shows that the oxygen reduction reaction (ORR) catalytic activity of Fe-containing sample (CFeN) is much higher than that of the Fe-free sample (CN). Additionally, the intermediates of CFeN formed during each synthetic procedure have been thoroughly characterized by multiple methods, and the function of each procedure has been discussed. The CFeN sample exhibits high electro-catalytic stability and superior electro-catalytic activity toward ORR in alkaline media, with its half-wave potential 20 mV lower than that of commercial Pt/C (40 wt%). It is further incorporated into alkaline polymer electrolyte fuel cell (APEFC) as the cathode material and led to a power density of 100 mW/cm2.Adenosine has been used to synthesize highly active Fe/N/C catalyst. The ORR catalytic activity of the catalyst is superior not only on RDE test but also on alkaline polymer electrolyte membrane fuel cell application.Download high-res image (127KB)Download full-size image

The performance and the cyclability of the Li–O2 batteries are strongly affected by the morphology and crystal structure of Li2O2 produced during discharge. In order to explore the details of growth and electrochemical decomposition of Li2O2, and its relationship with the cell performance, graphene films were used as model carbon electrodes and compared with electrodeposited Pd nanoparticles (NPs) on graphene. Multiple methods, including transmission/scanning electron microscopy (TEM/SEM), Raman spectroscopy, electrochemical impedance spectroscopy (EIS), and coin cell charge/discharge test, were employed for material characterization and reaction monitoring. The results showed that the presence of Pd NPs significantly changed the growth, morphology, and crystal structure of Li2O2 and reduced the charge overpotential by 1060 mV. All of these changes are ascribed to the stronger binding energy between LiO2 and the Pd surface, resulting in the generation of amorphous Li2O2 with higher ionic conductivity of Li+ and O22–, which in turn improve the cell charging performance.Keywords: adsorption energy of LiO2; amorphous; crystalline; electrocatalysis; graphene film; Li2O2 morphology; Li−O2 battery; overpotential

•A Pd skin with 2–3 atomic layers on AuCu intermetallic nanoparticles (PdSAuCu iNPs) is controllably fabricated.•The PdSAuCu iNPs exhibit excellent electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline media, far better and more stable than the commercial Pt/C catalyst.•The AuCu intermetallic substrate causes a shrink strain in Pd lattice of the skin, which reduces the oxygen affinity of Pd and thus enhances the catalytic activity.Core–shell structured catalysts have been widely investigated for fuel cell applications in the recent decade. The skin-substrate interaction has provided a well tunable basis for the design of better catalysts. Herein, we report an implementation of fabricating a Pd skin onto the AuCu intermetallic nanoparticles (denoted as PdSAuCu iNPs), and its exceptionally high activity towards the oxygen reduction reaction (ORR) in alkaline media. The structure of PdSAuCu iNPs was well characterized through combining a variety of techniques, including high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray (EDX) line scanning analysis, synchrotron X-ray diffraction patterns (SXRD), X-ray photoelectron spectra (XPS), X-ray fluorescence analysis (XRF), and electrochemical measurements. The AuCu intermetallic core was identified to be fully wrapped by a Pd skin with 2–3 atomic layers. The catalytic activity of PdSAuCu iNPs towards the ORR in alkaline is more than 8-times higher in surface-specific activity (SA), and 20-times higher in mass-specific activity (MA), than that of the commercial Pt/C catalyst, and remains reasonably stable in thousands cycles of potential sweep. Such an outstanding performance is attributed to the reduction in the oxygen affinity of the Pd skin caused by a proper and stable shrink in Pd lattice induced by the AuCu intermetallic substrate.

The dependence on Pt catalysts has been a major issue of proton-exchange membrane (PEM) fuel cells. Strategies to maximize the Pt utilization in catalysts include two main approaches: to put Pt atoms only at the catalyst surface and to further enhance the surface-specific catalytic activity (SA) of Pt. Thus far there has been no practical design that combines these two features into one single catalyst. Here we report a combined computational and experimental study on the design and implementation of Pt-skin catalysts with significantly improved SA toward the oxygen reduction reaction (ORR). Through screening, using density functional theory (DFT) calculations, a Pt-skin structure on AuCu(111) substrate, consisting of 1.5 monolayers of Pt, is found to have an appropriately weakened oxygen affinity, in comparison to that on Pt(111), which would be ideal for ORR catalysis. Such a structure is then realized by substituting the Cu atoms in three surface layers of AuCu intermetallic nanoparticles (AuCu iNPs) with Pt. The resulting Pt-skinned catalyst (denoted as PtSAuCu iNPs) has been characterized in depth using synchrotron XRD, XPS, HRTEM, and HAADF-STEM/EDX, such that the Pt-skin structure is unambiguously identified. The thickness of the Pt skin was determined to be less than two atomic layers. Finally the catalytic activity of PtSAuCu iNPs toward the ORR was measured via rotating disk electrode (RDE) voltammetry through which it was established that the SA was more than 2 times that of a commercial Pt/C catalyst. Taking into account the ultralow Pt loading in PtSAuCu iNPs, the mass-specific catalytic activity (MA) was determined to be 0.56 A/mgPt@0.9 V, a value that is well beyond the DOE 2017 target for ORR catalysts (0.44 A/mgPt@0.9 V). These findings provide a strategic design and a realizable approach to high-performance and Pt-efficient catalysts for fuel cells.

Albeit ultrahigh in energy density, the Li–O2 battery technology still suffers from the high overpotential of Li2O2 oxidation upon charging and the low cyclability. In the present work, we use Pt2Ru/C as the oxygen-electrode catalyst and study how it improves the cell performance and changes the reaction mechanism, as compared with a carbon electrode. Multiple methods, including X-ray diffraction, transmission/scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry, have been employed for material characterization and reaction monitoring. The Li–O2 cell with a Pt2Ru/C catalyst shows lower charge voltage, higher specific capacity, and enhanced cyclability than does a carbon catalyst. The key for this improvement is ascribed to the morphology change of Li2O2. Whereas the Li2O2 formed in the carbon electrode is rod-shaped, the Li2O2 in the Pt2Ru/C electrode is mud shaped and closely attached to the electrode substrate, thus benefiting the subsequent Li2O2 oxidation. This study indicates that the charging performance of the Li–O2 battery can be improved not only by using proper catalysts, but also by controlling the Li2O2 morphology during discharge.

•A noble way to fabricate Ni–Mo HER cathode.•NiMoO4 powders, with fixed Ni/Mo atomic ratio, was used as precursor.•Ni and Mo are uniformly distributed in the electrode.•The resulting electrode is suitable for MEA preparation.Among the catalysts for hydrogen evolution reaction (HER) in alkaline media, Ni–Mo turns out to be the most active one. Conventional preparations of Ni–Mo electrode involve repeated spraying of dilute solutions of precursors onto the electrode substrate, which is time-consuming and usually results in cracking and brittle electrodes. Here we report a noble fabrication of Ni–Mo electrode for HER. NiMoO4 powder was synthesized and used as the precursor. After reduction in H2 at 500 °C, the NiMoO4 powder layer was converted to a uniform and robust electrode containing metallic Ni and amorphous Mo(IV) oxides. The distribution of Ni and Mo components in this electrode is naturally uniform, which can maximize the interaction between Ni and Mo and benefit the electrocatalysis. The thus-obtained Ni–Mo electrode exhibits a very high catalytic activity toward the HER: the current density reaches 700 mA/cm2 at 150 mV overpotential in 5 M KOH solution at 70 °C. This new fabrication method of Ni–Mo electrode is not only suitable for alkaline water electrolysis (AWE), but also applicable to the alkaline polymer electrolyte water electrolysis (APEWE), an emerging technique for efficient production of H2.

Hematite has been a popular photoanode for photoelectrochemical water splitting; however, its performance varies widely in the literature. In-depth understanding of the structure–performance relationship of hematite photoanode is still lacking. Here, we report a finding that without the use of co-catalysts or any alteration in crystal structure, the performance of hematite photoanode can be markedly improved by properly enlarging the space among α-Fe2O3 nanocrystalline, i.e., by increasing the pore size in the electrode. Such a finding indicates that in addition to the known catalytic and crystal effects, the internal structure of the hematite electrode is also a very sensitive factor to PEC efficiency.

Combined computational and experimental studies reveal a noble, non-d-band effect on Ag activation and electrocatalysis: upon coating Ag onto the even more inert Au surface, the catalytic activity toward the oxygen reduction reaction in alkaline media can be improved by about half an order of magnitude in comparison to the usual Ag surface.

In the present work, a one-pot method is employed to synthesize AuCu intermetallic nanoparticles (AuCu iNPs) supported on high-surface-area carbon. To avoid blocking the active sites of the AuCu iNPs for the subsequent study of electrocatalysis, no surfactant has been applied in the entire synthetic process. After refluxing in glycerol at 300 °C, the ordered structure is formed in the carbon-supported AuCu iNPs, whose superlattice is evidently demonstrated by the X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations. Such intermetallic nanoparticles show very interesting electrochemical behaviors which have hitherto not been reported in the literature. In addition to the peculiar cyclic voltammetry (CV), the AuCu iNPs exhibit a superior catalytic activity, in comparison to that of ordinary Au nanoparticles, toward the oxygen reduction reaction (ORR) in alkaline media. The alteration in the surface electronic properties of Au, caused by the incorporation of Cu, has also been studied by X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations.

Although most transition metals have been tested as the promoter to Pt for electrocatalysis toward fuel cell reactions, semi-conductor elements, such as Si, have hitherto not been examined. Here we report a simple synthesis of intermetallic Pt2Si electrode using magnetron sputtering and the electrocatalysis toward ethanol oxidation reaction (EOR). In comparison to Pt, the intermetallic Pt2Si surface turns out to be much more active in catalyzing the EOR: the onset potential shifts negatively by 150 mV, and the current density at 0.6 V increases by a magnitude of one order. Such an enormous enhancement in EOR catalysis is ascribed to the promotion effects of Si, which can not only provide active surface oxygenated species to accelerate the removal of COads, but also strongly alter the electronic property of Pt, as clearly indicated by the core-level shift in XPS spectrum.Intermetallic Pt2Si electrode is produced by magnetron sputtering, which exhibits a profound enhancement in the catalytic activity toward the ethanol oxidation reaction in comparison to Pt.Download full-size image

Combined computational and experimental studies reveal a noble, non-d-band effect on Ag activation and electrocatalysis: upon coating Ag onto the even more inert Au surface, the catalytic activity toward the oxygen reduction reaction in alkaline media can be improved by about half an order of magnitude in comparison to the usual Ag surface.

In the present work, a one-pot method is employed to synthesize AuCu intermetallic nanoparticles (AuCu iNPs) supported on high-surface-area carbon. To avoid blocking the active sites of the AuCu iNPs for the subsequent study of electrocatalysis, no surfactant has been applied in the entire synthetic process. After refluxing in glycerol at 300 °C, the ordered structure is formed in the carbon-supported AuCu iNPs, whose superlattice is evidently demonstrated by the X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations. Such intermetallic nanoparticles show very interesting electrochemical behaviors which have hitherto not been reported in the literature. In addition to the peculiar cyclic voltammetry (CV), the AuCu iNPs exhibit a superior catalytic activity, in comparison to that of ordinary Au nanoparticles, toward the oxygen reduction reaction (ORR) in alkaline media. The alteration in the surface electronic properties of Au, caused by the incorporation of Cu, has also been studied by X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations.

Albeit ultrahigh in energy density, the Li–O2 battery technology still suffers from the high overpotential of Li2O2 oxidation upon charging and the low cyclability. In the present work, we use Pt2Ru/C as the oxygen-electrode catalyst and study how it improves the cell performance and changes the reaction mechanism, as compared with a carbon electrode. Multiple methods, including X-ray diffraction, transmission/scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry, have been employed for material characterization and reaction monitoring. The Li–O2 cell with a Pt2Ru/C catalyst shows lower charge voltage, higher specific capacity, and enhanced cyclability than does a carbon catalyst. The key for this improvement is ascribed to the morphology change of Li2O2. Whereas the Li2O2 formed in the carbon electrode is rod-shaped, the Li2O2 in the Pt2Ru/C electrode is mud shaped and closely attached to the electrode substrate, thus benefiting the subsequent Li2O2 oxidation. This study indicates that the charging performance of the Li–O2 battery can be improved not only by using proper catalysts, but also by controlling the Li2O2 morphology during discharge.