Facile synthesis of Pt-decorated Ir black as a bifunctional oxygen catalyst for oxygen reduction and evolution reactions.

Pt-Decorated Ir black (Pt@Ir) nanoparticles with two varying Pt mass fractions (Pt4@Ir96 and Pt16@Ir84) were generated by a facile method in water with the aid of Ir black. The Pt@Ir nanoparticles were investigated as a bifunctional oxygen catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in acidic medium. Benefiting from the good dispersion of ultrafine Pt nanodots on the Ir black surface and the synergistic effect between the Pt and underlying Ir atoms, Pt@Ir nanoparticles have exhibited outstanding ORR activity and comparable OER performance in comparison with commercial Ir black. In particular, Pt16@Ir84 shows an ORR mass activity of 2.6 times that of commercial Pt black and exhibits much better bifunctional performances than a mixture of Pt black and Ir black with a Ir/Pt mass ratio of 50/50 (Pt50Ir50). Our work highlights the effectiveness of decorating Ir black with Pt nanodots to fabricate bifunctional oxygen catalysts.

A novel IrNi@PdIr/C core-shell electrocatalyst with enhanced activity and durability for the hydrogen oxidation reaction in alkaline anion exchange membrane fuel cells.

Herein, a novel non-platinum core-shell catalyst, namely, IrNi@PdIr/C was prepared via a galvanic replacement reaction; it exhibits enhanced hydrogen oxidation activity and excellent stability under alkaline conditions. Electrochemical experiments demonstrated that the mass and specific activities at 50 mV of IrNi@PdIr/C are 2.1 and 2.2 times that of commercial Pt/C in 0.1 M KOH at 298 K, respectively. Moreover, accelerated degradation tests have shown that the electrochemically active surface area (ECSA) of IrNi@PdIr/C reduces by only 5.1%, which is almost 4 times less than that of commercial Pt/C and the mass activity at 50 mV of IrNi@PdIr/C after 2000 potential cycles is still 1.8 times higher than that of aged Pt/C. XRD and XPS analysis suggest that the enhanced HOR activity is attributed to the weakening of the hydrogen binding to the PdIr overlayers induced by the IrNi core. The better stability to potential cycling can be associated with the PdIr shell, which inhibits oxide formation. These results suggest that IrNi@PdIr/C is a promising non-platinum anode catalyst for alkaline anion exchange membrane fuel cells.

Investigation of water transport in fuel cells using water transport plates and solid plates.

Water management of proton exchange membrane fuel cells (PEMFCs) is of vital importance to achieve better performance and durability. In this study, porous hydrophilic water transport plates (WTPs) with different pore structures were prepared and employed to improve water management in PEMFCs. Polarization curves, electrochemical impedance spectroscopy (EIS) and water balance were tested to investigate the effect of pore structure on cell performance and water transport process. The results show that pore structure has little effect on drainage function due to excess liquid water flux of WTPs, while the membrane hydration is improved with increased surface evaporation rate of WTPs, resulting in better cell performance. The favorable cell performance shows that WTP is a promising technique to improve water management in PEMFCs.

3D Pd/Co core-shell nanoneedle arrays as a high-performance cathode catalyst layer for AAEMFCs.

A novel cathode architecture using vertically aligned Co nanoneedle arrays as an ordered support for application in alkaline anion-exchange membrane fuel cells (AAEMFCs) has been developed. The Co nanoneedle arrays were directly grown on a stainless steel sheet via a hydrothermal reaction and then a Pd layer was deposited on the surface of the Co nanoneedle arrays using a vacuum sputter-deposition method to form Pd/Co nanoneedle arrays. After transferring the Pd/Co nanoneedle arrays to an AAEM, a cathode catalyst layer was formed. Without the use of an alkaline ionomer, the AAEMFC with the prepared cathode catalyst layer showed an enhanced performance with ultra-low Pd loading of down to 33.5 µg cm-2, which is much higher than the conventionally used cathode electrode with a Pt loading of 100 µg cm-2. This is the first report where three-dimensional Co nanoneedle arrays have been used as the cathode support in an AAEMFC, which is able to deliver a higher power density without an alkaline ionomer than that of conventional membrane electrode assembly (MEA).

Highly stable nanostructured membrane electrode assembly based on Pt/Nb2O5 nanobelts with reduced platinum loading for proton exchange membrane fuel cells.

Proton exchange membrane fuel cells are promising candidates for the next-generation power sources; however, poor durability and high cost impede their widespread application. To address this dilemma, a nanostructured membrane electrode assembly (MEA) based on Pt/Nb2O5 nanobelts (NBs) was constructed through hydrothermal synthesis and the physical vapour deposition method. Pt/Nb2O5 NBs were directly aligned with Nafion membrane without ionomer as a binder. The prepared catalyst layer is ultrathin and has ultralow Pt loading. A single cell performance of 5.80 kW gPt-1 (cathode) and 12.03 kW gPt-1 (anode) was achieved by the Pt/Nb2O5 NBs-based MEA (66.0 µgPt cm-2). The accelerated durability test indicates that the Pt/Nb2O5 NBs-based MEA is far more stable than conventional Pt/C-based MEA.

Vertically Aligned FeOOH/NiFe Layered Double Hydroxides Electrode for Highly Efficient Oxygen Evolution Reaction.

Employing a low-cost and highly efficient electrocatalyst to replace Ir-based catalysts for oxygen evolution reaction (OER) has drawn increasing interest in renewable energy storage. In this work, a vertically aligned FeOOH/NiFe layered double hydroxides (LDHs) nanosheets supported on Ni foam (VA FeOOH/NiFe LDHs-NF) is prepared as a highly effective OER electrode in alkaline electrolyte. The VA FeOOH/NiFe LDHs-NF represents nanosheet arrays on nickel foam with some interspace among them. The vertically aligned and interlayer-structured architecture is binder-free and contributes to facile strain relaxation, relieving the exfoliation of the catalysts layer caused by the oxygen evolution process. The as-prepared electrode shows current densities of 10 and 500 mA cm-2 at overpotentials of 208 and 288 mV, and good stability in a half-cell electrolyzer. Besides, the alkaline polymer electrolyte water electrolyzer (APEWE) with this electrode showed 1.71 V at 200 mA cm-2, and 2.041 V at 500 mA cm-2, exhibiting the corresponding energy efficiency of 86.0% and 72.0% (based on the lower heating value of hydrogen), which is better than the typical commercial alkaline water electrolyzer.

Mass-transport-controlled, large-area, uniform deposition of carbon nanofibers and their application in gas diffusion layers of fuel cells.

The effect of mass transport on the growth characteristics of large-area vapor-grown carbon nanofibers (CNFs) was investigated by adjusting the substrate deposition angle (α). The catalyst precursor solution was coated onto one side of a 2D porous carbon paper substrate via a decal printing method. The results showed that the CNFs were grown on only one side of the substrate and α was found to significantly affect the growth uniformity. At α = 0°, the growth thickness, the density, the microstructure and the yield of the CNF film were uniform across the substrate surface, whereas the growth uniformity decreased with increasing α, suggesting that the large-area CNF deposition processes were mass-transport-controlled. Computational fluid dynamics simulations of the gas diffusion processes revealed the homogeneous distributions of the carbon-source-gas concentration, pressure, and velocity near the substrate surface at α = 0°, which were the important factors in achieving the mass-transport-limited uniform CNF growth. The homogeneity of the field distributions decreased with increasing α, in accordance with the variation in the growth uniformity with α. When used as a micro-porous layer, the uniform CNF film enabled higher proton exchange membrane fuel cell performance in comparison with commercial carbon black by virtue of its improved electronic and mass-transport properties confirmed by the electrochemical impedance spectroscopy results.

Carbonization of self-assembled nanoporous hemin with a significantly enhanced activity for the oxygen reduction reaction.

The scarcity and high cost of Pt-based electrocatalysts for the oxygen reduction reaction (ORR) hinder the practical application of proton exchange membrane fuel cells (PEMFCs). It is critical to replace platinum with non-noble metal electrocatalysts (NNMEs). Carbonized metalloporphyrins represent an important class of NNMEs, but most metalloporphyrins are costly and the corresponding NNMEs do not possess a high ORR activity. Herein, we report that the self-assembly of inexpensive hemin leads to porous nanomaterials in water under ambient conditions and subsequent heat-treatment of the unprecedented nanoporous hemin results in a magnetic NNME with a much enhanced ORR activity compared with directly carbonized hemin without self-assembly. The improvement of the ORR activity likely originates from the exposure of more ORR active sites, caused by the surface area increase of the nanoporous hemin after carbonization over that of micro-scale pristine hemin crystals. Moreover, the ORR activity of heat-treated nanoporous hemin is actually comparable to that of commercial Pt/C in alkaline solution. Additionally, the carbonized nanoporous hemin is much better than commercial Pt/C in terms of durability and tolerance to methanol. This study opens up a new avenue to the production of inexpensive metalloporphyrin-based NNMEs with a high ORR performance by using a self-assembly method in combination with traditional pyrolysis.

Ionic-liquid-based proton conducting membranes for anhydrous H2/Cl2 fuel-cell applications.

An ionic-liquid-doped poly(benzimidazole) (PBI) proton-conducting membrane for an anhydrous H2/Cl2 fuel cell has been proposed. Compared with other ionic liquids, such as imidazole-type ionic liquids, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) showed better electrode reaction kinetics (H2 oxidation and Cl2 reduction reaction at platinum) and was more suitable for a H2/Cl2 fuel cell. PBI polymer and [dema][TfO] were compatible with each other, and the hybrid membranes exhibited high stability and good ionic conductivity, reaching 20.73 mS cm(-1) at 160 °C. We also analyzed the proton-transfer mechanism in this ionic-liquid-based membrane and considered that both proton-hopping and diffusion mechanisms existed. In addition, this composite electrolyte worked well in a H2/Cl2 fuel cell under non-water conditions. This work would give a good path to study the novel membranes for anhydrous H2/Cl2 fuel-cell application.

Ethylene glycol adjusted nanorod hematite film for active photoelectrochemical water splitting.

We reported a facile adjusted method for the synthesis of high surface area nanorod hematite film as a photoanode for application in water splitting. Crystalline hematite nanorods (EG-α-Fe2O3) are fabricated by electrodeposition in Fe(2+) precursor solution with the addition of ethylene glycol (EG) and followed by annealing at 450 °C. The nanorod hematite film fabricated by the modified electrodeposition approach exhibits a more uncompact structure than α-Fe2O3 obtained by directly electrodepositing on the FTO substrate. The optical and structural characteristics of the obtained film are also tested. The results infer that EG can tune the morphology of hematite and improve the photoabsorption in the visible light region due to its inducement of one-dimensional growth of crystal hematite. It also enhances the photoresponse activity of hematite in water splitting by improving the activities at the semiconductor/solution interface. The photocurrent density of EG-α-Fe2O3 nanorods increased to 0.24 mA cm(-2) at 1.4 V vs. RHE in 1 M KOH (pH = 13.6), almost 5 times higher than the original α-Fe2O3 (0.05 mA cm(-2), measured under the same conditions).

Highly stable ternary tin-palladium-platinum catalysts supported on hydrogenated TiO2 nanotube arrays for fuel cells.

Herein the Pt nanocrystals were synthesized by a high-pressure methanol reduction method onto the hydrogenated TiO2 nanotube arrays pre-treated by Sn/Pd. Then Sn/Pd/Pt ternary catalysts were fabricated by hydrogen treatment. The composite catalysts with a diameter of about 18 nm were located uniformly at the inner nanotubes. The novel catalyst combined with hydrogenated TiO2 nanotube arrays exhibits excellent electro-catalytic activity and high durability. The electrochemical performance of the catalysts after 18,000 potential cycles between 0 and 1.2 V vs. RHE could reach the maximum, and the electrochemical surface area of the catalyst at 18,000 cycles is about 136 m(2) g(-1)Pt+Pd, which is 1.3 folds than the commercial JM Pt/C (104 m(2) g(-1)Pt). Furthermore, there is little decrease in the electrochemical surface area for the catalyst after additional 7300 potential cycles (total 24,300 cycles). In a full cell testing, the fabricated novel electrode with extra-low Pt loading (0.043 mg cm(-2)) generated power as 1.21 kW g(-1)Pt when it is used as the cathode in a fuel cell.

Supported noble metals on hydrogen-treated TiO2 nanotube arrays as highly ordered electrodes for fuel cells.

Hydrogen-treated TiO2 nanotube (H-TNT) arrays serve as highly ordered nanostructured electrode supports, which are able to significantly improve the electrochemical performance and durability of fuel cells. The electrical conductivity of H-TNTs increases by approximately one order of magnitude in comparison to air-treated TNTs. The increase in the number of oxygen vacancies and hydroxyl groups on the H-TNTs help to anchor a greater number of Pt atoms during Pt electrodeposition. The H-TNTs are pretreated by using a successive ion adsorption and reaction (SIAR) method that enhances the loading and dispersion of Pt catalysts when electrodeposited. In the SIAR method a Pd activator can be used to provide uniform nucleation sites for Pt and leads to increased Pt loading on the H-TNTs. Furthermore, fabricated Pt nanoparticles with a diameter of 3.4 nm are located uniformly around the pretreated H-TNT support. The as-prepared and highly ordered electrodes exhibit excellent stability during accelerated durability tests, particularly for the H-TNT-loaded Pt catalysts that have been annealed in ultrahigh purity H2 for a second time. There is minimal decrease in the electrochemical surface area of the as-prepared electrode after 1000 cycles compared to a 68 % decrease for the commercial JM 20 % Pt/C electrode after 800 cycles. X-ray photoelectron spectroscopy shows that after the H-TNT-loaded Pt catalysts are annealed in H2 for the second time, the strong metal-support interaction between the H-TNTs and the Pt catalysts enhances the electrochemical stability of the electrodes. Fuel-cell testing shows that the power density reaches a maximum of 500 mWcm(-2) when this highly ordered electrode is used as the anode. When used as the cathode in a fuel cell with extra-low Pt loading, the new electrode generates a specific power density of 2.68 kWg(Pt) (-1) . It is indicated that H-TNT arrays, which have highly ordered nanostructures, could be used as ordered electrode supports.

Highly effective Ir(x)Sn(1-x)O2 electrocatalysts for oxygen evolution reaction in the solid polymer electrolyte water electrolyser.

We developed an advanced surfactant-assistant method for the Ir(x)Sn(1-x)O(2) (0 < x ≤ 1) nanoparticle (NP) preparation, and examined the OER performances by a series of half-cell and full-cell tests. In contrast to the commercial Ir black, the collective data confirmed the outstanding activity and stability of the fabricated Ir(x)Sn(1-x)O(2) (x = 1, 0.67 and 0.52) NPs, which could be ascribed to the amorphous structure, good dispersion, high pore volume, solid-solution state and Ir-rich surface for bi-metal oxides, and relatively large size (10-11 nm), while Ir(0.31)Sn(0.69) exhibited poor electro-catalytic activity because of the separated two phases, a SnO(2)-rich phase and an IrO(2)-rich phase. Furthermore, compared with highly active IrO(2), the improved durability, precious-metal Ir utilization efficiency and correspondingly reduced Ir loading were realized by the addition of Sn component. When the Ir(0.52)Sn(0.48)O(2) cell operated at 80 °C using Nafion® 115 membrane and less than 0.8 mg cm(-2) of the noble-metal Ir loading, the cell voltages we achieved were 1.631 V at 1000 mA cm(-2), and 1.821 V at 2000 mA cm(-2). The IR-free voltage at the studied current density was very close to the onset voltage of oxygen evolution. The only 50 µV h(-1) of voltage increased for the 500 h durability test at 500 mA cm(-2). In fact, these results are exceptional compared to the performances for OER in SPEWE cells known so far. This work highlights the potential of using highly active and stable IrO(2)-SnO(2) amorphous NPs to enhance the electrolysis efficiency, reduce the noble-metal Ir loading and thus the cost of hydrogen production from the solid polymer electrolyte water electrolysis.

Lithium oxides precipitation in nonaqueous Li-air batteries.

Lithium-air/oxygen battery is a rising star in the field of electrochemical energy storage as a promising alternative to lithium ion batteries. Nevertheless, this alluring system is still at its infant stage, and the breakthrough of lithium-air batteries into the energy market is currently constrained by a combination of scientific and technical challenges. Targeting at the air electrode in nonaqueous lithium-air batteries, this review attempts to summarize the knowledge about the fundamentals related to lithium oxides precipitation, which has been one of the vital and attractive aspects of the research communities of science and technology.

High-temperature proton-exchange-membrane fuel cells using an ether-containing polybenzimidazole membrane as electrolyte.

Herein, poly[2,2'-(p-oxydiphenylene)-5,5'-benzimidazole] (PBI) is synthesized from 3,3'-diaminobenzidine and 4,4'-oxybisbenzoic acid, and the membrane is prepared by solvent casting. The main characteristics of PBI are studied. In the preparation of the PBI/H(3) PO(4) composite membrane, the absorbing temperature of H(3) PO(4) is 120 °C, which leads to a membrane with a high content of H(3) PO(4) . Membrane electrode assemblies (MEAs) are fabricated from PBI/H(3) PO(4) membranes with the catalyst layer made of Pt/C, PBI, and polyvinylidene fluoride (230:12:7 w/w). The fabricated MEA is tested at 150 °C with dry hydrogen and oxygen gas at 0.2 MPa for both anode and cathode feeds. No degradation of voltage is seen during stability testing of the PBI/H(3) PO(4) membrane at a constant current for 100 h. The maximum power density is 1.17 W cm(-2) , and the maximum current density is 6.0 A cm(-2) with a Pt loading of 0.5 mg cm(-2) . The high performance of these membrane materials demonstrates that PBI can be regarded as an alternative membrane material for high-temperature proton-exchange-membrane fuel cells.

A highly stable anode, carbon-free, catalyst support based on tungsten trioxide nanoclusters for proton-exchange membrane fuel cells.

Durability is an important issue in proton-exchange membrane fuel cells (PEMFCs). One of the major challenges lies in the degradation caused by the oxidation of the carbon support under high anode potentials (under fuel starvation conditions). Herein, we report highly stable, carbon-free, WO(3) nanoclusters as catalyst supports. The WO(3) nanoclusters are synthesized through a hard template method and characterized by means of electron microscopy and electrochemical analysis. The electrochemical studies show that the WO(3) nanoclusters have excellent electrochemical stability under a high potential (1.6 V for 10 h) compared to Vulcan XC-72. Pt nanoparticles supported on these nanoclusters exhibit high and stable electrocatalytic activity for the oxidation of hydrogen. The catalyst shows negligible loss in electrochemically active surface area (ECA) after an accelerated durability test, whereas the ECA of the Pt nanoparticles immobilized on conventional carbon decreases significantly after the same oxidation condition. Therefore, Pt/WO(3) could be considered as a promising alternative anode catalyst for PEMFCs.

A hard-template method for the preparation of IrO(2) , and its performance in a solid-polymer-electrolyte water electrolyzer.

Morphological control by SBA-15: The performance of catalysts for the oxygen evolution reaction (OER) depends strongly on their structural and morphological properties. An IrO(2) nanomaterial with a morphology suitable for the OER is prepared by using a synthetic scheme involving a zeolite template, and shows enhanced activity and stability compared to IrO(2) fabricated by the traditional Adams-fusion method.

Graphene-based electrochemical energy conversion and storage: fuel cells, supercapacitors and lithium ion batteries.

Graphene has attracted extensive research interest due to its strictly 2-dimensional (2D) structure, which results in its unique electronic, thermal, mechanical, and chemical properties and potential technical applications. These remarkable characteristics of graphene, along with the inherent benefits of a carbon material, make it a promising candidate for application in electrochemical energy devices. This article reviews the methods of graphene preparation, introduces the unique electrochemical behavior of graphene, and summarizes the recent research and development on graphene-based fuel cells, supercapacitors and lithium ion batteries. In addition, promising areas are identified for the future development of graphene-based materials in electrochemical energy conversion and storage systems.

An ultrathin self-humidifying membrane for PEM fuel cell application: fabrication, characterization, and experimental analysis.

An ultrathin poly(tetrafluoroethylene) (PTFE)-reinforced multilayer self-humidifying composite membrane (20 microm, thick) is developed. The membrane is composed of Nafion-impregnated porous PTFE composite as the central layer, and SiO2 supported nanosized Pt particles (Pt-SiO2) imbedded into the Nafion as the two side layers. The proton exchange membrane (PEM) fuel cell employing the self-humidifying membrane (Pt-SiO2/NP) turns out a peak power density of 1.40 W cm(-2) and an open circuit voltage (OCV) of 1.032 V under dry H2/O2 condition. The excellent performance is attributed to the combined result of both the accelerated water back-diffusion in the thin membrane and the adsorbing/releasing water properties of the Pt-SiO2 catalyst in the side layers. Moreover, the inclusion of the hygroscopic Pt-SiO2 catalyst inside the membrane results in an enhanced anode self-humidification capability and also the decreased cathode polarization (accordingly an improved cell OCV). Several techniques, such as transmission electronic microscopy, scanning electronic microscopy, energy dispersive spectroscopy, thermal analysis and electrochemical impedance spectroscopy etc., are employed to characterize the Pt-SiO2/NP membrane. The results are discussed in comparison with the plain Nafion/PTFE membrane (NP). It is established that the reverse net water drag (from the cathode to the anode) across the Pt-SiO2/NP membrane reaches 0.16 H2O/H+. This implies a good hydration of the Pt-SiO2/NP membrane and thus ensures an excellent PEM fuel cell performance under self-humidification operation.

Synthesis and structure-activity relationship exploration of carbon-supported PtRuNi nanocomposite as a CO-tolerant electrocatalyst for proton exchange membrane fuel cells.

A carbon-supported PtRuNi nanocomposite is synthesized via a microwave-irradiated polyol plus annealing synthesis strategy. The catalyst is characterized by transmission electron microscopy, powder X-ray diffraction, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. The data are discussed with respect to those for the carbon-supported PtRu nanocomposite prepared following the same way. The characterizations show that the inclusion of Ni in the PtRu system has only a small effect on the particle size, the structure, and the compositional homogeneity. CO-stripping voltammetry and measurements on the single proton exchange membrane fuel cells show that the PtRuNi/C catalyst has an improved activity for CO(ads) electro-oxidation. An accelerated durability test on the catalyst exhibits insignificant loss of activity in acidic media. On the basis of the exploration of the structure-activity relationship, a mechanism for the improved performance of the catalyst is proposed. It is suggested that the improved CO-tolerant performance of the PtRuNi/C nanocomposite should be related to the hydrogen spillover on the catalyst surface, the enhanced oxidation of CO(ads) by nickel hydroxides, and the high proton and electronic conductivity of the hydroxides. The nickel hydroxide passivated surface and/or anchoring of metallic nickel in the platinum lattice may contribute to the durability of the catalyst in acid solution.